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See discussion of abrupt climate change.

OVER VIEW: Global Climate Change : Syllabus 2005 Miami University, Global Climate Change, Spring 2005, Student Research Database

An Abrupt Climate Change Scenario and Its Implications for United States National Security, 10-2003 Schwartz and Randall (View as HTML)

Or view above Abrupt Climate Change Scenario as a pdf download

pdf Download: W. S. Broecker, "What If the Conveyor Were to Shut Down? Reflections on a Possible Outcome of the Great Global Experiment," GSA Today 9(1):1-7 (January 1999). See also http://www.geosociety.org/pubs/gsatoday/gsat9901.htm

View HTML: Climate Policy Preventing an Atlantic Thermohaline Circulation Collapse O Bahn, N Edwards, R Knutti, TF Stocker - gerad.ca ... the four modules of MERGE (energy, macro-economic, climate ... one to perform integrated assessment of climate policies ... corresponds to a bottom-up engineering model ...(Sept. 2004)

Abrupt Climate Change: Inevitable Surprises

Committee on Abrupt Climate Change, National Research Council

244 pages, 6x9, 2002
The climate record for the past 100,000 years clearly indicates that the climate system has undergone periodic and often extreme shifts, sometimes in as little as a decade or less. The causes of abrupt climate changes have not been clearly established, but the triggering of events is likely to be the result of multiple natural processes.

Abrupt climate changes of the magnitude seen in the past would have far-reaching implications for human society and ecosystems, including major impacts on energy consumption and water supply demands. Could such a change happen again? Are human activities exacerbating the likelihood of abrupt climate change? What are the potential societal consequences of such a change?

Abrupt Climate Change: Inevitable Surprises looks at the current scientific evidence and theoretical understanding to describe what is currently known about abrupt climate change, including patterns and magnitudes, mechanisms, and probability of occurrence. It identifies critical knowledge gaps concerning the potential for future abrupt changes, including those aspects of change most important to society and economies, and outlines a research strategy to close those gaps.

Based on the best and most current research available, this book surveys the history of climate change and makes a series of specific recommendations for the future.


Review
"...a thorough and readable look at the evidence for quick climate changes, theories about what is behind them, global warming as a possible trigger for such changes in the future, and the potential economic and ecological impacts of sudden climate changes."
-- USAToday.com

"Very important, perhaps more so in the long run than human terrorism, which has elicited a robust response."
-- Future Survey, June 2002

"Whilst this work concentrates on the USA, the issues are global... This is a valuable report that is most reasonably priced bearing in mind its specialist nature and hence it should be on the bookshelves of all government scientists, academics and industrialists who are involved or have responsibility for climate change, and atmospheric and other pollution."
-- The International Journal of Environmental Studies

"The book is interdisciplinary and written in an accessible style. It is a must-read for anybody interested in long-term climate policy."
-- Climatic Change, 2004


Link to read First 98 pages Abrupt Climate Change: Inevitable Surprises Committee on Abrupt Climate Change, National Research Council

Media Alerts Stories Archive

February 4, 2008

'TIPPING POINTS' COULD COME THIS CENTURY

A number of key components of the earth's climate system could pass their 'tipping point' this century, according to new research led by a scientist at the University of East Anglia.

Published today by the prestigious international journal Proceedings of the National Academy of Science (PNAS), the researchers have coined a new term, 'tipping elements', to describe those components of the climate system that are at risk of passing a tipping point.

The term 'tipping point' is used to describe a critical threshold at which a small change in human activity can have large, long-term consequences for the Earth's climate system.

In this new research, lead author Prof Tim Lenton of the University of East Anglia (UEA) and colleagues at the Postdam Institute of Climate Impact Research (PIK), Carnegie Mellon University, Newcastle University and Oxford University have drawn up a shortlist of nine tipping elements relevant to current policy-making and calculated where their tipping points could lie. All of them could be tipped within the next 100 years.

The nine tipping elements and the time it will take them to undergo a major transition are:

  • Melting of Arctic sea-ice (approx 10 years)
  • Decay of the Greenland ice sheet (more than 300 years)
  • Collapse of the West Antarctic ice sheet (more than 300 years)
  • Collapse of the Atlantic thermohaline circulation (approx 100 years)
  • Increase in the El Nino Southern Oscillation (approx 100 years)
  • Collapse of the Indian summer monsoon (approx 1 year)
  • Greening of the Sahara/Sahel and disruption of the West African monsoon (approx 10 years)
  • Dieback of the Amazon rainforest (approx 50 years)
  • Dieback of the Boreal Forest (approx 50 years)

The paper also demonstrates how, in principle, early warning systems could be established using real-time monitoring and modelling to detect the proximity of certain tipping points.

"Society must not be lulled into a false sense of security by smooth projections of global change," said Prof Lenton.

"Our findings suggest that a variety of tipping elements could reach their critical point within this century under human-induced climate change. The greatest threats are tipping of the Arctic sea-ice and the Greenland ice sheet, and at least five other elements could surprise us by exhibiting a nearby tipping point."

##

Contact:

Simon Dunford
University of East Anglia
44-016-035-92203
press@uea.ac.uk

This text derived from:
http://www1.uea.ac.uk/cm/home/services/units/mac/comm/media/press/2008/feb/homepagenews/%25E2%2580%2598Tipping%2Bpoints%25E2%2580%2599%2Bcould%2Bcome%2Bthis%2Bcentury

Greenland warming speeds rise in sea level
By Nic Fleming, Science Correspondent in St Louis, Missouri
(Filed: 21/02/2006)

Sea levels are rising quicker than previously thought because the amount of water Greenland's glaciers are dumping into the Atlantic Ocean has almost doubled in five years, according to research to be published today.

Scientists who carried out the first comprehensive analysis of changing speeds of the glaciers on the world's largest island were shocked to discover that many have doubled in speed within the past decade.

Warmer temperatures are "lubricating" the glaciers and have driven a 150 per cent increase in the amount of ice they are delivering to the ocean between 1996 and last year. The latitude at which this is happening is moving north.

The researchers fear that as a result current estimates that sea levels will rise by up to 90cms during the 21st century could underestimate the problem.

While there have been previous isolated reports of particular glaciers speeding up, the research presented yesterday at the American Association for the Advancement of Science conference in St Louis is the first detailed study showing the effect is widespread across Greenland.

Eric Rignot, of Nasa's Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, the leading author of the study, said: "Climate change can work in different ways, but generally speaking, if you warm up the ice sheet, the glacier will flow faster.

"The southern half of Greenland is reacting to what we think is climate warming. The northern half is waiting but I don't think it is going to take long. If more glaciers accelerate farther north, especially along the west coast, the mass loss from Greenland will continue to increase well above predictions."

The Intergovernmental Panel on Climate Change has estimated that global sea levels will increase by 10-90cms over the next century. Last century they rose by 10-20cm.

Previously models of the melting of the Greenland ice sheet have been based mainly on airborne laser altimetry and have suggested that while the interior is reasonably stable, the periphery was thinning, especially in areas where glaciers meet the sea.

Dr Rignot and colleagues set out to obtain accurate measurements to help to build a clearer picture of Greenland's current and future contribution to rising sea levels. They collected satellite data on the speeds of 27 glaciers and made estimates for two others.

The velocities of several large glaciers had doubled in recent years to 12km per year, making them among the fastest flowing in the world.

The scientists found that warmer air temperatures have increased the overall shrinkage of the Greenland ice sheet from 91 cubic km per year in 1996 to 138 cubic km per year in 2000 and to 224 cubic km per year in 2005.

About two-thirds of this was caused by the dumping of ice in the Atlantic by glaciers and so the ice loss attributable to glacier flow grew by 150 per cent from 60 cubic km a decade ago to 150 cubic km last year.

On this basis Dr Rignot, whose work is published in Science, concluded that Greenland's contribution to rising global sea levels increased from around 0.23mm per year in 1996 to around 0.57mm per year in 2005.

The Greenland ice sheet is 1.7 million sq km - a little smaller than Mexico - and three kilometres thick. If it melted completely sea levels would rise by seven metres.

