Tropical forests, climate change and carbon

Tropical rainforests are often called the "lungs of the planet" because they generally draw in carbon dioxide and breathe out oxygen. But the amount of carbon dioxide they absorb, or produce, varies hugely with year-to-year variations in the climate. A new paper published this week in the journal Nature shows that these variations reveal how vulnerable the rainforest is to climate change. Dr Chris Huntingford from CEH was a co-author on the paper and here he describes the technique the scientific team used to answer the question of whether the Amazon forest will die back under climate change.

In our new paper “Sensitivity of tropical carbon to climate change constrained by carbon dioxide variability” Nature (2013), doi:10.1038/nature11882, a technique called “emerging constraints” is used. This method has the starting premise that all climate models (e.g. from different research centres, or the same centre but with alternative parameterisations) contain key information about particular future behaviours of the Earth system. The technique also accepts that no individual model will be “spot on” in its projections. However if there are robust features common to all models, and that link something that can be measured in the present day to a future issue of interest (here, the likelihood of global warming-induced damage to tropical forests), then this can be used to improve and constrain future prediction.



Amazon rainforest



What we show in the paper is that across climate models, the size of the ratio of simultaneous fluctuations in temperature and atmospheric carbon dioxide concentrations are correlated to predicted future loss of carbon stores – i.e. potential extent of any rainforest “die-back”. Hence the amount of modelled carbon release in warm El Nino years, for instance, is a strong indicator across climate models to their modelled “die-back” risk in a future generally warmer world. This correlation is then exploited to give a more definitive prediction, substituting instead actual measurements of carbon dioxide and temperature variation as recorded in recent decades.

Climate research often focuses on explaining contemporary trends and how these may evolve in the approaching decades. What this new analysis demonstrates is that year-on-year variation also teaches us much about expected future average responses. The technique also shows how different model projections can be merged, along with present-day measurements, to exploit consistent inter-model features whilst simultaneously overcoming their individual biases.

Dr Chris Huntingford is a Climate Modeller based at the Centre for Ecology & Hydrology in Wallingford, Oxfordshire

Additional information

"Sensitivity of tropical carbon to climate change constrained by carbon dioxide variability". DOI: 10.1038/nature11882 published by Nature

Staff page and research interests of Dr Chris Huntingford

Tropical rainforests, 'lungs' of the planet, reveal true sensitivity to global warming - CEH News, 7 Feb 2013

A press release about the paper was issued by the University of Exeter