For every one degree Centigrade rise in temperature, tropical rainforests release about 2 billion extra tonnes of carbon-rich gases. It’s a sobering thought, and it proves tropical rainforests are suffering the effects of climate change.
What’s been happening so far?
About half the CO2 emitted by humans during the past two centuries has come from burning fossil fuels. A lot of it has been absorbed by the oceans and by land vegetation, particularly rainforests. The 50% or so held in the oceans is relatively stable, held safely in the long term. But our terrestrial CO2 sink is less stable because plants’ ability to absorb CO2 depends on heat and moisture. When you add human activities like deforestation and draining to the equation, land mass’s effectiveness as a carbon sink reduces even further.
50 years of temperature variations
A new study, covering 50 years, looks at the way rainforests have coped with variations in temperature over time. While rising levels of CO2 stimulate vegetation by giving it more ‘carbon fertiliser’, the benefits are outweighed by the extra heat and more frequent drought that higher concentrations of CO2 bring.
The study shows we can be fairly sure that future climate change will mean even more carbon is released from tropical regions. The scientists looked at carbon dioxide growth rates at two-decade intervals to identify how the sensitivity of tropical rainforests to carbon dioxide has changed over the years. It’s a good way to monitor tropical ecosystems’ response to a changing climate. And the hike in CO2 variability revealed by the report suggests tropical ecosystems are much more vulnerable to warming than they were in the 1960s and ‘70s.
Professor Peter Cox, a co-author of the research, explained to Nature magazine, “What we are seeing is that the tropical forests in particular are becoming more vulnerable to warming and we expect this to continue because we expect to see more warming in the future.”
Why hasn’t it been spotted before?
Apparently the computer models used to simulate global warming’s effects on vegetation don’t show the same increasing sensitivity to CO2, possibly because they underestimate the effects of drought on tropical ecosystems. Let’s hope we can halt or at least slow the effect before it’s too late.