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Saltier or not? Plus salé ou pas ?

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In a recent (of Sept. 16, 2005) publication in Science, Hatun et al. find that record-high salinities have been observed over the past decade in the region where water from the Atlantic flows into the northern oceans. They combine an analysis of observations with simulations using an ocean model, concluding that the salinity of the inflow to the northern oceans is controlled by ocean dynamics and the circulation in the sub-polar gyre. The observations by Hatun et al. may suggest that at the moment the warm and salty waters from the south are especially warm and salty.

In another publication paper in Science from June 17th 2005, on the other hand, Curry & Mauritzen conclude that as a whole the northern North Atlantic has become significantly fresher (less salty) in recent decades. The latter study was based entirely on observations (hydrographic data between Labrador and Europe in the past 50 years). The recent evidence for salinification provided by Hatun et al. has been interpreted by some as being inconsistent with the evidence for high-latitude North Atlantic freshening found in previous reports. So what is really happening? Is the salinity increasing or decreasing? And can the two recent Science studies be consistent with each other?

traduit de l’anglais par Claire Rollion-Bard
Dans une publication récente (du 16 Sept. 2005) dans Science, Hatun et al. ont trouvé que de fortes salinités ont été observées durant la dernière décennie dans la région où l’eau de l’Atlantique s’écoule dans les océans du Nord. Ils ont combiné une analyse des observations avec des simulations utilisant un modèle océanique, concluant que la salinité du courant vers les océans du Nord est contrôlée par la dynamique océanique et la circulation de l’enroulement sub-polaire. Les observations de Hatun et al. peuvent suggérer que les eaux chaudes et salées venant du sud sont spécialement chaudes et salées.

Dans une autre publication dans Science du 17 juin 2005, Curry & Mauritzen concluent que, dans l’ensemble, le nord de l’Atlantique Nord est devenu significativement plus doux (moins salé) au cours des récentes décennies. Cette étude était basée entièrement sur des observations (données hydrographiques entre le Labrador et l’Europe dans les derniers 50 ans). L’évidence récente pour une augmentation de la salinité fournie par Hatun et al. a été interprétée par certains comme étant inconsistante avec l’évidence de l’Atlantique Nord des hautes latitudes moins salé trouvé dans les précédentes publications. Que se passe-t’il donc réellement ? Est-ce que la salinité augmente ou baisse ? Et est-ce que les deux récentes études dans Science peuvent être compatibles l’une avec l’autre ?
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Inhofe and Crichton: Together at Last!

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Gavin Schmidt and Michael Mann

Today we witnessed a rather curious event in the US Senate. Possibly for the first time ever, a chair of a Senate committee, one Senator James Inhofe (R-Oklahoma), invited a science fiction writer to advise the committee (Environment and Public Works), on science facts–in this case, the facts behind climate change. The author in question? None other than our old friend, Michael Crichton whom we’ve had reason to mention before (see here and here). The committee’s ranking member, Senator James Jeffords (I) of Vermont, was clearly not impressed. Joining Crichton on climate change issues was William Gray of hurricane forecasting fame, Richard Benedick (a negotiator on the Montreal Protocol on ozone-depleting chemicals), and David Sandalow (Brookings Institution). As might be expected, we paid a fair bit of attention to the scientific (and not-so-scientific) points made. [Read more…] about Inhofe and Crichton: Together at Last!

What is a first-order climate forcing?

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Roger Pielke Sr. (Colorado State) has a blog (Climate Science) that gives his personal perspective on climate change issues. In it, he has made clear that he feels that apart from greenhouse gases, other climate forcings (the changes that affect the energy balance of the planet) are being neglected in the scientific discussion. Specifically, he feels that many of these other forcings have sufficient ‘first-order’ effects to prevent a clear attribution of recent climate change to greenhouse gases.

In general, I heartily agree – other forcings are important, even essential, for understanding observed climate variability and, as a community, we are only just starting to get to grips with some of the more complicated effects. Obviously, though, not all forcings are of the same magnitude (either globally or regionally) and so it is useful to separate the ‘first-order’ forcings from those that are relatively minor. But what exactly is ‘first-order’ and what is not? [Read more…] about What is a first-order climate forcing?

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

The tropical lapse rate quandary

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Guest commentary by Steve Sherwood

There are four independent instrumental records of sufficient length and potential accuracy to tell us about 20th-century climate change. The two longest ones are of temperature near the Earth’s surface: a vast network of weather stations over land areas, and ship data from the oceans. While land surface observations go back hundreds of years in a few places, data of sufficient coverage for estimating global temperature have been available only since the end of the 19th century. These have shown about a 0.7 C warming over land during the last century, with somewhat less increase indicated over oceans. The land records contain artifacts due to things like urbanization or tree growth around station locations, buildings or air conditioners being installed near stations, etc., but laborious data screening, correction procedures, and a-posteriori tests have convinced nearly all researchers that the reported land warming trend must be largely correct. Qualitative indicators like sea ice coverage, spring thaw dates, and melting permafrost provide strong additional evidence that trends have been positive at middle and high northern latitudes, while glacier retreat suggests warming aloft at lower latitudes.

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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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Storms & Global Warming II

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Earlier this year, we posted two discussions on the association between climate change and storms: Storms and Climate Change and Some recent updates. I will use the abbreviation TC here in the loose meaning of a tropical cyclone. These posts discussed the high number of TCs during the previous hurricane season and an essay on the relation between TCs and climate change. The uncertainty surrounding trends in storminess was underlined, and a point was being made about this subject being controversial. [Read more…] about Storms & Global Warming II

Did the Sun hit record highs over the last few decades?

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Guest commentary by Raimund Muscheler

[note: this is a restore (8/8/05) of an article from August 3, 2005 that was accidentally deleted due to a technical glitch. Unfortunately, most of the comments could not be retrieved. We sincerely apologize to our readers!]

The solar influence on climate is a controversial topic in climate research (see previous posts here and here). The irradiance changes are assumed to be relatively small and the importance of potential amplifying mechanisms is still a matter of current debate. One reason for these uncertainties is that there are only approximately 25 years of satellite-based observations of the solar irradiance. Sunspot observations for the last 400 years clearly indicate that current levels of solar activity are very different from the state of the sun during the Maunder minimum (from approx. 1645 to 1715 AD) where almost no sunspots could be observed.
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On record-breaking events

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NASA’s Earth Observatory reports that there was a record low Arctic sea ice concentration in June 2005. There was a record-number of typhoons over Japan in 2004. In June, there were reports of a number of record-breaking events in the US. And on July 28, the British News paper The Independent reported on record-breaking rainfall (~1 m) in India, claiming hundreds of lives. These are just a few examples of recent observations. So, what is happening?

[Read more…] about On record-breaking events

Scientists respond to Barton

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by Gavin Schmidt and Stefan Rahmstorf

Many readers will be aware that three scientists (two of which are contributors to this site, Michael Mann and Ray Bradley) have received letters from Representative Joe Barton (Texas), Chairman of the House Energy and Commerce Committee specifically requesting information about their work on the ‘hockey stick’ papers (Mann et al (1998) and Mann et al (1999)) as well as an enormous amount of irrelevant material not connected to these studies.

Many in the scientific community would welcome any genuine interest in climate change from the committee, but the tone and content of these letters have alarmed many scientists and their professional organisations. In the words of Alan Leshner, CEO of the American Association for the Advancement of Science, the Barton letters “give the impression of a search for some basis on which to discredit these particular scientists and findings, rather than a search for understanding.” Other organisations and individual scientists have also expressed strong concerns: [Read more…] about Scientists respond to Barton