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Heat Rising at the Washington Post

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The Washington Post has published a second op-ed in as many days about global warming (“Spinning Global Warming”, By Robert D. Novak, Page A19, April 03, 2006–story is no longer available on the website, but the Chicago Sun Times version is available here). In this one, Novak claims that Hansen in 1988 over-predicted global warming by 400% (a story originated by Pat Michaels and subsequently propagated by Michael Crichton). This story is a fabrication that has already been set right by us in 2004.

Smearing Hansen, a leading climate scientist and member of the National Academy of Sciences, appears to have become sport among contrarian commentators (see our earlier discussions here and here). As ad hominem attacks and “shoot the messenger” strategies are often the last refuge for those losing the substantive debate, this might be viewed by some as a positive sign, indicative of just how intellectually bankrupt the contrarian movement has become.
[Read more…] about Heat Rising at the Washington Post

Significant Warming of the Antarctic Winter Troposphere

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The “iconic” Antarctic temperature trends are the large warming seen on the Antarctic Peninsula, which has had various repercussions including the collapse of several ice shelves (some documented in a previous post). Elsewhere, though, the pattern of surface warming is more complex – trends are smaller, and while more are positive than negative they are generally not significant – see this map. Contrary to what you might have heard, this is in general agreement with model predictions.

But meanwhile, there is a record for the upper atmosphere derived from radiosondes, which we have been working on – finding old datasets and digitising them to fill in gaps. What this shows is that around East Antarctica there is a general warming of the troposphere, greatest at around mid-height (at 600 hPa) at 0.7 ºC/decade over the last 30+ years.

In itself, this is an interesting observation. The obvious question is, what does it mean? Is this natural variability; is it a response to global warming, or to changes in ozone; or something else? Ozone is unlikely, because this is winter (which conveniently means that the radiosonde temperature corrections, often a source of potential trouble, are not a problem). Two ways of trying to interpret the record are to see what GCMs run for the same period show; or to look at the re-analyses (essentially, the archived outputs from the weather-prediction models). The latter, of course, incorporate many of the radiosonde observations that we are using, and so don’t count as independant. Despite this, the ECMWF re-analyses show *greater* trends than we see in the observations; and a maximum trend over West Antarctica (which has no radisonde stations to allow us to verify this). A climate model (HadCM3, with an ensemble of four members) shows similar patterns to the observations, but this time too little warming; and a good deal of variation between the ensemble members. So neither of these is helps much with the interpretation.

So we are currently left with an open question; hopefully, this will stimulate us and other researchers to explain it in the future.

[Quick addendum: the paper itself is available via this.]

Bush on “The Fundamental Debate”

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The President of the United States, George W. Bush, recently voiced his opinions on the science of climate change:

We — first of all, there is — the globe is warming. The fundamental debate: Is it manmade or natural. Put that aside.

The first part is the silver lining: despite receiving novelist Michael Crichton in the White House recently, Bush obviously has not bought his theory that the globe is in fact not warming. Crichton is one of the last trend sceptics who deny the warming trend is real.
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Good climate debate FAQ

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There are a number of topics in climate science that are frequently misunderstood or mis-characterised (often by those trying to ‘scientize’ their political opinions) that come up again and again in climate-related discussions. RealClimate tries to provide context on many of these issues, and commentaries on the 1970s ‘global cooling myth‘ or whether water vapour is a feedback or a forcing are among our most referenced pieces (see our FAQ category). However, our explanations of specific points have often appeared in the middle of a larger piece, or in the comment section and are not clearly referencable. Since many of these same points keep coming up in comments and discussions, having a clear and precise resource for these explanations would be very useful and we have thought about doing just that. But it now appears that we have been beaten to the punch by a new blog run by Coby Beck, a frequent commenter here and at sci.env. His new blog ‘A few things ill-considered‘ has a point-by-point rebuttal of almost all the most common ‘contrarian’ talking points. The list of topics by category is a good place to start, and it shows the huge amount of work done so far. We’re very impressed!

Cloudy outlook for albedo?

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Guest Commentary by George Tselioudis (NASA GISS)

In the past few years several attempts have been made to assess changes in the Earth’s planetary albedo, and claims of global dimming and more recently brightening have been debated in journal articles and blogs alike. In a recent article entitled “Can the Earth’s Albedo and Surface Temperatures Increase Together,” that appeared in EOS, Enric Palle and co-authors use recently released cloud data from the International Satellite Cloud Climatology Project (ISCCP) to explain how it is possible for the Earth to be warming even as it’s albedo is increasing. The need for an explanation arises from the author’s claim that the earth’s albedo has increased since the year 2000, an increase that was not followed by a decrease in surface temperature. They base this claim on Earthshine data (a measurement of the glow of the dark side of the moon that they use to deduce the earth’s reflectance) and on an albedo proxy derived from ISCCP parameters after they are regressed with two years of overlapping, but not global, earthshine observations. Subsequently they claim that the rising reflectance of the Earth has not led to a reversal of global warming because the difference between low and middle-plus-high ISCCP clouds has increased in the last four years. This they say implies that as the low-level, cooling clouds have decreased during the most recent years, the high-level, warming clouds have increased even more negating any potential cloud-induced cooling.

