If humans ended greenhouse gas emissions tomorrow we would still see global temperatures continuing to rise for several centuries, a new study claims.
Scientists used a computer model called ESCIMO to simulate the effect of different greenhouse gas emission reductions on changes in the global climate between now and they year 2500, based on records spanning all the way back to 1850.
Even if all human-made greenhouse-gas emissions were reduced to zero this year, global temperatures would still be around 5.4°F (3°C) warmer in 2500 than on 1850, the model found.
Sea levels, meanwhile, would rise by around eight feet (2.5 metres) by 2500, compared to 1850, submerging glaciers and flooding land.
Even if human-induced greenhouse gas emissions can be reduced to zero, global temperatures may continue to rise for centuries afterwards, according to a simulation of the global climate between 1850 and 2500
‘Recently, there have been warnings that some of these tipping points are coming closer and are too dangerous to be disregarded,’ say the scientists, from BI Norwegian Business School in Oslo.
‘In this paper we report that in the ESCIMO climate model the world is already past a point-of-no-return for global warming.’
The team tried another scenario, stretching out the date at which humanity theoretically brings greenhouse gas emissions to zero.
Under this scenario, where human-made greenhouse gas emissions peak during the 2030s and decline to zero by 2100, global temperatures will be 5.4°F (3°C) warmer and sea levels 10 feet (three metres) higher by 2500 than they were in 1850 – an even greater sea level rise.
If global ice masses shrink, this changes how much of the sunlight that hits Earth’s surface is reflected back into space
The authors suggest continued melting of Arctic ice and carbon-containing permafrost – ground that’s continuously frozen – may increase the amount water vapour, methane and carbon dioxide in the atmosphere.
This would also reduce the area of ice that reflects heat and light from the Sun, causing more short-wave radiation to be absorbed by the Earth, heating the planet.
This could mean humanity will need to create more white buildings to reflect more sunlight back into space to compensate for the loss of ice.
The climate model suggests the world is already past a point-of-no-return for global warming
To prevent the projected temperature and sea level rises, the authors suggest that all human-made greenhouse gas emissions would have had to be reduced to zero between 1960 and 1970.
As it is, humans will have to take proactive measures to remove at least 33 gigatonnes of carbon dioxide from the atmosphere each year from 2020 onwards through carbon capture and storage methods, according to the authors.
This may help to limit the potentially catastrophic impacts of this on Earth’s ecosystems and human society, who may have to evacuate entire cities when rising sea levels cause severe flooding.
Professor Phillip Williamson, an environmental scientist at the University of East Anglia who was not involved in the research, said: ‘This study provides evidence for what we don’t want to hear – that global heating may have already become self-reinforcing, and that we have therefore passed the point of no-return.
‘But the findings should not be misinterpreted as saying that we are doomed, with nothing that can be done to make any difference.
‘On the contrary, the differences between their scenarios – net-zero by the end of the century and net-zero now – are dramatic, giving the choice of climate catastrophe within our children’s lifetimes or keeping future temperature increases below 1.5°C for at least a century.’
Professor Mark Maslin, a climate change expert at University College London, said the results need to be confirmed by more complex climate models used by the Intergovernmental Panel on Climate Change (IPCC).
The latest round of climate model simulations run by IPCC show that if greenhouse gas emissions were to stop immediately, there is likely to be very little further increase in temperatures and no sign of warming resuming in future.
‘These results come from one model which has not undergone the rigorous cross checking and testing that is usual for climate models,’ Professor Maslin said.
Sir Brian Hoskins, a climatologist at Imperial College London, who was also not involved with the study, questioned the team’s ‘toy’ model.
‘This is the sort of investigation with a toy model that should be done and is fun, but should not be given this sort of publicity until the processes involved have been investigated using more complex models and representations,’ he said.
The authors of the study, which has been published in Scientific Reports, encourage other researchers to explore their results using alternative models.
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.
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.