Climate change is making some forms of extreme weather events, such as heatwaves and heavy rainfall, more frequent and more intense.

Communities affected by those events inevitably suffer economic, social and societal impacts. The rising number of extreme weather events – and the losses and damages associated with them – poses a challenging question: who should pay?

This question is part of the so-called Loss and Damage agenda – which will be discussed at COP26 in Glasgow next month. Although the issue has been considered for some time there is currently no agreed method for calculating, apportioning liability or awarding such payments.

Fraser Lott is a Met Office scientist who has been developing scientific techniques to address this problem, in the hope of arriving at an objective solution.

Working with an international team of researchers, Fraser sought to show how the scientific capability of event attribution could be used to establish how individuals’ emissions affect extreme events through climate change. Fraser Lott said: “Event attribution is a climate science technique for calculating the likelihood that an extreme weather event was made more or less likely or severe because of climate change. By combining event attribution with population and emissions data, we realised that it was feasible to begin to calculate an individual’s contribution to a climate change event.”

It is believed to be the first time that anyone has attempted to express the impact of an individual’s emissions on an event based on event attribution: a scientific method of assessing to what extent an extreme event was influenced by individual human activity.

Aquaculture is an important economic sector in eastern China. Picture: Shutterstock

As a case study, this paper examined the impact of a 2018 heatwave in eastern China on the country’s aquaculture industry, which lost 6.87 billion yuan (around £790 million) as a result of the event. Using data on historical emissions since 1991 – the date when the first international consensus on carbon emissions was reached with the publication of the IPCC’s First Assessment Report – the team examined individuals from four representative nations (Sweden, China, Russia and the USA). The emissions of these countries were then divided equally among their population according to the number of years they had been over 18 (and therefore responsible adults) between 1991 and 2017, the year before the heatwave took place. Using this pioneering methodology, the potential cost to each individual could then be calculated, finding they were responsible for between 0.53 and 18.10 yuan of these aquaculture losses (around 6p to £2). This varied depending on the person’s age and their country’s emissions, showing how the scale of such responsibilities can be greatly affected by national development and demographics.

Fraser added: “As you’d expect with a newly-developed technique, our research doesn’t provide an answer to every situation and there are further issues and challenges which subsequent research will need to address. We believe it is especially important that a broader range of experts such as philosophers, ethicists, policy experts and economists assist with the continued development of this emerging research.”

The team noted that, if this technique were extended to cover multiple events, changes in the probabilities of events which did not occur because of climate change would also have to be factored into any cost calculation. Countries with weather which is difficult to simulate or with insufficient climate observations would also present challenges when assuring any payment system was fair: there are established techniques which can counter these issues.

The issue of Loss and Damage is very broad and this research does not take full account of important aspects contributing to the costs of extreme weather events including the exposure of people to the hazards of extreme weather events or their vulnerability. The team also acknowledge that there are many demographic factors other than nationality and age which could influence an individual’s contribution to extreme weather events.

Fraser added: “The preliminary approach in our paper has demonstrated that it’s possible to calculate an individual’s contribution by using the available climate and population data: how this develops will be a matter of discussion and debate by experts and the public.”

The paper – Quantifying the contribution of an individual to making extreme weather events more likely – is published today (12 October, 2021) in the journal Environmental Research Letters

The research also involved the following authors:

• Andrew D King of the School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Australia
• Simon F B Tett of the School of Geosciences, University of Edinburgh, Edinburgh, United Kingdom
• Dongqian Wang of the National Climate Center, China Meteorological Administration, Beijing, People’s Republic of China
• Andrew Ciavarella, John J Kennedy and Peter A Stott of the Met Office