Longer fire seasons. Stronger hurricanes. More intense heatwaves and floods. Across the world, climate events are getting more extreme. And while there’s little doubt that global warming is to blame, proving that fault for specific weather events hasn’t really been possible… until now.
An emerging field called extreme-event attribution is helping us measure and verify the relationship between the climate crisis and extreme weather. Not only does this have huge implications for predicting and modeling our planet’s future, but it could also help us better prepare for living in an increasingly extreme world.
For a long time, there was a distinction between climate and weather. And the reality is, extreme events are where we most acutely feel the climate system. It's critical that we understand how global warming is impacting the extremes. Because that's where the impacts from climate change are being played out.
When we talk about the impacts of the climate crisis, we’re really talking about distinguishing the influence of natural factors from anthropogenic factors on Earth’s climate cycle. Basically, this means teasing apart Earth’s natural climate cycles from human-caused climate change. A way to begin doing this is to examine the “fingerprints” we humans have left behind on Earth’s climate.
For example, our ice core records tell us that CO2 levels have risen by almost 50% in the last 150 years, and records show that since the industrial age began over a century ago, many regions of the world have warmed by more than 1.5 degrees Celsius.
By matching both the observed and modeled patterns of Earth’s climate, scientists can positively identify the “fingerprints'' associated with these changes. Following the tracks of these fingerprints has helped scientists link climate change with more general trends, like rising sea levels and global temperatures. But verifying the role of human influence on specific climate events, like Hurricane Harvey or the California drought? That’s not as easy.
It’s precisely this problem of attributing specific extreme weather events to climate change that researchers like Dr. Diffenbaugh are working on. While we can’t yet say for sure that these events wouldn’t have happened without climate change, we can talk about the probability of them happening… and how those odds are changing.
By comparing our climate predictions with how things actually play out, researchers can start to develop a real-world framework for posing and testing hypotheses. But the work doesn’t stop there. Observational data can only tell us if there's a change in the intensity or frequency of an event; it still can't tell us what caused those changes. This is where computer modeling comes in.
We can't run experiments on the global climate system. We can't stick the climate system in a lab. But we can say, our extreme event attribution framework predicts a probability of record-setting heat over a region of Europe to be X percent, and then we can wait and watch and see how often record-setting temperatures occur.
These computer models can use real-world climate influences, like how much CO2 is present in the atmosphere, to create a more complete timeline of extreme events. Or, they can create hundreds of hypothetical histories that span thousands of years to test our world against. This allows researchers to look at the world without human-caused climate change, and assess the probability of events happening. By comparing the probability between Earths with and without climate change, researchers can begin to quantify the changes in risk... and test how much the frequency and magnitude of extreme events have changed over time.
Over the past decade, the emerging field of extreme event attribution has used these tools to help researchers find strong evidence of climate change’s relationship to changing events like heat, as well as tropical cyclones, wildfires, sea ice coverage, and flooding.
By combining observational records with climate models and our growing knowledge of how global warming affects Earth’s natural processes, we’re also getting better at distinguishing between the roles that human influence on the climate system and climate variability play in specific climate events.
Being able to attribute specific climate events to climate change is extremely useful on many fronts. For one, it can help researchers develop better climate models that can then be used by governments to inform climate action plans. It can also help us better understand the impact we’re having on the climate and be better equipped to brace for these impacts.
A lot of our infrastructure, a lot of our planning is, is designed around, statistical analyses that assume stationarity in the climate system. If the global warming that's already happened has already changed the odds of those extremes, then everything that we've designed and built based on that, there's risk of those thresholds being exceeded.
The infrastructure in many communities, from sidewalks to levees to storm surge barriers, is built and managed based on the probability of the recurrence of climatic extremes. For cities sitting on a floodplain, the likelihood of a major flood happening in a given year will often determine how resilient their levees and dams must be. If a city uses the 100-year floodplain as its threshold, that means that its levees and dams are built to anticipate the 1% chance that a major flood could happen in any given year.
But the probability of these thresholds being exceeded is changing, and the fact is that too many communities just aren’t adequately prepared. Extreme events don’t just affect and disrupt essential infrastructure. They can have an outsized effect on public health, our food supply, and our global economy. The idea is that by being better able to know what to expect from the climate crisis, the world can brace for the worst while making informed decisions to stop the worst from happening.
We see it year after year in the US and around the world. We're living with a world where unprecedented, extreme events are more likely. They're happening more often. We're living with that now. And the impacts of those extremes are growing the cost that we're bearing.
While extreme event attribution is helping us more confidently connect the dots between climate change and individual weather events, it’s still a very new field and there’s a lot to learn.