During February we saw a number of extreme weather events globally, and Professor Stephen Belcher and Professor Jason Lowe OBE wrote a blog post about preparing the scientific response to increasing climate challenges.
So, it is as timely as ever that this month we will be taking a closer look at extreme events, in particular droughts, heat, wildfires and rainfall/flooding. Indeed, one of the five Reasons for Concern (RFCs) identified by the Intergovernmental Panel on Climate Change (IPCC) is the risk posed by extreme events. In this blog post Professor Peter Stott, Science Fellow in Climate Attribution at the Met Office Hadley Centre, will explore changes to extreme events we are already seeing around the world.
Climate change attribution
In order to determine whether a particular weather event has been made more severe or more likely by climate change, attribution studies use simulations of climate made by computer models. One of these set of simulations represents the current climate, including anthropogenic (human-induced) climate change, whilst the other set of simulations represents the natural climate where the influence of increasing greenhouse gas concentrations and other human factors has been removed. Comparing the outcomes from the two sets of simulations allows us to assess the level to which climate change has impacted the weather.
Rainfall and flooding
In the last week of February parts of the UK saw some significant flooding following a series of storms, a reminder of the impact the weather can have on lives and livelihoods. At the same time, communities in Australia have experienced devastating floods and a number of people have tragically lost their lives.
Analysis is needed to determine whether these specific events were made more likely due to anthropogenic climate change, but trends in climate data indicate that there have been increases in extreme rainfall globally since the beginning of the twentieth century – we explored this in a blog post last year. There is also a large body of evidence that has found links to climate change following a number of specific heavy rainfall events.
An attribution analysis of the wettest February on record for the UK (which occurred in 2020) showed that the extreme rainfall experienced was made about three times more likely due to climate change. Meanwhile an attribution study of the flooding in central Europe in July 2021 showed that climate change had increased the intensity of daily maximum rainfall by 3-19%.
The recent Working Group II report from the IPCC highlighted some of the impacts we are already seeing from extreme heat in terms of biodiversity and heat stress, for example in cities, in many regions around the world.
July 2019 saw record breaking temperatures across the UK and Western Europe. In Cambridge 38.7°C became the UK’s highest daily maximum temperature. An attribution study considered whether the intensity and likelihood of seeing such high temperatures in Europe has been influenced by climate change, concluding that the event was made 10 times more likely in the UK and temperatures were 1.5 to 3°C hotter due to human driven climate change.
In 2020 a rapid response review of 57 peer-reviewed papers concluded that wildfires are becoming more severe and widespread, highlighting the links between climate change and increased frequency or severity of fire weather. This conclusion was supported in the IPCC Working Group I report published in 2021 which stated that “fire weather conditions (compound hot, dry and windy events) have become more probable in some regions”.
In one high risk region, studies under the Climate Science for Services Partnership (CSSP) Brazil project (supported by the UK Government’s Newton Fund) have been looking at how wildfires in the Amazon rainforest may change in the future. Part of this work has led to the development of a fire probability forecast service to help support planning strategies to reduce the risk and impact of fires.
Currently the Iberian peninsula is experiencing a prolonged winter drought which began in November 2021. Identifying a direct link between climate change and drought is complicated, but there is increasing evidence that our changing climate is influencing rainfall patterns in many regions around the world. The IPCC Working Group I report highlighted the increased prevalence of observed droughts in recent years.
Specific research has drawn similar conclusions. Research within the CSSP China project indicated an increase in flash droughts. One attribution study focused on a severe drought event that occurred between May and June 2019, in southwestern China, severely damaging crops. At the peak of the event, average rainfall was the lowest on record since 1960 for the region and the lack of rainfall impacted the drinking water supply of over 824,000 people. Scientists from the project found that human driven climate change increased the likelihood of such an event by a factor of six.
An impetus for action
We can be more confident than we’ve ever been about linking extreme weather events to climate change, as seen in the evidence above. The increasing chances of these extreme events continue to rise as long as we continue to emit greenhouse gases. The science is clear that the faster we reduce our emissions of greenhouse gases, the more we can avoid the most severe impacts of climate change. In addition, we need to consider how we adapt to our changing climate to minimise the impacts we are already experiencing and can expect in the years ahead. Later this month we will take a look at what climate projections are telling us about extreme events in the future.
Learn more about why we need to adapt to our changing climate here and look out for more on reducing emissions – mitigation – next month.
 Davies et al 2021 https://rmets.onlinelibrary.wiley.com/doi/10.1002/wea.3955
 Kreienkamp et al 2021 https://biblio.ugent.be/publication/8732135/file/8732138
 IPCC, 2022: 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. In Press.
 IPCC, 2021: 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. In Press.