Results from the recent NASA-led study, published in Proceedings of the National Academy of Sciences, indicate that tropical rainforests absorb a significantly larger amount of atmospheric carbon dioxide than was ever thought before.
According to the researchers, tropical rainforests take up more than 1.4 billion metric tonnes of carbon dioxide out of a total global absorption of 2.7 billion – a markedly larger amount than the boreal forests of Canada, Siberia and other northern regions.
“This is good news, because uptake in boreal forests is already slowing, while tropical forests may continue to take up carbon for many years,” said David Schimel of NASA’s Jet Propulsion Laboratory in California, USA.
It is currently estimated that forests and other land vegetation absorb around 2.7 billion tonnes of CO2 or roughly 30 per cent of all human emissions via photosynthesis every year. If the rate of absorption were to slow down, global warming would proceed at an accelerated rate.
The research team claims their study is the first one to compare carbon dioxide estimates from a host of sources at different scales. To produce credible results, they used computer models of ecosystem processes, atmospheric models run backward in time to deduce the sources of today’s concentrations (called inverse models), satellite images, data from experimental forest plots and more.
“Until our analysis, no one had successfully completed a global reconciliation of information about carbon dioxide effects from the atmospheric, forestry and modelling communities,” explained co-author Joshua Fisher, also of JPL. “It is incredible that all these different types of independent data sources start to converge on an answer.”
Prior to this paper, calculating how much CO2 is absorbed by tropical rainforests was compounded by the fact that many studies seemed to produce entirely contradictory results. Based on the then-current understanding of global airflows and the effects of deforestation, thought to cause rainforests to release more carbon dioxide than they were absorbing, computer models suggested that boreal forests in the Northern Hemisphere absorb more CO2 than their counterparts in the tropics.
“What we’ve had up till this paper was a theory of carbon dioxide fertilization based on phenomena at the microscopic scale and observations at the global scale that appeared to contradict those phenomena. Here, at least, is a hypothesis that provides a consistent explanation that includes both how we know photosynthesis works and what’s happening at the planetary scale.” claimed Schimel.
While all of this is good news, there is a possibility that decreased water supply due to climate change and deforestation will eventually decimate the rate of absorption.
“The future tropical balance of deforestation and climate sources and re-growth and carbon dioxide sinks will only remain a robust feature of the global carbon cycle if the vast tropical forests are protected from destruction.”