There are several issues connected to the use of earthshine data to calculate the earth’s albedo that have been discussed in peer-reviewed publications and that I will not discuss in this posting. I will say a few things, however, about the selective use of ISCCP data in this article to construct qualitative arguments that do not stand up to detailed quantitative analysis . [Read more…] about Cloudy outlook for albedo?

An Aerosol Tour de Forcing

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Guest commentary from Ron Miller and Dorothy Koch (NASA GISS)

Scientists have confidence in a result to the extent that it can be derived by different investigators. Their confidence is increased if different techniques lead to the same conclusion. Concurrence provides evidence that the conclusion does not depend upon assumptions that occasionally are insufficiently supported. In contrast, two articles published last December on the same day arrive at very different and incompatible estimates of the effect of human-made aerosols on the radiative budget of the planet (Bellouin et al., 2005; Chung et al., 2005). They follow an earlier estimate published last year, (which included Dorothy as a co-author) that was in the middle (Yu et al., 2005). Aerosols are important to climate partly because their concentration is increased by the same industrial processes that increase the atmospheric concentration of greenhouse gases; yet aerosols generally oppose greenhouse warming. Because aerosols cause respiratory and other health problems and acid rain, they have been regulated more aggressively than greenhouse gases. Concentrations of some aerosols have decreased over the United States and Europe in recent decades as a result of environmental laws, although an increase has been observed in many thrid world regions, where economic development is a priority. In the twenty-first century, aerosol levels are anticipated to drop faster than greenhouse gases in response to future emission reductions, which will leave greenhouse warming unopposed and unmoderated.

Each published calculation of aerosol radiative forcing was a tour de force for integrating a wide variety of measurements ranging from absorption of radiation by individual particles to satellite estimates of aerosol amount. The disparate results emphasize the complexity and difficulty of the calculation. But let’s start at the beginning…. [Read more…] about An Aerosol Tour de Forcing

Can 2°C warming be avoided?

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Translations: (Français)

Guest comment by Malte Meinshausen, Reto Knutti and Dave Frame

Yesterday’s BBC article on the “Avoiding Dangerous Climate Change” report of the Exeter meeting last year, carried two messages that have left some a little confused. On the one hand, it said that a stabilization of greenhouse gases at 400-450 ppm CO2-equivalent concentrations is required to keep global mean warming below 2°C, which in turn is assumed to be necessary to avoid ‘dangerous’ climate change. On the other hand, people are cited saying that “We’re going to be at 400 ppm in 10 years’ time”.

So given that we will exceed 400 ppm CO2 in the near future, is a target of 2°C feasible? To make a long story short: the answer is yes.
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Daily Kos interview

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A brief welcome to anyone coming over from Daily Kos today. Three of us (Mike, Gavin and Stefan) are interviewed by DarkSyde on climate change, this site and walking the line between science and politics. To find something specific, check out the Highlights on the side bar, the index, or use the search bar above.

New look

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Hopefully readers will appreciate the new look we have given the site (you may need to reload for it to work properly). We have added some new features attached to the buttons above – an index which may prove useful in navigating the site, a more prominent Search function (which searches posts and comments), a link to the archives etc. This has allowed us to reduce some of the clutter and hopefully make this site a little more user friendly. If there are any problems, wrinkles that need to be ironed out, or if you have suggestions for further improvement, let us know at contrib -at- realclimate -dot- org.

Polar Amplification

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Guest commentary by Cecilia Bitz, University of Washington

“Polar amplification” usually refers to greater climate change near the pole compared to the rest of the hemisphere or globe in response to a change in global climate forcing, such as the concentration of greenhouse gases (GHGs) or solar output (see e.g. Moritz et al 2002). Polar amplification is thought to result primarily from positive feedbacks from the retreat of ice and snow. There are a host of other lesser reasons that are associated with the atmospheric temperature profile at the poles, temperature dependence of global feedbacks, moisture transport, etc. Observations and models indicate that the equilibrium temperature change poleward of 70N or 70S can be a factor of two or more greater than the global average. [Read more…] about Polar Amplification