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El Nino

Friday round-up

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Two items of interest this week. First, there is an atrocious paper that has just been published in JGR by McLean, de Freitas and Carter that is doing the rounds of the denialosphere. These authors make the completely unsurprising point that that there is a correlation between ENSO indices and global mean temperature – something that has been well known for decades – and then go on to claim that that all trends are explained by this correlation as well. This is somewhat surprising since their method of analysis (which involves taking the first derivative of any changes) eliminates the influence of any trends in the correlation. Tamino has an excellent demonstration of the fatuity of the statements in their hyped press-release and Michael Tobis deconstructs the details. For reference, we showed last year that the long term trends are still basically the same after you account for ENSO. Nevermore let it be said that you can’t get any old rubbish published in a peer-reviewed journal!

Second (and much more interestingly) there is an open call for anyone interested to contribute to setting the agenda for Earth System Science for the next couple of decades at the Visioning Earth Science website of the International Council for Science (ICS). This is one of the umbrella organisations that runs a network of committees and programs that prioritise research directions and international programs and they are looking for ideas. Let them know what your priorities are.

Global trends and ENSO

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Translations: (Español)

It’s long been known that El Niño variability affects the global mean temperature anomalies. 1998 was so warm in part because of the big El Niño event over the winter of 1997-1998 which directly warmed a large part of the Pacific, and indirectly warmed (via the large increase in water vapour) an even larger region. The opposite effect was seen with the La Niña event this last winter. Since the variability associated with these events is large compared to expected global warming trends over a short number of years, the underlying trends might be more clearly seen if the El Niño events (more generally, the El Niño – Southern Oscillation (ENSO)) were taken out of the way. There is no perfect way to do this – but there are a couple of reasonable approaches.

[Read more…] about Global trends and ENSO

Climate Change and Tropical Cyclones (Yet Again)

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By Rasmus Benestad & Michael Mann
Hurricane Katerina
Just as Typhoon Nargis has reminded us of the destructive power of tropical cyclones (with its horrible death toll in Burma–around 100,000 according to the UN), a new paper by Knutson et al in the latest issue of the journal Nature Geosciences purports to project a reduction in Atlantic hurricane activity (principally the ‘frequency’ but also integrated measures of powerfulness).

The close timing of the Knutson et al and Typhoon Nargis is of course coincidental. But the study has been accorded the unprecedented privilege (that is, for a climate change article published during the past 7 years) of a NOAA press conference. What’s the difference this time? Well, for one thing, the title of the paper: “Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions” (emphasis added).

[Read more…] about Climate Change and Tropical Cyclones (Yet Again)

El Nino, Global Warming, and Anomalous U.S. Winter Warmth

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Translations: (Slovenčina) (Svenska)

It has now become all too common. Peculiar weather precipitates immediate blame on global warming by some, and equally immediate pronouncements by others (curiously, quite often the National Oceanic and Atmospheric Administration in recent years) that global warming can’t possibly be to blame. The reality, as we’ve often remarked here before, is that absolute statements of neither sort are scientifically defensible. Meteorological anomalies cannot be purely attributed to deterministic factors, let alone any one specific such factor (e.g. either global warming or a hypothetical long-term climate oscillation).

Lets consider the latest such example. In an odd repeat of last year (the ‘groundhog day’ analogy growing ever more appropriate), we find ourselves well into the meteorological Northern Hemisphere winter (Dec-Feb) with little evidence over large parts of the country (most noteably the eastern and central U.S.) that it ever really began. Unsurprisingly, numerous news stories have popped up asking whether global warming might be to blame. Almost as if on cue, representatives from NOAA’s National Weather Service have been dispatched to tell us that the event e.g. “has absolutely nothing to do with global warming”, but instead is entirely due to the impact of the current El Nino event.

