Tag Archives: Clouds

Warming climate may cut cloud cover

FOR IMMEDIATE RELEASE One of the great unknowns of climate science is what effect clouds have in accelerating or slowing warming. A new study sheds a disturbing light on their possible impact. LONDON, 31 December – Australian and French scientists believe they have cracked one of the great puzzles of climate change and arrived at a more accurate prediction of future temperatures. The news is not good, according to Steven Sherwood of Australia’s Centre for Excellence for Climate System Science at the University of New South Wales. If carbon emissions are not reduced, then by 2100 the world will have warmed by 4°C. This figure does not, at first, sound high: researchers have been warning for 20 years on the basis of computer models that under the notorious business-as-usual scenario in which everybody goes on burning coal and oil, then as carbon dioxide levels double, global temperatures could rise by between 1.5°C and 4.5°C. Pessimists could cite one extreme, optimists the other: the range of uncertainty was a recognition that there were still some big unknowns in the machinery of climate, and one of those unknowns was the behaviour of the clouds in a warmer world. More warmth means more evaporation, more vapour could mean more clouds. Low-level clouds reflect sunlight back into space, and help cool the climate a bit. This is what engineers call negative feedback.

Drying the clouds

But if more water vapour actually led to less cloud, then more sunlight would reach the surface and the world would warm even more: positive feedback would be in play. Climate models cater for such possibilities, but cannot choose between them. What Sherwood and his colleagues from Pierre and Marie Curie University in Paris did was to start with some real-world observations of what happens when water vapour gets into the atmosphere. They report in Nature that updraughts of water vapour can rise 15 kms to form high clouds that produce heavy rains, or the vapour can rise just a few kilometers before coming back to the surface without forming rain clouds. When this happens the process actually reduces the overall cloud cover because it dessicates the clouds above: it draws away water vapour from the higher regions in a process called convective mixing. Climate models in the past have tended to predict high cloud formation that damps warming. What Sherwood and his colleagues have done is demonstrate that the world may not work like that.

Profound effects in prospect

So the next step was to feed the new understanding into computer simulations. These then showed that climate cycles could develop that would take vapour to a wider range of heights in the atmosphere, with the consequence that fewer clouds would form as climate warms. If so – and other climate scientists will have their own arguments with the findings – then as carbon dioxide levels double, which they will do in the next 50 years or so, the average planetary temperatures will increase by a colossal 4°C. Governments have expressed the wish – but not so far taken the necessary action – to contain planetary temperatures to a rise of no more than 2°C. If Sherwood and colleagues are right, they will not get their wish. And the process will go on. The temperatures will continue to soar beyond 2100, to reach an additional 8°C by 2200. “Climate skeptics like to criticise climate models for getting things wrong, and we are the first to admit they are not perfect, but what we are finding is that the mistakes are being made by those models that predict less warming, not those that predict more”, said Professor Sherwood. “Rises in global average temperatures of this magnitude will have profound impacts on the world and the economies of many countries if we don’t urgently curb our emissions.” – Climate News Network

FOR IMMEDIATE RELEASE One of the great unknowns of climate science is what effect clouds have in accelerating or slowing warming. A new study sheds a disturbing light on their possible impact. LONDON, 31 December – Australian and French scientists believe they have cracked one of the great puzzles of climate change and arrived at a more accurate prediction of future temperatures. The news is not good, according to Steven Sherwood of Australia’s Centre for Excellence for Climate System Science at the University of New South Wales. If carbon emissions are not reduced, then by 2100 the world will have warmed by 4°C. This figure does not, at first, sound high: researchers have been warning for 20 years on the basis of computer models that under the notorious business-as-usual scenario in which everybody goes on burning coal and oil, then as carbon dioxide levels double, global temperatures could rise by between 1.5°C and 4.5°C. Pessimists could cite one extreme, optimists the other: the range of uncertainty was a recognition that there were still some big unknowns in the machinery of climate, and one of those unknowns was the behaviour of the clouds in a warmer world. More warmth means more evaporation, more vapour could mean more clouds. Low-level clouds reflect sunlight back into space, and help cool the climate a bit. This is what engineers call negative feedback.

