Climate change science

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Climate change - what does the science tell us?

The scientific evidence is clear

Climate change is happening and it is set to get worse over the 21st century with serious impacts for water resources, food security, human health and biodiversity.

There are uncertainties about the details of exactly how much climate will change and patterns of rainfall, for example, however the overall message is clear and accepted by the vast majority of climate scientists across the world.

Climate has always changed, so why should we be concerned about the 20th century warming?

Throughout the Earth's history there have been natural changes in climate caused by many factors, including variations in the Earth's orbit around the Sun, volcanic eruptions, and changes in greenhouse gas concentrations. The scientific evidence now shows that people are changing the global climate.

Over the 20th century as a whole there has been a warming trend of 0.7 degrees centigrade and the warming has accelerated since the mid-20th century.  The current warmth is unusual in the context of  the last 1000 years (at least) and is not just part of a natural cycle.  Past changes are also thought to have occurred much more slowly than the warming over the 20th century.

The period from 2000 to 2009 has just been announced as the warmest decade since records began in 1850. Read more>>

How do we know that people are to blame for the warming?

Climate scientists look at both natural factors that cause climate to change and they look at the effect that people are having on climate. There is no doubt that human activity, such as burning fossil fuels and agriculture, is increasing greenhouse gases in the atmosphere.

The majority of scientists agree that much of the warming since the mid-20th century is very likely due to increasing greenhouse gases being produced by human activity. Scientists have looked at different possible causes for the warming. Natural changes (like changes in the Sun's output) cannot explain 20th century warming. The only way to reproduce the warming over the 20th century is to include the effects that people are having on the climate.

There have been periods of cooling over the 20th century, doesn't that disprove "global warming"?

The warming during the 20th century has not been steady and there have been periods of cooling. This is exactly what climate scientists would expect. As well as increasing greenhouse gases, natural factors (such as volcanic eruptions and changes in sea surface temeprature in the Pacific called El Nino) are also affecting global temperature. So scientists would expect there to be short periods where there is less warming and even cooling, but overall the trend is towards higher global temperatures. If greenhouse gas emissions continue at or above current rates, climate change is set to get worse over the 21st century.