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On Mid-latitude Storms

Filed under: — rasmus @ 29 December 2006

Statements often appear in the media about suggesting that more extreme mid-latitude storms will result from global warming. For instance, western Norway was recently battered by an unusually strong storm which triggered many such speculations. But scientific papers on how global warming may affect the mid-latitude storms give a more mixed picture. In a recent paper by Bengtsson & Hodges (2006), simulations with the ECHAM5 Global Climate Model (GCM) were analysed, but they found no increase in the number of mid-latitude storms world-wide. Another study by Leckebusch et al. (2006) showed that the projection of storm characteristics was model-dependent. (Note that the dynamics of tropical and mid-latitude (often called ‘extra-tropical’) storms involve different processes, and tropical storms have been discussed in previous posts here on RC: here, here, here, and here).

The factors that control this are often confounding and so make this a tricky prediction. Simple arguments based on the expected ‘polar amplification‘ and the fact that the surface temperature gradient between the tropics and the poles will likely decrease would reduce the scope for ‘baroclinic instability’ (the main generator of mid-latitudes storms). However, there are also increases in the upper troposphere/lower stratospheric gradients (due to the stratosphere cooling and the troposphere warming) and that has been shown to lead to increases in wind speeds at the surface. And finally, although latent heat release (from condensing water vapour) is not a fundamental driver of mid-latitude storms, it does play a role and that is likely to increase the intensity of the storms since there is generally more water vapour available in warmer world. It should also be clear that for any one locality, a shift in the storm tracks (associated with phenomena like the NAO or the sea ice edge) will often be more of an issue than the overall change in storm statistics.
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2006 Year in review

Filed under: — group @ 27 December 2006 - (Français)

A lighthearted look at the climate science goings-on over the last year:

Best highlight of the gap between the ‘two cultures’:
Justice Scalia: ‘Troposphere, whatever. I told you before I’m not a scientist. That’s why I don’t want to have to deal with global warming’ .

Least effective muzzling of government climate scientist by a junior public affairs political appointee:
George Deutsch met his match in Jim Hansen.

Most puzzling finding that has yet to be replicated:
Methane from plants

Worst reported story and least effectual follow-up press release:
Methane from plants

Best (err… only) climate science documentary on public release:
An Inconvenient Truth.

Most worn out contrarian cliche:
Medieval English vineyards.

Previously prominent contrarian cliche curiously not being used any more:
“The satellites show cooling”

Most bizarre new contrarian claim:
“Global warming stopped in 1998”.
By the same logic, it also stopped in 1973, 1983, and 1990 (only it didn’t).

Most ironic complaint about ‘un-balanced’ climate coverage on CNN:
Pat Michaels (the most interviewed commentator by a factor of two) complaining that he doesn’t get enough exposure.

Most dizzying turn-around of a climate skeptic:
Fred Singer “global warming is not happening” (1998,2000, 2002, 2005) to global warming is “unstoppable” (2006)

Best popular book on the climate change:
Elizabeth Kolbert’s “Field Notes from a Catastrophe

Least unexpected observations:
(Joint winners) 2006 near-record minima in Arctic sea ice extent, near-record maxima in Northern Hemisphere temperatures, resumed increase in ocean heat content, record increases in CO2 emissions

Best resource for future climate model analyses:
PCMDI database of IPCC AR4 simulations. The gift that will keep on giving.

Best actual good news:
Methane concentrations appear to have stabilised. Maybe they can even be coaxed downward….

Biggest increase in uncertainty as a function of more research:
Anything to do with aerosols.

Least apologetic excuse for getting a climate story wrong:
Newsweek explains its 1975 ‘The Cooling World’ story.

Most promising newcomer on the contrarian comedy circuit:
Viscount Monckton of Brenchley

Least accurate attempted insinuation about RealClimate by a congressional staffer:
‘There’s so much money’: Marc Morano (Senate EPW outgoing majority committee staff, 5:30 into the mp3 file)

Boldest impractical policy idea:
Geo-engineering

Boldest practical policy idea:
Creation of a National Climate Service, which could more effecitvely provide useful climate information to policymakers.

Most revealing insight into the disinformation industry (fiction):
Thank you for smoking

Most revealing insight into the disinformation industry (non-fiction) and year’s best self-parody:
‘CO2 is life’

Feel free to suggest your own categories and winners…

AGU Hangover

Filed under: — gavin @ 24 December 2006

It turns out that there were almost 14,000 attendees at AGU last week, which apparently makes it the largest Earth Science meeting ever held. To be sure, not all of that is climate related – there was lots of seismology, planetary and more theoretical/small-scale stuff, but a lot of it was. At most times there were at least half a dozen sessions that I would have been interested to attend – and they were often discussing overlapping themes.

