Clear human impact on climate

By Richard Black
Environment Correspondent, BBC News website

A scientific report commissioned by the US government has concluded there is "clear evidence" of climate change caused by human activities.

The report, from the federal Climate Change Science Program, said trends seen over the last 50 years "cannot be explained by natural processes alone".

It found that temperatures have increased in the lower atmosphere as well as at the Earth's surface.

However, scientists involved in the report say better data is badly needed.

Observations down the years have suggested that the troposphere, the lower atmosphere, is not warming up, despite evidence that temperatures at the Earth's surface are rising.

This goes against generally accepted tenets of atmospheric physics, and has been used by "climate sceptics" as proof that there is no real warming.

The new report, Temperature Trends in the Lower Atmosphere, re-analyses the atmospheric data and concludes that tropospheric temperatures are rising.

This means, it says, that the impact of human activities upon the global climate are clear.

"The observed patterns of change over the past 50 years cannot be explained by natural processes alone, nor by the effect of short-lived atmospheric constituents (such as aerosols and tropospheric ozone) alone," it says.

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