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13 Mar 2007
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
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.
12 Mar 2007
Swindled: Carl Wunsch responds
The following letter from Carl Wunsch is intended to clarify his views on global warming in general, and the The Great Global Warming Swindle which misrepresented them.
Partial Response to the London Channel 4 Film "The Global Warming Swindle"
Carl Wunsch 11 March 2007
believe that climate change is real, a major threat, and almost surely
has a major human-induced component. But I have tried to stay out of
the `climate wars' because all nuance tends to be lost, and the
distinction between what we know firmly, as scientists, and what we
suspect is happening, is so difficult to maintain in the presence of
rhetorical excess. In the long run, our credibility as scientists rests
on being very careful of, and protective of, our authority and
9 Mar 2007
By William and Gavin
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?
9 Mar 2007
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.
1 Mar 2007
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.
'Volcanoes emit more CO2 than humans'
(Part of the How to Talk to a Global Warming Skeptic
Objection: One decent-sized volcanic eruption puts more CO2 in the atmosphere than a decade
of human emissions. It's ridiculous to think reducing human CO2 emissions will have any
Answer: Not only is this false, it couldn't possibly
given the CO2 record from any of the dozens of sampling
around the globe.http://gristmill.grist.org/story/2006/12/17/223957/72
10 Nov 2006
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
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
In vino veritas (though not in this case).
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!
27 Oct 2006
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).
10 Oct 2006
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...?
12 Aug 2006
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.
16 May 2006
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...)
31 Mar 2006
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
5 Oct 2005
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.
22 Sep 2005
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.
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...)
3 Aug 2005
Did the Sun hit record highs over the last few decades?
Guest commentary by Raimund Muscheler
this is a restore (8/8/05) of an article from August 3, 2005 that was
accidentally deleted due to a technical glitch. Unfortunately, most of
the comments could not be retrieved. We sincerely apologize to our
The solar influence on climate is a controversial topic in climate research (see previous posts here
The irradiance changes are assumed to be relatively small and the
importance of potential amplifying mechanisms is still a matter of
current debate. One reason for these uncertainties is that there are
only approximately 25 years of satellite-based observations of the
solar irradiance. Sunspot observations for the last 400 years clearly
indicate that current levels of solar activity are very different from
the state of the sun during the Maunder minimum (from approx. 1645 to
1715 AD) where almost no sunspots could be observed.
15 Mar 2005
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.
15 Jul 2005
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.
6 Jul 2005
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.
14 Jan 2005
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.
10 Jan 2005
Senator Inhofe on Climate Change
by Michael Mann, Stefan Rahmstorf, Gavin Schmidt, Eric Steig, and William Connolley
Senator James Inhofe (R) of Oklahoma recently provided us with an update of his views on the issue of climate change in a speech given on the opening senate session, January 4, 2005. His speech opened with the statement:
As I said on the Senate floor on July 28, 2003, "much of the debate
over global warming is predicated on fear, rather than science." I
called the threat of catastrophic global warming the "greatest hoax
ever perpetrated on the American people," a statement that, to put it
mildly, was not viewed kindly by environmental extremists and their
Cutting through much of his polemic, Inhofe's
speech contains three lines of scientific argument which, according to
him, provide "compelling new scientific evidence" that anthropogenic
global warming is not threatening. We here submit his statements to
22 Dec 2004
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.
13 Dec 2004
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.
8 Dec 2004
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
4 Dec 2004
Myth vs. Fact Regarding the "Hockey Stick"
Numerous myths regarding the so-called "hockey stick"
reconstruction of past temperatures, can be found on various non-peer
reviewed websites, internet newsgroups and other non-scientific venues.
The most widespread of these myths are debunked below:
4 Dec 2004
Temperature Variations in Past Centuries and the so-called "Hockey Stick"
Instrumental data describing large-scale surface temperature changes
are only available for roughly the past 150 years. Estimates of surface
temperature changes further back in time must therefore make use of the
few long available instrumental records or historical documents and
natural archives or 'climate proxy'
indicators, such as tree rings, corals, ice cores and lake sediments,
and historical documents to reconstruct patterns of past surface
temperature change. Due to the paucity of data in the Southern
Hemisphere, recent studies have emphasized the reconstruction of
Northern Hemisphere (NH) mean, rather than global mean temperatures
over roughly the past 1000 years.
3 Dec 2004
What does the lag of CO2 behind temperature in ice cores tell us about global warming?
is an issue that is often misunderstood in the public sphere and media,
so it is worth spending some time to explain it and clarify it. At
least three careful ice core studies have shown that CO2
starts to rise about 800 years (600-1000 years) after Antarctic
temperature during glacial terminations. These terminations are
pronounced warming periods that mark the ends of the ice ages that
happen every 100,000 years or so. http://www.realclimate.org/index.php/archives/2004/12/co2-in-ice-cores/
28 Nov 2004
Medieval Warm Period ("MWP")
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