Writing in yesterday’s Nature, a group of academics says that if Copenhagen leads to a “weak” agreement then temperature rises could reach 4C, and to stay under 2C we have to aim for the most ambitious and dramatic emission cuts (although as discussed yesterday emission cuts don’t guarantee any outcome).  

A global temperature rise of 4C would mean plummeting food yields, water scarcity for about 3 bn people, heatwaves, floods, droughts.. It’s the climate porn scenario sceptics talk about. But most importantly 40% of ecosystems would switch from being carbon sinks to becoming net carbon emitters, and hundreds of gigatonnes of CO2 –dwarfing by orders of magnitude all the carbon we have emitted-- that is now locked away in vast volumes of mile-deep permafrost could be released within a span of decades. Almost all high-latitude forest and large parts of the Amazon forest could be lost.  

The problem with any global warming prediction is that it leads to a decrease in the planet’s carbon sinks. Forests are affected by warming and they are at risk if the water cycle is disrupted in key geographical latitudes.  

It may be the case that all efforts to tackle reforestation in the tropics and rainforest owning countries will be in vain by the end of the century if global warming changes our ecosystems significantly. This means that in order to plan ahead to manage mitigation we need to look for efficient carbon sinks, extrapolating what “efficient” means not now but in several decades’ time, in a warmer world. This could mean that large-scale reforestation in Europe and the United States can be in the long term a clever thing to do as it may be the case that in future tropical rainforests will be net carbon emitters and forests in higher latitudes could possibly lock away carbon more rapidly and as efficiently as tropical rainforests do now.  

After all, restoring Europe’s forests to about 75% of their natural extent in the nineteenth century could increase the Earth’s carbon sink capacity by as much as 10%, and this percentage would be much greater if Europe becomes a warmer and wetter place.