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Climate predictions vs. observations

In a Science paper last year (subscription required), Rahmstorf et al. pointed to 2001-2006 measurements of global temperature at the top end of the IPCC’s 2001 projections – and global sea level rise well beyond the range predicted in 2001 – as evidence that “the climate system, in particular sea level, may be responding more quickly to climate change than our current generation of models indicates.” Today in a letter to Nature Geoscience (subscription required), Roger Pielke, Jr, questions whether models from that 2001 generation improve on the predictive power of their forbears.

Pielke checks predictions from all four IPCC reports, dating back to 1990, against reality. Each report made a series of ‘if-then’ statements about the likely results of various emissions scenarios; in hindsight, Pielke can pick out which of these possible greenhouse experiments has actually been running on Earth since 1990 and compare the results to the IPCC’s shifting hypotheses.

Whereas the 2001 projections undershot the observed temperatures and sea levels, the 1990 projections overshot them, he concludes. Projections of temperature and sea level fell substantially between the 1990 and 1995 IPCC reports, when aerosols were added to models and carbon-cycle simulations were tweaked. But because they dropped too far, the adjusted post-1995 projections “are not obviously superior in capturing climate evolution”, says Pielke.

That’s not to say that 2001 models were no better than those a decade older. Including more information has made recent simulations more sophisticated – but so far it hasn’t much improved their ability to sketch out future climates, probably because important factors are still missing. Predictions from the two most recent reports do, however, seem to have crept toward the actual climate evolution, and additional rounds of of refinements may help the models to home in further.

Anna Barnett


  1. Report this comment

    Steve Bloom said:

    I find it interesting that a political scientist gets published on such a subject.

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    Mike Smith said:

    What possible difference does Roger’s background make?!

    One does not have to be a meteorologist or mathematician to compare forecasts to reality.

    Over the last few months, Roger has brought to light the woeful lack of verification (accountability) in climate science. More power to him.

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    Peter Larue said:

    Pielke’s own website says that he has a first degree in mathematics.

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    Tom Pollard said:

    From Roger Pielke’s homepage at the University of Colorado,

    “In 2006 Roger received the Eduard Brückner Prize in Munich, Germany for outstanding achievement in interdisciplinary climate research. Before joining the University of Colorado, from 1993-2001 Roger was a Scientist at the National Center for Atmospheric Research.”

    He’s a scientist who’s now doing science policy work.

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    Ralph Emerson said:

    A political scientist??? Roger Pielke was the Colorado State Climatologist and former head of the American Association of State Climatologists, as well as the head of the Colorado Climate Center.

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    Walt Whitman said:

    Ralph, that’s the resume for Pielke’s father.


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    Wayne said:

    Sorry if this post is in the wrong place as I am new to the site and you are welcome to move it to the right section.

    I am not a scientist although it doesn’t take a scientist to see that the climate is changing. I completely understand about why the sea levels are rising, the effects on the weather systems, and all the ice melting at the poles the global warming is causing. One thing I have noticed is that no one has discussed what happens to the weight distribution on the Earth and its axis when the ice melts.

    Right now the Earth’s axis has been where it is now for a very long time because of the ice weight concentrated at the poles and the rotation of the Earth. However, once the ice melts and the water returns to the seas. The weight associated with that ice will quickly be distributed equally throughout the Earth by the sea currents and not concentrations at the poles. What will happen to the Earth’s axis when the weight distribution changes? Will it change? If it changes, how much will it change or move? Will the shift be suddenly or gradually? What will be the effects on the planet and life as we know it?


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