Plants and soil usually soak up atmospheric CO2, but research published in Nature suggests that grasslands may absorb less CO2 after a really hot year, and can take up to two years to recover.

Scientists at the Desert Research Institute in Nevada spent four years studying 12 sealed 12-tonne grassland plots. During the first two years, they replicated the climate and rainfall the plants would encounter in the wild. They then exposed six plots to the high temperatures predicted to occur towards the end of this century.

They found that the grassland plots that had been exposed to high temperatures absorbed less CO2 for up to two years, and during this time, only stored about one third of the amount of carbon stored by the plots that experienced normal temperatures.

‘This is the first study to quantitatively track the response in CO2 uptake and loss in entire ecosystems during anomalously warm years,’ said lead author Professor Jay Arnone. ‘The “lagged” responses that carry over for more than one year are a dramatic reminder of the fragility of ecosystems that are key players in global carbon sequestration.’

November 2008