by Julia Gaus
New Year’s Day 2023 saw record high temperatures across Europe, setting the scene for yet another year of weather extremes . It follows a year of exceptional weather events, such as the record-breaking rains that led to a massive flooding in Pakistan, the longest and most extensive heatwave ever recorded in China and the fourth consecutive below-average rainy season in East Africa, to name a few . Although weather extremes are increasing in frequency and intensity due to the climate crisis, risks vary also according to the exposure and vulnerability of a population. And it is the ensuing disasters, creating human and economic costs, which mandate action (on all fronts: mitigation, adaptation and loss & damage).
Differentiating extreme weather and disaster (risk)
While “natural disaster” is used colloquially to describe the outcome of a flood, for example, there are non-natural factors that affect the scope of the disaster . Instead of attributing disasters solely to nature, the Intergovernmental Panel on Climate Change (IPCC) defines disasters as resulting from the interplay of a natural hazard (i.e. an extreme weather event), the exposure of the affected population or assets and their vulnerability .
In short, the disaster equation is: disaster risk or disaster impact = hazard x exposure x vulnerability
This definition highlights the socio-economic factors determining the actual impact of a certain natural hazard on a given population. For example, let’s imagine three villages:
Village A: located at a river delta in the Netherlands, houses are made of stone and are built according to a tested building code
Village B: located on a hill in the Netherlands, houses are made of stone and are built according to a tested building code
Village C: located at a river delta in Bangladesh, houses are makeshift made from cheaply available materials
In this scenario, all three villages receive the same natural hazard: torrential rains. The impact of this hazard varies based on exposure and vulnerability. . Village B, sitting on a hill, will have a lower exposure than the other two villages. Village A and C might have a similar exposure but village C’s vulnerability is higher, thus, all other things being equal, village C is at the highest risk from the disaster.
The disaster equation includes important socio-economic factors, which play a role in extreme weather impacts, as in the simplified example above.
Focus on the hazard factor – Extreme Weather Events
The climate crisis directly affects the hazard factor of the disaster equation by altering the frequency and intensity of a given extreme weather event at a certain location. The IPCC defines “an extreme weather event as ‘an event that is rare at a particular place and time of the year’, and an extreme climate event as ‘a pattern of extreme weather that persists for some time such as a season’” . These events are often grouped into temperature extremes, heavy precipitation, floods, droughts and extreme storms.
Over the last twenty years, there has been mounting evidence of human impacts on extreme weather events . This relatively young field of extreme event attribution science aims to establish the link between human activities, notably the emission of greenhouse gasses, global warming and the intensity and/or frequency of a particular event .
Attribution studies use observational data to conduct a trend analysis looking at how rare a given event was and how this has changed over time. This is then compared to the model of an alternative world in which the climate is not changing . The result is an overarching statement of how the hazard has changed.
When an extreme weather event occurs today people are routinely asking whether the event was caused by the climate crisis. While attribution science cannot determine whether climate change caused an event, it provides a statement about whether the climate crisis made it more likely for the event to occur or made it more severe . Such statements are increasingly relevant in legal debates, insurance policies and the discussion around loss and damage .
As a result of this growing demand, scientists founded the World Weather Attribution platform, conducting “real-time attribution analysis of extreme weather events as they happen around the world. This provides the public, scientists and decision-makers with the means to make clear connections between greenhouse gas emissions and impactful extreme weather events“ .
However, any attribution study is only as good as the data and models available with lower resolution models available for precipitation events. Thus, current models are less reliable for extreme precipitation events than for temperature events . Another problem is the availability of long-term data, which is scarce in many regions of the Global South. Still, attribution science is growing and with increasingly more data and better models, confidence in attribution statements is growing .
This is the first article of a series discussing the current evidence of the human impact on different extreme weather events. Check back for more on floods, droughts, heatwaves, and extreme storms.
References: Livingston, I. (02.01.2023), Thousands of records shattered in historic winter warm spell in Europe, The Washington Post, https://www.washingtonpost.com/weather/2023/01/02/record-warm-new-year-europe/ [Accessed: 31.01.2021]
 UN News (23.12.2022), WMO releases ‘tell-tale signs’ of extreme weather conditions around the world, UN, https://news.un.org/en/story/2022/12/1131992 [Accessed: 31.01.2023]
 PreventionWeb (n.d.), Understanding Disaster Risk, UNDRR, https://www.preventionweb.net/understanding-disaster-risk/component-risk/disaster-risk [Accessed: 01.02.2023]
 Ara Begum, R., R. Lempert, E. Ali, T.A. Benjaminsen, T. Bernauer, W. Cramer, X. Cui, K. Mach, G. Nagy, N.C. Stenseth, R. Sukumar, and P.Wester (2022), Point of Departure and Key Concepts. In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 121–196, doi:10.1017/9781009325844.003.
 Seneviratne, S.I., X. Zhang, M. Adnan, W. Badi, C. Dereczynski, A. Di Luca, S. Ghosh, I. Iskandar, J. Kossin, S. Lewis, F. Otto, I. Pinto, M. Satoh, S.M. Vicente-Serrano, M. Wehner, and B. Zhou (2021) Weather and Climate Extreme Events in a Changing Climate. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1513–1766, doi:10.1017/9781009157896.013. [p.1522]
 CarbonBrief (2022), Mapped: How climate change affects extreme weather around the world, CarbonBrief, https://www.carbonbrief.org/mapped-how-climate-change-affects-extreme-weather-around-the-world/ [Accessed: 01.02.2023]
 Climate Attribution (n.d.), Climate Attribution Database, Sabin Center for Climate Change Law, https://climateattribution.org/ [Accessed: 01.02.2023]
 van Oldenborgh, G. J., van der Wiel, K., Kew, S., Philip. S., Otto, F., van Aalst, M. (2021), Guest post: Lessons learned from five years of extreme weather ‘rapid attribution’, CarbonBrief, https://www.carbonbrief.org/guest-post-lessons-learned-from-five-years-of-extreme-weather-rapid-attribution/ [Accessed: 31.01.2023]
 Cho, R. (04.10.2021), Attribution Science: Linking Climate Change to Extreme Weather, Columbia Climate School, https://news.climate.columbia.edu/2021/10/04/attribution-science-linking-climate-change-to-extreme-weather/ [Accessed: 01.02.2023]  world weather attribution (n.d.), Home, World Weather Attribution, https://www.worldweatherattribution.org/ [Accessed: 01.02.2023]