EXTREME WEATHER ATTRIBUTION
The title photo shows storm damage in New Orleans following Hurricane Katrina.
We were subjected to regular interviews with so-called experts from both sides of the argument telling us yes, this was probably a climate change event, or no, this is just part of Earth's normal cycle of extreme weather that crops up every 50 years or so.
Then, in December the following year, a ground-breaking article was published in the science journal Nature entitled ‘Human contribution to the European heatwave of 2003’. In the abstract on the first page of the article, the authors write:
‘It is an ill-posed question whether the 2003 heatwave was caused, in a simple deterministic sense, by a modification of the external influences on climate — for example, increasing concentrations of greenhouse gases in the atmosphere — because almost any such weather event might have occurred by chance in an unmodified climate.’
How often do I hear climate change deniers point out that every kind of extreme weather event has been taking place on the planet since Homo sapiens first evolved in Africa 300,000 years ago and of course, they are correct. In July 1743, during a heatwave in China, Beijing reached 44.4 °C (111.9 °F), higher than any modern records. 11,400 people reportedly died. The Great Hurricane of 1780 which tore across the eastern Caribbean islands is estimated to have killed as many as 27,000 people, far more than died in the 1998 Hurricane Mitch. History is peppered with extreme weather events. But read on...
The article’s abstract continues:
'However, it is possible to estimate by how much human activities may have increased the risk of the occurrence of such a heatwave.'
And so was born the cutting-edge field of Extreme Weather Attribution which seeks to establish the role that human-caused warming plays in these events. As far as the 2003 heatwave was concerned, Peter Stott and co-workers concluded that human greenhouse gas emissions had doubled the risk of such a heatwave taking place.
Extreme Weather Attribution (EWA) involves scientists running climate models thousands of times in scenarios with and without human-caused climate change, then comparing the two. This allows them to say how much more likely, intense or long-lasting an event was due to climate change.
In the summer of 2003, a devastating heatwave struck Europe. Week upon week of extreme temperatures killed more than 70,000 people across the continent. The media began asking a question that has since been asked repeatedly after every extreme weather event:
Was this catastrophe made worse by human-caused global warming?
