Date published: 2006/05/03
The BBC says:
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.
But there are some big uncertainties which still need resolving.
Globally, the report concludes, tropospheric temperatures have risen by 0.10 and 0.20C per decade since 1979, when satellite data became generally available.
The wide gap between the two figures means, says the report, that "...it is not clear whether the troposphere has warmed more or less than the surface".
Peter Thorne, of the UK Meteorological Office, who contributed to the report, ascribes this uncertainty to poor data.
"Basically, we've not been observing the atmosphere with climate in mind," he told the BBC News website.
"We're looking for very small signals in data that are very noisy. From one day to the next, the temperature can change by 10C, but we're looking for a signal in the order of 0.1C per decade."
The report shows up a particular discrepancy concerning the tropics, where it concludes that temperatures are rising by between 0.02 and 0.19C per decade, a big margin of error.
Additionally, the majority of the available datasets show more warming at the surface than in the troposphere, whereas most models predict the opposite.
Well more data, and even this re-analysis of existing data, is always welcome. But it's ridiculous that people are still even discussing this question. With 6 or 7 billion people on the planet, it's obvious that humans are impacting the climate. But that is not (yet) illegal, and, after all, humans are part of the ecosystem just like every other species. Trees also are impacting the climate (just cut them all down and see what happens). Do we need perpetual reports about that? The real question is what, if anything, needs to be done about climate change, in particular, whether any of the proposed "solutions" are going to make the planet worse or better (by whatever measure you care to specify).
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