Tag Archives: IPCC

E. Antarctic ice basin ‘may be at risk’

The East Antarctic ice sheet is thought by most scientists to be stable. But a German team says it has found how part of it could in time melt unstoppably. LONDON, 4 May – Part of the East Antarctic ice sheet may be less stable than anyone had realised, researchers based in Germany have found. Writing in Nature Climate Change, two scientists from the Potsdam Institute for Climate Impact Research (PIK) say the melting of quite a small volume of ice on the East Antarctic shore could ultimately trigger a discharge of ice into the ocean which would result in unstoppable sea-level rise for thousands of years ahead. Their findings, which they say amount to the discovery of a hitherto overlooked source of sea level rise, appear unlikely to happen any time soon. They are based on computer simulations of the Antarctic ice flow using improved data of the ground profile beneath the ice sheet. “East Antarctica’s Wilkes Basin is like a bottle on a slant,” said Matthias Mengel, the lead author of the study. “Once uncorked, it empties out.” The basin is the largest region of marine ice on rocky ground in East Antarctica. At the moment a rim of ice at the coast holds the ice behind it in place, like a cork holding back the contents of a bottle. The air over Antarctica remains cold, but oceanic warming can cause the ice on the coast to melt. This could make the relatively small “cork” disappear. Once it had gone, the result would be a long-term sea level rise of three to four metres. “The full sea-level rise would ultimately be up to 80 times bigger than the initial melting of the ice cork,” says the study’s co-author, Anders Levermann. “Until recently, only West Antarctica was considered unstable, but now we know that its ten times bigger counterpart in the East might also be at risk.”

Stability ‘over-estimated’

Levermann is a lead author of the sea-level change chapter of the most recent scientific assessment report by the Intergovernmental Panel on Climate Change, the IPCC. Its report, published in September 2013, says Antarctica’s total sea level contribution could be up to 16 centimetres during this century. “If half of that ice loss occurred in the ice-cork region, then the discharge would begin. We have probably overestimated the stability of East Antarctica so far,” says Levermann. Melting would cause the retreat of the grounding line, where the ice on the solid continental landmass meets the sea and starts to float. The rocky ground beneath the ice in the Wilkes Basin forms a huge valley below sea-level which slopes downwards as it heads inland. When the grounding line retreats from its current position on a ridge into the valley, the rim of the ice facing the ocean becomes higher than before. More ice is then pushed into the sea, eventually breaking off and melting. And the warmer it gets, the faster this happens. For all the ice in the Wilkes Basin to be lost in this way would take 5,000-10,000 years, the simulations showed. But once it had started, the discharge of ice would slowly but relentlessly continue until the whole basin was empty, even if the climate ceased to warm.

Unavoidable consequences

“This is the underlying issue here”, said Matthias Mengel. “By emitting more and more greenhouse gases we might trigger responses now that we may not be able to stop in the future.” He told the Climate News Network: “While the sparse existing observations do not indicate warmer water inflow towards the Wilkes ice sheet margin at present, there is no reason why changes similar to those in West Antarctica could not also occur here.” The possibility remains a distant prospect. Mengel said some simulations produced the warm ocean conditions needed to remove the ice cork within the next 200 years, but It would take around 2,000 years to raise global sea levels by one metre. He added: “The issue is that this would then be unstoppable…We have detected a new and previously overlooked source of sea level rise, therefore these numbers have to be added to the present sea level rise projections of the IPCC. “Sea level as projected for the forthcoming centuries is already potentially devastating for many coastal areas around the globe. Every centimetre of sea level rise on top of these projections is even more significant.” – Climate News Network

