This post is part of WRI's "Extreme Weather Watch" series, which explores the link between climate change and extreme events. Read our other posts in this series.
Many people are understandably perplexed at the U.S.’s recent extreme weather events like record heat waves, torrential downpours, droughts, and wildfires. A new report published by scientists from the National Oceanic and Atmospheric Administration (NOAA) and other institutions may finally offer some insight into climate change’s connection to the damaging and costly extreme events that are on the rise.
Numerous studies have shown that the Earth is warming rapidly, due in large part to human activities. While existing research focuses on climate change’s implications for the intensity and frequency of extreme events like storms and heat waves, due to scientific complexities, most scientists to date have tip-toed around attributing any single event to climate change.
Until now, that is. Last week, scientists from NOAA, the UK’s Met Office, and other institutions published a special report in the Bulletin of the American Meteorological Society (BAMS) that attributed a number of recent extreme events to human-induced climate change. As the new report stated:
“In the past it was often stated that it simply was not possible to make an attribution statement about an individual weather or climate event. However, scientific thinking on this issue has moved on and now it is widely accepted that attribu¬tion statements about individual weather or climate events are possible, provided proper account is taken of the probabilistic nature of attribution."
Here are five emerging ideas from this groundbreaking report:
1) It is possible to attribute individual extreme weather events to human-induced climate change.
Due to recent advancements in analytical methods, climate scientists are beginning to be able to better determine how climate change impacts the odds of an individual extreme event occurring. Therefore, it’s becoming possible to discuss the degree to which human-induced changes in temperature and/or precipitation affect the probability of an event happening.
The new BAMS report provides a helpful analogy for understanding the concept of probabilistic attribution: Take a baseball player who starts taking steroids. He now hits more home runs than he had before taking steroids – say by 10 percent more over the course of a season. While it’s impossible to say whether each home run was the result of steroid use, we know steroids increased his chances of home runs by 10 percent in general. Therefore, we can quantify the higher chances (10 percent) of his hitting a particular home run due to steroids. Attribution of extreme events to climate change works similarly. Scientists can now quantify and attribute the changed odds of a given event happening.
2) Climate science is advancing in its ability to attribute extreme events to climate change.
The science of attribution is quite new, but it’s advancing quickly. Several papers have been published on this topic in recent years, and the authors of the BAMS report note that the new paper is only the first of what will be a series of annual reports. In addition, a group of scientists convened the “Attribution of Climate-related Events (ACE)” initiative and will meet in September to discuss strategies for advancing attribution science.
Most significantly, several different attribution methods have now been developed. As discussed above, one method quantifies the odds of an event happening. Other approaches involve climate models and focus on climate change’s role in physical processes – such as dynamic interactions between soil moisture and the atmosphere – at regional scales.
3) Some past “disagreements” about attribution of individual extreme events have not been true disagreements.
Prior to this report, only a handful of studies had investigated the attribution of single extreme events to climate change, yet some came to opposite conclusions. As the BAMS report notes, conclusions can differ because studies ask different questions. For example, one study (Dole et al. 2011) looked at the magnitude of the Russian heat wave in 2010 and concluded it was not human-induced, whereas another study (Rahmstorf and Coumou 2011) assessed the probability of the same heat wave occurring and concluded that it was due to human-induced warming. So while at face value these studies look like they conflict with one another, they are simply looking at different aspects of the heat wave (magnitude vs. probability of occurrence) and therefore cannot be compared with one another. This nuance has often been lost when communicating about the connection between climate change and extreme events and has led to considerable confusion.
4) We can’t blame climate change for every extreme event.
As the BAMS report noted,a recent special report from the Intergovernmental Panel on Climate Change finds that a warmer world will likely feature more extreme weather. However, this does not mean that every extreme event is due to climate change. In analyzing climate change’s role in half a dozen extreme events, authors of the BAMS report found that some recent events show no apparent connection to global warming. For example, according to the report, the rainfall levels that coincided with the 2011 floods in Thailand were not particularly unusual. Rather, non-climate factors—such as changes in water management and land-use patterns—played a larger role in determining the scale of disaster.
5) But a number of extreme events over the last year can now be attributed to climate change.
For example, scientists found that the conditions that led to the 2011 Texas drought are 20 times more likely to occur now than in the 1960s as a result of increases in greenhouse gas concentrations and associated climatic changes. In another example, scientists found that England’s 2010 and 2011 winter temperatures could be attributed to climate change. December’s 2010 freezing was half as likely to have occurred half a century ago, while the warmth experienced in November 2011 was 62 times more likely to have occurred then than in the 1960s.
What Do these Findings Mean?
We can expect more research in the coming years that examines the link between individual extreme events and climate change. The BAMS report not only advances the science of attribution, but also adds to a growing body of evidence that climate change’s connection to extreme events is a strong one. And this is not a distant phenomenon—it’s happening now. As decision makers around the world make reforms to contend with extreme events, maybe it’s time they pause to acknowledge the role that human-induced climate change is playing in our changing weather – and commit to policy changes that begin to reverse such trends.