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Hurricanes and Global Warming – Is There a Connection? Huracanes y calentamiento global ¿Hay conexión?Ouragans et réchauffement global – existe t’il un lien ?

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by Stefan Rahmstorf, Michael Mann, Rasmus Benestad, Gavin Schmidt, and William Connolley

On Monday August 29, Hurricane Katrina ravaged New Orleans, Louisiana and Missisippi, leaving a trail of destruction in her wake. It will be some time until the full toll of this hurricane can be assessed, but the devastating human and environmental impacts are already obvious.

Katrina was the most feared of all meteorological events, a major hurricane making landfall in a highly-populated low-lying region. In the wake of this devastation, many have questioned whether global warming may have contributed to this disaster. Could New Orleans be the first major U.S. city ravaged by human-caused climate change?

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by Stefan Rahmstorf, Michael Mann, Rasmus Benestad, Gavin Schmidt, and William Connolley (traduit par Claire Rollion Bard)
Le lundi 29 août, l’ouragan Katrina a ravagé la Nouvelle-Orléans, la Louisiane et le Mississipi, laissant une traînée de destruction dans son sillage. Il va se passer du temps avant que le bilan total de cet ouragan soit estimé, mais les impacts environnementaux et humains sont déjà apparents.
Katrina était le plus craint des évènements météorologiques, un ouragan majeur laissant un terrain vide dans une région très peuplée de faible élévation. Dans le sillage de sa dévastation, beaucoup se sont demandés si le réchauffement global pouvait avoir contribué à ce désastre. La Nouvelle-Orléans pourrait-elle être la première ville majeure des Etats-Unis à être ravagée par le changement climatique causé par les humains ?
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Et Tu LT?

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In previous posts we have stressed that discrepancies between models and observations force scientists to re-examine the foundations of both the modelling and the interpretation of the data. So it has been for the apparent discrepancies between the Microwave Sounding Unit (MSU) lower tropospheric temperature records (MSU 2LT), radiosonde records and the climate models that try to simulate the climate of the last few decades. Three papers this week in Science Express, Mears et al, Santer et al (on which I’m a co-author) and Sherwood et al show that the discrepancy has been mostly resolved – in favour of the models.

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The lure of solar forcing

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It’s obvious.

The sun provides 99.998% of the energy to the Earth’s climate (the rest coming from geothermal heat sources). The circulation patterns of the tropical Hadley Cell, the mid latitude storm tracks the polar high and the resulting climate zones are all driven by the gradients of solar heating as a function of latitude. So of course any significant change to solar output is bound to affect the climate, it stands to reason! Since we can see that there are changes in solar activity, it’s therefore just a question of finding the link. Researchers for over a century have therefore taken any climate records they can find and searched for correlations to the sunspots, the solar-cycle length, geomagnetic indices, cosmogenic isotopes or smoothed versions thereof (and there are many ways to do the smoothing, and you don’t even need to confine yourself to one single method per record). At the same time, estimates of solar output in the past are extremely uncertain, and so there is a great deal of scope in blaming any unexplained phenomena on solar changes without fear of contradiction.

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Planetary energy imbalance?

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The recent paper in Science Express by Hansen et al (on which I am a co-author) has garnered quite a lot of press attention and has been described as the ‘smoking gun’ for anthropogenic climate change. We have discussed many of the relevant issues here before, but it may be useful to go over the arguments again here.

The key points of the paper are that: i) model simulations with 20th century forcings are able to match the surface air temperature record, ii) they also match the measured changes of ocean heat content over the last decade, iii) the implied planetary imbalance (the amount of excess energy the Earth is currently absorbing) which is roughly equal to the ocean heat uptake, is significant and growing, and iv) this implies both that there is significant heating “in the pipeline”, and that there is an important lag in the climate’s full response to changes in the forcing.

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Pollution-Climate Connections Liens entre Pollution et Climat

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Guest commentary by Loretta Mickley, Harvard University

Every summer over much of the United States, we brace ourselves for heat waves. During these periods, the air turns muggy and usually smoggy. After a few days, a cold front moves in, sweeping away the pollution and ending the heat. Given that we are on a path towards global warming, atmospheric chemists are asking how climate change could affect air quality. Will warmer temperatures mean more pollution during these episodes? Will episodes last longer? Most importantly, what effect will changes in air quality have on human health?
Article invité par Loretta Mickley, Harvard University (Traduit par Pierre Allemand)

Tous les étés, dans la plupart des régions des USA, nous nous préparons aux vagues de chaleur. Pendant ces périodes, l’air devient très humide et généralement brumeux. Après quelques jours, un front froid survient, balayant la pollution et mettant fin à la chaleur. Etant donné que nous nous acheminons vers un réchauffement global, les spécialistes de la chimie de l’atmosphère se demandent de quelle façon le changement climatique pourrait affecter la qualité de l’air. Des températures plus élevées signifieront-elles plus de pollution durant ces épisodes ? Ces épisodes dureront-ils plus longtemps ? Plus important : quels sont les effets des changements dans la qualité de l’air sur la santé humaine ?
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Water vapour: feedback or forcing?