The East Antarctic ice sheet is thought by most scientists to be stable. But a German team says it has found how part of it could in time melt unstoppably. LONDON, 4 May – Part of the East Antarctic ice sheet may be less stable than anyone had realised, researchers based in Germany have found. Writing in Nature Climate Change, two scientists from the Potsdam Institute for Climate Impact Research (PIK) say the melting of quite a small volume of ice on the East Antarctic shore could ultimately trigger a discharge of ice into the ocean which would result in unstoppable sea-level rise for thousands of years ahead. Their findings, which they say amount to the discovery of a hitherto overlooked source of sea level rise, appear unlikely to happen any time soon. They are based on computer simulations of the Antarctic ice flow using improved data of the ground profile beneath the ice sheet. “East Antarctica’s Wilkes Basin is like a bottle on a slant,” said Matthias Mengel, the lead author of the study. “Once uncorked, it empties out.” The basin is the largest region of marine ice on rocky ground in East Antarctica. At the moment a rim of ice at the coast holds the ice behind it in place, like a cork holding back the contents of a bottle. The air over Antarctica remains cold, but oceanic warming can cause the ice on the coast to melt. This could make the relatively small “cork” disappear. Once it had gone, the result would be a long-term sea level rise of three to four metres. “The full sea-level rise would ultimately be up to 80 times bigger than the initial melting of the ice cork,” says the study’s co-author, Anders Levermann. “Until recently, only West Antarctica was considered unstable, but now we know that its ten times bigger counterpart in the East might also be at risk.”

Stability ‘over-estimated’

Levermann is a lead author of the sea-level change chapter of the most recent scientific assessment report by the Intergovernmental Panel on Climate Change, the IPCC. Its report, published in September 2013, says Antarctica’s total sea level contribution could be up to 16 centimetres during this century. “If half of that ice loss occurred in the ice-cork region, then the discharge would begin. We have probably overestimated the stability of East Antarctica so far,” says Levermann. Melting would cause the retreat of the grounding line, where the ice on the solid continental landmass meets the sea and starts to float. The rocky ground beneath the ice in the Wilkes Basin forms a huge valley below sea-level which slopes downwards as it heads inland. When the grounding line retreats from its current position on a ridge into the valley, the rim of the ice facing the ocean becomes higher than before. More ice is then pushed into the sea, eventually breaking off and melting. And the warmer it gets, the faster this happens. For all the ice in the Wilkes Basin to be lost in this way would take 5,000-10,000 years, the simulations showed. But once it had started, the discharge of ice would slowly but relentlessly continue until the whole basin was empty, even if the climate ceased to warm.

Unavoidable consequences

“This is the underlying issue here”, said Matthias Mengel. “By emitting more and more greenhouse gases we might trigger responses now that we may not be able to stop in the future.” He told the Climate News Network: “While the sparse existing observations do not indicate warmer water inflow towards the Wilkes ice sheet margin at present, there is no reason why changes similar to those in West Antarctica could not also occur here.” The possibility remains a distant prospect. Mengel said some simulations produced the warm ocean conditions needed to remove the ice cork within the next 200 years, but It would take around 2,000 years to raise global sea levels by one metre. He added: “The issue is that this would then be unstoppable…We have detected a new and previously overlooked source of sea level rise, therefore these numbers have to be added to the present sea level rise projections of the IPCC. “Sea level as projected for the forthcoming centuries is already potentially devastating for many coastal areas around the globe. Every centimetre of sea level rise on top of these projections is even more significant.” – Climate News Network

Climate scientists 3 Economists 0

FOR IMMEDIATE RELEASE Hold up the trophy. Open the champagne. Climate scientists have easily won the game. According to a recent study, when it comes to the accuracy of forecasts and projections, the climate side is much better at the game  than the economists’ team. London, 14 March – The study, by the New Economics Foundation (NEF), a UK based independent think-tank, examines the accuracy and precision of projections made by both climate scientists and economists over the past 20 years. First, the economists. The study looked at measures commonly used in long term UK government economic modelling and decision making, using 1995 as a baseline: the population forecast for England and the forecast for the UK Treasury’s  debt to Gross Domestic Product (GDP) ratio. In the US, the forecasts on oil prices over the period made by the US Energy Information Administration (EIA) were also examined.

