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1 February 2009

Irreversible Does Not Mean Unstoppable

Filed under: — david @ 9:50 AM

Susan Solomon, ozone hole luminary and Nobel Prize winning chair of IPCC, and her colleagues, have just published a paper entitled “Irreversible climate change because of carbon dioxide emissions” in the Proceedings of the National Academy of Sciences. We at realclimate have been getting a lot of calls from journalists about this paper, and some of them seem to have gone all doomsday on us. Dennis Avery and Fred Singer used the word Unstoppable as a battle flag a few years ago, over the argument that the observed warming is natural and therefore there is nothing that humanity can do to alter its course. So in terms of its intended rhetorical association, Unstoppable = Burn Baby Burn. But let’s not confuse Irreversible with Unstoppable. One means no turning back, while the other means no slowing down. They are very different words. Despair not!


31 January 2009

A global glacier index update

Filed under: — group @ 8:59 AM

Guest commentary by Mauri Pelto

For global temperature time series we have GISTEMP, NCDC and HadCRUT. Each has worked hard to assimilate global temperature data into reliable and accurate indices of global temperature. The equivalent for alpine glaciers is the World Glacier Monitoring Service’s (WGMS) record of mass balance and terminus behavior. Beginning in 1986, WGMS began to maintain and publish the collection of information on ongoing glacier changes that had begun in 1960 with the Permanent Service on Fluctuations of glaciers. This program in the last 10 years has striven to acquire, publish and verify glacier terminus and mass balance measurement data from alpine glaciers the world over on a timely basis. Spearheaded by Wlfried Haeberli with assistance from Isabelle Roer, Michael Zemp, Martin Hoelzle, at the University of Zurich, their efforts have resulted in the recent publication, “Global Glacier Changes: facts and figures” published jointly with UNEP. This publication summarizes the information collected and submitted by the national correspondents of WGMS portraying the global response of glaciers to climate change, as well as the regional response.

27 January 2009

Warm reception to Antarctic warming story

Filed under: — gavin @ 11:15 PM

What determines how much coverage a climate study gets?

It probably goes without saying that it isn't strongly related to the quality of the actual science, nor to the clarity of the writing. Appearing in one of the top journals does help (Nature, Science, PNAS and occasionally GRL), though that in itself is no guarantee. Instead, it most often depends on the 'news' value of the bottom line. Journalists and editors like stories that surprise, that give something 'new' to the subject and are therefore likely to be interesting enough to readers to make them read past the headline. It particularly helps if a new study runs counter to some generally perceived notion (whether that is rooted in fact or not). In such cases, the 'news peg' is clear.

And so it was for the Steig et al "Antarctic warming" study that appeared last week. Mainstream media coverage was widespread and generally did a good job of covering the essentials. The most prevalent peg was the fact that the study appeared to reverse the "Antarctic cooling" meme that has been a staple of disinformation efforts for a while now.

26 January 2009

Sea will rise ‘to levels of last Ice Age’

Filed under: — stefan @ 10:19 AM

cogee beachThe British tabloid Daily Mirror recently headlined that “Sea will rise 'to levels of last Ice Age'”. No doubt many of our readers will appreciate just how scary this prospect is: sea level during the last Ice Age was up to 120 meters lower than today. Our favourite swimming beaches – be it Coogee in Sydney or the Darß on the German Baltic coast – would then all be high and dry, and ports like Rotterdam or Tokyo would be far from the sea. Imagine it.

24 January 2009

Reindeer herding, indigenous people and climate change

Filed under: — rasmus @ 5:40 AM

Lavo The Sámi are keenly aware about climate change, and are thus concerned about their future. Hence, the existence of the International Polar Year (IPY) project called EALÁT involving scientists, Sámi from Norway/Sweden/Finland, as well as Nenets from Russia. The indigenous people in the Arctic are closely tuned to the weather and the climate. I was told that the Sámi have about 300 words for snow, each with a very precise meaning.


21 January 2009

State of Antarctica: red or blue?

A couple of us (Eric and Mike) are co-authors on a paper coming out in Nature this week (Jan. 22, 09). We have already seen misleading interpretations of our results in the popular press and the blogosphere, and so we thought we would nip such speculation in the bud.