9 February 2006: Krakatoa helps to keep Earth cool
31 January 2006: Change to our climate unstoppable, warns expert

 

Global warming 'past the point of no return'

http://news.independent.co.uk/world/science_technology/article312997.ece

By Steve Connor, Science Editor

Published: 16 September 2005

A record loss of sea ice in the Arctic this summer has convinced scientists that the northern hemisphere may have crossed a critical threshold beyond which the climate may never recover. Scientists fear that the Arctic has now entered an irreversible phase of warming which will accelerate the loss of the polar sea ice that has helped to keep the climate stable for thousands of years.

They believe global warming is melting Arctic ice so rapidly that the region is beginning to absorb more heat from the sun, causing the ice to melt still further and so reinforcing a vicious cycle of melting and heating.

The greatest fear is that the Arctic has reached a "tipping point" beyond which nothing can reverse the continual loss of sea ice and with it the massive land glaciers of Greenland, which will raise sea levels dramatically.

Satellites monitoring the Arctic have found that the extent of the sea ice this August has reached its lowest monthly point on record, dipping an unprecedented 18.2 per cent below the long-term average.

Experts believe that such a loss of Arctic sea ice in summer has not occurred in hundreds and possibly thousands of years. It is the fourth year in a row that the sea ice in August has fallen below the monthly downward trend - a clear sign that melting has accelerated.

Scientists are now preparing to report a record loss of Arctic sea ice for September, when the surface area covered by the ice traditionally reaches its minimum extent at the end of the summer melting period.

Sea ice naturally melts in summer and reforms in winter but for the first time on record this annual rebound did not occur last winter when the ice of the Arctic failed to recover significantly.

Arctic specialists at the US National Snow and Ice Data Centre at Colorado University, who have documented the gradual loss of polar sea ice since 1978, believe that a more dramatic melt began about four years ago.

In September 2002 the sea ice coverage of the Arctic reached its lowest level in recorded history. Such lows have normally been followed the next year by a rebound to more normal levels, but this did not occur in the summers of either 2003 or 2004. This summer has been even worse. The surface area covered by sea ice was at a record monthly minimum for each of the summer months - June, July and now August.

Scientists analysing the latest satellite data for September - the traditional minimum extent for each summer - are preparing to announce a significant shift in the stability of the Arctic sea ice, the northern hemisphere's major "heat sink" that moderates climatic extremes.

"The changes we've seen in the Arctic over the past few decades are nothing short of remarkable," said Mark Serreze, one of the scientists at the Snow and Ice Data Centre who monitor Arctic sea ice.

Scientists at the data centre are bracing themselves for the 2005 annual minimum, which is expected to be reached in mid-September, when another record loss is forecast. A major announcement is scheduled for 20 September. "It looks like we're going to exceed it or be real close one way or the other. It is probably going to be at least as comparable to September 2002," Dr Serreze said.

"This will be four Septembers in a row that we've seen a downward trend. The feeling is we are reaching a tipping point or threshold beyond which sea ice will not recover."

The extent of the sea ice in September is the most valuable indicator of its health. This year's record melt means that more of the long-term ice formed over many winters - so called multi-year ice - has disappeared than at any time in recorded history.

Sea ice floats on the surface of the Arctic Ocean and its neighbouring seas and normally covers an area of some 7 million square kilometres (2.4 million square miles) during September - about the size of Australia. However, in September 2002, this dwindled to about 2 million square miles - 16 per cent below average.

Sea ice data for August closely mirrors that for September and last month's record low - 18.2 per cent below the monthly average - strongly suggests that this September will see the smallest coverage of Arctic sea ice ever recorded.

As more and more sea ice is lost during the summer, greater expanses of open ocean are exposed to the sun which increases the rate at which heat is absorbed in the Arctic region, Dr Serreze said.

Sea ice reflects up to 80 per cent of sunlight hitting it but this "albedo effect" is mostly lost when the sea is uncovered. "We've exposed all this dark ocean to the sun's heat so that the overall heat content increases," he explained.

Current computer models suggest that the Arctic will be entirely ice-free during summer by the year 2070 but some scientists now believe that even this dire prediction may be over-optimistic, said Professor Peter Wadhams, an Arctic ice specialist at Cambridge University.

"When the ice becomes so thin it breaks up mechanically rather than thermodynamically. So these predictions may well be on the over-optimistic side," he said.

As the sea ice melts, and more of the sun's energy is absorbed by the exposed ocean, a positive feedback is created leading to the loss of yet more ice, Professor Wadhams said.

"If anything we may be underestimating the dangers. The computer models may not take into account collaborative positive feedback," he said.

Sea ice keeps a cap on frigid water, keeping it cold and protecting it from heating up. Losing the sea ice of the Arctic is likely to have major repercussions for the climate, he said. "There could be dramatic changes to the climate of the northern region due to the creation of a vast expanse of open water where there was once effectively land," Professor Wadhams said. "You're essentially changing land into ocean and the creation of a huge area of open ocean where there was once land will have a very big impact on other climate parameters," he said.

A record loss of sea ice in the Arctic this summer has convinced scientists that the northern hemisphere may have crossed a critical threshold beyond which the climate may never recover. Scientists fear that the Arctic has now entered an irreversible phase of warming which will accelerate the loss of the polar sea ice that has helped to keep the climate stable for thousands of years.

They believe global warming is melting Arctic ice so rapidly that the region is beginning to absorb more heat from the sun, causing the ice to melt still further and so reinforcing a vicious cycle of melting and heating.

The greatest fear is that the Arctic has reached a "tipping point" beyond which nothing can reverse the continual loss of sea ice and with it the massive land glaciers of Greenland, which will raise sea levels dramatically.

Satellites monitoring the Arctic have found that the extent of the sea ice this August has reached its lowest monthly point on record, dipping an unprecedented 18.2 per cent below the long-term average.

Experts believe that such a loss of Arctic sea ice in summer has not occurred in hundreds and possibly thousands of years. It is the fourth year in a row that the sea ice in August has fallen below the monthly downward trend - a clear sign that melting has accelerated.

Scientists are now preparing to report a record loss of Arctic sea ice for September, when the surface area covered by the ice traditionally reaches its minimum extent at the end of the summer melting period.

Sea ice naturally melts in summer and reforms in winter but for the first time on record this annual rebound did not occur last winter when the ice of the Arctic failed to recover significantly.

Arctic specialists at the US National Snow and Ice Data Centre at Colorado University, who have documented the gradual loss of polar sea ice since 1978, believe that a more dramatic melt began about four years ago.

In September 2002 the sea ice coverage of the Arctic reached its lowest level in recorded history. Such lows have normally been followed the next year by a rebound to more normal levels, but this did not occur in the summers of either 2003 or 2004. This summer has been even worse. The surface area covered by sea ice was at a record monthly minimum for each of the summer months - June, July and now August.

Scientists analysing the latest satellite data for September - the traditional minimum extent for each summer - are preparing to announce a significant shift in the stability of the Arctic sea ice, the northern hemisphere's major "heat sink" that moderates climatic extremes.

"The changes we've seen in the Arctic over the past few decades are nothing short of remarkable," said Mark Serreze, one of the scientists at the Snow and Ice Data Centre who monitor Arctic sea ice.

Scientists at the data centre are bracing themselves for the 2005 annual minimum, which is expected to be reached in mid-September, when another record loss is forecast. A major announcement is scheduled for 20 September. "It looks like we're going to exceed it or be real close one way or the other. It is probably going to be at least as comparable to September 2002," Dr Serreze said.

"This will be four Septembers in a row that we've seen a downward trend. The feeling is we are reaching a tipping point or threshold beyond which sea ice will not recover."

The extent of the sea ice in September is the most valuable indicator of its health. This year's record melt means that more of the long-term ice formed over many winters - so called multi-year ice - has disappeared than at any time in recorded history.

Sea ice floats on the surface of the Arctic Ocean and its neighbouring seas and normally covers an area of some 7 million square kilometres (2.4 million square miles) during September - about the size of Australia. However, in September 2002, this dwindled to about 2 million square miles - 16 per cent below average.

