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Can we distinguish man-made from natural climate changes?

The overwhelming consensus among climate change scientists is that human activities, particularly those producing greenhouse gases, are responsible for much of the climate change we're seeing. The climate also changes naturally over time. This may account for some of the warming, but not all.

This consensus is apparent from work that climate researchers (including many NERC scientists) have submitted to the United Nations Intergovernmental Panel on Climate Change (IPCC). The IPCC is recognised worldwide as the definitive source of information on climate change. In 1995 the IPCC reported that the balance of evidence suggests that humans have a noticeable influence on global climate. In a further report in 2001, the IPCC concluded that most of the warming seen over the last 50 years can probably be attributed to human activities.

Computer-based climate models and actual observations from the last 140 years match most closely when the models include emissions from human activities.

The greenhouse effect

Some gases in our atmosphere, for example carbon dioxide, methane, nitrous oxide, and especially water vapour, trap heat emitted from the Earth's surface, keeping the planet about 30°C warmer than it would otherwise be - warm enough to support life. This is the 'natural greenhouse effect' and is scientifically well understood.

Human activities, especially burning fossil fuels like coal and oil, have increased the amount of these greenhouse gases in our atmosphere. This is throwing the climate system out of balance, causing global warming.

Carbon dioxide levels in the atmosphere have increased from about 280 ppm in the mid 18th century - the start of the industrial revolution - to around 379 ppm today. You would need to go back at least 420,000 years to find another time when carbon dioxide was at such high levels in the atmosphere.