This is the most extensive land-based study of the Amazon to date. Shockingly, 100 researchers just revealed that the Amazon Rainforest is losing its capacity to absorb carbon from the atmosphere.
The results of this monumental 30-year survey of the South American rainforest, which involved an international team of almost 100 researchers, were published in the journal Nature.
The Amazon rain forest has long absorbed more carbon than it releases and acted as a vital brake on climate change. An extensive study now suggests that it is losing its ability to suck up the excess carbon dioxide being emitted into the atmosphere by human activities.
The main reason for this is the large-scale death of trees in the rain forest, according to the study.
Mortality rates of trees in the region have increased by more than a third since the mid-1980s.
Carbon sinks such as the Amazon “have been a big subsidy from nature for a long time now, because they take up a significant amount of our carbon-dioxide emissions. This is a first indication that the process is saturating” as trees die off, said Oliver Phillips, professor of tropical ecology at the University of Leeds in England and a co-author of the study, published Wednesday in the journal Nature.
Each year, human activity releases about 35 billion tons of CO2 into the atmosphere. For the past few decades, about a quarter of those emissions have been absorbed by the oceans, while another quarter is taken up by trees and other terrestrial sources. The other half stays in the atmosphere and is believed by many scientists to be the main driver of man-made climate change.
Initially, an increase in carbon dioxide in the atmosphere – a key ingredient for photosynthesis – led to a growth spurt for the Amazon’s trees, the researchers say. But the extra carbon appears to have had unexpected consequences.
Study co-author Professor Oliver Phillips, from the University of Leeds said: “With time, the growth stimulation feeds through the system, causing trees to live faster, and so die younger.”
The Nature paper shows how the Amazon’s carbon sink has declined as tree death accelerated. From a peak of two billion tonnes of carbon dioxide each year in the 1990s, the net uptake by the forest has weakened by a half, and is now, for the first time, being overtaken by fossil fuel emissions in Latin America.
The actual abstract of the study:
Atmospheric carbon dioxide records indicate that the land surface has acted as a strong global carbon sink over recent decades with a substantial fraction of this sink probably located in the tropics, particularly in the Amazon. Nevertheless, it is unclear how the terrestrial carbon sink will evolve as climate and atmospheric composition continue to change. Here we analyse the historical evolution of the biomass dynamics of the Amazon rainforest over three decades using a distributed network of 321 plots. While this analysis confirms that Amazon forests have acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation. Rates of net increase in above-ground biomass declined by one-third during the past decade compared to the 1990s. This is a consequence of growth rate increases levelling off recently, while biomass mortality persistently increased throughout, leading to a shortening of carbon residence times. Potential drivers for the mortality increase include greater climate variability, and feedbacks of faster growth on mortality, resulting in shortened tree longevity. The observed decline of the Amazon sink diverges markedly from the recent increase in terrestrial carbon uptake at the global scale and is contrary to expectations based on models.