Jan 24, 2024 - Energy & Environment

Climate change made Amazon Basin drought 30 times more likely: study

Photo of a dry riverbed in the Amazon Basin due to an ongoing, severe drought.

Boats and floating houses run aground along the lakes and streams of Cacau Pirera, Amazonas in Oct. 2023. Photo: Gustavo Basso/NurPhoto via Getty Images

By increasing temperatures, human-caused climate change made the severe drought affecting the Amazon Basin 30 times more likely, a new study finds.

Why it matters: The Amazon is the world's largest rainforest, and it absorbs vast amounts of carbon. It is already teetering on the edge of instability due to deforestation.

  • The Amazon Basin, which is shared by eight countries, is a global biodiversity hot spot as well.

The big picture: This region has been mired in intense drought since mid-2023, which has led to large wildfires that have reduced air quality in major cities in Brazil and emitted large amounts of greenhouse gases.

  • In addition, there have been die-offs of wildlife related to the drought, including more than 100 endangered pink river dolphins.
  • In recent years, studies have warned that climate change plus land use pressures are threatening to transform the rainforest into a much drier ecosystem known as a savannah, though that tipping point has not yet been passed for the majority of the region.
  • The new research comes from an international team of climate scientists who sift through weather and climate data to identify the roles played by natural variability and human-induced global warming in contributing to extreme weather and climate events.

Between the lines: They found that, by increasing temperatures and therefore supercharging evaporation, climate change has had a far larger impact on the drought's severity than the ongoing strong El Niño event in the tropical Pacific Ocean.

  • Typically, El Niño events lead to drier than average conditions in the Amazon region, the study says.
  • The researchers looked at two different drought metrics, one which measures rainfall shortages and is also known as meteorological drought. The other looks at agricultural drought through the inclusion of the evaporation of water from plants and soils, which increases along with air temperatures.

What they found: The study, which uses peer reviewed methods but is not yet itself peer-reviewed, found that both El Niño and climate change reduced rainfall across the Amazon by about the same amount, but the boost in high temperatures was climate change-driven and did more to worsen the drought.

  • In other words, while the El Niño worsened the drought, higher temperatures were the catalyst, and also vaulted it to more severe levels, the study shows.
  • Historical data supports this, the study states, since June through November rainfall is declining in the Amazon in concert with increasing temperatures.
  • With continued greenhouse gas emissions from the burning of fossil fuels, if global average temperatures reach 2°C above preindustrial levels, the study projects that similar periods of low rainfall would become four times more likely, occurring once every 33 years.
  • And similar agricultural droughts could become another three times more likely at that warming level, occurring on the order of once every 13 years.

How they did it: To conduct the study, scientists examined observational weather data and simulated atmospheric conditions using computer models.

  • This allowed them to look at what the likelihood of this intense drought would be in an atmosphere with and without the current level of warming and elevated greenhouse gas concentrations.

What they're saying: "With every fraction of a degree of warming caused by the burning of fossil fuels, the risk of drought in the Amazon will continue to increase, regardless of El Niño," said co-author Ben Clark of Imperial College London in a statement.

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