Drying the clouds

But if more water vapour actually led to less cloud, then more sunlight would reach the surface and the world would warm even more: positive feedback would be in play. Climate models cater for such possibilities, but cannot choose between them. What Sherwood and his colleagues from Pierre and Marie Curie University in Paris did was to start with some real-world observations of what happens when water vapour gets into the atmosphere. They report in Nature that updraughts of water vapour can rise 15 kms to form high clouds that produce heavy rains, or the vapour can rise just a few kilometers before coming back to the surface without forming rain clouds. When this happens the process actually reduces the overall cloud cover because it dessicates the clouds above: it draws away water vapour from the higher regions in a process called convective mixing. Climate models in the past have tended to predict high cloud formation that damps warming. What Sherwood and his colleagues have done is demonstrate that the world may not work like that.

Profound effects in prospect

So the next step was to feed the new understanding into computer simulations. These then showed that climate cycles could develop that would take vapour to a wider range of heights in the atmosphere, with the consequence that fewer clouds would form as climate warms. If so – and other climate scientists will have their own arguments with the findings – then as carbon dioxide levels double, which they will do in the next 50 years or so, the average planetary temperatures will increase by a colossal 4°C. Governments have expressed the wish – but not so far taken the necessary action – to contain planetary temperatures to a rise of no more than 2°C. If Sherwood and colleagues are right, they will not get their wish. And the process will go on. The temperatures will continue to soar beyond 2100, to reach an additional 8°C by 2200. “Climate skeptics like to criticise climate models for getting things wrong, and we are the first to admit they are not perfect, but what we are finding is that the mistakes are being made by those models that predict less warming, not those that predict more”, said Professor Sherwood. “Rises in global average temperatures of this magnitude will have profound impacts on the world and the economies of many countries if we don’t urgently curb our emissions.” – 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

Clouds 'cool Earth less than thought'

EMBARGOED until 2301 GMT on Thursday 16 May
The ability of clouds to reflect sunlight back into space and so help to cool the Earth appears to have been over-estimated, researchers say, in a study especially significant for major polluters.

LONDON, 17 May – Extra cloud cover caused by emissions of industrial pollutants is known to reduce the effects of global warming, but its impact in reducing temperatures has been over-estimated in the climate models, new research has found.

This is particularly significant for China and India, because it has been believed that these two giant countries would be partly shielded from the effects of climate change by their appalling industrial pollution. The Max Planck Institute for Chemistry in Germany believes this potential cooling effect has been exaggerated.

The Institute’s study looked at the behaviour of sulphate particles in the air created by the reaction of oxygen with sulphur dioxide released from factory chimneys and other sources of pollution.

In humid conditions the sulphates attract water droplets and form clouds. This increase in the cloud cover reflects more sunlight back into space and so cools the earth.

The Max Planck researchers went to study a cloud formed at the top of a mountain, taking samples at various times to see how the sulphates reacted progressively.  What was crucial was how the sulphates were formed in the first place.

Current climate models assume that hydrogen peroxide and ozone have a large role in creating the sulphates, but the new research shows that the catalysts for the chemical reaction are more likely to be metal ions like iron, manganese, titanium or chromium.

The key factor is that all of these are heavier than hydrogen peroxide and ozone, and because of this are more likely to fall out of the cloud through the pull of gravity, thus considerably reducing the cooling effect of the original pollution.

Less time aloft

 

Eliza Harris and Bärbel Sinha, with a number of other scientists, captured the air samples and examined the isotopes in a mass spectrometer.

Harris, who was recently awarded the Dieter Rampacher Prize as the youngest doctoral candidate of the Max Planck Society, said: “The relative reaction rates of isotopes are like fingerprints, which tell us how the sulphate was formed from the sulphur dioxide.

“As my colleagues and I compared the basic assumptions of climate models with my results we were very surprised, because only one of twelve models considers the role of transition metal ions in the formation of sulphate”, said Harris, who is now working at the Massachusetts Institute of Technology (MIT) in the USA.

Because of the extra size of the sulphates and hence their greater weight, compared with the previous assumptions, she believes that climate models have over-estimated the cooling effect of the sulphate aerosols by assuming they would stay airborne longer.

So far the findings have not been factored into calculations on the regional effect of climate change. Harris says that in Europe, where pollution from industrial processes is already on the decline, the change in the calculations on warming would be relatively small.

