The ability of the world's tropical forests to sequester carbon dioxide, and by extension play a role in slowing the rate of global warming, is in rapid decline, according to a new study. The research analyzed hundreds of forests around the Amazon and Africa and their ability to capture carbon across the last three decades, finding that it may have actually reached its peak in the 1990s.
The research was carried out by an international team and led by scientists at the University of Leeds. It looked at 300,000 individual trees over a 30-year period. These trees hailed from 565 tropical forests across Africa and the Amazon, and the scientists used data captured at regular intervals on tree height and tree death to calculate changes in the total carbon they are able to store.
In the 1990s, the scientists concluded, the tropical forests pulled around 46 billion tonnes of carbon dioxide from the air. In the 2010s, this had dropped to 25 billion tons. Viewed as a portion of total human-induced carbon emissions, tropical forests removed 17 percent of our CO2 in the 1990s, and just 6 percent in the 2010s.
"Extra carbon dioxide boosts tree growth, but every year this effect is being increasingly countered by the negative impacts of higher temperatures and droughts which slow growth and can kill trees," says study lead author Dr Wannes Hubau. "Our modeling of these factors shows a long-term future decline in the African sink and that the Amazonian sink will continue to rapidly weaken, which we predict to become a carbon source in the mid-2030s.”
The research also shone a light on the alarming rate of deforestation and its relationship with carbon emissions, which rose by 46 percent over the same timeframe while intact forest areas were reduced by 19 percent.
“The immediate threats to tropical forests are deforestation, logging and fires," says senior author Professor Simon Lewis, from the School of Geography at Leeds University. "These require urgent action. In addition, stabilizing Earth’s climate is necessary to stabilize the carbon balance of intact tropical forests. By driving carbon dioxide emissions to net-zero even faster than currently envisaged, it would be possible to avoid intact tropical forests becoming a large source of carbon to the atmosphere. But that window of possibility is closing fast.”
And while saving the world’s tropical forests to drastically reduce carbon emissions is certainly a priority, there are also other, often overlooked, carbon sinks that demand ongoing attention. This includes focusing resources on conserving and regenerating tundras and seagrass meadows, both of which actually have a superior ability to capture carbon but are in decline due to human activity.
The research was published in the journal Nature.
Source: University of Leeds
