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Arctic melt speeding up

March 9, 2014 in Arctic, Climate Sensitivity, Deep Ocean, Greenland, Marine ecology, Ocean Warming, Polar ice, Solar energy

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Measuring the sun's reflectivity in the Arctic Image: NASA/Kathryn Hansen via Wikimedia Commons

Measuring the sun’s reflectivity in the Arctic
Image: NASA/Kathryn Hansen via Wikimedia Commons

By Tim Radford

It’s long been established that Arctic ice is on the retreat but it’s the pace of change that’s surprising scientists: latest studies show the region is at its warmest for 40,000 years. 

LONDON, 9 March - Ice in the Arctic continues to retreat. The season without ice is getting longer by an average of five days every 10 years, according to a new study in Geophysical Research Letters.  And in some regions of the Arctic, the autumn freeze is now up to 11 days later every decade.

This means that a greater proportion of the polar region for a longer timespan no longer reflects sunlight but absorbs it. This change in albedo – the scientist’s term for a planet’s reflectivity – means that open sea absorbs radiation, stays warmer, and freezes again ever later.

Warming accelerates

None of this is news: sea ice in the Arctic has been both retreating and thinning in volume for four decades. Researchers have tracked the retreat of the snow line to find tiny plants exposed that had been frozen over 40,000 years ago: the implication is that the Arctic is warmer now than it has been for 40 millennia.

This warming threatens the animals that depend for their existence on a stable cycle of seasons  and is accelerating at such a rate that the polar ocean could be entirely free of ice in late summer in the next four decades.

So Julienne Stroeve, of University College London and her colleagues have provided yet further confirmation of an increasing rate of change in the region in their latest study.

The scientists examined satellite imagery of the Arctic for the last 30 years, on 25 square kilometer grid, to work out the albedo of each square for every month they had data.

Their headline figure of five days is an average: in fact the pattern of freeze and thaw in the Arctic varies. In one region the melt season has been extended by 13 days, in another the melt season is actually getting shorter.

Energy increases

This increasing exposure to summer sunlight means that ever greater quantities of energy are being absorbed: several times the energy of the atomic bomb dropped on Hiroshima hits every square kilometer of the open Arctic Ocean.

“The extent of sea ice in the Arctic has been declining for the last four decades,” said Professor Stroeve, “and the timing of when melt begins and ends has a large impact on the amount of ice lost each summer.

With the Arctic region becoming more accessible for longer periods of time, there is a growing need for improved prediction of when the ice retreats and reforms in the water.” - Climate News Network

 

Tropics’ climate sensitivity increases

January 30, 2014 in Carbon, Climate Sensitivity, Drought, Warming

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Mauna Loa solar observatory in Hawaii, where some of the research was completed Image: University Corporation for Atmospherica Research via Wikimedia Commons

Mauna Loa solar observatory in Hawaii, where some of the research was undertaken
Image: University Corporation for Atmospheric Research via Wikimedia Commons

By Tim Radford

The sensitivity to climate change of tropical ecosystems appears to be increasing and their ability to store carbon declining, a development which has surprised scientists.

LONDON, 30 January – Tropical ecosystems may be responding to global warming more energetically than anyone had expected. Scientists from China, Germany, France, the UK and the US report in Nature that the tropical carbon cycle – the uptake and release of carbon dioxide from and back into the atmosphere – has become twice as sensitive to temperature change in the last 50 years.

A one degree rise in average tropical temperature leads to a release of around two billion more tonnes of carbon per year from tropical forests and savannahs, compared with the 1960s and 1970s.

This is unexpected. Climate scientists had foreseen the ability of land-based ecosystems to store carbon declining through the coming century as average global temperatures rise, but not on this scale.

To arrive at their conclusions, the researchers looked not at the crude rise in carbon dioxide levels in the atmosphere, but the year-to-year variations of traces of the gas recorded both at the top of the Mauna Loa volcano in Hawaii and at the South Pole, and then matched these with mean annual temperature variations over the same timescale.

Together, the findings seem to show that tropical ecosystems are becoming more sensitive to climate change. This could be another example of what engineers call positive feedback – warmer summers make forests drier and release more carbon dioxide to make summers warmer, and so on.

More information needed

There is evidence that the tropical regions have experienced more drought over the last five decades. More to the point, the team’s conclusion really suggests that if existing climate models provide uncertain projections of the future, it is because the information available is still incomplete.

It does however also indicate that variations in carbon dioxide levels would provide a monitor of the way tropical forests and grasslands are responding to climate.