Sea ice data for August closely mirrors that for September and last month's record low - 18.2 per cent below the monthly average - strongly suggests that this September will see the smallest coverage of Arctic sea ice ever recorded.

As more and more sea ice is lost during the summer, greater expanses of open ocean are exposed to the sun which increases the rate at which heat is absorbed in the Arctic region, Dr Serreze said.

Sea ice reflects up to 80 per cent of sunlight hitting it but this "albedo effect" is mostly lost when the sea is uncovered. "We've exposed all this dark ocean to the sun's heat so that the overall heat content increases," he explained.

Current computer models suggest that the Arctic will be entirely ice-free during summer by the year 2070 but some scientists now believe that even this dire prediction may be over-optimistic, said Professor Peter Wadhams, an Arctic ice specialist at Cambridge University.

"When the ice becomes so thin it breaks up mechanically rather than thermodynamically. So these predictions may well be on the over-optimistic side," he said.

As the sea ice melts, and more of the sun's energy is absorbed by the exposed ocean, a positive feedback is created leading to the loss of yet more ice, Professor Wadhams said.

"If anything we may be underestimating the dangers. The computer models may not take into account collaborative positive feedback," he said.

Sea ice keeps a cap on frigid water, keeping it cold and protecting it from heating up. Losing the sea ice of the Arctic is likely to have major repercussions for the climate, he said. "There could be dramatic changes to the climate of the northern region due to the creation of a vast expanse of open water where there was once effectively land," Professor Wadhams said. "You're essentially changing land into ocean and the creation of a huge area of open ocean where there was once land will have a very big impact on other climate parameters," he said.

 

 
Insurers sound the alarm on climate change
By Fiona Harvey, Environment Correspondent
Published: June 28 2005 22:31 | Last updated: June 28 2005 22:31

from:  http://news.ft.com/cms/s/84370f42-e7f8-11d9-9786-00000e2511c8.html

The cost worldwide of storms, expected to become more frequent owing to climate change, is likely to rise by two-thirds to £15bn ($27bn, €22bn) a year in the next seven decades, the Association of British Insurers will warn on Wednesday.

Nick Starling, the ABI's director of general insurance, urged the leaders of the Group of Eight industrialised nations to take action on greenhouse gas emissions when they meet to discuss climate change next week.

“Governments now have a chance to make rational choices for the future, before it is too late,” he said. Making the right decisions based on assessment of the costs of climate change “will ensure lower costs for the public in future”.

By 2040, the average annual cost of hurricanes in the US alone would rise from $9.5bn to $11.4bn. In a bad year, hurricanes in the US would cost $71bn in the 2040s and $104bn in insured costs alone.

Separately, a poll carried out across Europe by the market research group TNS found that seven out of ten people thought governments would take serious action on environmental issues only if there were an environmental catastrophe.

In one of the most detailed estimates seeking to price the effects of climate change, the ABI said that in years with a high number of storms, the cost of Japanese typhoons could reach £19bn a year by 2080.

Though scientists cannot say exactly what will happen as the climate changes under the influence of the increased burning of fossil fuels, they estimate that the incidence of storms, floods, droughts and heatwaves will increase.

Joachim Faber, chief executive of Allianz Global Investors, said climate change was influencing financial markets: “In the interest of our clients and shareholders, we are obligated to take these risks into account when making decisions on insurance underwriting, investments, or credit.”

Sebastian Catovsky, adviser to the ABI on natural perils, added that the figures in the report were likely to be an underestimate, because they did not take into account the likely increase in the value of property in future decades. Insurance markets would also become more volatile.

Some of the costs could be avoided by taking preventative measures. Improved coastal defences could reduce the global annual damage from a 0.5m rise in sea level by up to £16bn. In the UK, where insurers have paid out £2.2bn in flood claims in the last five years, effective flood management could save 80 per cent of the costs of flood damage.

The report will be published on Wednesday at an ABI-organised conference on the financial risks of climate change. At the conference, Allianz and the environmental campaigning group WWF will urge financial managers and analysts to evaluate their client portfolios for climate change risk, in an effort to price such risk into the financial markets.

Allianz will pledge to invest between €300m and €500m in renewable energy over the next five years.

 

 

Sea life in peril -- plankton vanishing
Usual seasonal influx of cold water isn't happening

Glen Martin, Chronicle Environment Writer

Tuesday, July 12, 2005

Oceanic plankton have largely disappeared from the waters off Northern California, Oregon and Washington, mystifying scientists, stressing fisheries and causing widespread seabird mortality.

The phenomenon could have long-term implications if it continues: a general decline in near-shore oceanic life, with far fewer fish, birds and marine mammals. No one is certain how long the condition will last. But even a short duration could severely affect seabird populations because of drastically reduced nesting success, scientists say.

The plankton disappearance is caused by a slackening of what is known as "upwelling:" the seasonal movement of cold, nutrient-rich offshore water into areas near shore.

This cold water sustains vast quantities of phytoplankton and zooplankton, which are the basis of the marine food web. During periods of vigorous upwelling and consequent plankton "blooms," everything from salmon to blue whales fattens and thrives on the continental shelf of the West Coast.

The larger fish and baleen whales eat mostly krill: free-floating, shrimp- like crustaceans ranging from one to two inches, the upper size limit of the zooplankton realm.

When the water is cold, krill swarm off the Northern California coast by the tens of thousands of tons. Now that they are largely absent, fisheries and wildlife are feeling the effects.

In perhaps the most ominous development, seabird nesting has dropped significantly on the Farallon Islands off San Francisco, the largest Pacific Coast seabird rookery south of Alaska.

Bill Sydeman, the director of marine ecology for the Point Reyes Bird Observatory, a science and conservation organization that maintains a research station on the Farallones, said the collapse of the nesting season is unprecedented in the three decades the group has monitored the islands.

Cassin's auklets -- a relatively rare seabird that feeds almost extensively on krill -- have been particularly hard hit, Sydeman said.

"Normally they breed in March," Sydeman said. "They got started late this year, and by May they had virtually disappeared. We expect zero nesting success for them this year, or close to it. We've never seen anything like it."

Sydeman said other seabirds are also showing the effects of the reduced marine productivity.

"We have little or no nesting of pelagic cormorants (at the Farallones), and Brandt's cormorants are nesting at reduced numbers," he said. "Double- crested cormorant nesting is down by 50 percent (in the Bay Area)."

Upwelling cessation is typically caused by El Niño events -- warm water intrusions from the equatorial Pacific. But what is happening off the coast right now is not a true El Niño, Sydeman said.

"We really don't have a clear idea of what it is," Sydeman said, noting that standard El Niños can be tracked as they progress from the equator to temperate waters, something that hasn't occurred in the current case.

"Some are calling it an El Niño Norte; others think it's some sort of anomalous intrusion of warm offshore blue water onto the continental shelf," he said.

A recent study indicated the phenomenon may be long term, and linked to global warming.

Last week, Fisheries and Oceans Canada -- the federal agency dealing with Canada's marine and inland waters -- released a report saying 2004's spring and summer ocean surface temperatures in the Gulf of Alaska and off British Columbia were the warmest in 50 years.

The study concluded the record high temperatures were caused by abnormally warm weather in Alaska and western Canada, as well as "general warming of global lands and oceans."

Some pulses of upwelling occurred off Northern California in June, Sydeman said, but they're unlikely to significantly increase marine productivity.

"Upwelling has slackened along all the West Coast, except for a little bit of recent activity off Northern California," Sydeman said. "At this point, it's too little and too late. Things aren't going to turn around. For krill predators in this system, it's a very serious situation."

Juvenile rockfish numbers are also way down.

"We annually survey (juvenile rockfish) from San Diego to Cape Mendocino, and this is the lowest catch we've recorded in the 23 years we've been doing it," said Stephen Ralston, a supervising research biologist at the Santa Cruz office for the National Marine Fisheries Service, the federal agency that oversees fisheries in federal waters.

