Attributing extreme weather to climate change

Extreme weather events, such as heatwaves and floods, impact all levels of society. These events can lead to large economic costs, population displacement, and loss of life.

Many factors can contribute to extreme weather events. Some of these are natural, but we can link others to climate change, driven by human activity.

How do we link extreme weather to climate change?

An attribution study aims to answer the question, “Did climate change cause this?”

Scientists can look at specific weather events and see if climate change was a factor.

To do this, they start with a clear, scientific question in mind. For example, the question might relate to the severity or frequency of a weather event:

  • How much more intense is the extreme weather event because of climate change?
  • How much more common is the extreme weather event because of climate change?

How long does a climate change attribution study take?

Attribution studies can be lengthy because they rely on so much information. It takes time to:

  • collect observations
  • run computer models to simulate the Earth’s climate
  • analyse the results.

Thanks to new scientific advances, though, they are a lot faster. Today, we can sometimes complete attribution studies in the weeks after an event, rather than years.

What information do we use in a climate change attribution study?

Lots of information goes into the simulation behind attribution studies. This includes:

  • Natural climate variability
  • Weather patterns
  • Concentration of aerosols
  • Greenhouse gas emissions
  • Sea surface temperature
  • Topography
  • Observations

It’s important to understand these factors and how they influence a weather event. For example, natural climate variability and weather patterns are natural influences. Aerosols and greenhouse gases, though, are more affected by human action. The sea surface temperature can play a role, as can the local topography where the event took place.

Climate change attribution studies and model simulations

When we have all the data and observations, we feed them into a computer model. This model runs two different simulations.

The first model simulates the climate as it is today, including climate change driven by humans.

The second simulation removes the human influence on things like greenhouse gases. This model simulates a climate closer to what existed before the Industrial Revolution.

Comparing these simulations lets us see what effect climate change had on an event. This might include many variables, like temperature and rainfall.

An attribution case study: The European heatwave in 2019

In July 2019, we saw record breaking temperatures across the UK and Western Europe. In Cambridge, we saw a temperature of 38.7°C — the UK’s highest daily maximum temperature ever on record.

Vautard et al. (2019) did an attribution study on the 2019 European heatwave. They asked if climate change influenced the intensity and likelihood of the high temperatures we saw.

This is the full question they studied:

“...whether and how the probability of 3-day average temperature as high or higher than the observed temperature in different places in Western Europe has changed as a result of human-induced climate change.”

They collected observations from stations throughout Europe. Some locations held records going back as far as the 1800s.

Two different climate models generated the data. One simulated today’s climate, with human-driven climate change. Another model simulated the climate before the Industrial Revolution, without human-driven climate change.

Results from the study show that July 2019 heatwave was abouttentimes more likely because of climate change. The temperatures we saw were 1.5–3°C hotter than they would have been without human influence.

More information about extreme weather events and attribution studies

Extreme weather events in the UK

Extreme weather events around the world

Attribution studies into specific extreme weather events