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National Academies Synthesis Report

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The long-awaited NAS synthesis report on surface temperature reconstructions over the last few millennia is being released today. It’s a long (155 page) report and will take a while to digest, but we applaud the committee for having tried to master a dense thicket of publications and materials on the subject over a relatively short time.

It is probably expecting too much for one report might to put to rest all the outstanding issues in a still-developing field. And given the considerable length of the report, we have little doubt that keen contrarians will be able to mine the report for skeptical-sounding sentences and cherry-pick the findings. However, it is the big picture conclusions that have the most relevance for the lay public and policymakers, and it is re-assuring (and unsurprising) to see that the panel has found reason to support the key mainstream findings of past research, including points that we have highlighted previously:
[Read more…] about National Academies Synthesis Report

Sea level in the Arctic

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A recent conference presentation at AGU (reported here) while confirming that global sea level is indeed rising (in line with other estimates), showed that Arctic sea levels may actually be falling. On the face of it these preliminary results are a little puzzling (though note that this isn’t yet a properly peer reviewed paper, and so may not reflect what ends up in the journal), but it does reveal some of the complexities in analysing sea level in relatively small enclosed basins and so a brief overview of the different factors involved is probably useful. [Read more…] about Sea level in the Arctic

NOAA: Hurricane forecasts

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Guest commentary from Thomas Crowley

NOAA has issued its annual forecast for the hurricane season, along with its now-standard explanation that there is a natural cycle of multidecadal (40-60 year) length in the North Atlantic circulation (often referred to as the “Atlantic Multidecadal Oscillation”–see Figure), that is varying the frequency of Atlantic tropical cyclones, and that the present high level of activity is due to a concurrent positive peak in this oscillation. [Read more…] about NOAA: Hurricane forecasts

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.

[Read more…] about On a Weakening of the Walker Circulation

Buying a stairway to heaven?

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Just in the last year or so, a new type of scheme for reducing personal carbon emissions has appeared, the remarkably painless purchasing of “carbon offsets”. Carbonfund.org claims to neutralize a person’s CO2 footprint on the Earth for the low, low price of $99 per year, plus if you act now they will throw in an extra 5 tons for free! And you get a pen! Prices listed here range from $5-30 per ton of CO2 from a variety of similar organizations around the world. The average U.S. citizen is responsible for about 20 tons of CO2 release per year.

Compliance with Kyoto, a mere 5% reduction in carbon emissions, was forecast by Nordhaus [2001] to cost a few percent of GDP globally. The cost to stop emission completely and immediately may not even be calculable. Carbonfund.org promises zero net emissions, for a fraction of 1% of the average U.S. income. Can this possibly be real, or are we talking indulgences and snake oil?
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Positive feedbacks from the carbon cycle

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Two papers appeared in Geophysical Research Letters today claiming that the warming forecast for the coming century may be underestimated, because of positive feedbacks in the carbon cycle. One comes from Torn and Harte, and the other from Scheffer, Brovkin, and Cox. Both papers conclude that warming in the coming century could be increased by carbon cycle feedbacks, by 25-75% or so. Do we think it’s time to push the big red Stop the Press button down at IPCC? [Read more…] about Positive feedbacks from the carbon cycle

How Red are my Proxies?

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Guest commentary by David Ritson

Realclimate recently gave a detailed review of the issues surrounding the Von Storch et al. (2004) Science article that purported to show that the paleo-reconstructions of Mann et al. were invalid. Part of the review centered on a comment of Wahl, Amman and myself and the response to it by Von Storch et al that appeared on April 27 in Science. The response admitted that our critique of their original results was correct but then opened up a new area of debate. As in their original 2004 article von Storch et al had used a coupled climate model (AOGCM) to simulate the temperatures of the last two thousand years. They had then generated pseudo-proxies by adding noise at selected spatial locations to the AOGCM generated temperature histories. The added noise was purportedly designed to represent non-climatic effects such as disease or insect infestation. This simulated ‘noisy’ world then can be used as a test-bed for the reconstruction methodology. A given analysis procedure is validated if it successfully recovers the original AOGCM noise free results and could be rejected if it fails to recover the original results. Of course such testing only makes sense if the simulated test world has characteristics similar to the real-world. [Read more…] about How Red are my Proxies?

More on the Arctic

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By Michael Mann & Phil Jones (guest)

Svalbard, an Arctic island in the Northern North Atlantic, is predicted to warm considerably more than most of the rest of the earth in many model-based scenarios. See for example the figure to the right, which represents a relatively high-end IPCC Third Assessment Report scenario for the projected surface temperature difference between the period 2071 -2100 and 1961-1990. Svalbard is the island north of Norway at about 80N between 15-30E.

The enhanced warming in this region is related to the issue of polar amplification that we have discussed previously on RC. It also happens that the Svalbard meteorological station is the 2nd station in the World Meteorological Organization (WMO) meteorological station list. This means that it tends to get noticed. The Climatic Research Unit (CRU) of the University of East Anglia maintains one prominent version of the global surface temperature data set and as part of its routine quality control, CRU flags any unusual (anomalous warm or cold) new measurements that come in. Svalbard has now been flagged consistently over the past several months, but the values have been confirmed as accurate by the Norwegian Met Service, which operates the Svalbard station.
[Read more…] about More on the Arctic

Thank you for emitting

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A recent movie, ‘Thank You for Smoking‘, amusingly highlighted the lengths that PR reps for the tobacco companies would go to distort the public discourse on the health effects of smoking. Lest you thought that was of merely historical relevance, we would like to draw your attention to two of the funniest videos around. Lifting a page straight out of the Nick Naylor playbook, the CEI (an industry-funded lobby group) has launched a new ad campaign that is supposed to counteract all those pesky scientific facts about global warming.

The first ad (both available here) deserves to become a classic of the genre. It contains the immortal lines ‘CO2: they call it pollution, we call it Life!’ – it is beyond parody and without content – and so you should definitely see it. The second ad has a little more substance – but is as misleading as you might expect.
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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