Like krill, young rockfish are a significant food source for seabirds, large fish and marine mammals; they are also essential to maintaining healthy stocks of mature rockfish, esteemed by commercial fishermen and sport anglers.

Off the coast of Oregon, abnormally warm marine water is continuing unabated, affecting local birds and salmon.

"Things are pretty grim up here," said Bill Peterson, an oceanographer with the National Marine Fisheries Service office in Newport, Ore.

Peterson said a major die-off of double-crested cormorants recently occurred in Oregon, and juvenile salmon numbers have dropped precipitously. Both events, he said, are likely due to the warm water.

"We do salmon surveys every spring and summer," he said. "Normally, we catch several hundred salmon in the spring. This year we caught eight. And we usually get several thousand fish in the summer. This year, it was 80."

Peterson said the water temperature off Oregon in late June is normally 10 degrees Celsius (about 50 Fahrenheit), "and this year it's 16 degrees (about 61 F). Our (upper layer of warm water) is normally 15 meters thick, and this year it's 30 meters. Krill numbers are down, and the plankton we are seeing are as unusual as can be -- warm water species that you'd find off San Diego or Monterey."

Peterson said it is unlikely Oregon waters will cool significantly this summer.

"It takes an enormous amount of (offshore wind) energy to push that much warm water offshore, which is what we would need to see for significant upwelling," he said. "I don't see that happening anytime soon."

Near San Francisco, salmon have switched from krill to bait fish, and appear to be holding their own -- at least for now.

"The fishing is terrific," said Roger Thomas, the president of the Golden Gate Fishermen's Association and the owner of the recreational angling boat the Salty Lady.

"It's true there's not much krill, but there're lots of anchovies and sardines," Thomas said, "and the salmon are filling up on those."

Thomas acknowledged that the bait fish wouldn't benefit many coastal and offshore birds.

"Sardines are too big for the auklets, and even for other species like common murres," he said. "They rely on smaller prey species."

In fact, say scientists, krill are the keystone forage species for almost everything that swims off Northern California.

"It's the krill that drive the food web dynamics off this coast," said Ellie Cohen, the executive director of the Point Reyes Bird Observatory. "Their absence has tremendous implications for everything out there, right up to the humpback and blue whales. We don't know if this is a result of global warming or some natural cycling, but without the krill, you could be looking at a food web collapse."

E-mail Glen Martin at glenmartin@sfchronicle.com.

Page A - 1

 

 

From:

Sunday Times

http://www.timesonline.co.uk/article/0,,2087-1602579,00.html

 

May 08, 2005

Britain faces big chill as ocean current slows

 

CLIMATE change researchers have detected the first signs of a slowdown in the Gulf Stream — the mighty ocean current that keeps Britain and Europe from freezing.

They have found that one of the “engines” driving the Gulf Stream — the sinking of supercooled water in the Greenland Sea — has weakened to less than a quarter of its former strength.

 The weakening, apparently caused by global warming, could herald big changes in the current over the next few years or decades. Paradoxically, it could lead to Britain and northwestern and Europe undergoing a sharp drop in temperatures.

Such a change has long been predicted by scientists but the new research is among the first to show clear experimental evidence of the phenomenon.

Peter Wadhams, professor of ocean physics at Cambridge University, hitched rides under the Arctic ice cap in Royal Navy submarines and used ships to take measurements across the Greenland Sea.

“Until recently we would find giant ‘chimneys’ in the sea where columns of cold, dense water were sinking from the surface to the seabed 3,000 metres below, but now they have almost disappeared,” he said.

“As the water sank it was replaced by warm water flowing in from the south, which kept the circulation going. If that mechanism is slowing, it will mean less heat reaching Europe.”

Such a change could have a severe impact on Britain, which lies on the same latitude as Siberia and ought to be much colder. The Gulf Stream transports 27,000 times more heat to British shores than all the nation’s power supplies could provide, warming Britain by 5-8C.

Wadhams and his colleagues believe, however, that just such changes could be well under way. They predict that the slowing of the Gulf Stream is likely to be accompanied by other effects, such as the complete summer melting of the Arctic ice cap by as early as 2020 and almost certainly by 2080. This would spell disaster for Arctic wildlife such as the polar bear, which could face extinction.

Wadhams’s submarine journeys took him under the North Polar ice cap, using sonar to survey the ice from underneath. He has measured how the ice has become 46% thinner over the past 20 years. The results from these surveys prompted him to focus on a feature called the Odden ice shelf, which should grow out into the Greenland Sea every winter and recede in summer.

The growth of this shelf should trigger the annual formation of the sinking water columns. As sea water freezes to form the shelf, the ice crystals expel their salt into the surrounding water, making it heavier than the water below.

However, the Odden ice shelf has stopped forming. It last appeared in full in 1997. “In the past we could see nine to 12 giant columns forming under the shelf each year. In our latest cruise, we found only two and they were so weak that the sinking water could not reach the seabed,” said Wadhams, who disclosed the findings at a meeting of the European Geosciences Union in Vienna.

The exact effect of such changes is hard to predict because currents and weather systems take years to respond and because there are two other areas around the north Atlantic where water sinks, helping to maintain circulation. Less is known about how climate change is affecting these.

However, Wadhams suggests the effect could be dramatic. “One of the frightening things in the film The Day After Tomorrow showed how the circulation in the Atlantic Ocean is upset because the sinking of cold water in the north Atlantic suddenly stops,” he said.

“The sinking is stopping, albeit much more slowly than in the film — over years rather than a few days. If it continues, the effect will be to cool the climate of northern Europe.”

One possibility is that Europe will freeze; another is that the slowing of the Gulf Stream may keep Europe cool as global warming heats the rest of the world — but with more extremes of weather.

 

 

 

Global warming makes sea less salty

Researchers predict effects on 'conveyor belt' of ocean currents

 

 

Updated: 6:15 p.m. ET June 29, 2005

You won't want to drink water straight from the ocean anytime soon. But the salt content is on the decline, a sign of potentially worrisome consequences that scientists can't accurately predict.

Since the late 1960s, much of the North Atlantic Ocean has become less salty, in part due to increases in fresh water runoff induced by global warming, scientists say.  Now for the first time researchers have quantified this fresh water influx, allowing them to predict the long-term effects on a "conveyor belt" of ocean currents.

Climate changes in the Northern Hemisphere have melted glaciers and brought more rain, dumping more fresh water into the oceans, according to the analysis.

One of the expected high-profile consequences is a rising sea that will swamp coastal communities. But there are other possible effects.

"Precipitation and river runoff at high latitudes have been increasing," said Ruth Curry of the Woods Hole Oceanographic Institution (WHOI).  "In the last decade, fresh water has been accumulating in the Nordic Seas layer (the upper 1,000 meters) that is critical to the ocean conveyor, so it is something to watch."

What's going on
Curry and Cecilie Mauritzen of the Norwegian Meteorological Institute calculated that an extra 19,000 cubic kilometers of water flowed into and diluted the northern seas between 1965 and 1995.

For comparison, the Mississippi River releases about 500 cubic kilometers of freshwater into the Gulf of Mexico each year, while the Amazon, the Earth's largest river, discharges roughly 5,000 cubic kilometers annually. 

Because water with lower salinity is less dense, adding fresh water may affect ocean flows like the conveyor belt – a system of Atlantic currents that exchanges cold water in the Arctic region for warm water from the tropics.

The top part of this conveyor is made of warm ocean currents, like the Gulf Stream, flowing northward along the surface.  At high latitudes, this water cools and sinks – releasing its heat to the atmosphere and making for moderate winter climates in places like England.  

Deep, cold currents return some of the water to the south.

Slight changes in the currents -- both seasonal and longer-term variations -- affect everything from hurricane formation to droughts and heat waves.

Future uncertain
No significant change in the conveyor belt has yet been observed, however.  Curry and Mauritzen estimate that it would take another century to slow the ocean exchanges if the current rate of fresh water inflow continues.

Scientists disagree over whether the planet is warming and how much humans might be contributing. But most climate experts see a clear warming trend that they expect will continue for at least a century.