The paper shows that Antarctica has been warming for the last 50 years, and that it has been warming especially in West Antarctica (see the figure). The results are based on a statistical blending of satellite data and temperature data from weather stations. The results don't depend on the statistics alone. They are backed up by independent data from automatic weather stations, as shown in our paper as well as in updated work by Bromwich, Monaghan and others (see their AGU abstract, here), whose earlier work in JGR was taken as contradicting ours. There is also a paper in press in Climate Dynamics (Goosse et al.) that uses a GCM with data assimilation (and without the satellite data we use) and gets the same result. Furthermore, speculation that our results somehow simply reflect changes in the near-surface inversion is ruled out by completely independent results showing that significant warming in West Antarctica extends well into the troposphere. And finally, our results have already been validated by borehole thermometery — a completely independent method — at at least one site in West Antarctica (Barrett et al. report the same rate of warming as we do, but going back to 1930 rather than 1957; see the paper in press in GRL).

Here are some important things the paper does NOT show:

1) Our results do not contradict earlier studies suggesting that some regions of Antarctica have cooled. Why? Because those studies were based on shorter records (20-30 years, not 50 years) and because the cooling is limited to the East Antarctic. Our results show this too, as is readily apparent by comparing our results for the full 50 years (1957-2006) with those for 1969-2000 (the dates used in various previous studies), below.

2) Our results do not necessarily contradict the generally-accepted interpretation of recent East Antarctic cooling put forth by David Thompson (Colorado State) and Susan Solomon (NOAA Aeronomy Lab). In an important paper in Science, they presented evidence that this cooling trend is linked to an increasing trend in the strength of the circumpolar westerlies, and that this can be traced to changes in the stratosphere, mostly due to photochemical ozone losses. Substantial ozone losses did not occur until the late 1970s, and it is only after this period that significant cooling begins in East Antarctica.

3) Our paper — by itself — does not address whether Antarctica's recent warming is part of a longer term trend. There is separate evidence from ice cores that Antarctica has been warming for most of the 20th century, but this is complicated by the strong influence of El Niño events in West Antarctica. In our own published work to date (Schneider and Steig, PNAS), we find that the 1940s [edit for clarity: the 1935-1945 decade] were the warmest decade of the 20th century in West Antarctica, due to an exceptionally large warming of the tropical Pacific at that time.

So what do our results show? Essentially, that the big picture of Antarctic climate change in the latter part of the 20th century has been largely overlooked. It is well known that it has been warming on the Antarctic Peninsula, probably for the last 100 years (measurements begin at the sub-Antarctic Island of Orcadas in 1901 and show a nearly monotonic warming trend). And yes, East Antarctica cooled over the 1980s and 1990s (though not, in our results, at a statistically significant rate). But West Antarctica, which no one really has paid much attention to (as far as temperature changes are concerned), has been warming rapidly for at least the last 50 years.

Why West Antarctica is warming is just beginning to be explored, but in our paper we argue that it basically has to do enhanced meridional flow — there is more warm air reaching West Antarctica from farther north (that is, from warmer, lower latitudes). In the parlance of statistical climatology, the "zonal wave 3 pattern" has increased (see Raphael, GRL 2004). Something that goes along with this change in atmospheric circulation is reduced sea ice in the region (while sea ice in Antarctica has been increasing on average, there have been significant declines off the West Antarctic coast for the last 25 years, and probably longer). And in fact this is self reinforcing (less sea ice, warmer water, rising air, lower pressure, enhanced storminess).

The obvious question, of course, is whether those changes in circulation are themselves simply "natural variability" or whether they are forced — that is, resulting from changes in greenhouse gases. There will no doubt be a flurry of papers that follow ours, to address that very question. A recent paper in Nature Geosciences by Gillet et al. examined trends in temperatures in the both Antarctic and the Arctic, and concluded that "temperature changes in both … regions can be attributed to human activity." Unfortunately our results weren't available in time to be made use of in that paper. But we suspect it will be straightforward to do an update of that work that does incorporate our results, and we look forward to seeing that happen.

Some comment is warranted on whether our results have bearing on the various model projections of future climate change. As we discuss in the paper, fully-coupled ocean-atmosphere models don't tend to agree with one another very well in the Antarctic. They all show an overall warming trend, but they differ significantly in the spatial structure. As nicely summarized in a paper by Connolley and Bracegirdle in GRL, the models also vary greatly in their sea ice distributions, and this is clearly related to the temperature distributions. These differences aren't necessarily because there is anything wrong with the model physics (though schemes for handling sea ice do vary quite a bit model to model, and certainly are better in some models than in others), but rather because small differences in the wind fields between models results in quite large differences in the sea ice and air temperature patterns. That means that a sensible projection of future Antarctic temperature change — at anything smaller than the continental scale — can only be based on looking at the mean and variation of ensemble runs, and/or the averages of many models. As it happens, the average of the 19 models in AR4 is similar to our results — showing significant warming in West Antarctica over the last several decades (see Connolley and Bracegirdle's Figure 1).