“This enhancement is very unlikely to have resulted from chance, and may provide a new perspective on a possible shift in the terrestrial carbon cycle over the past five decades”, said Xuhui Wang of Peking University in Beijing, who led the study.

And Pierre Friedlingstein of the University of Exeter in the UK, one of the research team, said: “Current land carbon cycle systems do not show this increase over the last fifty years, because these models underestimate emerging drought effects on tropical ecosystems.” – Climate News Network

Earth ‘may be doubly sensitive’ to CO2

December 11, 2013 in Arctic, Climate Sensitivity, IPCC, Ocean acidification, Palaeoclimatology

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Bad news for bears - snd for us: Geological proof as well as models show rising CO2 is melting polar ice Image:Alastair Rae via Wikimedia Commons

Bad news for bears – snd for us: Geological evidence as well as models prove rising CO2 is melting polar ice
Image: Alastair Rae via Wikimedia Commons

By Alex Kirby

The sensitivity of the Earth system to a doubling of atmospheric carbon dioxide may be twice as great as scientists had thought, new climate records from the distant past suggest.

LONDON, 11 December – You may think the prospect of climate change is alarming, a call to action to slow down our emissions of carbon dioxide and other greenhouse gases.

You’re almost certainly right. But some scientists are now suggesting you should be much more concerned than you are, because they think we may be seriously underestimating the problem.

The Geological Society of London (GSL) says the sensitivity of the Earth’s climate to CO2 could be double earlier estimates.

The Society has published an addition to a report by a GSL working party in 2010, which was entitled Climate change: Evidence from the Geological Record.
The addition says many climate models typically look at short term, rapid factors when calculating the Earth’s climate sensitivity, which is defined as the average global temperature increase brought about by a doubling of CO2  in the atmosphere.

Scientists agree that a doubling of atmospheric CO2 levels could result in temperature increases of between 1.5 and 4.5°C, caused by rapid changes such as snow and ice melt, and the behaviour of clouds and water vapour.

But what the GSL now says is that geological evidence from palaeoclimatology (studies of past climate change) suggests that if longer-term factors are taken into account, such as the decay of large ice sheets, the Earth’s sensitivity to a doubling of CO2 could itself be double that predicted by most climate models.

CO2′s significance

Dr Colin Summerhayes, who led the statement’s working group, says: “The climate sensitivity suggested by modern climate models may be fine for the short term, but does not encompass the full range of change expected in the long term…”

But he cautions that there are really two “sensitivities” involved: “Climate sensitivity is what happens in the short term in response to a doubling of CO2. But the Earth system sensitivity is what happens in the longer time frame as ice sheets slowly melt, and as sea level slowly rises.

“…The IPCC focuses on… the climate sensitivity – what will happen in the next 100 years. Earth system sensitivity tells you what happens in the next couple of hundred years after that.”

The GSL’s addition also reports new data showing that temperature and CO2 levels recorded in Antarctic ice cores increase at the same time. This, says Summerhayes, “makes the role of CO2 in changing Ice Age climate highly significant.”

Atmospheric carbon levels are currently just below 400 parts per million (ppm) – a figure last seen  between 5.3 and 2.6 million years ago. Global temperatures were then 2-3°C higher than today, and sea levels were several metres higher, due to partial melting of the Antarctic ice sheet.

If the current rate of increase (2 ppm per year) continues, CO2 levels could reach 600 ppm by the end of this century; levels which, says Summerhayes, “have not been seen for 24 million years”.

Models match palaeoclimate

The new GSL statement outlines evidence that a relatively modest rise in atmospheric CO2 levels and temperature leads to significant sea level rise, with oceans more acidic and less oxygenated. Previous such events caused marine crises and extinctions, with the Earth system taking around 100,000 years to recover.

Dr Summerhayes said: “We now have even more confidence from the geological record that the only plausible explanation for current warming is the unprecedented exponential rise in CO2 and other greenhouse gases.

“Recent compilations of past climate data, along with astronomical calculations, show that changes in the Earth’s orbit and axis cooled the world over the past 10,000 years. This cooling would normally be expected to continue for at least another 1,000 years.

“And yet Arctic palaeoclimate records show that the period 1950-2000 was the warmest 50 year interval for 2,000 years. We should be cool, but we’re not.”

He told Climate News Network: “The main implication from my perspective is that the geological record tells us that increasing CO2 increases temperature, melts ice, and raises sea level. This we know independently of any fancy numerical model run by climate scientists.

