Science

Climate: Melting of light-coloured Arctic sea ice is accelerating global warming


Global warming is being accelerated by the melting of light-coloured Arctic sea ice, which exposes more ‘dark’ ocean water to absorb more sunlight, a study warned.

Researchers from Germany found that this process forms a ‘vicious circle’ of positive feedback — one that could lead to an additional temperature rise of 0.77°F (0.43°C).

The consequences of this increase could be considerable, the team warned — and lead to more extreme weather, rising sea levels and harm to wildlife.

Global warming is being accelerated by the melting of light-coloured Arctic sea ice — which exposes more 'dark' ocean water to absorb more sunlight, as pictured, a study warned

Global warming is being accelerated by the melting of light-coloured Arctic sea ice — which exposes more ‘dark’ ocean water to absorb more sunlight, as pictured, a study warned

‘If global ice masses shrink, this changes how much of the sunlight that hits Earth’s surface is reflected back into space,’ said paper author and climate scientist Nico Wunderling of the Potsdam Institute for Climate Impact Research.

‘Decreasing ice cover in the Arctic exposes more of the darker ocean water that absorbs more energy,’ he explained of the phenomenon, which scientists refer to as the ‘albedo effect’.

‘It is like wearing white or black clothes in summer. If you wear dark, you heat up more easily,’ Dr Wunderling continued.

Further factors include the rise of atmospheric water vapour hen more ice is melting. Warmer air can hold more — and water vapour boosts the greenhouse effect.

‘The melting of ice in polar and mountain regions around the world could lead to an additional 0.43°C increase in global warming in the long term,’ Dr Wunderling said.

In their study, the researchers ran a model of the Earth system under different greenhouse gas levels to create the first estimation of how much warming might be triggered by global ice losses.

Existing predictions have not taken into account the reactions of the planet’s land, ocean and ice masses to the rise in temperatures.

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Announcing the findings, the German team warned that ‘ice loss due to warming leads to warming due to ice loss — a vicious circle.’

The researchers estimated that at carbon dioxide levels of 400 parts per million — similar to that of today — the loss of the world’s ice sheets would result in an average temperature rise of 0.77°F (0.43°C).

‘This effect is robust for a whole range of carbon dioxide emission scenarios up to 700 parts per million. It corresponds to 29 per cent extra warming relative to a 1.5°C scenario.’ said Dr Wunderling said.

'If global ice masses shrink, this changes how much of the sunlight that hits Earth's surface is reflected back into space,' said paper author and climate scientist Nico Wunderling of the Potsdam Institute for Climate Impact Research

‘If global ice masses shrink, this changes how much of the sunlight that hits Earth’s surface is reflected back into space,’ said paper author and climate scientist Nico Wunderling of the Potsdam Institute for Climate Impact Research

The contributions to this rise range from 0.09°F (0.05°C) from the West Antarctic Ice Sheet to 0.36°F (0.2°C) as a result of the complete loss of Arctic summer sea ice — a scenario that we are likely to see within this century.

Such a total temperature increase will have substantial consequences, the team warned. The global mean temperature is currently about one degree higher than in pre-industrial times — with policymakers aiming to keep the rise below two degrees.

‘This is not a short-term risk. Earth’s ice masses are huge, which makes them very important for our Earth system as a whole,’ said paper author and climatologist Ricarda Winkelmann, also of the the Potsdam Institute.

‘It also means their response to manmade climate change, especially that of the ice sheets on Greenland and Antarctica, unfolds on longer timescales.’

‘But even if some of the changes might take hundreds or thousands of years to manifest, it is possible we trigger them within just a couple of decades.’

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The researchers carried out complex computer simulations. For instance, if a massive ice body on land is shrinking, there can still be snow — which can still reflect sunlight, just like the ice did.

If the mountain glaciers and the ice on Greenland and West Antarctica went, it would lead to another to 0.36°F (0.2°C) on top of the to 0.36°F due to Arctic summer sea-ice melting.

‘Yet every tenth of a degree of warming counts for our climate,’ said Dr Winkelmann.

Preventing Earth system feedback loops, or vicious circles, is thus more urgent than ever. Our findings imply an additional increase of the global mean temperature on intermediate to long time scales.’

'This is not a short-term risk. Earth's ice masses are huge, which makes them very important for our Earth system as a whole,' said paper author and climatologist Ricarda Winkelmann

‘This is not a short-term risk. Earth’s ice masses are huge, which makes them very important for our Earth system as a whole,’ said paper author and climatologist Ricarda Winkelmann

Professor Sir David King, a former chief scientific adviser under four Prime Ministers, has called for the UK to advance its climate targets by ten years.

He says that he is ‘scared’ by the number of extreme weather events we are facing — including the heatwave that swept Europe last year.

‘We predicted temperatures would rise, but we did not foresee these sorts of extreme events we are getting so soon,’ the UN’s weather chief told the BBC.

He referred especially to the loss of land and sea ice. The UK has committed to ‘net zero’ emissions by 2050.

The full findings of the study were published in the journal Nature Communications.

SEA LEVELS COULD RISE BY UP TO 4 FEET BY THE YEAR 2300

Global sea levels could rise as much as 1.2 metres (4 feet) by 2300 even if we meet the 2015 Paris climate goals, scientists have warned.

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The long-term change will be driven by a thaw of ice from Greenland to Antarctica that is set to re-draw global coastlines.

Sea level rise threatens cities from Shanghai to London, to low-lying swathes of Florida or Bangladesh, and to entire nations such as the Maldives.

It is vital that we curb emissions as soon as possible to avoid an even greater rise, a German-led team of researchers said in a new report.

By 2300, the report projected that sea levels would gain by 0.7-1.2 metres, even if almost 200 nations fully meet goals under the 2015 Paris Agreement.

Targets set by the accords include cutting greenhouse gas emissions to net zero in the second half of this century.

Ocean levels will rise inexorably because heat-trapping industrial gases already emitted will linger in the atmosphere, melting more ice, it said.

In addition, water naturally expands as it warms above four degrees Celsius (39.2°F).

Every five years of delay beyond 2020 in peaking global emissions would mean an extra 20 centimetres (8 inches) of sea level rise by 2300.

‘Sea level is often communicated as a really slow process that you can’t do much about … but the next 30 years really matter,’ lead author Dr Matthias Mengel, of the Potsdam Institute for Climate Impact Research, in Potsdam, Germany, told Reuters.

None of the nearly 200 governments to sign the Paris Accords are on track to meet its pledges.



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