Friday, August 1, 2008

Climate Sceptics: Is the sky falling?

It seems that the easiest way to get media coverage is to make claims that global warming isn't happening. The climate deniers' claims were aired on The ABC's Lateline and Q&A this week.

What do the scientists say? Ross Garnaut addressed recent claims about lower global temperatures in his draft report.

Is there a warming trend in global temperature
data?


Observations show that global temperatures have increased over the last 150 years (Figure 5.1). The data also suggests that the warming was relatively steep over the last 30–50 years. A comparison of three datasets shows that they differ slightly on the highest recorded temperatures — data from the Hadley Centre in the United Kingdom shows 1998 as the highest year, while data from the National Aeronautics and Space Administration and the National Climatic Data Centre in the United States show 2005 as the highest year.* All three datasets show that seven of the hottest 10 years on record have been in the last nine years between 1999 and 2007.
There has been considerable debate in recent months on the interpretation of the global temperatures over the past decade. Questions have been raised about whether the warming trend ended in about 1998.
To throw light on this question, the Review sought assistance from two eminent econometricians from the Australian National University to investigate the question. Trevor Breusch and Farshid Vahid have specific expertise in the statistical analysis of time series—a speciality that is well developed in econometrics.

They were asked two questions:

• Is there a warming trend in global temperature data in the past
century?
• Is there any indication that there is a break in any trend present in the
late 1990s, or at any other point?

They concluded that:
It is difficult to be certain about trends when there is so much variation
in the data and very high correlation from year to year. We investigate
the question using statistical time series methods. Our analysis shows
that the upward movement over the last 130–160 years is persistent and
not explained by the high correlation, so it is best described as a trend.
The warming trend becomes steeper after the mid-1970s, but there is no
significant evidence for a break in trend in the late 1990s.Viewed from the
perspective of 30 or 50 years ago, the temperatures recorded in most of
the last decade lie above the confidence band produced by any model that
does not allow for a warming trend (Breusch & Vahid 2008). Garnaut Climate Change Review, Draft Report June 2008. page 113
You have to wonder whether it's the global warming advocates or the deniers who think the sky is falling?

Bound to lots more fantasy science in the US election and its aftermath as the successful candidate tries to implement a cap and trade program.

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