Not all extreme weather due to climate change

But study finds that events involving heat most likely a result of climate change

MIAMI • A killer snowstorm in the Himalayas, a scorching heatwave in Argentina and lashing rainfall in southern France last year were all made worse by climate change, international scientists said.

But other major events, such as Hurricane Gonzalo over Europe and drought in Brazil, were not influenced by global warming, according to a peer-reviewed study called Explaining Extreme Events Of 2014 From A Climate Perspective, which was released on Thursday.

The scientific team consisted of 32 research groups from around the world analysing 28 storms, droughts, fires and floods in a bid to showcase the role of human-driven climate change and land development in extreme weather events.

"Globally, extreme heat is becoming more common," said Dr Stephanie Herring, report lead editor from the National Oceanic and Atmospheric Administration's (NOAA) National Centres for Environmental Information.

But with rain and snowfall, scientists reported "a much more mixed result when it comes to looking for the human influence", she told reporters, describing the findings as "pretty evenly split this year between those that did and did not find a signal".

Not all extreme weather events were included in the research, so the report does not offer a comprehensive picture of the world's extreme weather last year.

Rather, scientists contributed research based on extreme weather events they were interested in studying, often but not always in their home nations, Dr Herring said, noting that scientists were not offered funding or incentives by NOAA for their work.

Weather events involving heat were most likely to have a clear signal that climate change played a factor, with such influence detectable about 95 per cent of the time, the report found. Those involving precipitation were less certain, with human-driven climate change or other land use activities showing up about 40 per cent of the time.

"Climate change is happening. It is having impacts," said Dr Herring. "Is it having impact uniformly across the globe in everything that we see and do? At this point, not in a measurable way."

For the purposes of the study, human influence could include the burning of fossil fuels which drives global warming, or the development of land or changes to water use that can make droughts, floods and wildfires more devastating.

Both climate change and land use played a role in the flooding in the south-eastern Canadian prairies, it said. Extreme heat events in Korea and China were linked to human-caused climate change.

The Argentinian heatwave of December 2013 was made five times more likely because of human-induced climate change.

When analysing drought in East Africa, two studies showed that the situation was made more severe because of climate change.

Global warming and human influences are also making floods like the ones that struck Jakarta last year more likely, as well as the snowstorm last year that killed more than 40 people in Nepal.

Among the events that were not found to have been influenced by humans was the extreme 2013-14 winter storm season over much of North America, which was "driven mainly by natural variability and not human-caused climate change", said the report.

Nor could an all-time record number of storms over the British Isles, extreme rains in Britain, Hurricane Gonzalo in Europe or drought in north-eastern Asia be attributed to climate change.


A version of this article appeared in the print edition of The Straits Times on November 07, 2015, with the headline 'Not all extreme weather due to climate change'. Print Edition | Subscribe