Economic inaccuracies

The NEF finds the economists’ projections both inaccurate and imprecise in all three areas.  The economists saw the population of England growing at a fairly modest level from 1995 to the present – from around 49 million 20 years ago to 51.5 million now. In fact England’s population has risen steeply, particularly over the past 10 years and is now approaching 54 million.  The UK Treasury’s forecasts on the GDP to forecasts on the debt to GDP ratio fared no better, displaying “a bias towards optimism in government economic forecasts” says the study. Meanwhile the crystal ball gazing of economists at the EIA was a miserable failure: they predicted oil prices rising on a gentle curve in the 15 years 1995 to 2010. In fact prices have been extremely volatile, rising at some points by more than five times the predicted figure. And of course, the most damning judgement of the financial boffins forecasting skills is the failure of nearly all economic pundits to predict the 2008 recession.

Better projections

Contrast this with predictions made by climate scientists over the past 20 years, in particular those made by the Intergovernmental Panel on Climate Change (IPCC). Again the NEF looks at three specific areas of projection – carbon concentration in the atmosphere, the temperature anomaly and forecasts since 1995 of sea level rise.  There can be no doubt of the result, says the study. “Climate models outperform major economic forecasts on accuracy… global temperature, sea level and carbon concentration have all risen within the ranges originally forecast (by the IPCC) in 1995.” While on one level this can be looked at as a bit of amusing sparring between two academic disciplines, there is serious business going on here. The NEF makes the point that despite the dubious track record of economic forecasting, many government policy decisions are based on the data offered up.

Devious deniers

Meanwhile the climate deniers have succeeded in highlighting the narrow bands of uncertainty in the work of climate scientists – stalling action on the issue. Sections of the media collude in this process. “This emphasis on uncertainty has a negative impact on climate progress” says the report. “It slows down environmental policy and corrodes the public will to act.” The NEF draws attention to the IPCC’s 5th Assessment Report and its revised estimate of certainty – up to 95% – that humans have been the main cause of global warming from 1950 to the present. “This 95% has a precise scientific meaning. It is higher than the certainty that vitamins are good for your health and equivalent to the certainty that cigarettes cause lung cancer.” Despite this, the climate denial bandwagon continues to roll along. “We often hear the argument that climate models are too uncertain to bother taking action, but this is not borne out by the facts” says Aniol Esteban, the head of environmental economics at the NEF. “We can’t go on making huge policy and investment decisions based on financial advice no more reliable than a coin flip, while at the same time discrediting climate models with a 20 year track record of accuracy. The double standard has to end now.” – Climate News Network

FOR IMMEDIATE RELEASE Hold up the trophy. Open the champagne. Climate scientists have easily won the game. According to a recent study, when it comes to the accuracy of forecasts and projections, the climate side is much better at the game  than the economists’ team. London, 14 March – The study, by the New Economics Foundation (NEF), a UK based independent think-tank, examines the accuracy and precision of projections made by both climate scientists and economists over the past 20 years. First, the economists. The study looked at measures commonly used in long term UK government economic modelling and decision making, using 1995 as a baseline: the population forecast for England and the forecast for the UK Treasury’s  debt to Gross Domestic Product (GDP) ratio. In the US, the forecasts on oil prices over the period made by the US Energy Information Administration (EIA) were also examined.

Economic inaccuracies

The NEF finds the economists’ projections both inaccurate and imprecise in all three areas.  The economists saw the population of England growing at a fairly modest level from 1995 to the present – from around 49 million 20 years ago to 51.5 million now. In fact England’s population has risen steeply, particularly over the past 10 years and is now approaching 54 million.  The UK Treasury’s forecasts on the GDP to forecasts on the debt to GDP ratio fared no better, displaying “a bias towards optimism in government economic forecasts” says the study. Meanwhile the crystal ball gazing of economists at the EIA was a miserable failure: they predicted oil prices rising on a gentle curve in the 15 years 1995 to 2010. In fact prices have been extremely volatile, rising at some points by more than five times the predicted figure. And of course, the most damning judgement of the financial boffins forecasting skills is the failure of nearly all economic pundits to predict the 2008 recession.