"Given the projected 21st Century rise in greenhouse gas concentrations and increased fresh water input to the high-latitude ocean, we cannot rule out a significant slowing of the Atlantic conveyor in the next 100 years," Curry said.

She emphasized, however, that effects will be gradual.  "We are not suggesting that the Gulf Stream will shut down," she said.

A study last year concluded that an altered conveyor belt could actually plunge the planet into a global cooling event.

The new research was published in the June 17 issue of the journal Science.

© 2005 LiveScience.com. All rights reserved.

 

 

 

Clue to sudden climate change found in Arctic: study

Climate could change extremely rapidly with very dramatic effects

June 28, 2005


The sudden deep freeze of the northern hemisphere that occurred 13,000 years ago has been traced to events originating in northern
Canada, according to University of Toronto research. The findings could shed light on the future of climate change due to greenhouse gases.

 

The study, published in the June 2 issue of Nature, pinpoints the exact location where freshwater generated by the melting of the massive Canada-wide Laurentide ice sheet entered the global ocean and caused the Younger Dryas cold reversal, a frigid period where the planet temporarily plunged into ice age conditions. Contrary to previous thinking, the study shows that this meltwater entered the Arctic Ocean rather than the Atlantic and the point of entry was through the MacKenzie River. As the freshwater - lighter due to its lack of salt content - flowed into the ocean it was transported across the pole into the North Atlantic where it shut down the process whereby heavy surface water sinks into the abyss and leads to a warming of the northern hemisphere.

While the Younger Dryas cold reversal occurred just as the Earth was emerging from the most recent ice age, a rapid meltback of the
Greenland ice sheet - another large accumulation of land ice adjacent to the North Atlantic Ocean - could theoretically contribute to another such shutdown.

"
Greenland contains enough ice to raise sea level by about seven metres if it were all to melt," says the study's co-author University Professor Richard Peltier of U of T's Department of Physics. "If it were to melt very quickly we could easily have a similar event, so the question is just how Greenland will react to the ongoing warming due to the increasing concentration of atmospheric greenhouses gases. How probable this is remains an open question."

To pinpoint the location of where the Younger Dryas event occurred, Peltier and his co-author, physic's research associate Lev Tarasov, used the University of Toronto Glacial Systems Model (GSM) - a model that produces a three-dimensional view of the evolving ice-sheet as it expands and contracts over the North American continent in response to climate variations. The model also analyses how the shape of the Earth is affected by the evolution of the heavy ice loads. As the continental ice melted, a huge amount of deglaciation derived freshwater was added to the oceans. At the time of Younger Dryas onset the routing of this meltwater was into the
Arctic Ocean.

"In considering the issue of climate change, many people imagine that this could only happen very gradually," says Peltier. "This event shows that our climate could change extremely rapidly and with very dramatic effect."

Peltier stresses that climate changes, such as a massive Greenland melt, are very difficult to predict as Earth's climate system is highly non-linear, involving the interactions between a number of distinct and individually complex components such as sea ice and land surface processes as well as the atmosphere and oceans. "These systems are capable of responding in a way that is out of proportion to the stimulus," he says. "You can push them just a little bit and cause them to cross a threshold, such that the response is extremely surprising. From a physics standpoint, the climate system of the planet is a beautiful example of such non-linear systems."

The research was supported by the Natural Sciences and Engineering Research Council of Canada and by the Canadian Foundation for Climate and Atmospheric Science through a new collaborative research network called Polar Climate Stability which is led by Peltier. The network involves researchers from seven different Canadian universities.

Source:
University of Toronto

 

Abrupt Climate Change

FOR IMMEDIATE RELEASE
Contact: Shelley Dawicki
508-289-2270 or 3340
April 21, 2003
Media Relations Office
Woods Hole Oceanographic Institution

Rate of Ocean Circulation Directly Linked to Abrupt Climate Change in North Atlantic Region


Enlarge image
Great Ocean Conveyor Belt (From the Intergovernmental Panel on Climate Change)
A new study strengthens evidence that the oceans and climate are linked in an intricate dance, and that rapid climate change may be related to how vigorously ocean currents transport heat from low to high latitudes.

A new study, reported April 22 in the journal Nature, suggests that when the rate of the Atlantic Ocean's north-south overturning circulation slowed dramatically following an iceberg outburst during the last deglaciation, the climate in the North Atlantic region became colder. When the rate of the ocean's overturning circulation subsequently accelerated, the climate warmed abruptly.

Study author Jerry McManus and colleagues Roger Francois, Jeanne Gherardi, Lloyd Keigwin and Susan Brown-Leger at the Woods Hole Oceanographic Institution and in France report that the coldest interval of the last 20,000 years occurred when the overturning circulation collapsed following the discharge of icebergs into the North Atlantic 17,500 years ago. This regional climatic extreme began suddenly and lasted for two thousand years. Another cold snap 12,700 years ago lasting more than a thousand years and accompanied another slowdown of overturning circulation. Each of these two cold intervals was followed by a rapid acceleration of the overturning circulation and dramatically warmer climates over Northern Europe and the North Atlantic region.

McManus and colleagues studied a seafloor sediment core from the subtropical North Atlantic that was retrieved from an area known as the Bermuda Rise. The core contains sediments deposited over tens of thousands of years that include shells of small animals called foraminifera that record surface water conditions in their shells when alive. The researchers measured oxygen isotope ratios in each individual sandgrain-sized shell to determine climatic changes that occurred since the last ice age. They used a new tool, based on two daughter isotopes of uranium that occur naturally in seawater, as a proxy for changes in the rate of ocean circulation. The technique has been used for other purposes in the past, but this is the first time it has been used to generate a detailed time series that provides a history of variations in the strength of ocean circulation.

The isotopes, protactinium and thorium, are produced at constant rates in seawater by radioactive decay from dissolved uranium and are removed quickly by adhering to particles settling to the ocean floor. Thorium is removed so rapidly by particles that it resides in the water column no more than a few decades before nearly all of it is buried on the sea floor below where it was produced. Protactinium is removed less readily and thus remains in the water column 100 to 200 years. As a result, about half of the protactinium produced in North Atlantic water today is exported into the Southern Ocean as part of the ocean circulation system known as the great conveyor. At times when the rate of overturning circulation slows, the proportion of protactinium buried in the North Atlantic sediments increases, thus preserving the record of such changes in the accumulating sediments.

The research team found that the rate of ocean circulation varied remarkably following the last ice age, with strong reductions and abrupt reinvigorations closely tied to regional climate changes. McManus says this is the best demonstration to date of what many paleoclimatologists and ocean scientists have long suspected. "Strong overturning circulation leads to warm conditions in the North Atlantic region, and weak overturning circulation leads to cold conditions," he said. "We've known for some time from changes in the chemistry of the seawater itself that something was different about the ocean's circulation at times of rapid climate changes, and it now appears that the difference was related to changes in the rate of ocean circulation. One big question is why the circulation would collapse in the first place and possibly trigger abrupt climate change. We think it is the input of fresh water to the surface ocean at a particularly sensitive location."

McManus says the team is now applying this same technique to sea floor cores collected in other regions of the North Atlantic. "We've made a little step forward in understanding the ocean's role in the climate puzzle, but there are more pieces to fill in."

The WHOI study was funded by the National Science Foundation, the Institution's Ocean and Climate Change Institute and an Interdisciplinary and Independent Study Award, and by the Comer Science and Education Foundation.

Additional Resources
» Jerry F. McManus Profile Page
» National Science Foundation

From: 
 
Thursday, June 09, 2005 - 12:00 AM
 
Snow, cold weather sweep across Europe

William J. Kole THE ASSOCIATED PRESS

VIENNA, Austria -- It's nearly summertime -- and the living is chilly across much of Europe.

Fresh snow fell Wednesday on parts of Austria -- so much in some places that authorities closed roads to cars without tire chains -- and temperatures dipped below freezing in corners of Croatia, England and Scotland, fouling moods and spoiling picnic plans.

