Scientists see the hand of climate change in heat records and fires breaking out globally this summer.
SETH BORENSTEIN AND FRANK JORDANS, Associated Press US News 27 Jul 18;
Heat waves are setting all-time temperature records across the globe, again. Europe suffered its deadliest fire in more than a century, and one of nearly 90 large fires in the U.S. West burned dozens of homes and forced the evacuation of at least 37,000 people near Redding, California. Flood-inducing downpours have pounded the U.S. East this week.
It's all part of summer — but it's all being made worse by human-caused climate change, scientists say.
"Weirdness abounds," said Rutgers University climate scientist Jennifer Francis.
Japan hit 106 degrees on Monday, its hottest temperature ever. Records fell in parts of Massachusetts, Maine, Wyoming, Colorado, Oregon, New Mexico and Texas. And then there's crazy heat in Europe, where normally chill Norway, Sweden and Finland all saw temperatures they have never seen before on any date, pushing past 90 degrees. So far this month, at least 118 of these all-time heat records have been set or tied across the globe, according to the National Oceanic and Atmospheric Administration.
The explanations should sound as familiar as the crash of broken records.
"We now have very strong evidence that global warming has already put a thumb on the scales, upping the odds of extremes like severe heat and heavy rainfall," Stanford University climate scientist Noah Diffenbaugh said. "We find that global warming has increased the odds of record-setting hot events over more than 80 percent of the planet, and has increased the odds of record-setting wet events at around half of the planet."
Climate change is making the world warmer because of the build-up of heat-trapping gases from the burning of fossil fuels like coal and oil and other human activities. And experts say the jet stream — which dictates weather in the Northern Hemisphere — is again behaving strangely.
"An unusually sharply kinked jet stream has been stuck in place for weeks now," said Jeff Masters, director of the private Weather Underground. He says that allows the heat to stay in place over three areas where the kinks are: Europe, Japan and the western United States.
The same jet stream pattern caused the 2003 European heat wave, the 2010 Russian heat wave and fires, the 2011 Texas and Oklahoma drought and the 2016 Canadian wildfires, Pennsylvania State University climate scientist Michael Mann said, pointing to past studies by him and others. He said in an email that these extremes are "becoming more common because of human-caused climate change and in particular, the amplified warming in the Arctic."
Climate scientists have long said they can't directly link single weather events, like a heat wave, to human caused climate change without extensive study. In the past decade they have used observations, statistics and computer simulations to calculate if global warming increases the chances of the events.
A study by European scientists Friday found that the ongoing European heat wave is twice as likely because of human-caused global warming, though those conclusions have not yet been confirmed by outside scientists. The World Weather Attribution team said they compared three-day heat measurements and forecasts for the Netherlands, Denmark and Ireland with historical records going back to the early 1900s.
"The world is becoming warmer and so heatwaves like this are becoming more common," said Friederike Otto, a member of the team and deputy director of the Environmental Change Institute at the University of Oxford.
Erich Fischer, an expert on weather extremes at the Swiss Federal Institute of Technology in Zurich who wasn't part of the analysis said the authors used well-established methods to make their conclusions.
Georgia Tech climate scientist Kim Cobb said the link between climate change and fires isn't as strong as it is with heat waves, but it is becoming clearer.
A devastating fire in Greece — with at least 83 fatalities — is the deadliest fire in Europe since 1900, according to the International Disaster Database run by the Centre for the Research on the Epidemiology of Disasters in Brussels, Belgium.
In the United States on Friday there were 89 active large fires, consuming nearly 900,000 acres, according the National Interagency Fire Center. So far this year, fires have burned 4.15 million acres, which is nearly 14 percent higher than average over the past 10 years.
The first major science study to connect greenhouse gases to stronger and longer heat waves was in 2004. It was titled "More intense, more frequent and longer lasting heat waves in the 21st century." Study author Gerald Meehl of the National Center for Atmospheric Research said Friday that now it "reads like a prediction of what has been happening and will continue to happen as long as average temperatures continue to rise with ever-increasing emissions of greenhouse gases from burning fossil fuels. It's no mystery."
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Borenstein reported from Washington, Jordans from Berlin.
The Associated Press Health & Science Department receives support from the Howard Hughes Medical Institute's Department of Science Education. The AP is solely responsible for all content.