“However, those climate scientists’ models happen to come up with about the same answer as we get from the geological record, which suggests that the modellers  are likely to be on the right track.” – Climate News Network

2C rise will be a disaster say leading scientists

December 2, 2013 in Adaptation, Climate, Climate risk, Climate Sensitivity, Emissions reductions, Greenhouse Gases, Science, Warming

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Male maldives Image: Taichi via Wikimedia Commons

A 2C temperature rise would seriously threaten cities like Malé, the capital of the Maldives 
Image: Taichi via Wikimedia Commons

By Tim Radford

Countries round the world have pledged to try and limit the average global temperature rise to 2C above pre industrial figures. That’s way too high and would threaten major dislocations for civilization say a group of prominent scientists.

London, 3 December – Governments have set the wrong target to limit climate change. The goal at present – to limit global warming to a maximum of 2°C higher than the average for most of human history  - “would have consequences that can be described as disastrous”, say 18 scientists in a review paper in the journal PLOS One.

With a 2°C increase, “sea level rise of several meters could be expected,” they say.  “Increased climate extremes, already apparent at 0.8°C warming, would be more severe. Coral reefs and associated species, already stressed with current conditions, would be decimated by increased acidification, temperature and sea level rise.

Hansen at helm

The paper’s lead author is James Hansen, now at Columbia University, New York, and the former NASA scientist who in 1988 put global warming on the world’s front pages by telling a US government committee that “It’s time to stop waffling so much and say the evidence is pretty strong that the greenhouse effect is here.”

Hansen’s fellow authors include the economist Jeffrey Sachs of Columbia University and the biologist Camille Parmesan, of the University of Plymouth in the UK and the University of Texas at Austin, USA.

Their argument is that humanity and nature – “the modern world as we know it” – is adapted to what scientists call the Holocene climate that has existed for more than 10,000 years – since the end of the Ice Age, the beginnings of agriculture and the first settlement of the cities.

Warming of 1°C relative to 1880–1920 keeps global temperature close to the Holocene range, but warming of 2°C, could cause “major dislocations for civilization.”

Clear arguments

The scientists study, uncompromisingly entitled “Assessing ‘dangerous climate change’: required reduction of carbon emissions to protect young people, future generations and nature” differs from many such climate analyses because it sets out its argument with remarkable directness and clarity, and serves as a useful briefing document for anyone – politicians, journalists and lay audiences – anxious to better understand the machinery of climate, and the forces that seem to be about to dictate climate change.

Its critics will point out that it is also remarkably short on the usual circumlocutions, caveats, disclaimers and equivocations that tend to characterise most scientific papers. Hansen and his co-authors are however quite open about the major areas of uncertainty: their implicit argument is that if the worst outcomes turn out to be true, the consequences for humankind could be catastrophic.

Feedback is critical

The scientists case is that most political debate addresses the questions of reducing greenhouse gas emissions, but does not and perhaps cannot factor in the all potentially dangerous unknowns – the slow feedbacks that will follow the thawing of the Arctic, the release of frozen reserves of methane and carbon dioxide in the permafrost, and the melting of polar ice into the oceans. They point out that 170 nations have agreed on the need to limit fossil fuel emissions to avoid dangerous human-made climate change.

“However the stark reality is that global emissions have accelerated, and new efforts are underway to massively expand fossil fuel extractions by drilling to increasing ocean depths and into the Arctic, squeezing oil from tar sands and tar shale, hydro-fracking to expand extraction of natural gas, developing exploitation of methane hydrates and mining of coal via mountain-top removal and mechanised long wall-mining.”

Still time

The scientists argue that swift and drastic action to limit global greenhouse gas emissions and contain warming to around 1°C would have two useful consequences. One is that it would not be far from the climate variations experienced as normal during the last 10,000 years, and secondly that it would make it more likely that the biosphere, and the soil, would be able to sequester a substantial proportion of the carbon dioxide released by human industrial civilisation.

Trees are, in essence, captive carbon dioxide. But the warmer the world becomes, the more likely it is that existing forests – the Amazon, for example – will start to release more CO2 than they absorb, making the planet progressively even warmer.

Therefore the scientists make a case for limiting overall global carbon emissions to 500 gigatonnes rather than the 1,000 billion tonnes in the 2°C rise scenario.

