Global heating drives daily weather change

Abnormal daily weather is a pointer towards the bite of climate change. Image: By Timothy Ah Koy on Unsplash

Expect the climate, but prepare for the weather? Not any more. The statistics spell it out: global heating is causing daily weather change.

LONDON, 6 January, 2020 – Swiss scientists have done something many of their colleagues had claimed was impossible: they have linked the random events of the daily weather change we all experience directly to the climate crisis.

It has been an axiom of climate science for decades that – although global heating would inevitably increase the likelihood of more intense or more damaging windstorms, floods, droughts or heat waves – it would not be possible to say that this or that event could not have happened the way it did without the ominous rise in global average temperature, driven by profligate use of fossil fuels.

But that no longer holds, according to a new study in the journal Nature Climate Change.

“Weather when considered globally is now in uncharted territory,” researchers write. “On the basis of a single day of globally observed temperature and moisture, we detect the fingerprint of externally driven climate change, and conclude that the earth as a whole is warming.”

Climate scientists and statisticians from the Swiss Federal Institute of Technology, known simply as ETH Zurich, and from a partner institute in Lausanne known as EPFL, say that the seemingly normal variations in daily weather around the world are telling a clear story – just as long as the observers look at the global picture as well as the local measurements.

Clear pattern

For instance, on the same day as the Swiss study the UK Met Office announced a set of new temperature records for Britain in the last decade. The coldest March day ever recorded was in Gwent, Wales, in March 2018, when the thermometer fell to minus 4.7°C. But during the same decade the rest of Britain experienced four new and unprecedented monthly high temperatures, including an as yet unverified high of 18.7°C late in December.

In January 2020, a village in Norway registered a high of 19°C, a whole 25 degrees above the average for the winter month. But whereas local temperatures can fluctuate wildly, the variation in global average data is very small.

The Swiss scientists combed through the daily mean temperature and rainfall and snowfall data for the years 1951 to 1980, and for 2009 to 2018. They drew bell-shaped curves for each sequence of the years and then tried to match them. Without any overall rise in average global temperatures, the two curves would cover much the same space on the graph paper. They barely overlapped.

They then used a range of sophisticated statistical techniques to make detailed sense of the information in the two patterns of decadal weather. Beyond the jargon of the statistician’s trade – the paper talks of regression coefficients and regularised linear regression models, mean squared errors and Pearson correlations – a clear pattern emerged.

“Weather when considered globally is now in uncharted territory”

The often-wild swings of natural variation could be disentangled from the intensification powered by global heating. Climate change could be detected from global weather in any single year, month or even day. No longer can climate researchers use the old escape clause, “Climate is what you expect, weather is what you get,” to explain away seeming seasonal inconsistencies.

Global heating driven by greenhouse gases released by human economic growth is now shaping the world’s daily weather, from the catastrophic heat extremes and wildfires in Australia to the uncharacteristic winter weather in Moscow.

“The fingerprint of climate change is detected from any single day in the observed global record since early 2012”, the scientists write, “and since 1999 on the basis of a year of data. Detection is robust even when ignoring the long-term global warming trend.” – Climate News Network