It used to be that one could go to a meeting like this and get a wide overview of the work being done much more efficiently (and speedily) than reading the journals. However, that is clearly no longer true. And of course, we can’t keep up with all the relevant journal articies in the wider field either, and so how do scientists manage?
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Not just ice albedo

Filed under: — rasmus @ 22 December 2006 - (Français)

A recent paper by Francis & Hunter provides an interesting discussion about reasons for the recent decline in the Arctic sea-ice extent, based on new satellite observations. One common proposition about sea ice is that it involves a positive feed-back because the ice affects the planetary albedo (how the planet reflects the sunlight back to space before the energy enters the ‘climate system’). Yet, there is more to the story, as the ice acts more-or-less like an insulating lid on top of the sea. There are subtle effects such as the planet losing more heat from the open sea than from ice-covered region (some of this heat is absorbed by the atmosphere, but climates over ice-covered regions are of more continental winter character: dry and cold). The oceanic heat loss depends of course on the sea surface temperature (SST). Open water also is a source of humidity, as opposed to sea-ice (because its cold, not because its dry), but the atmospheric humidity is also influenced by the moisture transport associated with the wind (moisture advection). Francis & Hunter found a positive correlation between lack of ice and the downward long-wave radiation, something they attributed primarily to cloudiness. Hence, clouds play a role, both in terms of influencing the albedo as well as trapping out-going heat. Francis & Hunter suggest that the changes in the long-wave radiation is stronger than the clouds’ modulation of the direct sunlight.
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Fall AGU

Filed under: — gavin @ 9 December 2006

The Fall AGU meeting in San Francisco is always an exhilarating/exhausting (take your pick) fixture of the Earth Science calendar. This year will be no different, and since about half of us will be there, RealClimate will probably be a little quiet next week. Hopefully, we should be able to report on any highlights when we get back.

N.B. If any readers will be attending and want to say hi, I will be giving a talk on ‘Science blogging: RealClimate.org and the Global Warming debate‘ on Friday (PA53A, 13:40, MCS 309).

Update: AGU went well – lot’s of good stuff. The actual RealClimate presentation is available here – it’s pretty basic though (only 15 minutes worth)).

Inhofe’s last stand

Filed under: — gavin @ 7 December 2006

Part of me felt a little nostalgic yesterday watching the last Senate hearing on climate change that will be chaired by Sen. James Inhofe. It all felt very familiar and comforting in some strange way. There was the well-spoken ‘expert’ flown in from Australia (no-one available a little closer to home?), the media ‘expert’ from the think tank (plenty of those about) and a rather out-of-place geologist. There were the same talking points (CO2 leads the warming during the ice ages! the Medieval Warm Period was warm! it’s all a hoax!*) that are always brought up. These easy certainties and predictable responses are so well worn that they feel like a pair of old slippers.
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Further comment on the Supreme Court briefs

Filed under: — group @ 7 December 2006

Comment from Scott Saleska (elevated from previous post). The discussion refers to the brief submitted in support of the EPA position organised by CEI in opposition to the ‘Scientists’ brief‘ that Scott was a party to.

Was there was a reply to CEI brief?

There was no formal venue for a reply, at least not before the court. The general consensus of those of us who discussed it was that the CEI brief was pretty poor anyway. For what it is worth, below are some comments I emailed to my colleagues after I reviewed the CEI brief, followed by comments by Dr. Curt Covey, whose work was cited in the CEI brief:

— begin quoted excerpts of my email —

Our climate scientist brief focused narrowly and conservatively on two questions: (1) whether the state of the science was accurately represented by the EPA and by the lower court, and (2) whether the science is sufficiently compelling to support a judgement that the legal standard for regulation is met (i.e., may greenhouse gas emissions “reasonably be anticipated to endanger public health or welfare”?)

A relevant claim that our scientists brief is wrong or misleading would therefore have to consist of an argument that either (1) the state of the science was in fact accurately characterized by the EPA or the Appeals Court, or (2) that in fact, greenhouse gas emissions may NOT be reasonably anticipated to endanger public health or welfare. The CEI brief does neither, so I suspect it will not have much relevance to the case at hand.

The CEI brief discusses a range of broad questions on which the Climate Scientist’s brief takes no position (e.g. whether the “net” effects of CO2 emissions “will” endanger public health or welfare, or what history would have been like if industrial development had taken a less CO2-intensive trajectory), and quibbles with technical details which have little or no effect on the answer to the overall question no matter how they are resolved (e.g. whether the NRC/NAS statement in 2001 that post-1950 ocean warming was 0.050C is meaningfully different from the Levins et al. 2005, more recent figure of 0.037C).

As far as the technical details, a quick survey convinces me there is not much there. Just to cite a few, taken more or less at random (I have not had time to look at all):

CO2 growth rates (CEI, p. 11): arguments about what growth rates for CO2 emissions that some models use are besides the point of what the science says about the climate sensitivity of the earth system (emissions growth rates are if anything an economic question). It is well-recognized that many of the original emissions scenarios in IPCC overstated the trajectories that were actually realized (indeed, this was a minor point made in the NRC/NAS 2001 report that was picked up on, and misunderstood or misrepresented, by the Appeals Court), but so what? Unless they are arguing that actual BAU emissions will be so low as to prevent CO2 from any further significant build up (or at least stay under a doubling), this is a detail entirely irrelevant to climate science, and almost entirely irrelevant to the question about “reasonable anticipation of endangerment”.