Heatwave made more than twice as likely by climate change, scientists find
Fingerprints of global warming clear, they say, after comparing northern Europe’s scorching summer with records and computer models
Damian Carrington The Guardian 27 Jul 18;
The heatwave searing northern Europe was made more than twice as likely by climate change, according to a rapid assessment by scientists.
The result is preliminary but they say the signal of climate change is “unambiguous”. Scientists have long predicted that global warming is ramping up the number and intensity of heatwaves, with events even worse than current one set to strike every other year by the 2040s.
“The logic that climate change will do this is inescapable – the world is becoming warmer, and so heatwaves like this are becoming more common,” said Friederike Otto, at the University of Oxford and part of the World Weather Attribution (WWA) consortium that did the work.
“What was once regarded as unusually warm weather will become commonplace, and in some cases, it already has,” she said. “So this is something that society can and should prepare for. But equally there is no doubt that we can and should constrain the increasing likelihood of all kinds of extreme weather events by restricting greenhouse gas emissions as sharply as possible.”
The new analysis is a climate-change attribution study. By comparing extreme weather with historical measurements and with computer models of a climate unaltered by carbon emissions, researchers can find how much global warming is increasing the risk of dangerous weather.
The researchers analysed records of the hottest three-day period at seven weather stations in northern Europe, from Ireland to the Netherlands to Scandinavia, where data was easily accessible.
“We found that for the weather station in the far north, in the Arctic Circle, the current heatwave is just extraordinary – unprecedented in the historical record,” said Geert Jan van Oldenborgh, at the Royal Netherlands Meteorological Institute and also part of WWA.
Across northern Europe, the group found global warming more than doubled the risk of scorching temperatures. “We can can see the fingerprints of climate change on local extremes,” he said. “It is amazing now that it is something you can really see at a local level.”
“Most heatwave studies have been done on large scale averages, so European-wide temperatures,” said Otto. “In this study, we have looked at individual locations, where people live, to represent the heatwave people are actually experiencing.” The analysis is a preliminary study as a full study requires many climate models to be run on high-powered computers, which takes months.
Previous attribution analyses have shown very strong connections between climate change and extreme weather events. The scorching summer in New South Wales, Australia, in 2016-17 was made at least 50 times more likely by global warming, meaning it can be “linked directly to climate change”, said the scientists.
The “Lucifer” heatwave across Europe’s Mediterranean nations in 2017 summer was made at least 10 times more likely by climate change, while the unprecedented deluge delivered in the US by Hurricane Harvey also in 2017 was made three times more likely by climate change, new research has found. However, other events, such as storms Eleanor and Friederike, which hit western Europe in January, were not made more likely by climate change, according to the scientists.
In Europe, the heatwave has been caused by the stalling of the jet stream wind, which usually funnels cool Atlantic weather over the continent. This has left hot, dry air in place for two months – far longer than than usual. The stalling of the northern hemisphere jet stream is being increasingly firmly linked to global warming, in particular to the rapid heating of the Arctic and resulting loss of sea ice.
The role of climate change in driving extreme weather events may actually be underestimated by these attribution studies, according to Prof Michael E Mann at Penn State University in the US. The work is good, he said, but computer models cannot yet reliably account for the complex jet stream changes caused by global warming, making the attribution studies “inherently conservative”.
Serious climate change is “unfolding before our eyes”, said Prof Rowan Sutton, director of climate research at the University of Reading. “No one should be in the slightest surprised that we are seeing very serious heatwaves and associated impacts in many parts of the world.”
The wide geographical spread of the heatwave, right across four continents, points to global warming as the culprit, said Prof Peter Stott, a science fellow at the UK’s Met Office: “That pattern is something we wouldn’t be seeing without climate change.”
The heatwave across northern Europe has seen wildfires in the Arctic Circle and prolonged heat across the UK and the European continent. In the south, fierce blazes have devastated parts of Greece, with scores of people killed.
But extreme weather has struck across the globe. Severe floods killed at least 220 people in Japan in early July, with the nation then hit by an “unprecedented” heatwave that peaked at 41.1C and left 35,000 people in hospital. In the US, extreme heat in the west is feeding wildfires, with Yosemite national park being evacuated, while flooding is affecting the east.
