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Forecast: chance of climate change
special report Extreme weatHer
Forecast: chance of climate change Weather reports could discuss when climate is to blame. Catherine Brahic reports “Well, the record-breakingly hot summer is showing no sign of cooling down. No thanks to us: the heatwave was made 35 per cent more likely by human greenhouse gas emissions.”
emissions, and one without – to assess the likelihood of a heatwave of that scale striking where it did, when it did. They calculated that human emissions doubled the odds of it happening (Nature, doi.org/c7hxpt). Since then, several studies have used similar methods (see “Blame warming?”, opposite), but they all have dealt with events long after they have left the public
CLIMATE scientists tend to shy away from assigning blame for extreme weather events like the fictional heatwave described above. But that may be about to change, thanks to a new type of climate study that can connect individual weather events with the impact of human-made greenhouse gas emissions. So far, these studies have been done retroactively, a year or more after specific extreme events. But the latest techniques are making it possible to examine the role that climate change played in shaping the season that has just past – whether it was a scorching summer or a particularly wet winter, for instance. The ultimate goal is for this to happen in real-
time so that climate analysis can become part of the daily weather report. “Explaining why we’re getting the weather we’re getting should be part of the job of meteorological offices, as well as predicting it,” says Myles Allen at the University of Oxford. Allen was part of a team that carried out pioneering research that examined the impact of greenhouse gas emissions on weather. After a deadly heatwave in 2003 contributed to the deaths of some 70,000 people in Europe, the team used two simulations of the climate – one including human-made greenhouse 8 | NewScientist | 30 August 2014
REUTERS/Jonathan Alcorn
“We can connect individual weather events with the impact of human-made greenhouse gas emissions”
consciousness. Peter Stott of the UK Met Office, who also worked on the heatwave study, and Allen are part of a growing cadre of climate scientists who want that to change. This year, Nathalie Schaller, also at Oxford, took a closer look at the unusual weather that the southeast of England was experiencing. Record rain fell at the Oxford weather observatory from late 2013 through to early 2014, and
there was widespread flooding. To explore whether climate change was making such precipitation more likely, Schaller and her team ran a similar experiment to Stott and Allen’s. They used real-world data to simulate the season that had just passed, then stripped the data of the influence of greenhouse gas emissions and ran the simulation again. The scenario was simulated
In this section n How your bacteria take over when you die, page 10 n Mapping Nairobi’s bacterial connections, page 14 n Supercomputer makes its own discoveries, page 19
thousands of times in order to calculate the odds of getting a bout of extremely wet weather at that particular time of year. They concluded that what was a 1-in-100-year event without global warming had become a 1-in-80year event. In other words, human emissions made the extreme levels of rainfall experienced in south-east England 25 per cent more likely. The team’s results were published online on 30 April, just two months after the flooding abated. To speed things up even more, a project called European Climate and Weather Events: Interpretation and Attribution
(EUCLEIA), led by Stott and funded computers – is one way around by the European Union, will test the problem. Roberto Mera at a new system. Instead of waiting the Union of Concerned Scientists for an event to happen, the idea in Washington DC is currently is to incorporate seasonal using this approach to look at forecasts, which are done a the role of climate change in the record-setting drought now month or more ahead of time, hitting California. into the climate models. Modelling specific extreme “One of the designs EUCLEIA is events helps us understand how looking at is to use forecast seasurface temperatures,” says Allen. and why they happened, says Stephanie Herring of the US Sea-surface temperature is an National Oceanographic and important driver of the weather, Atmospheric Administration and because the oceans change in Boulder, Colorado. “We aren’t temperature very slowly compared with the air and land, just curious about whether they form a key, predictable climate change had an impact component of seasonal forecasts. on an event – we’re also asking what can this tell us about the In the new set-up, a real-world seasonal forecast driven by data on current sea-surface temperatures “It shows that what’s going on outside someone’s will be run alongside a simulated window is directly linked “no global warming” seasonal forecast, in which greenhouse gas to climate change” emissions have been stripped out. likelihood and magnitude of If an extreme weather event events in future.” occurs, researchers can look to International climate talks see if the models predicted it. If it could be affected too. At recent was predicted in the real-world United Nations meetings, it has seasonal forecast but not in the been broadly agreed that money scenario which is stripped of needs to be channelled from rich emissions, then it was made nations, which are historically more likely by climate change – a responsible for the bulk of likelihood that can be calculated. emissions, to poorer nations, For now, assigning a share of which tend to suffer most from blame for past temperature anomalies like heatwaves and cold the impacts of those emissions. One way to do that would be to