Better projections

Contrast this with predictions made by climate scientists over the past 20 years, in particular those made by the Intergovernmental Panel on Climate Change (IPCC). Again the NEF looks at three specific areas of projection – carbon concentration in the atmosphere, the temperature anomaly and forecasts since 1995 of sea level rise.  There can be no doubt of the result, says the study. “Climate models outperform major economic forecasts on accuracy… global temperature, sea level and carbon concentration have all risen within the ranges originally forecast (by the IPCC) in 1995.” While on one level this can be looked at as a bit of amusing sparring between two academic disciplines, there is serious business going on here. The NEF makes the point that despite the dubious track record of economic forecasting, many government policy decisions are based on the data offered up.

Devious deniers

Meanwhile the climate deniers have succeeded in highlighting the narrow bands of uncertainty in the work of climate scientists – stalling action on the issue. Sections of the media collude in this process. “This emphasis on uncertainty has a negative impact on climate progress” says the report. “It slows down environmental policy and corrodes the public will to act.” The NEF draws attention to the IPCC’s 5th Assessment Report and its revised estimate of certainty – up to 95% – that humans have been the main cause of global warming from 1950 to the present. “This 95% has a precise scientific meaning. It is higher than the certainty that vitamins are good for your health and equivalent to the certainty that cigarettes cause lung cancer.” Despite this, the climate denial bandwagon continues to roll along. “We often hear the argument that climate models are too uncertain to bother taking action, but this is not borne out by the facts” says Aniol Esteban, the head of environmental economics at the NEF. “We can’t go on making huge policy and investment decisions based on financial advice no more reliable than a coin flip, while at the same time discrediting climate models with a 20 year track record of accuracy. The double standard has to end now.” – Climate News Network

Amazon is 'at higher risk of tree loss'

FOR IMMEDIATE RELEASE
Part of the Amazon rainforest may be more vulnerable to the effects of climate change than first thought, US researchers say.

LONDON, 21 October – Researchers say the southern part of the Amazon rainforest is at a far higher risk of dieback than the models used in the most recent report by the Intergovernmental Panel on Climate Change (IPCC).

The research team, led by Professor Rong Fu of the University of Texas, say that this is because the forest is drying out much quicker than projected.

If the damage is severe enough, they say the loss of rainforest could cause the release of large volumes of carbon dioxide into the atmosphere, and could also disrupt plant and animal communities in one of the world’s most biodiversity-rich regions, as outlined in the Proceedings of the National Academy of Sciences.

The team used ground-based rainfall measurements from the past three decades. Findings showed that since 1979, the dry season in southern Amazonia lasted about a week longer in each decade.

At the same time, the annual fire seasons have become longer. The researchers say the most likely explanation for the increasingly longer dry seasons is global warming.

“The dry season over the southern Amazon is already marginal for maintaining rainforest,” says Professor Fu. “At some point, if it becomes too long, the rainforest will reach a tipping point.”

She says the length of the dry season is the most important climate factor controlling the southern Amazon rainforest. If it is too long, the forest will not survive.

A study published earlier this year suggested that rainforests worldwide might be able to withstand the impacts of climate change more successfully than thought.

The new results also contrast sharply with forecasts made by the models used by the IPCC: even under future scenarios in which greenhouse gases rise dramatically, those models project the southern Amazon dry season will be at most 10 days longer by the end of the century, and that the risk of climate change-induced rainforest dieback should therefore be relatively low.

Rainfall limited

Professor Fu and her colleagues say the water stored in the forest soil at the end of each wet season is all that the trees have to last them through the dry months. The longer that lasts – regardless of how wet the wet season was – the more stressed the trees become and the more susceptible they are to forest fires.

They say the most likely explanation for the lengthening dry season in recent decades is human-caused greenhouse warming, which inhibits rainfall in two ways: It makes it harder for warm, dry air near the surface to rise and freely mix with cool, moist air above; and it blocks incursions by cold weather fronts from outside the tropics which could trigger rainfall.

The team says the IPCC’s climate models represent these processes poorly, which might explain why they project only a slightly longer Amazonian dry season.

The Amazon rainforest normally acts as a carbon sink, removing atmospheric CO2 and storing it. But during a severe drought in 2005 it went into reverse, releasing one petagram of carbon (one billion tonnes – about one-tenth of annual human emissions) to the atmosphere.

Fu and her colleagues estimate that if dry seasons continue to lengthen at just half the rate seen in recent decades, the 2005 Amazon drought could become the norm rather than the exception by the end of this century.

