As they photosynthesise and grow, tropical forests remove enormous amounts of carbon from the atmosphere, reducing global warming. However, forests are also themselves affected by this warming. If it gets too hot or too dry, trees will grow less and may start to die faster, decomposing and releasing that carbon back into the atmosphere.
Rain forests are found right across the tropics. Some forests at the southern edge of the Amazon reach 35˚C in the hottest months of the year, while others towards the foothills of the Andes reach no more than 26˚C. The jungles of the western Amazon and Borneo are wet all year round, while elsewhere in Amazonia and in Africa there are ‘rainforests’ that have no rainfall in the driest months.
Scientists have found that tropical forests can tolerate small changes in temperatures, but only up to a point. Once annual mean daytime temperatures in the warmest part of the year hit 32˚C or more, these forests release four times as much carbon to the atmosphere per degree increase in temperature as they would below the threshold.
We still have an opportunity to ensure forests can adapt to climate change. Firstly, we need to protect and connect the forests that remain, so that tree species are able to move as the climate warms. But trees can only “move” when animals or the wind carry their seeds somewhere else where climatic conditions are suitable.
The more fragmented the forests, the less likely seeds can reach other places. Also, smaller patches are more affected by increased light, drier air and fire risks, creating challenging conditions for seeds to germinate and grow. Therefore, keeping forests connected is crucial.
Secondly, we need to limit emissions. As each degree increase above the heat threshold releases 100 billion tonnes of CO2 from tropical forests to the atmosphere.During the current pandemic, emissions have been significantly reduced. So this shows that humans can do it.