Michael Mann and Gavin Schmidt

[update 3/20/07: The New York Times has run a short letter from us w/ a link to RealClimate for more info (scroll down to 5th letter; the 2nd letter from James McCarthy of Harvard is quite good too, as are some of the others).]

The first rule when criticizing popular science presentations for inaccuracies should be to double check any 'facts' you use. It is rather ironic then that William Broad's latest piece on Al Gore plays just as loose with them as he accuses Gore of doing.

We criticized William Broad previously (Broadly Misleading) for a piece that misrepresented the scientific understanding of the factors that drive climate change over millions of years, systematically understating the scientifically-established role of greenhouse gases, and over-stating the role of natural factors including those as speculative as cosmic rays (see our recent discussion here). In this piece, Broad attempts to discredit Gore's "An Inconvenient Truth" by exaggerating the legitimate, but minor, criticisms of his treatment of the science by experts on climate science, and presenting specious or unsubstantiated criticisms by a small number of the usual, well-known contrarians who wouldn't agree even if Gore read aloud from the latest IPCC report.
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By William and Gavin

On Thursday March 8th, the UK TV Channel 4 aired a programme titled "The Great Global Warming Swindle". We were hoping for important revelations and final proof that we have all been hornswoggled by the climate Illuminati, but it just repeated the usual specious claims we hear all the time. We feel swindled. Indeed we are not the only ones: Carl Wunsch (who was a surprise addition to the cast) was apparently misled into thinking this was going to be a balanced look at the issues (the producers have a history of doing this), but who found himself put into a very different context indeed [Update: a full letter from Wunsch appears as comment 109 on this post]

So what did they have to say for themselves?
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In a recent issue of the journal Astronomy and Geophysics (A&G), Henrik Svensmark coined a new term: 'cosmoclimatology' . I think 'cosmoclimatology' is a good and refreshing name for anything combining our cosmos with our climate. However, all other aspects of the article I found very disappointing. We have already covered most of these topics before, but the A&G articles provides us with some new aspects to discuss. Furthermore, Svensmark is the Director for Center for Sun-Climate Research, Danish National Space Center, and therefore influential. He is also the co-author of a recent book with Nigel Calder that received some attention. Furthermore, a laboratory experiment of his also managed to make some headlines. It seems that solar forcing is one of the sceptics' last trenches in the debate about climate change. In my view the A&G paper therefore merits a comment as long as the same old and worn arguments resurface without discussing misgivings from the critics.

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The big problem with much of the discussions about trends in hurricane activity is that the databases that everyone is working from are known to have significant inhomogeneities due to changes in observing practice and technology over the years. So it's not surprising that a new re-analysis (Kossin et al, published yesterday) has been generating significant interest and controversy among the hurricane research community (see e.g. Prometheus or Chris Mooney). However, rather than this study being taken for what it is - a preliminary and useful attempt to make homogeneous a part of the data (1983 to 2005) - it is unfortunately being treated as if it was the definitive last word. We've often made the point that single papers are not generally the breakthroughs that are sometimes implied in press releases or commentary sites and this case is a good example of that.
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Readers may recall a thorough examination of the history of English wine here a few months ago - chiefly because the subject tends to come up as a contrarian climate talking point every now and again. The bottom line from that post was that the English wine industry is currently thriving and has a geographical extent and quality levels that are unprecedented in recorded history. So whether vineyards are a good proxy for climate or not, you certainly can't use the supposed lack of present day English vineyards in any serious discussion about climate....

So along comes this quote today (promoting Fred Singer's latest turnaround) (my emphasis):

"The Romans wrote about growing wine grapes in Britain in the first century," says Avery, "and then it got too cold during the Dark Ages. Ancient tax records show the Britons grew their own wine grapes in the 11th century, during the Medieval Warming, and then it got too cold during the Little Ice Age. It isn't yet warm enough for wine grapes in today's Britain. Wine grapes are among the most accurate and sensitive indicators of temperature and they are telling us about a cycle. They also indicate that today's warming is not unprecedented."

Hmmm.... so where did that bottle of Chapel Down in my fridge come from? (thanks Dad!) Or the winners of the 'Best Sparkling Wine' for the last two years at the International Wine and Spirit Competition? This is of course a trivial point, but it demonstrates (once again) that our contrarian friends don't even have a semblence of a desire to get it right. The lure of a talking point clearly trumps the desire for accuracy.

