Nature Climate Change | Climate Feedback

4 Degrees and Beyond: How soon is it coming?

Unless major breakthroughs in policy, industry and individual behavior turn around our emissions trajectory pronto, this century could well see average global temperatures 4 degrees Celsius or more above their pre-industrial baseline. That’s the starting point for the 4 Degrees and Beyond conference in Oxford this week. Here, 130 scientists and policy experts are taking a detailed look at a world warmed by twice the amount that’s usually considered dangerous.

Putting weight behind the 4-degree premise was new modelling research presented this morning by Richard Betts of the UK Hadley Centre (press release, Guardian). Betts’s team used a complex, coupled ocean-atmosphere model to simulate the IPCC’s extreme-emissions A1FI scenario (the FI stands for fossil fuel intensive) – an emissions trajectory that’s previously been run only on simpler models. It’s time to take this scenario seriously, argues Betts, given that our emissions are running at the upper end of what the IPCC projected a decade ago.

They also tried out weakening climate sinks on land and sea – feedbacks that are increasingly apparent in recent research, Betts says. Depending on the strength of the feedbacks, 4 degrees of average warming could be reached well before 2100 – as early as 2060 in a worst case scenario, and in the 2070s according to the team’s best guess. Regional warming would be far greater, they found – 7 degrees in many areas, up to 10 in western and southern Africa, and 10 or more in the Arctic.

Sessions afterwards started sketching out consequences in detail. Philip Thornton of the University of Edinburgh looked at agriculture in Africa, where projected impacts are predictably devastating, with yields falling over 50% for certain crops and crop failure years growing more frequent in many regions. Adaptations for this amount of change are a big question mark. Intensive agriculture in highlands – among the few spots that will benefit – may be one possibility for preserving the food supply.

Meanwhile in Finland – where you might expect balmier weather to be a boon – intense climate change may also prove a curse to farmers, reports Reimund Rotter of MTT Agrifood Research Finland. The picture there is complicated – the possible responses depend on many variables. A new type of barley that might compensate for losses to rising temperature or drought would only work in certain soil types, for example. But it’s clear that the North as well as the South will have its problems with the radically different 4-degree world.

Anna Barnett

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