Runaway warming warned
A new study claims that even if human-induced greenhouse gas emissions can be reduced to zero, global temperatures may continue to rise for centuries afterwards.
A new model of the global climate between 1850 and 2500 has been published in Scientific Reports.
A reduced complexity earth system model (ESCIMO) was used to study the effect of different greenhouse gas emission reductions on changes in the global climate from 1850 to 2500 and create projections of global temperature and sea level rises.
The modelling suggests that under conditions where anthropogenic greenhouse gas emissions peak during the 2030s and decline to zero by 2100, global temperatures will be 3°C warmer and sea levels 3 metres higher by 2500 than they were in 1850.
Under conditions where all anthropogenic greenhouse-gas emissions are reduced to zero during the year 2020 the authors estimate that, after an initial decline, global temperatures will still be around 3°C warmer and sea levels will rise by around 2.5 metres by 2500, compared to 1850.
The authors suggest that global temperatures could continue to increase after anthropogenic greenhouse gas emissions have reduced, as continued melting of Arctic ice and carbon-containing permafrost may increase the levels of water vapour, methane and carbon dioxide in the atmosphere.
Melting of Arctic ice and permafrost may also reduce the area of ice reflecting heat and light from the sun.
To prevent the projected temperature and sea level rises, the authors suggest that all anthropogenic greenhouse gas emissions would have had to be reduced to zero between 1960 and 1970.
To prevent global temperature and sea level rises after greenhouse gas emissions have ceased, at least 33 gigatonnes of carbon dioxide would need to be removed from the atmosphere each year from 2020 onwards through some kind of carbon capture and storage methods, according to the authors.
The modelling is at odd with simulations run in support of the 6th Assessment Report of the Intergovernmental Panel on Climate Change.
These models have shown 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.
Dr James Renwick, Professor of Physical Geography at the Victoria University of Wellington has criticised the approach.
“The ESCIMO model has been shown to have a tendency towards ‘runaway’ climate change generally, partly because it overstates the warming effect of decreasing albedo and the amount of greenhouse gases released from thawing permafrost,” he said.
“In short, the results presented in this paper are very implausible and should not be seen as cause for alarm.
“Effective climate action by the global community… would be effective at stopping climate change at somewhere between 1.5 and 2°C of warming above pre-industrial levels. This would be associated with further increases in weather and climate extremes that would have significant consequences for communities worldwide, but there is no sign of any form of runaway climate change.”