Climate change is likely to have exacerbated the South Asian monsoons that have swept Pakistan in recent weeks, killing more than 1,000 people and destroying nearly 2 million homes.
This is attribution according to a new analysis by World Weather, a company that uses climate models, weather observations and other tools to determine whether global warming has increased the likelihood of recent extreme weather events or Severity Network of Scientists.
However, how much of a role climate change plays in this case is unclear.
It is relatively straightforward to conduct an attribution study to assess the warming effects of heatwaves, with hotter average temperatures pushing up the baseline for such muggy events.
The team has calculated precisely how much climate change last year will affect the likelihood of extreme heat in the Pacific Northwest (which would be “at least 150 times less” if there was no anthropogenic climate change), a recent UK Heat waves (climate change makes them “at least 10 times more likely”), and heat waves in Pakistan and India earlier this year (“30 times more likely”).
But using the climate models used to determine the role of global warming in amplifying the entire monsoon season has proven trickier, the researchers noted in a press statement. World Weather Attribution attributes the uncertainty to wide variations in long-term rainstorm patterns, natural processes that models may not fully capture, and weather quirks in the region. The Indus Valley is located on the western edge of the region’s monsoon zone, and rainfall trends vary widely between dry west and wet east.
On the other hand, the weather records clearly show that , the region’s heaviest periods of rainfall have become more intense in recent decades, falling by about 75 percent in the two hardest-hit provinces. Some models have found that climate change may have increased rainfall by as much as 50 percent on the five wettest days of the two-month monsoon season in these regions.
“Thus, while it is difficult to give a precise figure for the contribution of climate change, the fingerprint of global warming is evident,” said Frederick, Senior Lecturer in Climate Science at Imperial College London Friederike Otto and a leader of the World Weather Attribution said in a statement.
In a scientific paper released Thursday, the team noted that a combination of meteorological forces drives extreme rainfall. These include La Niña, an event that cools the upper ocean and brings more rain than usual across much of the world, combined with Pakistan’s unusually hot spring and summer weather. Rising temperatures have also accelerated the melting of the thousands of glaciers that feed the Indus River, although it is unclear how much this will affect flooding.
Climate scientists have long warned that global rainfall patterns will become more frequent. Unstable as the planet warms, making very wet and very dry periods more common. Among other factors, warmer air contains more moisture, pulling moisture away from soil and plants, and altering the atmospheric pressure system. The UN climate panel predicts that the variation of the South Asian monsoon will increase year by year in the coming decades, but the intensity will generally increase throughout the 21st century.
Pakistan’s wettest days could turn into more extreme conditions as temperatures rise, World Weather Attribution found. This underscores the need for the country to strengthen its riverbanks, homes and other infrastructure to protect citizens — and the need for wealthy nations, which are disproportionately responsible for climate pollution, to do what they can to help.