In vino veritas (though not in this case).

Update: We had the Chapel Down Flint Dry last night. Fruity, hints of apple and pear and one of better whites I've had in a while. Highly recommended!

The ice age is coming, the sun’s zooming in / Engines stop running and the wheat is growing thin /A nuclear error, but I have no fear /’Cause London is drowning, and I live by the river (chorus from Londons Calling, by Strummer/Jones, 1979).

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In an earlier post, we discussed a review article by Frohlich et al. on solar activity and its relationship with our climate. We thought that paper was quite sound. This September saw a new article in the Geophysical Research Letters with the title «Phenomenological solar signature in 400 years of reconstructed Northern Hemisphere temperature record» by Scafetta & West (henceforth referred to as SW). This article has now been cited by US Senator James Inhofe in a senate hearing that took place on 25 September 2006 . SW find that solar forcing accounts for ~50% of 20C warming, but this conclusion relies on some rather primitive correlations and is sensitive to assumptions (see recent post by Gavin on attribution). We said before that peer review is a necessary but not sufficient condition. So what wrong with it...?

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Sometimes, I encounter arguments suggesting that since we cannot predict the weather beyond a couple of weeks, then it must be impossible to predict the climate in 100 years. Such statements tend to present themselves as a kind of revelation, often in social settings and parties after I have revealed for some of the guests that I'm a climatologist (if I say I work for the Meteorological Institute, I almost always get the question "so, what's the weather going to be like tomorrow?"). Such occasions also tend to be times when I'm not too inclined to indulge in deep scientific or technical explanations. Or when talking to a journalist who wants an easy answer. In those cases I try to provide a short and simple, but convincing, explanation that is easy for most people to understand why climate can be predicted despite the chaotic nature of the weather (a more theoretical discussion is provided in the earlier post Chaos and Climate). One approach is to try to relate the topic to something with which they are familiar, such as to point to empirical observations which most accept (I suppose with hindsight it could be similar to the researchers in the early 20th century trying to convince that nuclear reactions were possible - just look at the Sun, and there is the proof! Or before that, the debate about whether atoms were real or not - just look at the blue sky, and you look at the proof...). I like to emphasised the words 'weather' and 'climate' above, because they mean different things.

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There has been a lot in the news recently about current volcanic activity - Merapi in Indonesia and Bezymianny in the Kamchatka peninsula in Russia, but while most reports have focussed on the very real dangers to the local populace and air traffic, volcanoes can have important impacts on climate as well. However, there are a number of conditions that need to be fulfilled before an eruption will show up in the climate record. (more...)

In a recent paper in Geophysical Research Letters, Scafetta & West (S&W) estimate that as much as 25-35% of the global warming in the 1980-2000 period can be attributed changes in the solar output. They used some crude estimates of 'climate sensitivity' and estimates of Total Solar Irradiance (TSI) to calculate temperature signal (in form of anomalies). They also argue that their estimate, which is based on statistical models only, has a major advantage over physically based considerations (theoretical models), because the latter would require a perfect knowledge about the underlying physical and chemical mechanisms.

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Guest contribution by Steinn Sigurdsson.

Recently, there have been some suggestions that "global warming" has been observed on Mars (e.g. here). These are based on observations of regional change around the South Polar Cap, but seem to have been extended into a "global" change, and used by some to infer an external common mechanism for global warming on Earth and Mars (e.g. here and here). But this is incorrect reasoning and based on faulty understanding of the data.

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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? (more...)

Guest commentary from David Archer (U. Chicago)

The notion is pervasive in the popular and scientific literature that the lifetime of anthropogenic CO₂ released to the atmosphere is some fuzzy number measured most conveniently in decades or centuries. The reality is that the CO₂ from a gallon out of every tank of gas will continue to affect climate for tens and even hundreds of thousands of years into the future.

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It's obvious.

