Get ready for hotter summers and more flooding in the UK, say scientists
Weather-wise, the UK saw it all last year. The coldest spring for 50 years, a sweltering summer heat wave and the wettest winter since records began. Today, a new report examines whether climate change is upping the odds of these events occurring.
The collection of papers, published in a bumper edition of journal Bulletin of the American Meteorological Society, looks at 16 weather events that took place last year across the world. From Colorado to Korea, the scientists examine heatwaves, droughts, heavy rain and storms.
Human fingerprints
Globally, there is evidence for changes in some types of extreme weather, and evidence for a human fingerprint in those changes. But different types of event are affected differently.
Climate change is greatly increasing the odds of heatwaves worldwide, today’s report concludes. For storms, rainfall and drought the picture is less clear, however. Big differences between regions, natural variability in the climate and limited data make detecting changes over time far more difficult.
The science of disentangling human and natural influences on our climate is known as attribution. Dr Peter Stott, head of the climate change detection and attribution team at the Met Office and an editor on the report, explained more in a recent guest blog for us:
“[The aim is] to compare what actually happened with what might have happened in a world without anthropogenic climate change.”
Understanding how our activities are changing the risk of some types of extremes is important for making decisions about how we can prepare for the future.
Hot summers
In summer 2013, western Europe experienced an extreme heatwave. Average temperatures for the June to August period sit just below those of 2003 – the hottest summer in Europe for at least 500 years.
At the same time, the UK experienced its hottest day since 2006 with temperatures of 33.5 degrees Celsius recorded at Heathrow airport, the report notes.
Image - UKheatwave 2014 (note)
Sun-seekers flock to Margate in July 2013. Source: UK heatwave via Shutterstock
A paper in today’s collection concludes that while natural variability played a role in warmer than average sea surface temperatures in the North Atlantic, human activity played a “substantial part” in bringing about the prolonged hot, dry spell.
These conclusions build on previous research suggesting human influence has at least doubled the risk of a heatwave like the one Europe experienced in 2003.
Professor Rowan Sutton, lead author on the new paper, says:
“Climate change has increased the odds of hot summers in the UK. Summer 2013 was a good example, and Britain should expect more hot summers in the future, although not every year.”
We should still expect the odd extreme cold event despite average temperatures rising, the report notes. Spring 2013 in the UK was the coldest for more than half a century, for example.
But climate change means we’ll see such events less often. A paper in today’s collection suggests warming has made events like the UK’s 2013 cold spring 30 times less likely. Globally, extreme cold events that used to occur every 20 years are now happening every 35 years, other research notes.
Wetter or drier?
Thanks to our notoriously complicated weather systems in the UK, whether climate change will make our summers wetter or drier is more difficult to unravel, Sutton adds.
“Given the UK’s position on the edge of the Atlantic, we think that – at present – natural changes in winds and ocean currents play a bigger role in summer rainfall patterns than emissions of greenhouse gases.”
But while it’s unclear from today’s research what the change in the total amount of rainfall might be in the UK, the risk of flooding is on the up. Sutton adds:
“[I]n a warmer world, when summer rain does occur, it’s likely to be the heavy kind that can cause floods.”
Recent research suggested climate change has made the sort of heavy and prolonged rainfall we experienced in the UK last year 25 percent more likely.
Image - Record Rainfall _Jan 2014 (note)
Total rainfall (mm) for January in southern England from records going back to 1910. Source: “The recent storms and floods in the UK” report ( Met Office)
Bigger picture
The report looks further afield at extreme weather beyond the UK and Europe.
A collection of papers found human-caused climate change has significantly increased the likelihood of the record heatwave Australia experienced in 2013. As Professor David Karoly from the University of Melbourne puts it:
“If we were climate detectives then Australia’s hottest year on record in 2013 wasn’t just a smudged fingerprint at the scene of the crime, it was a clear and unequivocal handprint showing the impact of human caused global warming.”
The impacts of man-made climate change were felt in Australia during its hottest year on record in 2013. Source: UNSW, P3, Helena Brusic.
Human influence on the ongoing California drought is less clear. Overall, the scientists “did not find conclusive evidence of human impacts”, the report notes.
One paper suggests the atmospheric pattern scientists think is causing the current drought is becoming more likely under climate change. But other research in today’s special issue that uses a different approach isn’t so confident.
We’ve looked more closely at what the report says about the California drought here.
Communicating risk
Finding ways to effectively communicate extreme weather attribution, and the complex science that underpins it, is “a considerable and ongoing challenge”, the report notes.
Scientists can’t say a single event is ever solely caused by climate change, instead they talk about climate change altering the odds of different types of extreme weather. Even more so than in other aspects of climate science, it’s important to clear about what question is being asked – and it’s not a one-size fits all answer for every different type of event.
The report also makes the point that while some of today’s research doesn’t find a definitive link between some types of extreme event and climate change, that doesn’t mean there isn’t one. It might mean the signal from man-made warming hasn’t yet risen above the noise of natural variability, but that could change in the future.
Today’s new report adds a lot to the steadily growing body of literature on climate change attribution. The nuances of researching and communicating extreme weather show why a reasoned and evidenced-based approach is a must when it comes to reducing climate risk.