Fa uns dies en jmones va titular una nota amb el mateix títol que jo utilitzo avui. No és casualitat, en la seva nota en jmones criticava les estupideses que Cory Doctorow havia escrit en un article sobre DRM, estupideses que ens preocupen ja que resten credibilitat al moviment del copyleft.

Doncs avui a BoingBoing tornen a publicar una animalada monumental: Katrina’s real name: global warming. Pur sensacionalisme climàtic. Aquesta manca de rigor fa molt de mal als que lluitem en contra de l’escalfament global de la Terra.

Si voleu escoltar opinions més sensates us recomano el següent podcast de ScienceFriday: Hurricane Katrina: Hurricane Science and Prediction, aquest fantàstic article de Real Cimate, Hurricanes and Global Warming - Is There a Connection?, o l’informe de l’IPCC que diu:

9.3.6.4 Tropical cyclones

Some of the global climate models suggest an increase in tropical storm intensities with CO2-induced warming (Krishnamurti et al., 1998), though a limitation of that study is the short two year model run. However, the highest resolution global climate model experiment reported to date (Bengtsson et al., 1996; see Chapter 10) still has a resolution too coarse (about 1°) to simulate the most intense storms or realistically simulate structures such as the hurricane eye.

Indices of tropical cyclone activity (Gray, 1979) summarise the necessary large-scale conditions for tropical cyclone activity from coarse resolution GCMs (Evans and Kempisty, 1998; Royer et al., 1998). The latter study examined large-scale atmospheric and oceanic conditions (vertical shear, vorticity and thermo-dynamic stability), and suggested that only small changes in the tropical cyclone frequencies would occur (up to a 10% increase in the Northern Hemisphere primarily in the north-west Pacific, and up to a 5% decrease in the Southern Hemisphere). Climate change studies to date show a great sensitivity to the measure of convective activity chosen, and depend less on the model produced fields. Additionally, the broad geographic regions of cyclogenesis, and therefore also the regions affected by tropical cyclones, are not expected to change significantly (Henderson-Sellers et al., 1998). This is because results from Holland’s (1997) Maximum Potential Intensity model show that even with substantial (1 to 2°C) SST increases in the tropics from global warming, one would also get a correspondingly much bigger warming in the upper troposphere leading to very little change in the moist static stability (Holland, 1997). Another study shows areas of deep convection that can be associated with tropical cyclone formation would not expand with increases in CO2 due to an increase of the SST threshold for occurrence of deep convection (Dutton et al., 2000). Additionally, since tropical storm activity in most basins is modulated by El Niño/La Niña conditions in the tropical Pacific, projections of future regional changes in tropical storm frequencies may depend on accurate projections of future El Niño conditions, an area of considerable uncertainty for climate models (as noted in Section 9.3.5.2).

En altres paraules, malgrat la recerca està encara molt verda, fet que s’ha de tenir molt present, s’espera un lleuger augment de l’activitat però no grans canvis. Què us sembla ara el titular de BoingBoing?

Actualització: Acabo d’afegir l’article de RealClimate. Com que em fa mandra modificar la meva nota, us afegeixo aquí alguns paràgrafs destacats:

Due to this semi-random nature of weather, it is wrong to blame any one event such as Katrina specifically on global warming - and of course it is just as indefensible to blame Katrina on a long-term natural cycle in the climate.

Yet this is not the right way to frame the question. As we have also pointed out in previous posts, we can indeed draw some important conclusions about the links between hurricane activity and global warming in a statistical sense. The situation is analogous to rolling loaded dice: one could, if one was so inclined, construct a set of dice where sixes occur twice as often as normal. But if you were to roll a six using these dice, you could not blame it specifically on the fact that the dice had been loaded. Half of the sixes would have occurred anyway, even with normal dice. Loading the dice simply doubled the odds. In the same manner, while we cannot draw firm conclusions about one single hurricane, we can draw some conclusions about hurricanes more generally. In particular, the available scientific evidence indicates that it is likely that global warming will make - and possibly already is making - those hurricanes that form more destructive than they otherwise would have been.

But ultimately the answer to what caused Katrina is of little practical value. Katrina is in the past. Far more important is learning something for the future, as this could help reduce the risk of further tragedies. Better protection against hurricanes will be an obvious discussion point over the coming months, to which as climatologists we are not particularly qualified to contribute. But climate science can help us understand how human actions influence climate. The current evidence strongly suggests that:
(a) hurricanes tend to become more destructive as ocean temperatures rise, and
(b) an unchecked rise in greenhouse gas concentrations will very likely increase ocean temperatures further, ultimately overwhelming any natural oscillations.

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