Some scientists think the combination of longer dry seasons, higher surface temperatures and more fragmented forests caused by deforestation could eventually convert much of southern Amazonia from rainforest to savanna.

Earlier studies have shown that human-caused deforestation in the Amazon can alter rainfall patterns. But the researchers did not see a strong sign of that in the pattern of increasing dry season length. That was most pronounced in the south-western Amazon, while the most intense deforestation occurred in the south-east.

Because the north western Amazon has much higher rainfall and a shorter dry season than the south, the researchers think it is much less vulnerable to climate change – Climate News Network

FOR IMMEDIATE RELEASE
Part of the Amazon rainforest may be more vulnerable to the effects of climate change than first thought, US researchers say.

LONDON, 21 October – Researchers say the southern part of the Amazon rainforest is at a far higher risk of dieback than the models used in the most recent report by the Intergovernmental Panel on Climate Change (IPCC).

The research team, led by Professor Rong Fu of the University of Texas, say that this is because the forest is drying out much quicker than projected.

If the damage is severe enough, they say the loss of rainforest could cause the release of large volumes of carbon dioxide into the atmosphere, and could also disrupt plant and animal communities in one of the world’s most biodiversity-rich regions, as outlined in the Proceedings of the National Academy of Sciences.

The team used ground-based rainfall measurements from the past three decades. Findings showed that since 1979, the dry season in southern Amazonia lasted about a week longer in each decade.

At the same time, the annual fire seasons have become longer. The researchers say the most likely explanation for the increasingly longer dry seasons is global warming.

“The dry season over the southern Amazon is already marginal for maintaining rainforest,” says Professor Fu. “At some point, if it becomes too long, the rainforest will reach a tipping point.”

She says the length of the dry season is the most important climate factor controlling the southern Amazon rainforest. If it is too long, the forest will not survive.

A study published earlier this year suggested that rainforests worldwide might be able to withstand the impacts of climate change more successfully than thought.

The new results also contrast sharply with forecasts made by the models used by the IPCC: even under future scenarios in which greenhouse gases rise dramatically, those models project the southern Amazon dry season will be at most 10 days longer by the end of the century, and that the risk of climate change-induced rainforest dieback should therefore be relatively low.

Rainfall limited

Professor Fu and her colleagues say the water stored in the forest soil at the end of each wet season is all that the trees have to last them through the dry months. The longer that lasts – regardless of how wet the wet season was – the more stressed the trees become and the more susceptible they are to forest fires.

They say the most likely explanation for the lengthening dry season in recent decades is human-caused greenhouse warming, which inhibits rainfall in two ways: It makes it harder for warm, dry air near the surface to rise and freely mix with cool, moist air above; and it blocks incursions by cold weather fronts from outside the tropics which could trigger rainfall.

The team says the IPCC’s climate models represent these processes poorly, which might explain why they project only a slightly longer Amazonian dry season.

The Amazon rainforest normally acts as a carbon sink, removing atmospheric CO2 and storing it. But during a severe drought in 2005 it went into reverse, releasing one petagram of carbon (one billion tonnes – about one-tenth of annual human emissions) to the atmosphere.

Fu and her colleagues estimate that if dry seasons continue to lengthen at just half the rate seen in recent decades, the 2005 Amazon drought could become the norm rather than the exception by the end of this century.

Some scientists think the combination of longer dry seasons, higher surface temperatures and more fragmented forests caused by deforestation could eventually convert much of southern Amazonia from rainforest to savanna.

Earlier studies have shown that human-caused deforestation in the Amazon can alter rainfall patterns. But the researchers did not see a strong sign of that in the pattern of increasing dry season length. That was most pronounced in the south-western Amazon, while the most intense deforestation occurred in the south-east.