Temperature records have also fallen in Taiwan, with a temperature of 40.3C in Tianxiang, and in Ouargla in Algeria’s Sahara desert, which reported a maximum temperature of 51.3C, the highest temperature ever reliably recorded in Africa. The first six months of the 2018 are the hottest recorded for any year without an El Niño event, a natural climate cycle that raises temperatures.
Climate change driven by humans made heatwave 'twice as likely'
Matt McGrath BBC 27 Jul 18;
Climate change resulting from human activities made the current Europe-wide heatwave more than twice as likely to occur, say scientists
Researchers compared the current high temperatures with historical records from seven weather stations, in different parts of Europe.
Their preliminary report found that the "signal of climate change is unambiguous," in this summer's heat.
They also say the scale of the heatwave in the Arctic is unprecedented.
The scale and breadth of the current heat being experienced across Europe has prompted many questions about the influence of global warming on extreme events.
To try and see if there is a connection, researchers looked at data from seven weather stations, in Finland, Denmark, Ireland, the Netherlands, Norway and Sweden.
They chose these locations because they all had digitised records dating back to the early 1900s, unlike the UK. The team also used computer models to assess the scale of human-influenced climate change.
The researchers found that in the weather stations in the Netherlands, Ireland and Denmark, climate change has generally increased the odds of the current heatwave by more than two-fold.
So what exactly is a heatwave?
There are several different definitions of what exactly makes a heatwave but the researchers in this study have gone with the hottest consecutive 3 day period in a year. This has allowed them to compare the data from the seven different locations over the past 100 years or so.
"In many parts of Europe three day heat is not very exceptional and you could argue that it would be better to look at longer," said Dr Friederike Otto from the University of Oxford, one of the study's authors.
"But we've looked at longer periods and it doesn't change the result very much."
The researchers also say the warmest three days in succession this year may not yet have happened but they believe that even if next week is warmer, it won't change the overall impact.
Is this definitive proof of the impact of climate change?
Scientists are loath to say a specific event was "caused" by climate change - however they believe that this new study joins a growing list of solid links between rising temperatures and extreme events.
One thing the researchers can't say right now is whether the high pressure system that has been blocked over Europe for almost two months was caused by climate change. The scientists, from the World Weather Attribution group say they will address this question when they formally publish their findings in a scientific journal later this year.
Can they tell us when another heatwave will strike Europe?
They can't be that definite. However the study does give figures for what are termed "return periods" or the chances of something happening again.
They estimate that in southern Scandinavia it's likely there will be a similar heatwave every ten years, while further south, in the Netherlands, it's likely to be once every five years. This ties in with projections from several scientists that the type of heatwave we've had this summer could occur every second year by the 2040s.
"The logic that climate change will do this is inescapable - the world is becoming warmer, and so heatwaves like this are becoming more common," said Dr Friederike Otto, from the University of Oxford.
"What was once regarded as unusually warm weather will become commonplace - in some cases, it already has," she added.
What about the Arctic?
While acknowledging that the current heatwave in the Arctic is unprecedented in the historical record, the researchers were not able to clearly resolve the impact of human influence.
That's because summer temperatures there vary a good deal from year to year so the trend was impossible to estimate from the observations, the authors said.
Despite their reservations about the Arctic they argue that their initial findings should prompt more action on cutting carbon from governments.
"We are not taking the right measures," said Dr Robert Vautard, from the CNRS in France.
"We are discovering climate change rather than doing something against it."
How do you work out the influence of climate change?
It involves some serious number crunching!
This new research is called an attribution study - The researchers work out how often these type of extreme heat events have happened at each of the weather stations they looked at.
They compare those findings to modelled results of the climate without the influence of human emissions of carbon dioxide. This way they can work out how much climate change has tipped the odds of a rare event happening.
Have other extreme events been linked to climate change?
The list continues to grow.
The major European heatwave of 2003 was among the first events to be linked though it took scientists several years to do it - Eventually they concluded that human induced climate change had made the event 500% more likely!
These days the attributions studies are much faster - just last year scientists concluded that the flooding in Houston, Texas was made 38% more likely by climate change while the so-called "Lucifer" heatwave in Eastern Europe was made ten times more likely. This new study was completed in less than a week.
