When asked about a particular weather event’s link to climate change, scientists are typically cautious to make definitive statements — especially in the immediate aftermath, before they’ve had the chance to study the event.
But according to a new study, it’s getting easier for scientists to make the link between climate change and some forms of extreme weather. The study, published Friday by the National Academies Press, found that scientific advances over the past several years have helped scientists link increases in frequency and intensity of temperature and precipitation-related events like droughts and heat waves to climate change.
“In the past, a typical climate scientist’s response to questions about climate change’s role in any given extreme weather event was ‘we cannot attribute any single event to climate change,'” the report, completed by a committee of scientists, reads. “The science has advanced to the point that this is no longer true as an unqualified blanket statement. In many cases, it is now often possible to make and defend quantitative statements about the extent to which human-induced climate change (or another causal factor, such as a specific mode of natural variability) has influenced either the magnitude or the probability of occurrence of specific types of events or event classes.”
The report calls this branch of science, wherein researchers work to determine whether climate change contributed to a certain event, “event attribution.” To determine how and if climate change is linked to a certain event, scientists typically either reference the observational record of similar events — i.e. the recorded history of droughts leading back several decades — or use models to determine how likely a similar event would be in different warming scenarios. Most studies, the report states, use both of these tactics.
These methods make it easier to study climate change’s effect on heat waves and extreme cold events than on cyclones and wildfires. Extreme heat and cold events are easy to simulate in models, have a well-kept-up observational record, and scientists have a good understanding of how climate change interacts with them. Cyclones, hurricanes, and typhoons, on the other hand, are more complicated. They’re hard to simulate in models, don’t have a high-quality observational record, and scientists are less certain about how they interact with climate change: these storms are affected by multiple environmental factors, including water temperatures and in some cases Saharan dust.
But for other kinds of weather events, past research has given glimpses into how much climate change plays a role. In August, for instance, a study quantified how much climate change contributed to California’s historic drought, finding that human-caused warming was responsible for between 8 to 27 percent of the drought conditions between 2012 and 2014 and between 5 to 18 percent in 2014. The scientists were able to come to that conclusion with the help of high-quality data on soil moisture content in California over the last 100 years. Scientists have also linked flooding in Texas last spring to climate change.
It’s still impossible to say, however, that climate change “caused” a specific weather event, because natural variability “almost always plays a role,” according to the study. What scientists can examine is whether certain kinds of events are “becoming more or less likely because of climate change” and how much a weather event was “intensified or weakened, or its precipitation increased or decreased, because of climate change.”