 

The unseasonably cold June has even caused headaches in Italy, a country that's normally balmy at this time of year: officials say cooler-than-usual temperatures and hailstorms have inflicted millions in damage on crops.

In agricultural areas near Verona in northeastern Italy -- one of the hardest-hit areas -- between 30 percent and 40 percent of peaches and apples were lost after hail pummeled trees, according to Coldiretti, an Italian farmers' association.

 

Heavy rain and strong winds flooded some of Rome's cobblestone streets overnight, uprooting trees and forcing authorities to close several roads to traffic. The gusts continued Wednesday, rustling Pope Benedict XVI's white vestments during his open-air audience in St. Peter's Square and forcing the pontiff to take off his skullcap.

 

"Strong wind in the sacred scripture is a symbol of the Holy Spirit, and we hope that the Holy Spirit illuminates us now as we meditate on Psalm 110," the pope said as his robes fluttered in the breeze.

Parts of Austria's Alps were blanketed with nearly 16 inches of fresh snow, and the country's automobile club said numerous tow trucks were called to aid stranded motorists. No injuries were reported.

 

Although the snow was limited to higher elevations, temperatures dipped to 44 degrees in Vienna. Austrians call the late spring chill "Schafskaelte," or "sheep's cold" -- invoking the image of the livestock shivering in the fields after being shorn of their first wool of the season.

 

The wet and chilly weather was decidedly uncool for 90,000 rock fans descending on the eastern town of Nickelsdorf for an open-air music festival that opens Thursday. Promoters of the concert, which will feature Weezer, Marilyn Manson and other bands, urged fans to pack sweaters and umbrellas.

 

To be sure, not all of Europe was chilly. In three of Portugal's northern districts, firefighters were on maximum alert Wednesday as a heat wave sharply increased the risk of forest fires.

 

But in Croatia, a few inches of snow fell overnight on the southern mountain of Biokovo, where the mercury plunged to 27 degrees, officials said.

 

Strong winds that reached 60 mph around the southern coastal town of Makarska prompted police to warn drivers and cancel ferry service with the popular resort island of Brac.

 

Rescue teams in southern Croatia were searching for a German tourist who fell off his sailboat Tuesday in a storm at sea. They managed to save his wife. A surfer also disappeared in northern Croatia after heavy winds whipped up waves.

 

Heavy rain flooded several villages in central Serbia. A deluge fell on the region of Leskovac, and fresh snow blanketed the mountains of southern Serbia, the state weather bureau said.

 

It's been far colder than usual in parts of Germany, where overnight temperatures recently have dropped as low as 35 in the east, and in neighboring Switzerland, where high winds swept away several tents at a fairground last weekend.

 

Many parts of Britain also have had an unusually cold June.

 

Temperatures fell below freezing on Tuesday, with thermometers in the village of Aboyne, Scotland, recording 30 degrees, the Meteorological Office said, predicting more chilly nights this week.

 

The Royal Air Force base at Benson in Oxfordshire notched its lowest June temperature ever at 31.46 degrees Tuesday, beating the mark of 32 recorded in 1962.

 

This story appeared in The Daily Herald on page A11.

 

Abrupt Climate Change

FOR IMMEDIATE RELEASE
Contact: Shelley Dawicki
508-289-2270 or 3340
December 17, 2003
Media Relations Office
Woods Hole Oceanographic Institution

New Study Reports Large-scale Salinity Changes in the Oceans
Saltier tropical oceans and fresher ocean waters near the poles are further signs of global warming's impacts on the planet

Tropical ocean waters have become dramatically saltier over the past 40 years, while oceans closer to Earth's poles have become fresher, scientists reported today in the journal Nature.   Earth's warming surface may be intensifying evaporation over oceans in the low latitudes--raising salinity concentrations there--and transporting more fresh water vapor via the atmosphere toward Earth's poles.

These large-scale, relatively rapid oceanic changes suggest that recent climate changes, including global warming, may be altering the fundamental planetary system that regulates evaporation and precipitation and cycles fresh water around the globe.

The study was conducted by Ruth Curry, a research specialist in the WHOI Physical Oceanography Department, Bob Dickson of the Centre for Environment, Fisheries, and Aquaculture Science in Lowestoft, United Kingdom , and Igor Yashayaev of the Bedford Institute of Oceanography in Dartmouth, Nova Scotia, Canada.

An acceleration of Earth's global water cycle can potentially affect global precipitation patterns that govern the distribution, severity, and frequency of droughts, floods, and storms. It would exacerbate global warming by rapidly adding more water vapor--itself a potent, heat-trapping greenhouse gas--to the atmosphere. It could also continue to freshen northern North Atlantic Ocean waters -- to a point that could disrupt ocean circulation and trigger further climate changes.

The oceans and atmosphere continually exchange fresh water.   Evaporation over warm, tropical and subtropical oceans transfers water vapor to the atmosphere, which transports it toward both poles. At higher latitudes, that water vapor precipitates as rain or snow and ultimately returns to the oceans, which complete the cycle by circulating fresh water back toward the equator. The process maintains a balanced distribution of water around our planet.

The oceans contain 96% of the Earth's water, experience 86% of planetary evaporation, and receive 78% of planetary precipitation, and thus represent a key element of the global water cycle for study, the scientists said. Since evaporation concentrates salt in the surface ocean, increasing evaporation rates cause detectable spikes in surface ocean salinity levels. In contrast, salinity decreases generally reflect the addition of fresh water to the ocean through precipitation and runoff from the continents.

Curry, Dickson, and Yashayaev analyzed a wealth of salinity measurements collected over recent decades along a key transect in the Atlantic Ocean, from the tip of Greenland to the tip of South America.   Their analysis showed that "the properties of Atlantic water masses have been changing--in some cases radically--over the five decades for which reliable and systematic records of ocean measurements are available."

The scientists observed that surface waters in tropical and subtropical Atlantic Ocean regions became markedly more saline.   Simultaneously, much of the water column in the high latitudes of the North and South Atlantic became fresher.

This trend appears to have accelerated since 1990--when ten of the warmest years since records began in 1861 have occurred.   The scientists estimated that net evaporation rates over the tropical Atlantic have increased by 5% to 10% over the last four decades.

"These results indicate that fresh water has been lost from the low latitudes and added at high latitudes, at a pace exceeding the ocean circulation's ability to compensate," the authors said.   Taken together with other recent studies revealing parallel salinity changes in the Mediterranean, Pacific, and Indian Oceans, a growing body of evidence suggests that the global hydrologic cycle has revved up in recent decades.

Among other possible climate impacts, an accelerated evaporation /precipitation cycle would continue to freshen northern North Atlantic waters--a linchpin and potential Achilles' heel in Earth's climate system. The North Atlantic is one of the few places on Earth where surface waters become dense enough to sink to the abyss. The plunge of this great mass of cold, salty waters helps drive a global ocean circulation system, often called the Ocean Conveyor. This Conveyor helps draw warm Gulf Stream waters northward in the Atlantic, pumping heat into the northern regions that significantly moderates wintertime air temperatures, especially in Europe.

If the North Atlantic becomes too fresh, its waters would stop sinking, and the Conveyor could slow down. Analyses of ice cores, deep-sea sediment cores, and other geologic evidence have clearly demonstrated that the Conveyor has abruptly slowed down or halted many times in Earth's history. That has caused the North Atlantic region to cool significantly and brought long-term drought conditions to other areas of the Northern Hemisphere-- over time spans as short as years to decades.

Melting glaciers and Arctic sea ice, another consequence of global warming, are one source of additional fresh water to the North Atlantic. An accelerated water cycle also appears to be increasing precipitation in higher latitudes, contributing to the freshening of North Atlantic waters and increasing the possibility of slowing the Conveyor.

A cooling of the North Atlantic region would slow the melting process, curtail the influx of fresh water to the North Atlantic, and the Conveyor would again begin to circulate ocean waters. However, global warming and an accelerated water cycle would continue to bring fresh water to high latitudes--possibly enough to   maintain a cap on the Conveyor even if the Arctic melting ceased. Monitoring Earth's hydrological cycle is critical, the scientists said, because of its potential near-term impacts on Earth's climate.

