Tropical forests are losing the ability to suck up carbon dioxide decades earlier than expected as climate change slows growth and kills trees

  • Researchers monitored 300,000 trees in Africa and the Amazon for 30 years
  • The forests’ ability to remove CO2 from the atmosphere peaked in the 1990s 
  • At this time, the trees removed some 46 billion tonnes of carbon dioxide
  • But by the 2010s, this figure had fallen to around 25 billion tonnes of carbon 
  • Deforestation and increasing emissions have exacerbated this problem

Tropical forests are losing the ability to suck up carbon dioxide decades earlier than expected as climate change slows growth and kills trees, a study has found.

Traditionally, these forests have served as a crucial global carbon store, or ‘sink’, helping to mitigate emissions from activities such as burning fossil fuels.

However, experts led from the University of Leeds found that drought and higher temperatures are reducing the amount of carbon dioxide being stored in trees.

The findings make efforts to cut greenhouse gas emissions and curb rising global temperatures even more urgent, the researchers said.

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Tropical forests are losing the ability to suck up carbon dioxide decades earlier than expected as climate change slows growth and kill trees, a study has found. Pictured, the Amazon forest

Climate models have typically predicted that forests will help compensate for humanity’s greenhouse gas emissions for decades to come.

However, the researchers suggest that tropical forests have already begun to switch from being a a carbon sink to being a source of extra carbon dioxide,  putting out more of the gas from the death of trees than their living counterparts absorb.

The team monitored around 300,000 trees in Africa and the Amazon for over 30 years — finding that the overall uptake of carbon by intact tropical forests appears to have peaked in the 1990s.

By the 2010s, the ability of these forests to absorb carbon dioxide had declined by around a third on average.

The boost to plant growth that extra carbon dioxide provides is increasingly being countered by the higher temperatures and droughts that slow growth and can kill trees, causing carbon losses, the researchers said.

The land area covered by intact forests also declined by 19 per cent as a result of deforestation over those two decades — with levels of man-made carbon dioxide emissions increasing by 46 per cent across the same period.

As a result, intact forests removed 17 per cent of the carbon emissions caused by humans in the 1990s, but only 6 per cent by the 2010s.

Traditionally, tropical forests have served as a crucial global carbon store, or ‘sink’, helping to mitigate emissions from activities such as burning fossil fuels. Pictured, forest in the Ivindo National Park, in central Gabon, Africa

However, experts led from the University of Leeds found that drought and higher temperatures are reducing the amount of carbon dioxide being stored in trees. Pictured, researchers measure trees in the Amazon rainforest, in Peru

Overall, undisturbed tropical forests removed around 46 billion tonnes of carbon dioxide in the 1990s but only 25 billion tonnes by the 2010s.

As climate models appear to have been overestimating the amount of carbon tropical forest will absorb in the future, we will have to drive down emissions faster and reach ‘net zero’ greenhouse gases earlier, the experts warn.

The study — which involved researchers from nearly 100 different institutions —repeatedly measured trees in 244 intact African tropical forests across 11 countries to assess their carbon storage, comparing this to 321 plots in the Amazon.

The team found that the ability of Amazon forests to absorb carbon started to fall in the mid-1990s, while the African carbon sink began its decline about 15 years later.

The findings make efforts to cut greenhouse gas emissions and curb rising global temperatures even more urgent, the researchers said. Pictured, a technician from the Ghana Forestry Commission collects data

‘Intact tropical forests remain a vital carbon sink,’ said senior paper author and geographer Simon Lewis of the University of Leeds.

‘But this research reveals that unless policies are put in place to stabilise Earth’s climate, it is only a matter of time until they are no longer able to sequester carbon.’

‘One big concern for the future of humanity is when carbon-cycle feedbacks really kick in, with nature switching from slowing climate change to accelerating it.’

‘After years of work deep in the Congo and Amazon rainforests, we’ve found that one of the most worrying impacts of climate change has already begun.’

‘This is decades ahead of even the most pessimistic climate models. There is no time to lose in terms of tackling climate change.’

Stopping deforestation and managing tropical forests to help them weather the impacts of climate change — as well as restoring forests in the tropics and temperate parts of the world — are also important, Professor Lewis added.

The full findings of the study were published in the journal Nature. 

MAP REVEALS THE DEVASTATING RATE OF DEFORESTATION AROUND THE GLOBE

Using Landsat imagery and cloud computing, researchers mapped forest cover worldwide as well as forest loss and gain. Over 12 years, 888,000 square miles (2.3 million square kilometers) of forest were lost, and 309,000 square miles (800,000 square kilometers) regrew

The destruction caused by deforestation, wildfires and storms on our planet have been revealed in unprecedented detail.

High-resolution maps released by Google show how global forests experienced an overall loss of 1.5 million sq km during 2000-2012.

For comparison, that’s a loss of forested land equal in size to the entire state of Alaska.

The maps, created by a team involving Nasa, Google and the University of Maryland researchers, used images from the Landsat satellite.

Each pixel in a Landsat image showing an area about the size of a baseball diamond, providing enough data to zoom in on a local region.

Before this, country-to-country comparisons of forestry data were not possible at this level of accuracy.

‘When you put together datasets that employ different methods and definitions, it’s hard to synthesise,’ said Matthew Hansen at the University of Maryland.

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