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The influence of climate change on severe weather

As shared in our recent blog post on understanding weather and climate extremes, we are seeing an increase of extreme weather around the world including in the UK. Since the industrial revolution, the average temperature of the planet has risen by around 1.26 °C (based on the suggested approach of Met Office researchers). This is a rapid change in terms of our global climate system and has already led to the changes in the extreme weather we are experiencing.

The Met Office’s dedicated team looking at weather and climate extremes has collated the latest published academic literature on severe weather in the UK in the context of our changing climate. In this blog post, Climate Extremes Principal Fellow and Chief Meteorologist Paul Davies shares some of the findings from that work.

Flood water with trees

Extreme heat

The frequency and intensity of heatwaves have increased worldwide. A number of major heatwaves in the UK have occurred in the past 5 years (2018, 2019, 2021 and 2022), each seeing new temperature records set. Notably the England record has been set three times over. Numerous climate attribution studies have shown that human influences have increased the chances of occurrence of specific extreme heat events such as the summer of 2018 and July 2022. Almost all studies on extreme heat events indicate human influence.

Looking ahead, the headline findings from UK Climate Projections (UKCP) indicate that on average, summers will become hotter. Met Office UKCP Local projections indicate that hot spells will become more frequent in our future climate, particularly over the south-east of the UK, with temperatures projected to rise in all seasons.

Heavy rainfall

In the recent climate, it has generally become wetter, particularly during winter. The winters of 2014, 2016 and 2020 are all in the top five wettest (the other winters being 1995 and 1990). One reason for this is the large annual, seasonal and decadal variability in rainfall, but in winter the emerging climate change signal resulting from increased atmospheric moisture is an important secondary factor. Rainfall totals on the wettest days have increased, this is more strongly linked to climate change.

In the future, climate projections for the UK indicate there being a greater risk of heavy precipitation and prolonged events in the future, particularly during winter.

As the atmosphere warms due to human induced climate change it can hold more moisture, at a rate of around 7% more moisture for every degree of warming. This means that when it does rain it can be more intense. On a simple level, this explains why in many regions of the world projections show an increase in precipitation as a consequence of human induced climate change.

Intense rainfall from thunderstorms

In the recent climate, trends in short rainfall events lasting less that one day are difficult to detect, due to historically sparse sub-daily observations and natural year-to-year and decade-to-decade variability. Extreme precipitation associated with thunderstorms, is, however, projected to intensify with climate change.

In the future, rainfall events exceeding 20mm per hour, which can cause flash flooding, are expected to be four times as frequent by the 2070s compared to the 1980s, under a high emissions scenario i.e., if greenhouse gas emissions continue unabated at a high level. Changes are not projected to happen gradually, but instead extreme years with lots of events could tend to cluster. When and by how much these changes are projected to occur varies in different regions of the UK.

Windstorms

In the recent climate, there is no evidence of positive or negative trends in windstorm number or intensity over the UK. Trends in windstorm numbers are difficult to detect, due to how these naturally vary year-to-year and decade-to-decade. As well as wind damage, windstorms can cause impacts from storm surges and high waves in coastal areas. These are expected to worsen as sea level rises.

Most climate projections indicate that winter windstorms will increase slightly in number and intensity over the UK i.e., more winter storms, including disproportionately more severe storms. However, there is medium rather than high confidence in this projection because some climate models indicate differently.

Drought

Whilst there have been observed changes in the drivers of drought in the UK, there is much less evidence of trends in many drought metrics at present. However, the impact of extreme hot periods in summer has been noticeable in recent years (2018 and 2022) and shows the impact rising temperatures can have on water supply and demand.

Currently, there are no UK climate attribution studies available that clearly link human induced climate change with an altered risk of drought events. However, attribution studies have been carried out for extreme temperature events, which can lead to increases in evaporation, drier soil and considerable impacts on water supplies.

Most studies into our future climate point towards general increases in frequency and length of meteorological drought for the UK. This general rainfall deficit can exacerbate other forms of drought such as hydrological drought or agricultural drought, but these other forms of drought can have other drivers such as groundwater storage, drier soil and low river flows.

Extreme cold and snow

Despite the warming climate, extreme cold events still occur in the UK due to natural variability. The decrease in the frequency, duration, and intensity of these events over recent decades is clearly linked to the observed warming of the planet and can be attributed to human activity. For example, attribution studies have found that the unusually cold European winter of 2009/2010, UK cold snap in March 2018 (which included the event widely known as the Beast from the East) and the cold UK spring of 2013 would be much more likely without human influence on the climate.

The number of air and ground frost days in recent years has also decreased, with 4% fewer days of air frost in the most recent decade (2013-2022) than the 1991–2020 average, and 15% fewer than the 1961–1990 average. 2013-2022 also had 7% fewer days of ground frost than the 1991-2020 average and 24% fewer than the 1961-1990 average.

Future UK winter climate will still be variable year to year, so severely cold winters are still likely to occur – just less often – so it is important to remain resilient to severe winters when they do occur. Snow in the UK is very conditional on the setup of the weather; it is not just low temperatures that lead to snow. Overall, projections show that the frequency of snow events will decrease in the UK in future. There is less certainty about the intensity of future snow events due to more complex atmospheric interactions.

Tackling climate change

Mitigating against a changing climate by reducing greenhouse gas emissions is critical to limiting warming which would help us avoid the worst impacts of climate change. We also need to adapt to the climate changes we are already seeing and the changes that are expected in the coming decades to make sure we avoid the most significant impacts.

Action is required across all levels of society – to find out more about how you can make a difference, take a look at our Get Climate Ready webpages.

Follow the #GetClimateReady hashtag on X (formerly Twitter) to learn more about weather and climate extremes this month.

 

Channel website: http://www.metoffice.gov.uk

Original article link: https://blog.metoffice.gov.uk/2024/01/18/the-influence-of-climate-change-on-severe-weather/

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