14 January 2009

CNN is spun right round, baby, right round

With the axing of the CNN Science News team, most science stories at CNN are now being given to general assignment reporters who don't necessarily have the background to know when they are being taken for a ride. On the Lou Dobbs show (an evening news program on cable for those of you not in the US), the last few weeks have brought a series of embarrassing non-stories on 'global cooling' based it seems on a few cold snaps this winter, the fact that we are at a solar minimum and a regurgitation of 1970s vintage interpretations of Milankovitch theory (via Pravda of all places!). Combine that with a few hysterical (in both senses) non-scientists as talking heads and you end up with a repeat of the nonsensical 'Cooling world' media stories that were misleading in the 1970s and are just as misleading now.

Exhibit A. Last night's (13 Jan 2009) transcript (annotations in italics).

12 January 2009

Communicating the Science of Climate Change

It is perhaps self-evident that those of us here at RealClimate have a keen interest in the topic of science communication. A number of us have written books aimed at communicating the science to the lay public, and have participated in forums devoted to the topic of science communication (see e.g. here, here, and here). We have often written here about the challenges of communicating science to the public in the modern media environment (see e.g. here, here, and here).

It is naturally our pleasure, in this vein, to bring to the attention of our readers a masterful new book on this topic by veteran environmental journalist and journalism educator Bud Ward. The book, entitled Communicating on Climate Change: An Essential Resource for Journalists, Scientists, and Educators, details the lessons learned in a series of Metcalf Institute workshops held over the past few years, funded by the National Science Foundation, and co-organized by Ward and AMS senior science and communications fellow Tony Socci. These workshops have collectively brought together numerous leading members of the environmental journalism and climate science communities in an effort to develop recommendations that might help bridge the cultural divide between these two communities that sometimes impedes accurate and effective science communication.

I had the privilege of participating in a couple of the workshops, including the inaugural workshop in Rhode Island in November 2003. The discussions emerging from these workshops were, at least in part, the inspiration behind "RealClimate". The workshops formed the foundation for this new book, which is an appropriate resource for scientists, journalists, editors, and others interested in science communication and popularization. In addition to instructive chapters such as "Science for Journalism", "Journalism for Scientists" and "What Institutions Can Do", the book is interspersed with a number of insightful essays by leading scientists (e.g. "Mediarology–The Role of Climate Scientists in Debunking Climate Change Myths" by Stephen Schneider) and environmental journalists (e.g. "Hot Words" by Andy Revkin). We hope this book will serve as a standard reference for how to effectively communicate the science of climate change.

7 January 2009

The Younger Dryas comet-impact hypothesis: gem of an idea or fool’s gold?

There was a paper in Science last week that has gotten quite a bit of press. It reports further evidence in support of the idea that the Younger Dryas — a distinct period towards the end of the last ice age when the deglaciation in the Northern Hemisphere was interrupted for a period of about 1300 years — was caused by a barrage of comets hitting North America.

When the first papers on this came out last year, we expressed skepticism. We remain skeptical and our reasons remain unchanged. But we think it is worth saying a bit more on this, because the reporting on this issue has largely ignored just how big an idea this is, and therefore how much more work would need to be done before it could be taken very seriously.

6 January 2009

FAQ on climate models: Part II

Filed under: — gavin @ 8:09 AM

This is a continuation of a previous post including interesting questions from the comments.

More Questions

  • What are parameterisations?

    Some physics in the real world, that is necessary for a climate model to work, is only known empirically. Or perhaps the theory only really applies at scales much smaller than the model grid size. This physics needs to be 'parameterised' i.e. a formulation is used that captures the phenomenology of the process and its sensitivity to change but without going into all of the very small scale details. These parameterisations are approximations to the phenomena that we wish to model, but which work at the scales the models actually resolve. A simple example is the radiation code - instead of using a line-by-line code which would resolve the absorption at over 10,000 individual wavelengths, a GCM generally uses a broad-band approximation (with 30 to 50 bands) which gives very close to the same results as a full calculation. Another example is the formula for the evaporation from the ocean as a function of the large-scale humidity, temperature and wind-speed. This is really a highly turbulent phenomena, but there are good approximations that give the net evaporation as a function of the large scale ('bulk') conditions. In some parameterisations, the functional form is reasonably well known, but the values of specific coefficients might not be. In these cases, the parameterisations are 'tuned' to reproduce the observed processes as much as possible.


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