Because the north western Amazon has much higher rainfall and a shorter dry season than the south, the researchers think it is much less vulnerable to climate change – Climate News Network

Amazon is ‘at higher risk of tree loss’

FOR IMMEDIATE RELEASE Part of the Amazon rainforest may be more vulnerable to the effects of climate change than first thought, US researchers say. LONDON, 21 October – Researchers say the southern part of the Amazon rainforest is at a far higher risk of dieback than the models used in the most recent report by the Intergovernmental Panel on Climate Change (IPCC). The research team, led by Professor Rong Fu of the University of Texas, say that this is because the forest is drying out much quicker than projected. If the damage is severe enough, they say the loss of rainforest could cause the release of large volumes of carbon dioxide into the atmosphere, and could also disrupt plant and animal communities in one of the world’s most biodiversity-rich regions, as outlined in the Proceedings of the National Academy of Sciences. The team used ground-based rainfall measurements from the past three decades. Findings showed that since 1979, the dry season in southern Amazonia lasted about a week longer in each decade. At the same time, the annual fire seasons have become longer. The researchers say the most likely explanation for the increasingly longer dry seasons is global warming. “The dry season over the southern Amazon is already marginal for maintaining rainforest,” says Professor Fu. “At some point, if it becomes too long, the rainforest will reach a tipping point.” She says the length of the dry season is the most important climate factor controlling the southern Amazon rainforest. If it is too long, the forest will not survive. A study published earlier this year suggested that rainforests worldwide might be able to withstand the impacts of climate change more successfully than thought. The new results also contrast sharply with forecasts made by the models used by the IPCC: even under future scenarios in which greenhouse gases rise dramatically, those models project the southern Amazon dry season will be at most 10 days longer by the end of the century, and that the risk of climate change-induced rainforest dieback should therefore be relatively low.

Rainfall limited

Professor Fu and her colleagues say the water stored in the forest soil at the end of each wet season is all that the trees have to last them through the dry months. The longer that lasts – regardless of how wet the wet season was – the more stressed the trees become and the more susceptible they are to forest fires. They say the most likely explanation for the lengthening dry season in recent decades is human-caused greenhouse warming, which inhibits rainfall in two ways: It makes it harder for warm, dry air near the surface to rise and freely mix with cool, moist air above; and it blocks incursions by cold weather fronts from outside the tropics which could trigger rainfall. The team says the IPCC’s climate models represent these processes poorly, which might explain why they project only a slightly longer Amazonian dry season. The Amazon rainforest normally acts as a carbon sink, removing atmospheric CO2 and storing it. But during a severe drought in 2005 it went into reverse, releasing one petagram of carbon (one billion tonnes – about one-tenth of annual human emissions) to the atmosphere. Fu and her colleagues estimate that if dry seasons continue to lengthen at just half the rate seen in recent decades, the 2005 Amazon drought could become the norm rather than the exception by the end of this century. Some scientists think the combination of longer dry seasons, higher surface temperatures and more fragmented forests caused by deforestation could eventually convert much of southern Amazonia from rainforest to savanna. Earlier studies have shown that human-caused deforestation in the Amazon can alter rainfall patterns. But the researchers did not see a strong sign of that in the pattern of increasing dry season length. That was most pronounced in the south-western Amazon, while the most intense deforestation occurred in the south-east. Because the north western Amazon has much higher rainfall and a shorter dry season than the south, the researchers think it is much less vulnerable to climate change – Climate News Network

FOR IMMEDIATE RELEASE Part of the Amazon rainforest may be more vulnerable to the effects of climate change than first thought, US researchers say. LONDON, 21 October – Researchers say the southern part of the Amazon rainforest is at a far higher risk of dieback than the models used in the most recent report by the Intergovernmental Panel on Climate Change (IPCC). The research team, led by Professor Rong Fu of the University of Texas, say that this is because the forest is drying out much quicker than projected. If the damage is severe enough, they say the loss of rainforest could cause the release of large volumes of carbon dioxide into the atmosphere, and could also disrupt plant and animal communities in one of the world’s most biodiversity-rich regions, as outlined in the Proceedings of the National Academy of Sciences. The team used ground-based rainfall measurements from the past three decades. Findings showed that since 1979, the dry season in southern Amazonia lasted about a week longer in each decade. At the same time, the annual fire seasons have become longer. The researchers say the most likely explanation for the increasingly longer dry seasons is global warming. “The dry season over the southern Amazon is already marginal for maintaining rainforest,” says Professor Fu. “At some point, if it becomes too long, the rainforest will reach a tipping point.” She says the length of the dry season is the most important climate factor controlling the southern Amazon rainforest. If it is too long, the forest will not survive. A study published earlier this year suggested that rainforests worldwide might be able to withstand the impacts of climate change more successfully than thought. The new results also contrast sharply with forecasts made by the models used by the IPCC: even under future scenarios in which greenhouse gases rise dramatically, those models project the southern Amazon dry season will be at most 10 days longer by the end of the century, and that the risk of climate change-induced rainforest dieback should therefore be relatively low.

