Bjørn Lomborg: Climate change decisions should be based on science, not political activism

lomborgI pointed out that one conference participant, Stefan Rahmstorf, argues that sea level rises will be much higher than those anticipated by most researchers. Rahmstorf is a well-established, serious researcher on climate change who holds a minority view on the rise in the sea-level — the IPCC’s estimate is an 18cm to 59cm rise by the end of the century. I mentioned him to make the point that meeting with like-minded colleagues does not somehow create a new global scientific consensus.

In arguing that sea levels are rising much more than the consensus view of thousands of scientists, he makes a lot of the fact that the 1993-2003 sea level estimates were 50% higher than the IPCC’s models expected, indicating that future sea level rises would also be higher. He fails to mention that the particular decade centred on 1998 has one of the highest sea level rises, which in the past has varied dramatically over decades. The decade before, the sea level was almost not rising or possibly even dropping (as one can see on p413 of IPCC’s first report). One cannot pick the timeframes to fit the argument. (Read more)

Stefan Rahmstorf: Climate sceptics confuse the public by focusing on short-term fluctuations

rahmstorfLomborg argues that 18 years could be too short for a robust trend comparison because of decadal variations in trend – but the 42-year period analysed by IPCC yields the same result. And it is telling that he then goes on to draw an “inescapable” conclusion about a slow-down of sea level rise from just four years of data. This is another well-worn debating trick: confuse the public about the underlying trend by focusing on short-term fluctuations. It’s like claiming spring won’t come if there is a brief cold snap in April.

Why does Lomborg cite the trend since 2005? Last October, he cited that of the previous two years. Why now four years? Because the trend of the past two years (2007-2008) is now + 3.7 mm/year? It is even worse. The trend since the beginning of any year of the data series varies between 1.6 mm/year and 9.0 mm/year, depending on the start year chosen. Using 2005, Lomborg cherry-picked the by far lowest. He’s done this before, see for example his recent claim that the globe is cooling. (Read More)

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