The world is likely to warm by an average of more than 1.5°C above pre-industrial levels, according to a new report from the Grantham Research Institute on Climate Change and the Environment, theCentre for Climate Change Economics and Policy, and the Met Office Hadley Centre.
Climate scientists regard a rise of more than 2 degrees as taking the planet beyond the limit of safety.
The research was published to coincide with the current round of climate change negotiations, now taking place in Bonn. One of the topics of discussion, which also dominated the agenda for several days at Copenhagen, is whether the current international goal - enshrined in the Copenhagen Accord- of holding temperatures to 2°C should be toughened, to oblige nations to try to hold warming to no more than 1.5°C.
Global average temperature has already risen by about 0.8°C since the end of the 19th century.
Monday’s report suggests that efforts to hold to the 1.5°C target are likely to be futile and that, as many scientists and politicians have long argued, efforts should be focused on the 2 degree target.
Or as the report puts it: “Even if global emissions fall from 47bn tonnes of carbon-dioxide-equivalent in 2010 to 40bn tonnes in 2020, and are then reduced to zero immediately afterwards, we estimate that there would be a maximum probability of less than 50 per cent of avoiding global warming of more than 1.5°C above the pre-industrial level.”
However, the scientists argue that the temperature could be reduced again to 1.5°C above pre-industrial levels after overshooting this target. But they warn that higher temperature rises could result in other effects - the climate could reach “tipping points” at which certain effects start to reinforce themselves. For instance, loss of sea ice in the Arctic could accelerate because ice-less sea is darker and absorbs more heat. Melting permafrost in Siberia could release vast quantities of methane, a greenhouse gas many times more potent than carbon dioxide, which in turn would increase the warming effect.
Therefore, they conclude: “More research is needed into the likelihood of triggering feedbacks or irreversible impacts, such as large rises in sea level, during temporary overshooting of a 1.5°C goal.”