Rainfall limited

Professor Fu and her colleagues say the water stored in the forest soil at the end of each wet season is all that the trees have to last them through the dry months. The longer that lasts – regardless of how wet the wet season was – the more stressed the trees become and the more susceptible they are to forest fires. They say the most likely explanation for the lengthening dry season in recent decades is human-caused greenhouse warming, which inhibits rainfall in two ways: It makes it harder for warm, dry air near the surface to rise and freely mix with cool, moist air above; and it blocks incursions by cold weather fronts from outside the tropics which could trigger rainfall. The team says the IPCC’s climate models represent these processes poorly, which might explain why they project only a slightly longer Amazonian dry season. The Amazon rainforest normally acts as a carbon sink, removing atmospheric CO2 and storing it. But during a severe drought in 2005 it went into reverse, releasing one petagram of carbon (one billion tonnes – about one-tenth of annual human emissions) to the atmosphere. Fu and her colleagues estimate that if dry seasons continue to lengthen at just half the rate seen in recent decades, the 2005 Amazon drought could become the norm rather than the exception by the end of this century. Some scientists think the combination of longer dry seasons, higher surface temperatures and more fragmented forests caused by deforestation could eventually convert much of southern Amazonia from rainforest to savanna. Earlier studies have shown that human-caused deforestation in the Amazon can alter rainfall patterns. But the researchers did not see a strong sign of that in the pattern of increasing dry season length. That was most pronounced in the south-western Amazon, while the most intense deforestation occurred in the south-east. Because the north western Amazon has much higher rainfall and a shorter dry season than the south, the researchers think it is much less vulnerable to climate change – Climate News Network

Greenland’s great melt is pinned on climate change

FOR IMMEDIATE RELEASE The forensic search for the mysterious agent that almost melted Greenland goes on. The latest suspect to be rounded up for questioning is the jet stream, according to scientists in Sheffield, in the UK. LONDON, 18, June – First: the story so far. For a few days in July 2012, almost 97% of the surface of Greenland began suddenly to thaw. This was a melt on an unprecedented scale. Greenland carries a burden of three million cubic kilometres of ice and even in the summer, most of it stays frozen, partly because of the island’s high latitude and partly because ice reflects sunlight, and tends normally to serve as its own insulator. The event was so unusual, and so unexpected, and on such a scale that nobody seriously suggested that the dramatic conversion of snow to slush was direct evidence of climate change because of human-induced global warming. Soot, smoke and heat At first, climatologists were inclined to see the thaw as a consequence of the record-breaking heat waves and forest fires that afflicted North America last summer: snow could have been darkened by columns of soot and smoke from forest fires, just enough to start absorbing the sunlight, some reasoned. Then in April a team at the University of Wisconsin-Madison suggested that freak cloud behaviour over Greenland at the time might have caused the melting. Clouds normally block sunlight and keep the terrain below them cool. But these clouds could have been thin enough to let solar radiation through, but thick enough to trap the consequential infra-red radiation from the ground, and raise the local temperature levels. Now Edward Hanna and colleagues at Sheffield report in the International Journal of Climatology that they have another explanation. Unusual atmospheric circulation and changes in the jet stream – the same changes that almost washed away summer in England – sent a blister of warm air sweeping over the ice sheet. Hanna and his team analysed all the weather data collected by the Danish Meteorological Institute and by US researchers, and then employed satellite readings and a computer simulation called SnowModel to reconstruct the strange turn of events. And climate change may after all be a suspect.   High melt years The Greenland Ice Sheet is a highly sensitive indicator of regional and global change, and, says Prof Hanna, been undergoing rapid warming, and losing ice, for at least the last five years and probably the last 20. “Our research found that a ‘heat dome’ of warm southerly winds over the ice sheet led to widespread surface melting.” This was not predicted by the climate models used by the Intergovernmental Panel on Climate Change, and perhaps that indicated a deficiency in those models, he suggested. The event seemed to be linked to changes in a phenomenon known to oceanographers and meteorologists as the summer North Atlantic Oscillation (NAO), another well-observed high pressure system called the Greenland Blocking Index, and the polar jet stream, all of which sent warm southerly winds sweeping over Greenland’s western coast. “The next five to 10 years will reveal whether or not 2012 was a rare event resulting from natural variability of the NAO or part of an emerging pattern of new extreme high melt years.” It was hard to predict future changes in the Greenland climate in the current state of knowledge, but important to keep on trying. There is an awful lot of ice on top of Greenland. Once it starts to melt, it is likely to be, say the Sheffield scientists,  “dominant contributor to global sea level change over the next 100 to 1,000 years.”- Climate News Network