However, in the growing industrial giants like India and China, where coal-fired power stations and other forms of industrial pollution are throwing out sulphur dioxide at an ever-greater rate, then the effect could be considerable. Further research on this is continuing. – Climate News Network

EMBARGOED until 2301 GMT on Thursday 16 May
The ability of clouds to reflect sunlight back into space and so help to cool the Earth appears to have been over-estimated, researchers say, in a study especially significant for major polluters.

LONDON, 17 May – Extra cloud cover caused by emissions of industrial pollutants is known to reduce the effects of global warming, but its impact in reducing temperatures has been over-estimated in the climate models, new research has found.

This is particularly significant for China and India, because it has been believed that these two giant countries would be partly shielded from the effects of climate change by their appalling industrial pollution. The Max Planck Institute for Chemistry in Germany believes this potential cooling effect has been exaggerated.

The Institute’s study looked at the behaviour of sulphate particles in the air created by the reaction of oxygen with sulphur dioxide released from factory chimneys and other sources of pollution.

In humid conditions the sulphates attract water droplets and form clouds. This increase in the cloud cover reflects more sunlight back into space and so cools the earth.

The Max Planck researchers went to study a cloud formed at the top of a mountain, taking samples at various times to see how the sulphates reacted progressively.  What was crucial was how the sulphates were formed in the first place.

Current climate models assume that hydrogen peroxide and ozone have a large role in creating the sulphates, but the new research shows that the catalysts for the chemical reaction are more likely to be metal ions like iron, manganese, titanium or chromium.

The key factor is that all of these are heavier than hydrogen peroxide and ozone, and because of this are more likely to fall out of the cloud through the pull of gravity, thus considerably reducing the cooling effect of the original pollution.

Less time aloft

 

Eliza Harris and Bärbel Sinha, with a number of other scientists, captured the air samples and examined the isotopes in a mass spectrometer.

Harris, who was recently awarded the Dieter Rampacher Prize as the youngest doctoral candidate of the Max Planck Society, said: “The relative reaction rates of isotopes are like fingerprints, which tell us how the sulphate was formed from the sulphur dioxide.

“As my colleagues and I compared the basic assumptions of climate models with my results we were very surprised, because only one of twelve models considers the role of transition metal ions in the formation of sulphate”, said Harris, who is now working at the Massachusetts Institute of Technology (MIT) in the USA.

Because of the extra size of the sulphates and hence their greater weight, compared with the previous assumptions, she believes that climate models have over-estimated the cooling effect of the sulphate aerosols by assuming they would stay airborne longer.

So far the findings have not been factored into calculations on the regional effect of climate change. Harris says that in Europe, where pollution from industrial processes is already on the decline, the change in the calculations on warming would be relatively small.

However, in the growing industrial giants like India and China, where coal-fired power stations and other forms of industrial pollution are throwing out sulphur dioxide at an ever-greater rate, then the effect could be considerable. Further research on this is continuing. – Climate News Network

Pollution helps clouds to slow warming

FOR IMMEDIATE RELEASE  Unexpected, perhaps, but true – clouds are sending more sunlight back out into space because pollution from human activities is making them more reflective. LONDON, 8 May – Manmade pollution from vehicle exhausts and factories is having the unexpected effect of cooling the atmosphere by making clouds brighter and so reflecting more sunlight back into space, say researchers from Manchester University, UK. The role of clouds in climate change as the world warms is one of the great uncertainties of science. The findings, published in Nature Geoscience, are a considerable advance in showing how humans are influencing the climate. NASA, which runs the US space programme, says that clouds have an enormous impact on the Earth’s climate, reflecting back into space one third of the total amount of sunlight that would otherwise warm the planet. “Because clouds are such powerful climate actors, even small changes in average cloud amounts, locations, and type could speed warming, slow it, or even reverse it”, NASA says. Clouds are made up of tiny water droplets suspended in the air. These can begin from natural particles like sea spray or dust but can also be formed from man-made pollutants from vehicle exhausts or factory chimneys. According to Professor Gordon McFiggans, from Manchester University’s School of Earth, Atmospheric and Environmental Sciences, organic material from these sources is quite volatile and in warm conditions exists as a vapour. Under moist, cooler conditions where clouds form, the molecules of pollution make large particles that act as seeds for cloud droplets.

