Do Forests Absorb Carbon?

Since plants rely on carbon dioxide (CO2) to survive, they have traditionally acted as a reliable carbon sink. By absorbing the greenhouse gas (GHG) from our atmosphere, they help to offset the damaging effects of carbon emissions created by industry, transportation and other anthropogenic sources. Large-scale rainforests in Africa and South America have been particularly effective at this.

However, new research indicates that forests might not absorb carbon for much longer. Due to deforestation, exploitation of the land and the harmful impact of climate change, tropical rainforests could turn into sources of carbon themselves in a matter of decades. Should such a scenario come to pass, we may pass a catastrophic tipping point in which global warming becomes an exponentially ever more devastating downward spiral.

Peak of their powers

The amount of carbon absorbed by tropical rainforests across the globe peaked during the 1990s, when as many as 46 billion tonnes of the stuff were removed from the air through forested areas alone. That accounts for approximately half of all terrestrial carbon uptake at the time, equivalent to around 17% of anthropogenic emissions of CO2 at the time.

However, the new study, published in the scientific journal Nature, has demonstrated how the ability of these forests to store carbon has fallen over time. Deforestation and exploitation of the timber, coupled with rising temperatures and increased periods of drought, have meant that only 25 billion tonnes, or a mere 6% of global emissions, were absorbed during the 2010s.

A bleak vision of the future

The discrepancy between the absorption rates in the 1990s and the 2010s is roughly the same as an entire decade’s worth of emissions from Canada, France, Germany and the UK combined. To make matters worse, the authors of the study concluded that the situation is only going to worsen as the global population continues to grow and more land becomes exploited for agriculture, industry or other purposes.

So while greenhouse gas emissions trends in the EU might show tentatively positive indications in many member states, all of that could be for naught if the world’s biggest carbon sinks are no longer capable of carrying out that vital function. In fact, the study raises very valid fears that we might pass a point of no return, after which global warming will continue to deteriorate at an unprecedented rate.

Avoiding the tipping point

Should rainforests become carbon sources rather than carbon sinks, they will comprise one of many known so-called “feedback mechanisms”, which will result in a self-sustaining cycle of global warming. The melting of the Arctic ice (where enhanced nitrous oxide emissions in field warming experiments have already been witnessed) is another of these mechanisms, leading to a tipping point after which there will be no reversing or stopping the process of climate change.

“For years, we have had scientific warnings about tipping points in the Earth system and they’ve been largely ignored by policy and decision-makers,” explained Doug Parr, who is currently the highest-ranking scientists working for the British arm of environmental organisation Greenpeace. “That forests are now seemingly losing the ability to absorb pollution is alarming. What more of a wake-up call do we need?”