New climate modelling suggests that even ceasing all greenhouse gas emissions today might not be enough to stop global warming.
The reduced complexity model suggests that even with no further emissions, global temperatures will rise enough for Arctic ice and permafrost to continue melting and thawing for hundreds of years—releasing their stored greenhouse gases into the atmosphere and reducing the amount of sunlight reflected away from Earth.
Researchers say at least 33 gigatonnes of carbon dioxide needs to be removed from the atmosphere annually from 2020 to limit the worst effects of climate change. The study authors encourage other researchers to test their findings in other climate models.
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 would 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 carbon capture and storage methods, according to the authors.