“…the cooling effect on global climate of the increase in cloud seed effectiveness is at least as great as the previously found entire uncertainty in the effect of pollution on clouds”

The mechanism for producing these cloud droplets is the same as natural processes from forests. Professor McFiggans gives as an example the aroma of pine, a form of organic gas. The droplets that give off the delightful smell later form the basis of clouds. The organic gas from pollution does not smell as good, but has the same effect in producing cloud droplets. “We discovered that organic compounds, such as those formed from forest emissions or from vehicle exhausts, affect the number of droplets in a cloud and hence its brightness, so affecting climate”, he said. “We developed a model and made predictions of a substantially enhanced number of cloud droplets from an atmospherically reasonable amount of organic gases. “More cloud droplets lead to brighter cloud when viewed from above, reflecting more incoming sunlight. “We did some calculations of the effects on climate and found that the cooling effect on global climate of the increase in cloud seed effectiveness is at least as great as the previously found entire uncertainty in the effect of pollution on clouds”,  Professor McFiggans said. – Climate News Network

FOR IMMEDIATE RELEASE  Unexpected, perhaps, but true – clouds are sending more sunlight back out into space because pollution from human activities is making them more reflective. LONDON, 8 May – Manmade pollution from vehicle exhausts and factories is having the unexpected effect of cooling the atmosphere by making clouds brighter and so reflecting more sunlight back into space, say researchers from Manchester University, UK. The role of clouds in climate change as the world warms is one of the great uncertainties of science. The findings, published in Nature Geoscience, are a considerable advance in showing how humans are influencing the climate. NASA, which runs the US space programme, says that clouds have an enormous impact on the Earth’s climate, reflecting back into space one third of the total amount of sunlight that would otherwise warm the planet. “Because clouds are such powerful climate actors, even small changes in average cloud amounts, locations, and type could speed warming, slow it, or even reverse it”, NASA says. Clouds are made up of tiny water droplets suspended in the air. These can begin from natural particles like sea spray or dust but can also be formed from man-made pollutants from vehicle exhausts or factory chimneys. According to Professor Gordon McFiggans, from Manchester University’s School of Earth, Atmospheric and Environmental Sciences, organic material from these sources is quite volatile and in warm conditions exists as a vapour. Under moist, cooler conditions where clouds form, the molecules of pollution make large particles that act as seeds for cloud droplets.

“…the cooling effect on global climate of the increase in cloud seed effectiveness is at least as great as the previously found entire uncertainty in the effect of pollution on clouds”

The mechanism for producing these cloud droplets is the same as natural processes from forests. Professor McFiggans gives as an example the aroma of pine, a form of organic gas. The droplets that give off the delightful smell later form the basis of clouds. The organic gas from pollution does not smell as good, but has the same effect in producing cloud droplets. “We discovered that organic compounds, such as those formed from forest emissions or from vehicle exhausts, affect the number of droplets in a cloud and hence its brightness, so affecting climate”, he said. “We developed a model and made predictions of a substantially enhanced number of cloud droplets from an atmospherically reasonable amount of organic gases. “More cloud droplets lead to brighter cloud when viewed from above, reflecting more incoming sunlight. “We did some calculations of the effects on climate and found that the cooling effect on global climate of the increase in cloud seed effectiveness is at least as great as the previously found entire uncertainty in the effect of pollution on clouds”,  Professor McFiggans said. – Climate News Network

Clouds 'caused Greenland's 2012 thaw'

FOR IMMEDIATE RELEASE
Last year’s brief but startlingly rapid melting of the Greenland ice sheet probably had nothing to do with climate change. What it did reveal was the limits of our current knowledge.

LONDON, 5 April – US scientists think they can explain why the Greenland ice sheet started melting at an unexpected and alarming rate in the summer of 2012. They blame it on unusual clouds.

In four days during July last year, Nasa satellite measurements revealed that 97% of the surface of the Greenland ice sheet had begun to thaw. The slush was even recorded at the summit of the icecap, more than three kilometres above sea level. This sudden, dramatic thaw was brief, but without precedent.

