PARIS, May 11, 2022 (BSS/AFP) - All heatwaves today bear the unmistakable and 
measurable fingerprint of global warming, top experts on quantifying the 
impact of climate change on extreme weather said Wednesday.

Burning fossil fuels and destroying forests have released enough greenhouse 
gases into the atmosphere to also boost the frequency and intensity of many 
floods, droughts, wildfires and tropical storms, they detailed in a state-of-
science report.

"There is no doubt that climate change is a huge game changer when it comes 
to extreme heat," Friederike Otto, a scientist at Imperial College London's 
Grantham Institute, told AFP.

Extreme hot spells such as the heatwave that gripped South Asia in March and 
April are already the most deadly of extreme events, she added. 

"Every heatwave in the world is now made stronger and more likely to happen 
because of human-caused climate change," Otto and co-author Ben Clarke of the 
University of Oxford said in the report, presented as a briefing paper for 
the news media.

Evidence of global warming's impact on extreme weather has been mounting for 
decades, but only recently has it been possible to answer the most obvious of 
questions: To what extent was a particular event caused by climate change?

The most scientists could say before is that an unusually severe hurricane, 
flood or heatwave was consistent with general predictions of how global 
warming would eventually influence weather.

News media, meanwhile, sometimes left climate change out of the picture 
altogether or, at the other extreme, mistakenly attributed a weather disaster 
entirely to rising temperatures.

With more data and better tools, however, Otto and other pioneers of a field 
known as event attribution science have been able to calculate -- sometimes 
in near realtime -- how much more likely or intense a particular storm or hot 
spell has become due to global warming.

- Courtroom evidence -

Otto and colleagues in the World Weather Attribution (WWA) consortium, for 
example, concluded that the heatwave that gripped western North America last 
June -- sending temperatures in Canada to a record 49.6 C (121 F) -- would 
have been "virtually impossible" without human-induced climate change.

A heatwave that scorched India and Pakistan last month is still under review, 
Otto told AFP, but the larger picture is frighteningly clear.

"What we see right now in terms of extreme heat will be very normal, if not 
cool, in a 2-degree to 3-degree Celsius world," she said, referring to 
average global temperatures above preindustrial levels.

The world has warmed nearly 1.2C so far. 

That increase made record-setting rainfall and flooding last July in Germany 
and Belgium that left more than 200 dead up to nine times more likely, the 
WWA found. 

But global warming is not always to blame.

A two-year drought in southern Madagascar leading to near famine conditions 
attributed by the UN to climate change was in fact a product of natural 
variability in the weather, experts reported. 

Quantifying the impact of global warming on extreme weather events using 
peer-reviewed methods has real-world policy implications.

Attribution studies, for example, have been used as evidence in landmark 
climate litigation in the United States, Australia and Europe.

In one case set to resume later this month, Saul Luciano Lliuya v. RWE AG, a 
Peruvian farmer is suing the German energy giant for the costs of preventing 
harmful flooding from a glacial lake destabilised by climate change. 

A scientific assessment entered into evidence concluded that human-caused 
global warming is directly responsible for creating a "critical threat" of a 
devastating outburst, putting a city of some 120,000 people in the path of 
potential floodwaters.