[Update 1/9/07: NOAA coincidentally has announced today that 2006 was officially the warmest year on record for the U.S.]
[Update 2/11/08: It got bumped to second place. ]
[Read more…] about El Nino, Global Warming, and Anomalous U.S. Winter Warmth

Ocean heat content: latest numbers

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Net ocean heat content changes are very closely tied to the net radiative imbalance of the planet since the ocean component of the climate system has by far the biggest heat capacity. Thus we have often made the point that diagnosing this imbalance through measurements of temperature in the ocean is a key metric in evaluating the response of the system to changes in CO2 and the other radiative forcings (see here).
In a paper I co-authored last year (Hansen et al, 2005), we compared model results with the trends over the 1993 to 2003 period and showed that they matched quite well (here). Given their importance in evaluating climate models, new reports on the ocean heat content numbers are anticipated quite closely.

Recently, a new preprint with the latest observations (2003 to 2005) has appeared (Lyman et al, hat tip to Climate Science) which shows a decrease in the ocean heat content over those two years, decreasing the magnitude of the long-term trend that had been shown from 1993 to 2003 in previous work (Willis et al, 2004) – from 0.6 W/m2 to about 0.33 W/m2. This has generated a lot of commentary in some circles, but in many cases the full context has not been appreciated.
[Read more…] about Ocean heat content: latest numbers

On a Weakening of the Walker Circulation

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by Ray Pierrehumbert and Rasmus Benestad

Second article of our 3-part series on atmospheric circulation and global warming

In Part I we outlined some general features of the tropical circulation, and discussed ways in which increases in anthropogenic greenhouse gases might affect El Niño. Now we take up the question of how global warming might affect the quasi-steady east-west overturning circulation known as the Walker Circulation. The Walker circulation affects convection and precipitation patterns, the easterly Trade Winds, oceanic upwelling and ocean biological productivity; hence, changes in this circulation can have far-reaching consequences. It also provides the background state against which El Niño events take place, and so changes in the Walker circulation should form an intrinsic part of thinking about how global warming will affect El Niño. In a paper that recently appeared in Nature, Vecchi, Soden, Wittenberg, Held, Leetmaa and Harrison present intriguing new results which suggest that there has already been a weakening of the Walker circulation in the past century, and that the observed changes are consistent with those expected as a response to increases in anthropogenic greenhouse gases. The discussion in Vecchi et al. also raises some very interesting issues regarding the way the hydrological cycle might change in a warming world.

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El Niño and Global Warming

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By Rasmus Benestad & Raymond Pierrehumbert

This is the first part of a planned mini-series of 3 posts on tropical climate, circulation, and oceanic response in conjunction with a global warming. Climate change related to a global warming is more than just temperature and precipitation -massive atmospheric circulations change too, and these changes can have consequences.

[Read more…] about El Niño and Global Warming

Global warming on Earth

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Translations: (Français)

The Washington Post picked up on the latest update to the 2005 temperature anomaly analysis from NASA GISS. The 2005 Jan-Sep land data (which is adjusted for urban biases) is higher than the previously warmest year (0.76°C compared to the 1998 anomaly of 0.75°C for the same months, and a 0.71°C anomaly for the whole year) , while the land-ocean temperature index (which includes sea surface temperature data) is trailing slightly behind (0.58°C compared to 0.60°C Jan-Sep, 0.56°C for the whole of 1998). The GISS team (of which I am not a part) had predicted that it was likely the 2005 would exceed the 1998 record (when there was a very large El Niño at the beginning of that year) based on the long term trends in surface temperature and the estimated continuing large imbalance in the Earth’s radiation budget.

In 1998 the last three months of the year were relatively cool as the El Niño pattern had faded. For the 2005 global land-ocean index to exceed the annual 1998 record, the mean anomaly needs to stay above 0.51°C for the next three months. Since there was no El Niño this year, and the mean so far is significantly above that, this seems likely. [Read more…] about Global warming on Earth

Hurricanes and Global Warming – Is There a Connection?

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Translations: (Français) (Español)

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?

[Read more…] about Hurricanes and Global Warming – Is There a Connection?