The research was supported by the National Science Foundation, Framework V Programme of the European Community, the National Oceanic and Atmospheric Administration's Consortium on the Ocean's Role in Climate, and the Ocean and Climate Change Institute at Woods Hole Oceanographic Institution.

WHOI is a private, independent marine research and engineering, and higher education organization located in Falmouth, MA. Its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment. Established in 1930 on a recommendation from the National Academy of Sciences, the Institution is organized into five departments, interdisciplinary institutes and a marine policy center, and conducts a joint graduate education program with the Massachusetts Institute of Technology.

 
www.innovations-report.com  
University of California - Santa Cruz
New evidence of global warming in Earth’s past supports greenhouse climate theory


New evidence of global warming in Earth’s past supports current models for how climate responds to greenhouse gases

CA--Scientists have filled in a key piece of the global climate picture for a period 55 million years ago that is considered one of the most abrupt and extreme episodes of global warming in Earth’s history. The new results from an analysis of sediment cores from the ocean floor are consistent with theoretical predictions of how Earth’s climate would respond to rising concentrations of greenhouse gases in the atmosphere.

The new study, led by James Zachos, professor of Earth sciences at the University of California, Santa Cruz, will be published online by Science Express on October 23, and will appear in a later print edition of Science magazine.

The researchers analyzed sediments deposited on the seafloor during a period known as the Paleocene-Eocene Thermal Maximum, when a massive release of heat-trapping greenhouse gases is thought to have triggered a runaway process of global warming. Climate theory predicts that the increase in greenhouse gases would have caused temperatures to rise all over the planet, with greater increases in sea surface temperatures at high latitudes than at low latitudes.

Zachos and a team of researchers at UCSC and several other institutions have now obtained the first reliable estimates of the change in tropical sea surface temperatures during this period. When combined with existing records of sea surface temperatures at high latitudes, the findings fit well with the predictions of computer simulations based on current climate theory.

The study provides important backing for the climate models that scientists are using to predict the effects of the current rise in atmospheric carbon dioxide due to industrial emissions, Zachos said.

"The predictions from the models seem to be consistent with the geologic record, so I’d say greenhouse climate theory is alive and well," he said. "People have raised questions about how accurate these models are in terms of handling heat transport in response to rising greenhouse gases, but this study indicates that the climate people have got it right or close to right."

The Paleocene-Eocene Thermal Maximum, starting about 55 million years ago and lasting about 150,000 years, is marked by dramatic changes in the fossil record of life in the ocean and on land. Average global temperatures increased by about 5 degrees Celsius (9 degrees Fahrenheit). The increase in sea surface temperatures at high latitudes was 8 to 10 degrees Celsius, and the new study shows a 4- to 5-degree Celsius increase in tropical sea surface temperatures.

"This event is the best example of greenhouse warming in the geologic record, and for the first time we have been able to document the climate response on a relatively broad planetary scale, from the tropics to polar latitudes," Zachos said.

The temperature estimates were derived from chemical analyses of the shells of microscopic plankton preserved in the seafloor sediments. The chemical composition of the plankton’s calcite shells reflects the temperature of the water in which they were formed. A key measurement examined in this study was the ratio of magnesium to calcium, which increases exponentially with the temperature at which the shells formed.

"The ratio of magnesium to calcium in seawater is relatively constant over the timescale of this event, so the ratio in the shells is really only sensitive to one variable, the calcification temperature," Zachos said.

UCSC graduate students Michael Wara and Steven Bohaty performed most of the chemical analyses. The researchers analyzed sediment cores recovered from a site called Shatsky Rise in the tropical Pacific during an expedition of the ship JOIDES Resolution in 2001 (Leg 198 of the Ocean Drilling Program). The cores provided a complete sequence of deposits representing the boundary between the Paleocene and Eocene epochs.

"There aren’t many places in the Pacific where you can recover sediments of this age in which the fossils are not so recrystallized that they’ve lost their original geochemical signatures," Zachos said.

ODP Leg 198 and a complementary drilling expedition in the Atlantic earlier this year (ODP Leg 208) were designed to test the leading explanation for the Paleocene-Eocene Thermal Maximum, which attributes it to a massive release of methane. Methane, a potent greenhouse gas, accumulates in frozen deposits known as clathrates found in the deep ocean near continental margins and also in the Arctic tundra. For reasons that remain unclear, the clathrates suddenly began to decompose, releasing an estimated 2,000 gigatons (2 trillion tons) of methane.

Once released, the methane would have reacted with dissolved oxygen in the ocean to produce carbon dioxide, another greenhouse gas. Large amounts of both carbon dioxide and methane would have entered the atmosphere, raising temperatures worldwide.

In addition to Zachos, Wara, and Bohaty, the coauthors on the Science paper are Margaret Delaney, professor of ocean sciences at UCSC, Maria Rose Petrizzo and Isabella Premoli-Silva of the University of Milan, Amanda Brill of the University of North Carolina, and Timothy Bralower of Pennsylvania State University. Bralower and Premoli-Silva were co-chief scientists on ODP Leg 198.

Weitere Informationen finden Sie im WWW:

24.10.2003 / Tim Stephens / Source: EurekAlert!

 
 
Ocean May Sponge Up Some Warmth Over Next 50 Years
 

This is an image of global sea surface temperatures taken from Japan National Space Development Agency's (NASDA) AMSR-E instrument aboard NASA's Aqua spacecraft on August 27, 2003. The colors in this false-color map represent temperatures of the ocean's surface waters, ranging from a low of -2°C (28°F) in the darkest green areas to a high of 35°C (95°F) in the brightest yellow-white regions. Sea ice is shown as white and land is dark gray. CREDIT: NASDA/NASA.
  • MPG movie of process
  • Greenbelt - Sep 04, 2003
    NASA's improved global climate computer model, which simulates and projects how the Earth's climate may change, indicates that the oceans have been absorbing heat since 1951 and will continue to absorb more heat from the atmosphere over the next 50 years.

    This increasing ocean heat storage suggests that global surface temperatures may warm less than previous studies projected, while the ocean acts as a bigger heat sponge. Further, such additional ocean heating would likely change regional climate patterns.

    Shan Sun and James Hansen, both of NASA's Goddard Institute for Space Studies, New York, NY, used NASA's Global Climate Model (GCM), one of the world's leading computer climate models that simulate past and potential future climate changes.

    The GCM has been enhanced with new "ocean models" that better simulate how oceans currently absorb heat and will respond to a warming global climate. The study appears in the latest issue of the American Meteorological Society's Journal of Climate.

    One of the leading reports on climate change, the Intergovernmental Panel on Climate Change (IPCC) report of 2001, suggests that between the years 1990 and 2100 the world's average temperature will rise between 0.6 and 2.5 degrees Celsius (C) or 1.1 and 4.5 Fahrenheit (F). "The enhanced GCM shows that the average global temperature would rise between 0.4 and 1.2 C (between 0.7 and 2.2 F) through the year 2050, for plausible increases of greenhouse gases, Sun said.

    Scientists measure ocean heat storage in Watts per meter squared, the rate of heating a square meter area. For example, a miniature Christmas tree bulb dissipates about 1 Watt of energy, so one bulb over every square meter would heat at a rate of 1 Watt per meter squared.

    The enhanced GCM showed the world's oceans were storing heat at a rate of about 0.2 Watts per square meter in 1951, and in the past 50 years, as atmospheric temperatures warmed, the rate of heat storage increased to about .75 Watts per square meter, capturing more heat from the atmosphere.

    This increase in ocean heat storage shows that the planet is out of energy balance, Hansen said. "This energy imbalance implies that the atmosphere and ocean will continue to warm over time, so we will see continuing climate change."

    It is important to know accurately how much heat oceans are storing, because the amount of heat stored provides a measurement of the Earths energy imbalance and indicates how much global temperature may increase in the future. It's also important to see where heat is increasing in the world's oceans, in order to predict climate changes in various geographical regions.

