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Human impacts - climate change
Introduction The observed changes in global climate are likely to be due to a combination of both natural and human causes. The main human influence on global climate is likely to be through increasing emissions of greenhouse gases such as carbon dioxide and methane. At present about 6.5 billion tonnes of carbon is emitted globally into the atmosphere each year, mostly through the combustion of coal, oil and gas. Changes in land use result in a further net annual emission of between 1 and 2 billion tonnes of carbon. Increasing concentrations of so-called greenhouse gases in the atmosphere over the last 200 years have trapped more energy in the lower atmosphere, thereby altering global climate. The picture is complicated by other pollutants from human activities, for example sulphur dioxide which transforms into small particles (aerosols) which act to cool climate. The Intergovernmental Panel on Climate Change (IPCC) concluded in their Third Assessment Report that, ".. most of the warming observed over the last 50 years is likely to have been due to increasing concentrations of greenhouse gases." The most useful index describing the state of global climate is the average surface air temperature of the planet. The records show that global temperature has risen by about 0.6°C since the beginning of the 20th century, with about 0.4°C of this warming occurring since the 1970s. 1998 was the warmest on record, and 2001 was the third warmest. The 1990s were the warmest decade in the last 100 years.
Observed change in the UK climate Analysis of the climate data has revealed the following changes in UK climate:
After adjusting for natural land movements, average sea level around the UK is now about 10cm higher than it was in 1900.
The Future UK Climate The UKCIP02 scenarios present four different descriptions of how the world may develop in the decades to come, being based on four different emission scenarios from the Intergovernmental Panel on Climate Change, IPCC. It is not possible to say which scenario is more likely, as this is dependent upon the future choices made by society. Rather, the scenarios provide alternative views of the future, and together show a broad range of changes that we may face. The resulting four scenarios are described by the emission scenarios on which they are based: Low Emissions, Medium-Low Emissions, Medium-High Emissions and High Emissions.
A summary of the key findings of the scenarios are outlined below.
Temperature There will be greater warming in the south and east rather than in the north and west, and there may be greater warming in summer and autumn than in winter and spring. By the 2080s for the High Emissions scenario, parts of the southeast may be up to 0.5°C warmer than the north west in summer. The temperature of UK coastal waters will also increase, although not as rapidly as over land. High summer temperatures will become more frequent, whilst very cold winters will become increasingly rare.
A very hot August, such as experienced in 1995 when temperatures over England and Wales averaged 3.4°C above normal, may occur one year in five by the 2050s for the Medium-High Emissions scenario, and as often as three years in five by the 2080s. Even for the Low Emissions scenario, by the 2080s about two summers in three may be as hot as, or hotter than, the exceptionally warm summer of 1995.
Precipitation (rain and snow) Snowfall amounts will decrease throughout the UK. The reductions in average snowfall over Scotland might be between 60% and 90% (depending on the region) by the 2080s for the High Emissions scenario.
Heavy winter precipitation will become more frequent.
By the 2080s, heavy winter precipitation intensities that are currently experienced around once every two years, may become between 5% (Low Emissions) and 20% (High Emissions) heavier.
Sea Level Changes
Extreme sea levels will be experienced more frequently.
For some east coast locations, extreme sea levels could occur between 10 and 20 times more frequently by the 2080s than they do now, under the Medium-High Emissions scenario.
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