Hurricanes (CEI, p. 16). We barely mention this, as a parenthetical (not as a “prediction” but as a citation of IPCC TAR’s reference to “likely increases” in tropical storm intensities). I am surprised they went after this, with all the recent work showing that the evidence for this has only gotten stronger since 2001. Yes, there is still debate about whether it has reached canonical levels of statistical significance (95% confidence), and there are problems with data quality yet to be fully resolved, but the standard in the law is lower (“may reasonably anticipate” endangerment). Are they arguing, in the light of Emanual 2005, and Webster et al., 2005, that it would be entirely unreasonable to anticipate stronger hurricanes in the future? If not, what is the point?

Satellite and surface temp records (CEI p. 23). The main substantive thing we said with respect to this is that “all available data sets show that both the surface and the troposphere have warmed,” which the CEI brief criticizes. But the quote they criticize is not ours, it is from the U.S. CSSP (2006) re-assessment (the subtitle of which is “understanding and reconciling differences”). An author of the CSSP (and of the Executive Summary, from which our quote is taken) is John Christy, who is an amicus on the CEI brief. Is he arguing against himself? Perhaps he didn’t realize this CEI comment was in there when he signed on.

—- end Saleska quotes —-

With regard to the CO2 scenarios, the CEI brief cited a paper by Curt Covey. My colleague and co-amici David Battisti inquired of Dr. Covey if he had any comments about the way CEI cited his work, and he responded, saying we were free to circulate his comments. Here they are:

— begin quote of Covey email —-

Dear Prof. Battisti,

Part of my job here at LLNL is to accurately communicate the results of my work to scientific colleagues and the public. Accordingly, you should feel free to share the comments below.

Page 11 of the brief begins, “As shown below, computer models predicting future warming must overestimate warming, because they generally use an incorrect increase in carbon dioxide concentration of 1% per year.” It is not true that models “generally use” this rate of increase. Model
simulations of 20th century global warming typically use actual observed amounts of atmospheric carbon dioxide, together with other human (for example chloroflorocarbons or CFCs) and natural (solar brightness variations, volcanic eruptions, …) climate-forcing factors. Model simulations of future global warming use analogous input; of course it is not possible to observe the future, so a variety of scenarios involving possible atmospheric concentrations of carbon dioxide, etc., are employed. These range from stabilization of atmospheric carbon dioxide at twice its pre-industrial value by the end of this century (IPCC SRES B1) to continuously increasing atmospheric carbon dioxide at the rate of a bit less than 1% per year (IPCC SRES A2). Each climate model simulating the future is run several times, with several different scenarios. All of this has been standard practice in climate modeling for the past ten years.

Pages 11-12 quote my 2003 review paper correctly regarding idealized simulations in which atmospheric carbon dioxide is assumed to increase at the precise rate of 1% per year. Note that in the end of the quoted passage, I say that this rate of increase could “perhaps” be considered realistic “as an extreme case in which the world accelerates its consumption of fossil fuels while reducing its production of anthropogenic aerosols.” I’m no expert on scenarios, but from what I hear about China and India I wonder if the world is already on that track. In any case, the purpose of the 1%-per-year scenarios is to compare different models’ responses to identical input — not to produce realistic possibilities of future climate. For the latter purpose, climate model output from the IPCC SRES B1, A2 and other scenarios has been widely used for several years and has been publicly available for
over two years on my group’s Web site at http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php.

Finally it is not true, as implied on Page 12, that “sole reliance on models to the exclusion of observed behavior” is the basis of future climate prediction. As noted above, modern climate models are used to
retrospectively simulate the 20th century as well. Simulation of 20th century global warming is an important confidence-builder for climate models. Indeed, the observed warming during the 20th century cannot be explained other than by assuming that the models are reasonably accurate
in their response to greenhouse gases. This point was clearly made by the IPCC report published in 2001. Pages 12-13 ignore all this and instead use “a constant-rate warming” of 1.8 degrees C per century “based on actual observations.” A constant-rate (i.e. straight-line) extrapolation of global warming from the 20th to the 21st century, as in the brief’s Figure 2, is a favorite technique of one of the authors, Pat Michaels. This technique gives 21st century warming at the low end of the spectrum of possibilities resulting from the different model-input scenarios. It is one possible future, but it’s never been clear to me (or to anyone else I know besides Pat) why the other possibilities — all of which involve more global warming — should be ignored.

Sincerely,
Curt Covey

—- end of Covey email —

Hope that is helpful to you and other interested parties.

Best,
Scott