The science of linking climate change to extreme weather events

“Would this heatwave or severe rainfall have happened without climate change?” That is the form of query that policymakers and businesses are asking scientists.

Climate attribution science can assist us understand the answers to questions like this, because the probability and intensity of maximum weather changes in a hotter world. This may help countries, communities and businesses turn into more resilient to a changing climate.

Earlier this month we checked out what is supposed by Loss and Damage.

A dwelling in Kerala lies almost submerged after heavy rainfall led to extensive flooding in 2018. Picture: Shutterstock

Climate attribution science plays an element within the evidence base needed on this complex area, and here the Met Office’s Dr Fraser Lott – a Climate Monitoring and Attribution Scientist – explains how attribution works and the challenges it presents.

What’s an extreme weather and climate event, and the way does it differ from a ‘normal’ event?

Extreme weather and climate events affect all features of society, and impacts can include large economic costs, displacement and lack of life. An extreme weather event – reminiscent of a heatwave or extreme rainfall – is defined as an event which ranks above a threshold, or is near the upper or lower ends of the historical range of values; making it significantly different from the standard weather pattern. For example, this might be temperatures above a certain threshold for a sustained period. Some extreme events would have happened inside natural variability, but their likelihood will change with climate change. Climate attribution science can assist us to discover this difference.

How does climate attribution help us to know whether extreme weather is attributable to climate change?

Climate-related attribution studies take a look at individual extreme weather events reminiscent of a heatwave and ask: “Would this have happened without climate change?” And if that’s the case: “How much hotter or longer is that this heatwave due to climate change?” And: “How way more likely are these heatwave conditions due to climate change?” There may be also climate trend attribution, which take a look at trends beyond individual extreme events.

Attribution science compares modelled worlds with and without the human influence on greenhouse gas emissions to know the impact of climate change on the intensity and frequency of specific weather events. It could possibly then say for example: “climate change has made this heatwave 30 times more likely”. This is known as an attribution statement.

How accurate is climate attribution?

Climate attribution studies depend on numerous information, which implies they’ve historically taken years to analyse whether a particular extreme event is linked to climate change. The last 20 years have seen huge developments in climate attribution; meaning that now scientists are capable of conduct rapid climate attribution in a number of days to weeks after an event. These are timescales relevant to the general public and disaster recovery programmes.

Because of the speed of research, the scientists behind these rapid attribution studies don’t all the time have time to conduct the additional simulations that may be a part of a longer-term study of the precise details of the event. This results in a trade-off between speed and level of confidence within the result, meaning we may have to make more general statements in a rapid study than we’d in a scientific paper.

Confidence within the attribution studies also depends upon the standard of observations going into the model, the power of the models to simulate a selected variety of extreme event, and the way well the physical processes causing this extreme event are understood (in addition to how they could change with climate change).

For example, current climate models are good at replicating conditions which result in extreme heat and cold, however it is harder to simulate conditions which result in severe convective storms and tropical cyclones. This implies confidence in attributing extreme events reminiscent of heatwaves to climate change is higher than attributing cyclonic activity to climate change.

Can climate attribution be applied to extreme weather across the globe?

The necessities for making a confident attribution statement mean that climate attribution will not be yet utilized in all situations. For example, regions that lack a reliable and sufficient set of historical observations (an issue encountered particularly in developing countries), will struggle to offer a dataset to base their model on. Not all climate models perform well over all regions of the globe. For instance, some climate models do higher in mid-latitudes in comparison with tropical ones, which is usually a barrier to doing attribution studies in regions where climate models struggle to simulate the relevant physical processes.

Developing countries – including those more vulnerable to extreme weather – may lack resources, tools and training to perform studies. This will create a bias with attribution studies focussing on more developed nations in the worldwide north, moderately than being truly representative of maximum events which have occurred globally. This also implies that scientists from the worldwide north often have to conduct attribution studies for a region wherein they usually are not experts.

The Met Office has been supporting the event of experience in other parts of the globe, in addition to helping improve observations, through work reminiscent of that delivered by the Weather and Climate Science for Services Partnership programme, supported by the UK Government’s Department for Science, Innovation and Technology.

Carbon Transient has an interactive map of up-to-date attribution studies, and UK-based attribution studies may be found on the Met Office website.

In the subsequent in our series of blog posts across the theme of Loss and Damage, we can be exploring how climate attribution science helps increase understanding and supply an evidence-base in relation to this complex topic. Follow this blog or #GetClimateReady on Twitter to maintain up thus far.