Thursday, January 17, 2013

Two new papers predict fewer Northern Hemisphere cyclones in future


Simple uncertainty frameworks for selecting weighting schemes and interpreting multi-model ensemble climate change experiments

Philip G. Sansom*
University of Exeter, Exeter, United Kingdom
David B. Stephenson
University of Exeter, Exeter, United Kingdom
Christopher A. T. Ferro
University of Exeter, Exeter, United Kingdom
Giuseppe Zappa
National Centre for Atmospheric Sciences, University of Reading, Reading, United Kingdom
Len Shaffrey
National Centre for Atmospheric Sciences, University of Reading, Reading, United Kingdom

Abstract
Future climate change projections are often derived from ensembles of simulations from multiple global circulation models using heuristic weighting schemes. This study provides a more rigorous justification for this by introducing a nested family of three simple analysis of variance frameworks. Statistical frameworks are essential in order to quantify the uncertainty associated with the estimate of the mean climate change response.

The most general framework yields the “one model, one vote” weighting scheme often used in climate projection. However, a simpler additive framework is found to be preferable when the climate change response is not strongly model-dependent. In such situations, the weighted multi-model mean may be interpreted as an estimate of the actual climate response, even in the presence of shared model biases.
Statistical significance tests are derived to choose the most appropriate framework for specific multi-model ensemble data. The framework assumptions are explicit and can be checked using simple tests and graphical techniques. The frameworks can be used to test for evidence of non-zero climate response and to construct confidence intervals for the size of the response.

The methodology is illustrated by application to North Atlantic storm track data from the CMIP5 multi-model ensemble. Despite large variations in the historical storm tracks, the cyclone frequency climate change response is not found to be model-dependent over most of the region. This gives high confidence in the response estimates. Statistically significant decreases in cyclone frequency are found on the flanks of the North Atlantic storm track and in the Mediterranean basin.


CIMP5 multimodel ensemble projection of storm track change under global warming

Edmund K. M. Chang, Yanjuan Guo, Xiaoming Xia
[1] CMIP5 multimodel ensemble projection of midlatitude storm track changes has been examined. Storm track activity is quantified by temporal variance of meridional wind and sea level pressure (psl), as well as cyclone track statistics. For the Southern Hemisphere (SH), CMIP5 models project clear poleward migration, upward expansion, and intensification of the storm track. For the Northern Hemisphere (NH), the models also project some poleward shift and upward expansion of the storm track in the upper troposphere/lower stratosphere, but mainly weakening of the storm track toward its equatorward flank in the troposphere. Consistent with these, CMIP5 models project significant increase in the frequency of extreme cyclones during the SH cool season, but significant decrease in such events in the NH. Comparisons with CMIP3 projections indicate high degrees of consistency for SH projections, but significant differences are found in the NH. Overall, CMIP5 models project larger decrease in storm track activity in the NH troposphere, especially over North America in winter, where psl variance as well as cyclone frequency and amplitude are all projected to decrease significantly. In terms of climatology, similar to CMIP3, most CMIP5 models simulate storm tracks that are too weak and display equatorward biases in their latitude. These biases have also been related to future projections. In the NH, the strength of a model's climatological storm track is negatively correlated with its projected amplitude change under global warming, while in the SH, models with large equatorward biases in storm track latitude tend to project larger poleward shifts.

4 comments:

  1. Cyclones prove nothing about whether climate change is natural or man-made. These are the reasons Hansen was wrong ...

    It should be clear from the recent comments on Roy Spencer's latest thread that Jeff Condon (owner of “The Air Vent” website) was wrong in assuming that microbolometers (infra red thermometers) disproved what Prof Claes Johnson said about how one-way spontaneous radiation cannot transfer heat from a cooler source to a warmer target.

    My March 2012 paper “Radiated Energy and the Second Law of Thermodynamics” was in large part a review of what Claes had written. He and I are in frequent communication, along with about half a dozen core members of PSI who really know their physics, and we have not been proven to be incorrect on any of this by anyone offering a valid rebuttal based on valid physics.

    The significance of what Claes proved in “Computational Blackbody Radiation” is that back radiation cannot affect the rate of cooling by non-radiative processes. The latter account for at least two-thirds of all the thermal energy transferred from the surface to the atmosphere.

    The rate of cooling by non-radiative processes is slowed, not by back radiation, but by the presence of all air molecules at a very close temperature at the surface/atmosphere boundary. These air molecules are at the temperature they are, because Loschmidt was right and his physics, nearly 150 years old, has stood the test of time, and now been proven correct empirically. A thermal gradient does develop autonomously in a gravitational field and is more than sufficient to explain that “33 degrees of warming” supposedly due to WV and GHG. So the greenhouse is demolished and falls to the ground, which it never was warming in the first place. QED.

    Doug Cotton
    http://climate-change-theory.com

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    1. Thanks for your comments Doug & agreed. I'm also a big fan & supporter of Claes Johnson.

      This blog also shows, even if one falsely assumed that AGW was true, that the scientific literature is full of contradictions to CAGW.

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  2. I'm concerned about the use of CMIP models in this way. These models presume warming from rising CO2, amplified by positive water feedback. That warming is projected to decrease the thermal difference between equator and poles, and thus result in fewer cylones.
    If the presumption is wrong, then there may be more, not less cyclones, but it will be due to global cooling, not warming.
    And yet the media is full of voice claiming that extreme weather proves man made global warming, in contraction to alarmist theory.
    Could it get any more confused?

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    1. Yes
      And anyone who points this out will be labeled a "climate denier"

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