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Whenever three or more contrarians are gathered together, one will inevitably claim that water vapour is being unjustly neglected by ‘IPCC’ scientists. “Why isn’t water vapour acknowledged as a greenhouse gas?”, “Why does anyone even care about the other greenhouse gases since water vapour is 98% of the effect?”, “Why isn’t water vapour included in climate models?”, “Why isn’t included on the forcings bar charts?” etc. Any mainstream scientist present will trot out the standard response that water vapour is indeed an important greenhouse gas, it is included in all climate models, but it is a feedback and not a forcing. From personal experience, I am aware that these distinctions are not clear to many, and so here is a more in-depth response (see also this other attempt).

Eine Übersetzung in deutsch finden Sie hier.
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Doubts about the Advent of Spring

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A “consensus view” amongst climate scientists holds that the Northern Hemisphere will be warming this month, as spring is coming. This is thought to be due to the Earth’s orbit around the sun and the inclination of the Earth’s axis, tilting the Northern Hemisphere progressively towards the sun throughout March and April and increasing the amount of solar radiation received at northern latitudes.

In a new novel, State of Euphoria, bestselling author Michael Crikey uncovers major flaws in this theory and warns against false hopes for the arrival of spring.
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IPCC in action: Part II

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The primary purpose of the Intergovernmental Panel for Climate Change (IPCC) is to assess the available scientific knowledge about climate change, not to initiate new research. The next IPCC report (Assessment Report 4, or AR4) is due in 2007, and in order to update of the state of knowledge it will only consider papers published in peer-review scientific journals between 2000 and papers submitted by May 1st 2005 (must be accepted before December 2005). It is essential that the papers be published in scientific quality journals in order to ensure the credibility of the results. Nevertheless the IPCC reports undergo several additional reviews and revisions involving a large number of independent referees. Thus, the IPCC reports undergo a more stringent review process than common papers in the scientific literature.

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IPCC in action: Part I

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This is the first of two pieces on the recent IPCC workshop in Hawaii, This brought together independent researchers from all over the world to analyse computer model simulations of the last 150 years and to assess whether they are actually any good.

Guest commentary from Natassa Romanou (Columbia University)

During the first 3 days of March 2005, balmy downtown Honolulu in Hawaii was buzzing with agile scientists conversing, chatting, announcing, briefing and informing about IPCC assessment reports, climate models, model evaluations, climate sensitivities and feedbacks. These were the participants of the Climate Model Evaluation Project workshop (CMEP) and came here from most (if not all) the major, most prestigious climate research laboratories of the world, including; The US labs National Center for Atmospheric Research, the Geophysical Fluid Dynamics Laboratory and the Goddard Institute for Space Studies, the British Hadley Centre for Climate Prediction, the German Max Planck Institute for Meteorology, the Canadian Centre for Climate Modelling and Analysis, the French Centre National de Recherches Meteorologiques and the IPSL/LMD/LSCE, the Australian CSIRO Atmospheric Research, the Chinese Institute of Atmospheric Physics, the Russian Institute for Numerical Mathematics and the Japanese Meteorological Research Institute. This meeting was sponsored by the benevolent NSF, NOAA, NASA and DOE.

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Why looking for global warming in the oceans is a good idea Voici pourquoi rechercher le réchauffement global dans les océans est pertinent

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A lot of press and commentary came out this week concerning a presentation and press release from Tim Barnett and Scripps colleagues presenting at the AAAS meeting (The Independent, John Fleck ,(and again) David Appell…etc). Why did this get so much attention given that there is no actual paper yet?
par Gavin Schmidt (traduit par Pierre Allemand)

Un grand nombre d’articles de presse et de commentaires sont sortis cette semaine concernant une présentation et un communiqué de presse de Tim Barnett, Scripps et collègues au congrès de l’AAAS (American Society for the Advancement of Science), (The Independent, John Fleck ,(et de nouveau ici) David Appell…etc. (NdT : sites en anglais). Pourquoi cela a-t-il donné lieu à autant d’attention, alors qu’aucune publication n’est encore disponible ?

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