Tracking Extremes in a Changing Climate

It is often through extreme weather events, such as heatwaves and heavy rainfall, that the impacts from climate change first affect us, presenting the greatest shocks to our wellbeing, key infrastructure, the economy and our environment.

Scientists from the Met Office Hadley Centre have produced a dashboard monitoring key indicators of global climate extremes. These include changes in both high and low temperature extremes and changes in rainfall intensity extremes.

The dashboard is the result of a continuing project to present clearly and simply how climate change is affecting the planet. Using a dataset known as HadEX3, which provides historical observations of changes in temperature and precipitation extremes, it informs how the risk from extreme events has changed.

Indicators show that globally, the number of warm days has risen, with around an additional 20 “warm” days per year in the most recent decade when compared to the 1970s.

Met Office Hadley Centre global climate extremes dashboard showing high temperature extremes.

Three indicators in the dashboard monitor changes in intense rainfall globally – wettest day of the year, amount of rain falling in heavy events and the fraction of the total annual precipitation coming from heavy events. All indicators show gentle increases since the beginning of the 20th Century. On a global average, we see that on the wettest day in a year, a few more mm of rain will fall on average now than in similar events 100 years ago. Over 20mm more rain is falling on the wettest days of the year than the average over 1961-90. Nowadays, an extra 2% of the total annual rainfall is falling in these wet days, compared to 1961-90.

Met Office Hadley Centre global climate extremes dashboard showing rainfall intensity extremes.

These indices provide a different perspective on climate change, complementing other global indicators of change such as annual average temperature, CO2 concentration and Arctic Sea ice extent, which the Met Office Hadley Centre reports in its climate dashboard to provide a more complete picture of what’s happening in the climate. Dr Robert Dunn, Climate Scientist at the Met Office said: “As individual extreme and exceptional events capture the headlines, the observations in this dashboard show that across the globe extreme events are changing their character.  For example, warm nights are becoming warmer, daily rainfall more intense, and warm spells are lasting longer.  These give context to our recent, current and projected future climate.”

These historical observations form part of mounting evidence which suggests that intense rainfall and heat extremes are becoming more frequent and intense in a warming climate. Nikos Christidis is a climate attribution scientist with the Met Office who looked at the record-breaking heatwave currently devastating parts of north western North America. He said: “Without human-induced climate change, it would have been almost impossible to hit such record-breaking mean June temperatures in the Western United States as the chances of natural occurrence is once every tens of thousands of  years.”

Last year, the prolonged Siberian heat where overall temperatures were more than 5°C above average from January to June 2020 is further evidence of the extreme temperatures we can expect to see more frequently around the world in a warming global climate. Met Office Climate Attribution scientist Andrew Ciavarella said that “climate change increased the chances of the prolonged heat in Siberia by at least 600 times.”

Closer to home, October 2020 will be remembered for containing one of the wettest days on record for the UK with an exceptional average of 30mm of rain falling  across the country in a single day. The record rainfall is estimated to have become about 2.5 times more likely because of human influence on the climate.

Monitoring extreme events is a key area of science and the new Met Office Hadley Centre climate programme will look at how global warming translates into local-scale changes in weather and climate extremes. Decision makers can use this information to inform adaptation and mitigation plans for future climate risk. At the COP26 climate conference in Glasgow later this year, a clear goal is agreeing adaptation measures to protect communities and natural habitats. Only the best climate science will enable us to build the resilience we need to face the challenges of the future.

HadEX3 was released last year and developed by the Met Office in collaboration with scientists from ARC Centre of Excellence for Climate Extremes at the University of New South Wales, Environment and Climate Change Canada and Barcelona Supercomputing Centre.  We are continuing to develop our global climate extremes dashboard. Please get in touch if you have any feedback via email to knowledge.integration@metoffice.gov.uk

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