“Although there is merit in simply chronicling what is happening, there is still opportunity for humanity to exercise free will,” says Hansen. – Climate News Network

 

Warming is twice as fast – or half

November 21, 2013 in Arctic, CFCs, Climate Sensitivity, El Niño, Ozone, Warming slowdown

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Alaska's North Slope: Scientists think some Arctic warming may be going undetected Image: US NOAA vis Wikimedia Commons

Alaska’s North Slope: Scientists think some Arctic warming may be going undetected
Image: US NOAA vis Wikimedia Commons

By Tim Radford

The world may be warming more than twice as fast as thought because some key data has been overlooked, two scientists argue. But others think seasonal changes in the Pacific have led to an over-estimate of the warming.

LONDON, 21 November – Two scientists have yet another explanation for the apparent slowdown in global warming: the meteorologists just haven’t been looking in the right places. And two climate researchers in Alabama have a counter proposal: the influence of a natural cycle of warming and cooling in the Pacific is more powerful than anybody first thought and right now, the ocean is in a cooling phase.

First, a restatement of the puzzle: carbon dioxide emissions in the atmosphere are increasing. Carbon dioxide traps infrared radiation, which means that the planet warms. From 1970 to 1998, average global temperatures rose at a rate of 0.17°C per decade. Since 1999, the rate of warming has slowed to 0.04°C per decade.

But the world is still burning fossil fuels. The planet ought to be hotter by now than the measurements suggest. Where is the missing heat?

Global warming sceptics scoffed and claimed that climate scientists had been wrong all along. Climate scientists patiently explained that the heat must be going somewhere, perhaps into the deep oceans far below the surface.

One team recently proposed that the apparent slowdown could be a consequence of the phasing out of ozone-destroying chlorofluorocarbon (CFC) refrigerant gases: these were released in small quantities but were very potent greenhouse gases.

Yet another group suggested that there was a long-term cycle of fluctuation – they called it the stadium wave theory – that meteorologists had simply not yet noticed, because climate records were all relatively recent.

No warming pause detected

And now Kevin Cowtan, a computational scientist at the University of York in the United Kingdom, and Robert Way of the University of Ottawa in Canada have put forward yet another suggestion. They propose, in the Quarterly Journal of the Royal Meteorological Society, that the warming is there but is not being measured.

The dataset used by the UK Met Office, for instance, covers five sixths of the globe – but some of the missing one-sixth is around the Arctic Circle, and that might be crucial. The Arctic is warming at about eight times the rate of the rest of the planet and the polar ice is in dramatic retreat.

Data tends to be collected most intensely where the scientists are based, which is why parts of Africa and the very high latitudes are not well-represented in the measurements. So Cowtan and Way reconstructed the “missing” global temperatures with observations from satellites and surface data from weather stations and ships around the unsampled regions.

And they conclude that with this extra, hitherto absent information, the world could be warming at two and a half times the rate that the Met Office findings suggest.

Cowtan is not a climate scientist, although his calculations are good enough for a respected meteorological journal, and in any case the conclusions are tentative. He says: “There’s a perception that global warming has stopped, but in fact our data suggests otherwise.

“The reality is that 16 years is too short a period to draw a reliable conclusion. We find only weak evidence of any change in the rate of global warming.”

Climate sensitivity halved?

But across the Atlantic at the University of Alabama in Huntsville, Roy Spencer and Danny Braswell propose another explanation. More frequent natural cooling in the oceans – these are the so-called La Niña events – could be offsetting any expected global warming.

Conversely, some of the already observed global warming since 1950 could be a consequence of a series of sweltering El Niño events in the Pacific up to 1998. El Niño means The Child, and Spanish-speaking fishermen gave the phenomenon that name because it tends to occur around Christmastide.

These natural cycles of warming and cooling in the oceans complicate the picture and cause head-scratching among climate researchers, but they also present much more alarming portents for farmers and townspeople on both sides of the Pacific, and far beyond, as weather patterns reverse, fish catches fail, tropical rainforests catch fire, harvests shrivel, normally dry and sunny coasts become flooded and so on.

Spencer and Braswell’s research, published in the Asia-Pacific Journal of Atmospheric Sciences, is also based on computational calculation, but it reveals a pattern of change in cloud cover that if confirmed might make a serious difference to long-term climate projections.

During La Niña events, global cloud cover increases, and more solar energy is reflected back into space, with a consequent lowering of global average temperatures. During an El Niño event, the skies are clearer, and the world palpably hotter.

“As a result, because as much as 50% of the warming could be attributed to stronger El Niño activity, it suggests that the climate system is only about half as sensitive to increasing CO2 as previously believed,” said Spencer. – Climate News Network