snaps is perfectly feasible, says assign compensation after a Stott. Rainfall is more complex nation suffers losses due to to model, though Schaller’s climate change. But in order for study shows it is possible. Hurricanes and tornadoes require that to work, there needs to be a specialised models to predict, but way to show that an island hit by a typhoon, say, would probably Allen says that in theory they have been spared if global could be used to run the same warming hadn’t been a factor. type of experiment. Weather-attribution studies A main obstacle to bringing could provide that information. this kind of powerful climate Ultimately, though, the key modelling into standard weather contribution of this work may be forecasts is computing power. to get through to a general public Models must be run many for whom climate change has thousands of times to obtain long been an abstract concept. statistically significant results, By showing that what’s going on which requires expensive outside someone’s window is supercomputers. directly linked to climate change, Web-based distributed researchers hope it will become computing, by which models obvious that what they are saying are run remotely on borrowed –Feeling the heat in Los Angeles– downtime on volunteers’ personal isn’t just a load of hot air. n
Blame warming? It is difficult to attribute individual weather events to human-induced climate change, but several recent studies are suggesting the role that greenhouse gases played in weather extremes. 2003 European heatwave contributes to the deaths of about 70,000 people. In 2004, Peter Stott of the UK Met Office and colleagues found that global warming had doubled the likelihood of such an event (Nature, doi.org/c7hxpt). 2010 A heatwave, and smog from resulting fires in Russia, contribute to 56,000 deaths. In 2011 Stefan Rhamstorf of Potsdam University in Germany estimated that there was an 80 per cent chance that the heatwave would not have happened without global warming (PNAS, doi.org/dhnggk). 2011 Drought and extreme heat strike Texas. David Rupp of Oregon State University and his colleagues estimate that the conditions were 20 times as likely to occur in the late 2000s as in the 1960s, due to the added greenhouse gases (Bulletin of the American Meteorological Society, doi.org/j7r). 2011-2012 Thailand suffers severe floods, more than 800 people perish and damages are estimated at $45 billion. A study by Geert Jan van Oldenborgh of the Royal Netherlands Meteorological Institute concluded that climate change was not to blame, but that development along the banks of the Chao Phraya river contributed to the disaster (Bulletin of the American Meteorological Society, doi.org/j7r). 2012 Floods in south-eastern Australia bring a sudden end to a 13-year drought that had afflicted the region. Two separate studies of the floods found no link to climate change (Bulletin of the American Meteorological Society, doi.org/vc3).
30 August 2014 | NewScientist | 9
Forecast: chance of climate change Weather reports could discuss when climate is to blame. Catherine Brahic reports “Well, the record-breakingly hot summer is showing no sign of cooling down. No thanks to us: the heatwave was made 35 per cent more likely by human greenhouse gas emissions.”
emissions, and one without – to assess the likelihood of a heatwave of that scale striking where it did, when it did. They calculated that human emissions doubled the odds of it happening (Nature, doi.org/c7hxpt). Since then, several studies have used similar methods (see “Blame warming?”, opposite), but they all have dealt with events long after they have left the public
CLIMATE scientists tend to shy away from assigning blame for extreme weather events like the fictional heatwave described above. But that may be about to change, thanks to a new type of climate study that can connect individual weather events with the impact of human-made greenhouse gas emissions. So far, these studies have been done retroactively, a year or more after specific extreme events. But the latest techniques are making it possible to examine the role that climate change played in shaping the season that has just past – whether it was a scorching summer or a particularly wet winter, for instance. The ultimate goal is for this to happen in real-
time so that climate analysis can become part of the daily weather report. “Explaining why we’re getting the weather we’re getting should be part of the job of meteorological offices, as well as predicting it,” says Myles Allen at the University of Oxford. Allen was part of a team that carried out pioneering research that examined the impact of greenhouse gas emissions on weather. After a deadly heatwave in 2003 contributed to the deaths of some 70,000 people in Europe, the team used two simulations of the climate – one including human-made greenhouse 8 | NewScientist | 30 August 2014
REUTERS/Jonathan Alcorn
“We can connect individual weather events with the impact of human-made greenhouse gas emissions”
consciousness. Peter Stott of the UK Met Office, who also worked on the heatwave study, and Allen are part of a growing cadre of climate scientists who want that to change. This year, Nathalie Schaller, also at Oxford, took a closer look at the unusual weather that the southeast of England was experiencing. Record rain fell at the Oxford weather observatory from late 2013 through to early 2014, and
there was widespread flooding. To explore whether climate change was making such precipitation more likely, Schaller and her team ran a similar experiment to Stott and Allen’s. They used real-world data to simulate the season that had just passed, then stripped the data of the influence of greenhouse gas emissions and ran the simulation again. The scenario was simulated
