In this case, however, it is not clear what role climate change played.
It is relatively simple to conduct an attribution study that assesses the influence of warming on heat waves, where warmer average temperatures raise the baseline from which these sweltering events take off. The group has calculated precisely how much climate change altered the odds of last year’s Pacific Northwest heat wave (such conditions would have been “at least 150 times rarer without human-induced climate change” ), the recent UK heat wave (climate change made is “at least 10 times more likely”), and the one in Pakistan and India earlier this year (“30 times more likely”).
But using climate models to identify the role of global warming in amplifying the full monsoon season proved more complicated, the researchers noted in a press release. World Weather Attribution attributed the uncertainty to some combination of wide variability in heavy rainfall patterns over long periods, natural processes at work that models may not fully capture, and the terrain’s meteorological peculiarities. The Indus River basin is located on the western edge of the region’s monsoon area, where there are large differences in rainfall trends between the dry west and wet east.
PAULA BRONSTEIN/ GETTY IMAGES
On the other hand, weather records clearly show that the heaviest periods of rain in the region have become more intense in recent decades, by about 75% in the two most affected provinces. Some models found that climate change may have increased rainfall by as much as 50% during the five wettest days of the two-month monsoon season in these areas.
“So while it is difficult to put a precise figure on the contribution of climate change, the fingerprints of global warming are clear,” Friederike Otto, senior lecturer in climate science at Imperial College London and a of the leaders of World Weather Attribution. he said in a statement.
