Human activity appears to be supercharging extreme weather events, such as floods, storms, droughts and heat waves. As storms get stronger, society tends to wonder what role climate change plays.
A recent report from the National Academies of Sciences, Engineering and Medicine addresses this question, suggesting that scientists can now determine, with some confidence, the degree to which man-made climate change has influenced some, but not all, extreme weather events.
"In the past, many scientists have been cautious of attributing specific extreme weather events to climate change. People frequently ask questions such as, 'Did climate change cause Hurricane Sandy?' Science can't answer that because there are so many relevant factors for hurricanes," explained David Titley, a professor from Penn State's Department of Meteorology and founding director of Penn State's Center for Solutions to Weather and Climate Risk. "What this report is saying is that we can attribute an increased magnitude or frequency of some extreme weather events to climate change."
The report follows a decade of research conducted by a variety of scientists dedicated to the new field of study known as "extreme event attribution." In some cases, researchers are now able to identify the influence humans have had on climate in relation to individual weather events.
For example, researchers are generally able to link extreme weather events to climate change when the effects are closely related to temperature. Extreme heat and extreme cold are the easiest to attribute to climate change, followed by drought and extreme rainfall. However, the effect of climate change on tornadoes and wildfires is more difficult to assess because there are many variables that come into play.
"If we can actually understand how and why frequencies or magnitudes change of extreme events are changing, those are two components of risk. Understanding that risk is crucial for governments and businesses. For example, if you're managing a business, you may need to know whether there may be more droughts in the future because that may impact supply chain logistics and, ultimately, your bottom dollar," added Titley, who chaired the committee that wrote the report.
Man-made climate change is largely caused by the burning of fossil fuels such as gas, coal and oil, which releases greenhouse gases like carbon dioxide into the atmosphere. As a result, temperatures of the atmosphere and oceans rise. Under these conditions the atmosphere can hold more water vapor, which ultimately fuels extreme storms and causes global sea levels to rise.
In order to link a specific weather even to climate change, researchers need to understand any underlying physical causes of weather events; have enough observational data to place a specific event within a historical context; and they must be able to replicate the event using computer models.
Attributing the cause of extreme weather to climate change or other factors can "enhance scientists' ability to accurately predict and project future weather and climatic states," Titley concluded.
