Climate change - what does the science tell us?
The scientific evidence is clear
There is vast body of reputable scientific research which provides overwhelming evidence that climate change is happening and
is set to get worse over the 21st century with serious impacts for water resources,
food security, human health and biodiversity. See UN IPCC Climate Panel Reports>>
There is also growing evidence that humans are already altering the risks from some extreme events and that risks from heat waves and heavy rainfall are set to rise through the 21 st century.
Of course we can't assume that all changes in extreme events are due to greenhouse gases. Natural forces like the periodic El Nino/La Nina events in the tropical Pacific have profound effects on extreme events around the world. We have to take account of natural variations in climate AND the changes that people are causing.
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 was the warmest decade since records began in 1850. Read more>>
2010 was the second warmest year on record. 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.
See UN IPCC Working Group I 2007 report Chapter 8 on attributing climate change>>
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.
See UN IPCC Climate Panel Reports>> |
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