Shifts in the number, severity and location of extreme weather events are among the most important impacts of climate change.

Basic physics suggest that global warming should affect the occurrence of extreme weather. More energy is being added to the atmosphere, and as it warms, it can hold more water vapour. On this basis alone, cold weather events should decline, heatwaves should increase, and there should be changes in the intensity and frequency of the dry and wet periods that cause droughts and floods.

However, the Earth’s climate system is very complex and natural variability, including El Niño and La Niña events, as well as important local and regional variations, make it difficult to separate out human influence on extreme weather events from other factors. In addition, extreme weather is, by definition, relatively rare and it can take a long time to identify statistically significant trends from small datasets.

It is not possible to attribute individual weather events to climate change but a recent review by the Intergovernmental Panel on Climate Change (IPCC) of scientific research on extreme weather concluded that there is already strong evidence that the number of extreme cold days around the world is decreasing, while hot days are on the rise, and patterns of rainfall in many regions are being altered as well.

Global sea level is also rising by more than 3mm per year, which means surges that are generated by storms over large bodies of water are also becoming higher. Surges are created ahead of storms by the impact of winds on the surface of the water.

There is still uncertainty about the extent to which climate change may already be affecting some other types of extreme weather events, such as tropical cyclones and tornadoes.

How much human populations are affected by changes in extreme weather also depends on whether they are exposed, by living in high-risk areas such as low-lying coastal areas, and vulnerable, due to, for example, poor quality housing. Worldwide, the number of reported deaths from weather-related events has decreased over the past 100 years due to increased efforts to reduce vulnerability and exposure.

However, extreme weather can still kill large numbers of people, particularly in poor countries. There were up to 138,000 deaths when Cyclone Nargis hit Myanmar in 2008, for example. In total, more than 200 million people globally are killed or affected by weather-related events on average each year.

Damage and losses from weather-related events have increased markedly over the past 30 years, mostly due to an increase in the number and value of homes and businesses that are exposed to severe weather. This has meant a big increase in insurance claims in many countries. About $150bn in economic losses worldwide were caused by weather-related events in 2012, according to the company Munich Re.

In the UK, the main ways in which climate change may already be affecting extreme weather are through the occurrence of very wet periods, leading to river and flash floods, and sea level rise, increasing the risk of coastal flooding. Four of the five wettest years in the UK since records began in 1910 have occurred since 2000, and preliminary research by the Met Office indicates that the number of extremely wet days is increasing.

The government’s Climate Change Risk Assessment, published in 2012, identified a number of potentially serious impacts due to more extreme weather, particularly flooding. In 2012, the second wettest year on record in the UK, insurers paid out £1.19bn to households, businesses and motorists that were affected by storms and floods.

An increase in the number of homes and businesses that are at risk of flooding has created a crisis for the insurance industry, which is planning to launch a new scheme to offer cover to those most likely to be affected.

Most of the efforts in the UK and elsewhere to adapt to the impacts of climate change mean making society more resilient to current and future extreme weather. Poor people in developing countries remain particularly vulnerable but even rich countries have trouble protecting themselves against extreme weather, as Hurricane Katrina demonstrated when it flooded New Orleans in 2005.

If global warming of more than 2°C is not avoided through reductions in greenhouse gas emissions, impacts from extreme weather could overwhelm the capacity of some countries to cope, leading to wider impacts, from large-scale migration of populations to an increased risk of conflict.

This article was written by Bob Ward and is a reproduction of the following article “extreme weather and climate change: is there a link?” ©, 2013, The Guardian, used under a Creative Commons No Derivative Works licence.

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