In this case, however, it is not clear how large the role of climate change was.
It is relatively easy to conduct an attribution study that assesses the impact of warming on heat waves, where hotter average temperatures raise the baseline from which such heat events originate.
The group has calculated exactly how much climate change has altered the likelihood of last year’s blistering Pacific Northwest heatwave (such conditions would be “at least 150 times rarer without man-made climate change”), the recent UK heatwave (climate change made it “at least 10 times more likely”) and that in Pakistan and India earlier this year (“30 times more likely”).
However, using climate models to determine the role of global warming in amplifying the overall monsoon season proved more difficult, the researchers noted in a press statement. World Weather Attribution attributed the uncertainty to a combination of the large variability in heavy rain patterns over long periods, natural processes that the models may not fully capture, and the territory’s weather errors. The Indus River Basin lies on the western edge of the region’s monsoon range, where there are large differences in precipitation trends between the dry west and the wet east.
On the other hand, weather records clearly show that the region’s heaviest rainy spells have become more intense in recent decades, by about 75% in the two hardest-hit provinces. Some models found that climate change could have increased precipitation by up to 50% during the five wettest days of the two-month monsoon season in these areas.
“While it is difficult to put a precise figure on the contribution of climate change, the fingerprints of global warming are evident,” Friederike Otto, a lecturer in climate science at Imperial College London and one of the leaders of World Weather Attribution, said in a statement.