In this section n How your bacteria take over when you die, page 10 n Mapping Nairobi’s bacterial connections, page 14 n Supercomputer makes its own discoveries, page 19
thousands of times in order to calculate the odds of getting a bout of extremely wet weather at that particular time of year. They concluded that what was a 1-in-100-year event without global warming had become a 1-in-80year event. In other words, human emissions made the extreme levels of rainfall experienced in south-east England 25 per cent more likely. The team’s results were published online on 30 April, just two months after the flooding abated. To speed things up even more, a project called European Climate and Weather Events: Interpretation and Attribution
(EUCLEIA), led by Stott and funded computers – is one way around by the European Union, will test the problem. Roberto Mera at a new system. Instead of waiting the Union of Concerned Scientists for an event to happen, the idea in Washington DC is currently is to incorporate seasonal using this approach to look at forecasts, which are done a the role of climate change in the record-setting drought now month or more ahead of time, hitting California. into the climate models. Modelling specific extreme “One of the designs EUCLEIA is events helps us understand how looking at is to use forecast seasurface temperatures,” says Allen. and why they happened, says Stephanie Herring of the US Sea-surface temperature is an National Oceanographic and important driver of the weather, Atmospheric Administration and because the oceans change in Boulder, Colorado. “We aren’t temperature very slowly compared with the air and land, just curious about whether they form a key, predictable climate change had an impact component of seasonal forecasts. on an event – we’re also asking what can this tell us about the In the new set-up, a real-world seasonal forecast driven by data on current sea-surface temperatures “It shows that what’s going on outside someone’s will be run alongside a simulated window is directly linked “no global warming” seasonal forecast, in which greenhouse gas to climate change” emissions have been stripped out. likelihood and magnitude of If an extreme weather event events in future.” occurs, researchers can look to International climate talks see if the models predicted it. If it could be affected too. At recent was predicted in the real-world United Nations meetings, it has seasonal forecast but not in the been broadly agreed that money scenario which is stripped of needs to be channelled from rich emissions, then it was made nations, which are historically more likely by climate change – a responsible for the bulk of likelihood that can be calculated. emissions, to poorer nations, For now, assigning a share of which tend to suffer most from blame for past temperature anomalies like heatwaves and cold the impacts of those emissions. One way to do that would be to snaps is perfectly feasible, says assign compensation after a Stott. Rainfall is more complex nation suffers losses due to to model, though Schaller’s climate change. But in order for study shows it is possible. Hurricanes and tornadoes require that to work, there needs to be a specialised models to predict, but way to show that an island hit by a typhoon, say, would probably Allen says that in theory they have been spared if global could be used to run the same warming hadn’t been a factor. type of experiment. Weather-attribution studies A main obstacle to bringing could provide that information. this kind of powerful climate Ultimately, though, the key modelling into standard weather contribution of this work may be forecasts is computing power. to get through to a general public Models must be run many for whom climate change has thousands of times to obtain long been an abstract concept. statistically significant results, By showing that what’s going on which requires expensive outside someone’s window is supercomputers. directly linked to climate change, Web-based distributed researchers hope it will become computing, by which models obvious that what they are saying are run remotely on borrowed –Feeling the heat in Los Angeles– downtime on volunteers’ personal isn’t just a load of hot air. n
Blame warming? It is difficult to attribute individual weather events to human-induced climate change, but several recent studies are suggesting the role that greenhouse gases played in weather extremes. 2003 European heatwave contributes to the deaths of about 70,000 people. In 2004, Peter Stott of the UK Met Office and colleagues found that global warming had doubled the likelihood of such an event (Nature, doi.org/c7hxpt). 2010 A heatwave, and smog from resulting fires in Russia, contribute to 56,000 deaths. In 2011 Stefan Rhamstorf of Potsdam University in Germany estimated that there was an 80 per cent chance that the heatwave would not have happened without global warming (PNAS, doi.org/dhnggk). 2011 Drought and extreme heat strike Texas. David Rupp of Oregon State University and his colleagues estimate that the conditions were 20 times as likely to occur in the late 2000s as in the 1960s, due to the added greenhouse gases (Bulletin of the American Meteorological Society, doi.org/j7r). 2011-2012 Thailand suffers severe floods, more than 800 people perish and damages are estimated at $45 billion. A study by Geert Jan van Oldenborgh of the Royal Netherlands Meteorological Institute concluded that climate change was not to blame, but that development along the banks of the Chao Phraya river contributed to the disaster (Bulletin of the American Meteorological Society, doi.org/j7r). 2012 Floods in south-eastern Australia bring a sudden end to a 13-year drought that had afflicted the region. Two separate studies of the floods found no link to climate change (Bulletin of the American Meteorological Society, doi.org/vc3).
30 August 2014 | NewScientist | 9