permaculture

["Lawrence F. London, Jr." <lfl@intrex.net>]

<http://news.bbc.co.uk/2/hi/science/nature/6321351.stm>
        
Last Updated: Thursday, 1 February 2007, 20:10 GMT
Warming 'very likely' human-made
By Richard Black
Environment correspondent, BBC News website, Paris

Residents in New Orleans' 9th Ward in September 2005
The IPCC is likely to back a link from warming to stronger storms
Climatic changes seen around the world are "very likely" to have a human cause, the Intergovernmental Panel on Climate 
Change (IPCC) will conclude.

By "very likely", the IPCC means greater than 90% probability.

The scientific body is finalising its positions on some key issues, notably forecasts of sea level rise, as it prepares 
to publish a major report.

But a new study released on the eve of publication suggests its previous 
reports may have been too conservative.

        
There is no doubt that for this period, the climate has been changing faster 
than the IPCC predicted
Stefan Rahmstorf

Research by an international group of scientists concludes that temperatures and sea levels have been rising at or above 
the maximum rates proposed during the last IPCC report in 2001.

The first part of its 2007 report will be formally released on Friday morning 
in Paris.

Strong language

Some of the language which the agency has agreed it will use to assess humanity's influence on climatic change this time 
is stronger than it has used previously.

In 2001, it was "likely" that human activities lay behind the trends observed at various parts of the planet; "likely" 
in IPCC terminology means "between 66% and 90%".

Now, the agency concludes, it is at least 90% certain that human emissions of greenhouse gases rather than natural 
variations are warming the planet's surface.

Patagonia glacier 30 years ago and today. (From An Inconvenient Truth)
Scientists are unsure how much weight to give melting glaciers
"This report closes the doors to those who were able to detract from the issue, and puts an end to the notion of 
uncertainty and doubt about man's role in climate change," commented United Nations Environment Programme executive 
director Achim Steiner.

On key scientific questions - how much the Earth's surface will warm by, and how high sea levels will rise - the experts 
are still locked in discussion.

It is widely believed they will predict an average global temperature rise by the end of the century of between about 2C 
and 4.5C, without ruling out higher numbers completely.

On sea level, there is a more fundamental debate. Computer models of climate do not generally include water coming into 
the oceans as icecaps melt; so should the IPCC exclude this from its calculations, or estimate the effect of a process 
which scientists do not understand well, but which could have a big impact?

There is likely to be some backing to a theory which has proved highly controversial in recent years, with the IPCC set 
to conclude that it is likely - meaning a greater probability than 66% - that rising temperatures have contributed to 
more powerful tropical storms in some areas of the world.

At variance

As discussions entered their final phase, the journal Science published a study comparing the IPCC's 2001 projections on 
temperature and sea level change with what has actually happened.

IPCC models start from the year 1990, so that gives 16 years of data to 
compare.

The models had forecast a temperature rise between about 0.15C and 0.35C over this period. The actual rise of 0.33C is 
very close to the top of the IPCC's range.

Graphs
A new study suggest warming is outpacing earlier forecasts
A more dramatic picture emerges from the sea level comparison.

The actual average level, measured by tide gauges and satellites, has risen faster than the IPCC predicted it would due 
to simple thermal expansion of seawater, and at the maximum which the scientific body considered possible if its 
estimates for the melting of land-based glaciers and ice sheets was included.

"Our intention with this study was to demonstrate how temperatures and sea levels have actually gone up," said study 
leader Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research in Germany, "because 'climate sceptics' 
have cast doubt on IPCC projections and whether they are exaggerated."

The group suggests that if anything, the IPCC has been conservative.

The most obvious cause of the discrepancy - a faster-than expected rise in carbon dioxide concentrations - is ruled out, 
as the observed CO2 rise has mimicked model projections fairly well.

Another explanation could be that the effect on temperature of increasing carbon dioxide levels in the atmosphere - the 
factor called "climate sensitivity" - is higher than scientists had believed when they built their computer models.

Alternatively it could be natural climate variability.

"We cannot conclude the exact cause," commented Professor Rahmstorf, "but there is no doubt that for this period, the 
climate has been changing faster than the IPCC predicted."

        
HAVE YOUR SAY
Who is going to tell a billion people that they can't have air-conditioning 
or an automobile?
Tooba, Rockville, USA

Send us your views
Together with his co-researchers on this project, Professor Rahmstorf is in Paris for the IPCC discussions, which will 
on Friday morning end with the release of summary conclusions on the current state of climate science, drawing on the 
work of thousands of researchers.

The full climate science report will be released later in the year, as will other IPCC chapters looking at the probable 
impacts of climate change, options for adapting to those impacts, and possible routes to reducing emissions of 
greenhouse gases.

Richard.Black-INTERNET@bbc.co.uk