Role of the Amazon as a carbon sink is declining: nature study

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The Amazon is home to the largest tropical forests on earth and has proven to be an important carbon sink. However, this carbon sink appears to be in decline due to factors like deforestation and climate change, according to a new paper published in Nature.

The study was led by Lucia Gatti, group leader of the Brazilian National Institute for Space Research / Center for Earth System Science and member of the steering committee for the WMO-led integrated global greenhouse gas information system.

The authors examined the Amazon’s carbon budget and the main reasons behind its transition to a carbon source. The group used an observation-based approach to assess the ecosystem’s carbon fluxes and performed 590 vertical aircraft profile measurements of the concentrations of carbon dioxide and carbon monoxide in the lower troposphere at four locations in the Amazon from 2010 to 2018.

They found that total carbon emissions are greater in the eastern Amazon than in the western part, as this part experiences a greater rise in dry season temperature and less rainfall. Southeast Amazon in particular acts as a net source of carbon (total carbon flux minus fire emissions) into the atmosphere.

“In the past 40 years, the eastern Amazon has seen more deforestation, warming and moisture stress than the western part, especially during the dry season, with the southeast showing the strongest trends,” the study said.

“We study the effects of climate change and deforestation trends on carbon emissions at our study sites and find that the intensification of the dry season and an increase in deforestation are reducing ecosystem stress, increasing fires and higher carbon emissions in the eastern Amazon. This is in line with recent studies suggesting an increase in tree mortality and a decrease in photosynthesis as a result of climatic changes throughout the Amazon, ”it says.

Carbon sinks, such as carbon uptake by the terrestrial biosphere, are an important regulator of climate change by removing a quarter of the carbon dioxide emitted into the atmosphere by humans.

If sinks like the Amazon become net emitters through deforestation and fires, as well as climate change, there is the potential for this to become a “tipping point” in the climate system. This would therefore have far-reaching implications for slowing down climate change and rising temperatures.

Achieving the goals of the Paris Agreement requires a certain balance between sources and sinks of greenhouse gases. In the race for net zero, other countries are examining reforestation projects to increase the uptake of carbon dioxide from the atmosphere. Tropical forests have traditionally been considered a sink for CO2, but temperature changes and rainfall patterns create a harsh environment for vegetation that can turn them into sources of carbon. About a quarter of the mitigation pledged by countries under the Paris Agreement in their initial Nationally Determined Contributions (NDCs) for 2030 is expected to come from land-based mitigation options.

The special report of the Intergovernmental Panel on Climate Change on Land said: “Simultaneously with these changes in the climatic envelope, new hot climates will appear in the tropics and the frequency, intensity and duration of extreme events (e.g. rain, drought). These emerging hot climates will negatively impact land use (through changes in crop productivity, irrigation needs, and management practices) and land cover through loss of vegetation productivity in many parts of the world, and would have all of the land use and land cover benefits that result , nullify increased atmospheric CO2 concentrations “

Atmospheric concentrations of CO2 continue to rise to record levels, and deforestation is one of the reasons, according to WMO’s Greenhouse Gas Bulletin.

WMO’s Global Atmosphere Watch network, which spans more than 50 countries, provides accurate measurements that form the basis of our understanding of greenhouse gas concentrations, including their many sources, sinks and chemical transformations in the atmosphere.

Details on the Nature study can be found here.

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