    Sun and Hansen also looked at changes of precipitation and ocean currents, other factors that warmer world-wide waters may impact. If greenhouse gases continue to increase rapidly, the model projects significant ocean warming during the next 50 years in the Eastern Pacific Ocean, off the U.S. west coast, which could have biological consequences for ocean life.

    The results also project increased precipitation and evaporation over the North Atlantic Ocean, increasing the fresh water in the region. An increase in freshwater has long been suspected as something that could weaken the northward transport of heat by the Atlantic Ocean, thus causing Europe to become cooler, even while the world becomes warmer. Sun and Hansen find, however, that the ocean circulation does not weaken significantly according to their model, so they expect no cooling effect on Europe.

    More monitoring of ocean temperatures is needed to further the studies of ocean behavior. Ocean temperature readings currently do not reach full ocean depths, as is needed to increase the accuracy of future predictions.

    With the new Ocean Models included in the GCM, if measurements of the amount of heat held by oceans are improved, it may be possible to begin to better quantify the Earth's changing radiation imbalance and its causes with an accuracy of about one decade.

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    Abrupt climate change: can society cope?
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    Cited by 24 - Web Search - met.rdg.ac.uk - maelstrom.seos.uvic.ca

     

    Abrupt climate change and thermohaline circulation: Mechanisms and predictability
    J Marotzke - Perspectives, 2000 - intl.pnas.org
    ... Indian Ocean), via the Southern Ocean, requires increased ... Abrupt climate change may
    not have been merely a feature ... 23) have shown that global warming can lead ...
    Cited by 24 - Web Search - pubmedcentral.nih.gov - dx.doi.org - pnas.org - all 5 versions »

    Study of abrupt climate change by a coupled ocean-atmosphere model
    S Manabe, RJ Stouffer - Quaternary Science Reviews, 2000 - gfdl.noaa.gov
    ... Study of abrupt climate change by a coupled ocean-atmosphere model SVUKURO MANABE
    and RONALD J. STOUFFER Institute for Global Change, 7F SEAVANS N Bldge.. ...
    Cited by 16 - View as HTML - Web Search - gfdl.gov - gfdl.gov - all 4 versions »

    Ocean circulation and climate during the past 120, 000 years
    S Rahmstorf… - Nature, 2002 - nature.com
    ... 207 T he world ocean is one of the main constituents of the climate system and affects
    climate in a multitude of ways. ... Ocean circulation and climate ...
    Cited by 46 - Web Search - adsabs.harvard.edu - ncbi.nlm.nih.gov - csa.com - all 5 versions »

    Intrinsic limits to predictability of abrupt regional climate change in IPCC SRES scenarios
    M Schaeffer, FM Selten, JD Opsteegh, H Goosse - Geophysical Research Letters, 2002 - knmi.nl
    ... RJ Stouffer, Simulation of abrupt climate change induced by ... boundary conditions in
    ocean models, Tellus ... Ganopolski, Long-term global warming scenarios computed ...
    Cited by 10 - View as HTML - Web Search - adsabs.harvard.edu - csa.com - Library Search

    New chronology for the late Paleocene thermal maximum and its environmental implications
    U Roehl, TJ Bralower, RD Norris, G Wefer - Geology, 2000 - geology.geoscienceworld.org
    ... Thomas and Shackleton, 1996); global warming also may have ... 165: College Station,
    Texas, Ocean Drilling Program ... SW, Jr, 1993, Abrupt climate change and transient ...
    Cited by 45 - Web Search - gsajournals.org - geology.geoscienceworld.org

    Response of a coupled ocean-atmosphere model to increasing atmospheric carbon dioxide: sensitivity …
    RJ Stouffer, S Manabe - Journal of Climate, 1999 - ams.allenpress.com
    ... 1997 ), and abrupt climate change (Manabe and Stouffer 1995 , 1997 ... in absolute humidity
    associated with global warming in the ... of freshwater at the ocean surface ...
    Cited by 57 - Web Search - gfdl.gov - gfdl.noaa.gov - adsabs.harvard.edu - all 8 versions »

    Abrupt climate changes: from the past to the future—a review
    TF Stocker - International Journal of Earth Sciences, 1999 - springerlink.com
    ... most likley due to reorganisations of the atmosphere–ocean system. ... Key words Abrupt
    climate change 7 Thermohaline circulation 7 Deglaciation 7 Paleoclimate 7 ...
    Cited by 16 - Web Search - climate.unibe.ch - sheridan.geog.kent.edu - hps.elte.hu

    High-resolution records of the late Paleocene thermal maximum and circum-Caribbean volcanism: Is …
    TJ Bralower, DJ Thomas, JC Zachos, MM Hirschmann, … - Geology, 1997 - oceanography.tamu.edu
    ... that resulted in rapid global warming and dramatic ... 165: College Station, Texas, Ocean
    Drilling Program ... Wise, SW, Jr., 1993, Abrupt climate change and transient ...
    Cited by 41 - View as HTML - Web Search - geology.geoscienceworld.org

    Integrated assessment of abrupt climatic changes
    M Mastrandrea, SH Schneider - Climate Policy, 2001 - iis-db.stanford.edu
    ... considered rate-dependent damages from global warming (Peck and ... al., 1997), and specific
    abrupt climate change damages from ocean circulation changes ...
    Cited by 40 - Web Search - iiasa.ac.at - adsabs.harvard.edu - all 4 versions »

    New evidence for abrupt climate change in the Cretaceous and Paleogene: An Ocean Drilling Program …
    TJ Bralower, I Premoli-Silva, MJ Malone… - GSA Today, 2000 - gsajournals.org
    ... New evidence for abrupt climate change in the Cretaceous and ... to a profound change
    in deep ocean circulation ... Predictions for modern global warming resulting from ...
    Cited by 5 - Web Search - indiana.edu

    Abrupt Non-Linear Climate Change, Irreversibility and Surprise
    S Schneider - consideration and review to the participants of the OECD …, 2002 - oecd.org
    ... Table 1. Projected Effects of Global Warming During the 21st Century ... of the processes
    and interrelationships involved (such as coupled ocean, atmosphere and ...
    Cited by 17 - View as HTML - Web Search - stephenschneider.stanford.edu - iis-db.stanford.edu

    Past and future reorganizations in the climate system
    TF Stocker - Quat. Sci. Rev, 2000 - climate.unibe.ch
    ... to obtain a clearer picture of possible regional expressions of abrupt climate change
    in
    Antarctica
    . ... of a rapid turn on of the ventilation of the deep ocean. ...
    Cited by 52 - View as HTML - Web Search - 130.92.227.10 - pages.unibe.ch - pages.unibe.ch - all 5 versions »

    Mechanisms determining the Atlantic thermohaline circulation response to greenhouse gas forcing in a …
    RB Thorpe, JM Gregory, TC Johns, RA Wood, JFB … - J. Climate, 2001 - ams.allenpress.com
    ... a probable cause of past abrupt climate change (Duplessy et ... 2 -induced changes of
    the ocean's circulation and ... On the modification of global warming by sulphate ...
    Cited by 43 - Web Search - ams.allenpress.com - adsabs.harvard.edu

    Changes in atmospheric circulation over northern hemisphere oceans associated with the rapid warming …
    C Fu, HF Diaz, D Dong, JO Fletcher - International Journal of Climatology, 1999 - doi.wiley.com
    ... Hemisphere (mostly in the Pacific Ocean) in the ... Theoretical work on abrupt climate
    change has flourished only ... the occurrence of the rapid global warming in the ...
    Cited by 21 - Web Search - doi.wiley.com

    Geophysical, archaeological, and historical evidence support a solar-output model for climate change
    CA Perry, KJ Hsu - Proc Natl Acad Sci USA, 2000 - pnas.org
    ... people moved to the ocean shores great ... Throughout history, global warming has brought
    prosperity whereas ... & Labeyrie, LD (1987) Abrupt Climate Change (D. Reidel ...
    Cited by 10 - Web Search - pnas.org - pubmedcentral.nih.gov - ncbi.nlm.nih.gov

     
     
     
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