FOR IMMEDIATE RELEASE The forensic search for the mysterious agent that almost melted Greenland goes on. The latest suspect to be rounded up for questioning is the jet stream, according to scientists in Sheffield, in the UK. LONDON, 18, June – First: the story so far. For a few days in July 2012, almost 97% of the surface of Greenland began suddenly to thaw. This was a melt on an unprecedented scale. Greenland carries a burden of three million cubic kilometres of ice and even in the summer, most of it stays frozen, partly because of the island’s high latitude and partly because ice reflects sunlight, and tends normally to serve as its own insulator. The event was so unusual, and so unexpected, and on such a scale that nobody seriously suggested that the dramatic conversion of snow to slush was direct evidence of climate change because of human-induced global warming. Soot, smoke and heat At first, climatologists were inclined to see the thaw as a consequence of the record-breaking heat waves and forest fires that afflicted North America last summer: snow could have been darkened by columns of soot and smoke from forest fires, just enough to start absorbing the sunlight, some reasoned. Then in April a team at the University of Wisconsin-Madison suggested that freak cloud behaviour over Greenland at the time might have caused the melting. Clouds normally block sunlight and keep the terrain below them cool. But these clouds could have been thin enough to let solar radiation through, but thick enough to trap the consequential infra-red radiation from the ground, and raise the local temperature levels. Now Edward Hanna and colleagues at Sheffield report in the International Journal of Climatology that they have another explanation. Unusual atmospheric circulation and changes in the jet stream – the same changes that almost washed away summer in England – sent a blister of warm air sweeping over the ice sheet. Hanna and his team analysed all the weather data collected by the Danish Meteorological Institute and by US researchers, and then employed satellite readings and a computer simulation called SnowModel to reconstruct the strange turn of events. And climate change may after all be a suspect.   High melt years The Greenland Ice Sheet is a highly sensitive indicator of regional and global change, and, says Prof Hanna, been undergoing rapid warming, and losing ice, for at least the last five years and probably the last 20. “Our research found that a ‘heat dome’ of warm southerly winds over the ice sheet led to widespread surface melting.” This was not predicted by the climate models used by the Intergovernmental Panel on Climate Change, and perhaps that indicated a deficiency in those models, he suggested. The event seemed to be linked to changes in a phenomenon known to oceanographers and meteorologists as the summer North Atlantic Oscillation (NAO), another well-observed high pressure system called the Greenland Blocking Index, and the polar jet stream, all of which sent warm southerly winds sweeping over Greenland’s western coast. “The next five to 10 years will reveal whether or not 2012 was a rare event resulting from natural variability of the NAO or part of an emerging pattern of new extreme high melt years.” It was hard to predict future changes in the Greenland climate in the current state of knowledge, but important to keep on trying. There is an awful lot of ice on top of Greenland. Once it starts to melt, it is likely to be, say the Sheffield scientists,  “dominant contributor to global sea level change over the next 100 to 1,000 years.”- Climate News Network