Greenland is home to three million cubic kilometres of ice. If all of it melted, sea levels globally would rise by more than seven metres. So climate scientists have for decades taken a keen interest in Greenland, and report that such sudden periods of dramatic melting occur roughly only once in 150 years.

In July 2012, observers blamed the record North American heat waves, and even wild fires in the tundra that might have sent columns of sunlight-absorbing soot to darken the snow.

But now Ralf Bennartz of the University of Wisconsin-Madison thinks he has the answer. He and colleagues report in Nature that while there would be more than one cause for such a huge change in the pattern of summer thaw, they focused on the role of low-level clouds.

Snow keeps itself cool by reflecting sunlight back into space. Low-level clouds, too, should keep land masses cool, by reflecting sunlight back into space.

But the scientists calculated that, under particular temperature conditions, clouds could be thin enough to permit solar radiation to filter through, but thick enough to trap some of the Sun’s energy as infra-red radiation even if it was reflected by the snow and ice on the ground. The extra heat trapped close to the ice surface was enough to push temperatures above freezing.

Complex influences

 

There would have been other factors to consider: air pressure, regional temperatures, wind speeds, turbulence, ocean currents and so on. Nobody last year was inclined to blame global warming for such an entirely unexpected phenomenon.

The short, sudden and very unusual event was just that, an unusual event, to be reconstructed months later by a combination of observations on the ground, remote sensing data and computer models.

But it told meteorologists and climate scientists something about the complexities of the interplay of light, land, air, water and ice in those latitudes.

“We know that these thin, low-level clouds occur frequently. Our results may help to explain some of the difficulties that current global climate models have in simulating the Arctic surface energy budget”, said Professor Bennartz.

“Above all, this study highlights the importance of continuous and detailed ground-based observations over the Greenland ice sheet and elsewhere.” – Climate News Network

FOR IMMEDIATE RELEASE
Last year’s brief but startlingly rapid melting of the Greenland ice sheet probably had nothing to do with climate change. What it did reveal was the limits of our current knowledge.

LONDON, 5 April – US scientists think they can explain why the Greenland ice sheet started melting at an unexpected and alarming rate in the summer of 2012. They blame it on unusual clouds.

In four days during July last year, Nasa satellite measurements revealed that 97% of the surface of the Greenland ice sheet had begun to thaw. The slush was even recorded at the summit of the icecap, more than three kilometres above sea level. This sudden, dramatic thaw was brief, but without precedent.

Greenland is home to three million cubic kilometres of ice. If all of it melted, sea levels globally would rise by more than seven metres. So climate scientists have for decades taken a keen interest in Greenland, and report that such sudden periods of dramatic melting occur roughly only once in 150 years.

In July 2012, observers blamed the record North American heat waves, and even wild fires in the tundra that might have sent columns of sunlight-absorbing soot to darken the snow.

But now Ralf Bennartz of the University of Wisconsin-Madison thinks he has the answer. He and colleagues report in Nature that while there would be more than one cause for such a huge change in the pattern of summer thaw, they focused on the role of low-level clouds.

Snow keeps itself cool by reflecting sunlight back into space. Low-level clouds, too, should keep land masses cool, by reflecting sunlight back into space.

But the scientists calculated that, under particular temperature conditions, clouds could be thin enough to permit solar radiation to filter through, but thick enough to trap some of the Sun’s energy as infra-red radiation even if it was reflected by the snow and ice on the ground. The extra heat trapped close to the ice surface was enough to push temperatures above freezing.

Complex influences

 

There would have been other factors to consider: air pressure, regional temperatures, wind speeds, turbulence, ocean currents and so on. Nobody last year was inclined to blame global warming for such an entirely unexpected phenomenon.

The short, sudden and very unusual event was just that, an unusual event, to be reconstructed months later by a combination of observations on the ground, remote sensing data and computer models.

But it told meteorologists and climate scientists something about the complexities of the interplay of light, land, air, water and ice in those latitudes.

“We know that these thin, low-level clouds occur frequently. Our results may help to explain some of the difficulties that current global climate models have in simulating the Arctic surface energy budget”, said Professor Bennartz.

“Above all, this study highlights the importance of continuous and detailed ground-based observations over the Greenland ice sheet and elsewhere.” – Climate News Network