The sun provides 99.998% of the energy to the Earth's climate (the rest coming from geothermal heat sources). The circulation patterns of the tropical Hadley Cell, the mid latitude storm tracks the polar high and the resulting climate zones are all driven by the gradients of solar heating as a function of latitude. So of course any significant change to solar output is bound to affect the climate, it stands to reason! Since we can see that there are changes in solar activity, it's therefore just a question of finding the link. Researchers for over a century have therefore taken any climate records they can find and searched for correlations to the sunspots, the solar-cycle length, geomagnetic indices, cosmogenic isotopes or smoothed versions thereof (and there are many ways to do the smoothing, and you don't even need to confine yourself to one single method per record). At the same time, estimates of solar output in the past are extremely uncertain, and so there is a great deal of scope in blaming any unexplained phenomena on solar changes without fear of contradiction.

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In a new review paper in Nature this week, Andreae, Jones and Cox expand on the idea that uncertainty in climate sensitivity is directly related to uncertainty in present day aerosol forcing (see also this New Scientist commentary). This was discussed here a couple of months back in the Global Dimming and the climateprediction.net posts, and so it is worth revisiting the question in the light of their analysis.

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Every now and again, the myth that "we shouldn't believe global warming predictions now, because in the 1970's they were predicting an ice age and/or cooling" surfaces. Recently, George Will mentioned it in his column (see Will-full ignorance) and the egregious Crichton manages to say "in the 1970's all the climate scientists believed an ice age was coming" (see Michael Crichton’s State of Confusion ). You can find it in various other places too [here, mildly here, etc]. But its not an argument used by respectable and knowledgeable skeptics, because it crumbles under analysis. That doesn't stop it repeatedly cropping up in newsgroups though.

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Note:This is an update to an earlier post, which many found to be too technical. The original, and a series of comments on it, can be found here. See also a more recent post here for an even less technical discussion.

Over the last 150 years, carbon dioxide (CO₂) concentrations have risen from 280 to nearly 380 parts per million (ppm). The fact that this is due virtually entirely to human activities is so well established that one rarely sees it questioned. Yet it is quite reasonable to ask how we know this.

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In a departure from normal practice on this site, this post is a commentary on a piece of out-and-out fiction (unlike most of the other posts which deal with a more subtle kind). Michael Crichton's new novel "State of Fear" is about a self-important NGO hyping the science of the global warming to further the ends of evil eco-terrorists. The inevitable conclusion of the book is that global warming is a non-problem. A lesson for our times maybe? Unfortunately, I think not.

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This is one of a number of popular myths regarding temperature variations in past centuries. At hemispheric or global scales, surface temperatures are believed to have followed the "Hockey Stick" pattern, characterized by a long-term cooling trend from the so-called "Medieval Warm Period" (broadly speaking, the 10th-mid 14th centuries) through the "Little Ice Age" (broadly speaking, the mid 15th-19th centuries), followed by a rapid warming during the 20th century that culminates in anomalous late 20th century warmth. The late 20th century warmth, at hemispheric or global scales, appears, from a number of recent peer-reviewed studies, to exceed the peak warmth of the "Medieval Warm Period". Claims that global average temperatures during Medieval times were warmer than present-day are based on a number of false premises that a) confuse past evidence of drought/precipitation with temperature evidence, b) fail to distinguish regional from global-scale temperature variations, and c) use the entire "20th century" to describe "modern" conditions , fail to differentiate between relatively cool early 20th century conditions and the anomalously warm late 20th century conditions.

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Period of relative warmth in some regions of the Northern Hemisphere in comparison with the subsequent several centuries. Also referred to as the Medieval Warm Epoch (MWE). As with the 'Little Ice Age'(LIA) no well-defined precise date range exists. The dates A.D. 900–1300 cover most ranges generally used in the literature. Origin is difficult to track down, but it is believed to have been first used in the 1960s (probably by Lamb in 1965). As with the LIA, the attribution of the term at regional scales is complicated by significant regional variations in temperature changes, and the utility of the term in describing regional climate changes in past centuries has been questioned in the literature. As with the LIA, numerous myths can still be found in the literature with regard to the details of this climate period. These include the citation of the cultivation of vines in Medieval England, and the settlement of Iceland and southwestern Greenland about 1000 years ago, as evidence of unusual warmth at this time. As noted by Jones and Mann (2004) [Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002, doi: 10.1029/2003RG000143, 2004], arguments that such evidence supports anomalous global warmth during this time period is based on faulty logic and/or misinterpretations of the available evidence.