Storms are one of the most powerful manifestations of extreme weather, with associated high winds and heavy rain causing loss of life, disruption and damage to property and infrastructure.
In February 2022, high winds associated with storms Dudley, Eunice and Franklin caused more than three billion euros (£2.6 billion) damage across Europe, tearing the roof off the O2 at London. In November 2021 Arwen left 200,000 UK homes without power and fell eight million trees in Scotland.
A very different type of storm, a slow-moving one known as a “cut-off low”, caused extreme rainfall and extensive flooding in Germany and Belgium in July 2021, which claimed 243 lives and more than 10 billion. euros of damage. . Understanding how these different types of extreme weather might change as the climate warms is key to understanding how risks might change in the future.
Those affecting the UK and Scotland tend to form over the North Atlantic Ocean, in the large temperature difference across the Gulf Stream between the warm subtropics and the cold Arctic. As the storms cross the North Atlantic, they accumulate moisture and the subsequent precipitation warms and intensifies the storm.
As the climate warms, storms will be able to carry much more moisture and thus produce more precipitation. This will lead to a much higher risk of flooding and potentially more intense storms. Acting in the opposite direction, the Arctic is expected to warm much faster than the rest of the Earth, which means that the temperature difference between the warm subtropics and the Arctic will be reduced. This will potentially lead to weaker and fewer storms.
Having two processes pushing in different directions means we have to use complex climate model projections to understand how the weather might change in the future. The latest climate projections from last year’s Intergovernmental Panel on Climate Change report suggest there could be 5-20% more winter storms in the UK and North West Europe by the end of the 21st century under the strongest global warming scenarios. These winter storms will also produce significantly more precipitation, leading to an increased risk of flooding.
It should be noted, however, that we still have a lot to understand about the response of storms to climate change. For example, some of the strongest winds generated are thought to be caused by processes such as ‘prickly jets’, as seen during Storm Eunice in February this year. Prickly jets are very intense winds that are produced in the cold air that coils behind a storm, descending in a narrow band from the middle troposphere to the surface.
Typical models used to make climate projections usually have too low resolutions to properly represent narrow features such as stinging jets. However, new research with much higher resolution climate models suggests that this phenomenon may become more common in a warmer climate, and that we need to take these processes into account if we are to have a more complete picture of how the climate change will affect extreme storms. over the UK and Europe.
Another major area of concern is how the intensity and number of tropical cyclones – such as hurricanes in the Atlantic and typhoons in the Pacific – will change in a warmer climate. Tropical cyclones can have huge impacts when they make landfall. For example, when Hurricane Ian hit Florida and the US this year, it caused damage estimated at $67billion (£60billion). In December 2021, Typhoon Rai hit the Philippines, killing 410 people.
Humidity and precipitation are important drivers of tropical cyclones. As the climate warms, we expect them to become more intense due to increased evaporation from warmer oceans. However, climate model projections also suggest that changes in atmospheric circulation over the tropics, and particularly over the Atlantic, could reduce the overall number of tropical cyclones. One would therefore expect fewer such storms, but that they will be more intense in response to climate change.
Another area of active research is trying to understand whether climate change will impact the number of post-tropical storms, which can sometimes affect the UK and Europe. Examples include Storm Ophelia in October 2017, which was caused by a severe hurricane in the Eastern Tropical Atlantic moving north over Ireland, resulting in significant property damage and three fatalities.
Storm Katia in September 2011 was another post-tropical storm that caused £100 million in damage in Scotland. Katia began life as a hurricane in the Atlantic, which moved along the eastern seaboard of North America, then eastward over the North Atlantic Ocean. New research suggests that the number of post-tropical storms could increase in a warmer climate, mainly because the tropical cyclone portion of these storms will be able to move further north over warmer oceans.
Climate change will have substantial impacts on extreme weather, both for tropical cyclones and for the North Atlantic storms that affect us in the UK. The warmer the world gets, the greater these impacts will become, potentially leading to more damage and more costly measures to adapt to changing storm risk. It is therefore imperative to aim for net greenhouse gas emissions and to limit the rise in global temperature to 1.5°C if we are to avoid the worst impacts of climate change.
Len Shaffrey is Professor of Climate Science at the University of Reading