RealClimate

9 Dec 2004

Welcome to RealClimate

Filed under: — group @ 9:00 pm

Climate science is one of those fields where anyone, regardless of their lack of expertise or understanding, feels qualified to comment on new papers and ongoing controversies. This can be frustrating for scientists like ourselves who see agenda-driven ‘commentary’ on the Internet and in the opinion columns of newspapers crowding out careful analysis.

Many scientists participate in efforts to educate the public and to rebut or debunk rather fanciful claims or outright mis-representations by writing in popular magazines such as EOS and New Scientist or in the Comments section of journals. However, this takes time to put together, and by the time it’s out, mainstream attention has often moved elsewhere. Since these rebuttals appear in the peer-reviewed literature, these efforts (in the long run) are useful. However, a faster response would sometimes be helpful in ensuring that the context of breaking stories is more widely distributed at the time.

Journalists with deadlines and scant knowledge of the field quite often do not know where to go for this context on papers that are being pushed by some of the partisan think-tanks or other interested parties. This can lead to some quite mainstream outlets inadvertently publishing some very dubious and misleading ideas.

RealClimate is a commentary site on climate science by working climate scientists for the interested public and journalists. We aim to provide a quick response to developing stories and provide the context sometimes missing in mainstream commentary.

In order to limit the scope to those issues where we can claim some competence, the discussion here is restricted to scientific topics. Thus we will not get involved in political or economic issues that arise when discussing climate change. The validity of scientific information is completely independent of what society decides to do (or not) about that information. Constructive comments and questions are welcome, as are guest articles from other scientists who may choose to contribute on an occasional basis.


8 Dec 2004

Are Temperature Trends affected by Economic Activity?

Filed under: — rasmus @ 8:14 am

In a recent paper, McKitrick and Michaels (2004) bring up an important question regarding whether eco­nomic activity and other non-climatic conditions may affect the estimate of true tem­perature trends derived from a climate station network. They proposed that local temperature trends may be linked to various economic factors, such as national coal consumption, income per capita, GPD growth rate, literacy rates, and whether or not temperature stations were located within the former Soviet Union. McKitrick and Michaels focussed on land observations and did not investigate the issue of whether or not clear warming trends in sea surface temperatures are consistent with their hypotheses. An important question they might have addressed would be: How can there be a general warming of the sea surface while the surface warming is only local and due to economic activity?

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7 Dec 2004

Why does the stratosphere cool when the troposphere warms?

Filed under: — gavin @ 11:21 am

Recent discussions of climate change (MSU Temperature Record, ACIA) have highlighted the fact that the stratosphere is cooling while the lower atmosphere (troposphere) and surface appear to be warming. The stratosphere lies roughly 12 to 50 km above the surface and is marked by a temperature profile that increases with height. This is due to the absorbtion by ozone of the sun’s UV radiation and is in sharp contrast to the lower atmosphere. There it generally gets colder as you go higher due to the expansion of gases as the pressure decreases. Technically, the stratosphere has a negative ‘lapse rate’ (temperature increases with height), while the lower atmosphere’s lapse rate is positive.

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6 Dec 2004

The Surface Temperature Record and the Urban Heat Island

Filed under: — william @ 6:33 pm

There are quite a few reasons to believe that the surface temperature record - which shows a warming of approximately 0.6°-0.8°C over the last century (depending on precisely how the warming trend is defined) - is essentially uncontaminated by the effects of urban growth and the Urban Heat Island (UHI) effect. These include that the land, borehole and marine records substantially agree; and the fact that there is little difference between the long-term (1880 to 1998) rural (0.70°C/century) and full set of station temperature trends (actually less at 0.65°C/century). This and other information lead the IPCC to conclude that the UHI effect makes at most a contribution of 0.05°C to the warming observed over the past century.

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Recent Warming But No Trend in Galactic Cosmic Rays

Filed under: — rasmus @ 8:14 am

There is little evidence for a connection between solar activity (as inferred from trends in galactic cosmic rays) and recent global warming.
Since the paper by Friis-Christensen and Lassen (1991), there has been an enhanced controversy about the role of solar activity for earth’s climate. Svensmark (1998) later proposed that changes in the inter-planetary magnetic fields (IMF) resulting from variations on the sun can affect the climate through galactic cosmic rays (GCR) by modulating earth’s cloud cover. Svensmark and others have also argued that recent global warming has been a result of solar activity and reduced cloud cover. Damon and Laut have criticized their hypothesis and argue that the work by both Friis-Christensen and Lassen and Svensmark contain serious flaws. For one thing, it is clear that the GCR does not contain any clear and significant long-term trend (e.g. Fig. 1, but also in papers by Svensmark).

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5 Dec 2004

The Arctic Climate Impact Assessment

Filed under: — stefan @ 8:23 pm

In early November 2004 the results of the Arctic Climate Impact Assessment (ACIA) were published, a uniquely detailed regional study compiled by 300 scientists over 3 years. The study describes the ongoing climate change in the Arctic and its consequences: rising temperatures, loss of sea ice, unprecedented melting of the Greenland ice sheet, and many impacts on ecosystems, animals and people. The ACIA is the first comprehensively researched, fully referenced, and independently reviewed evaluation of arctic climate change and its impacts for the region and for the world.

Sadly, in recent years we have become accustomed to a ritual in which the publication of each new result on anthropogenic climate change is greeted by a flurry of activity from industry-funded lobby groups, think tanks and PR professionals, who try to discredit the science and confuse the public about global warming.

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The Arctic Climate Impact Assessment II

Filed under: — gavin @ 12:11 pm

Another apparent ‘refutation’ appears in a CNS news story (a right-wing internet news service). The piece is predominantly an interview with Pat Michaels and other less prominent skeptics. We take their scientific points one at a time:

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The Arctic Climate Impact Assessment III

Filed under: — gavin @ 11:32 am

Does the ACIA overstate the problem of ozone depletion? The overview report states that the “stratospheric ozone layer over the Arctic is not expected to improve significantly for at least a few decades". This is partly because CFC concentrations (that enhance stratospheric ozone destruction) are only expected to decrease slowly as a function of restrictions imposed by the Montreal Protocol and subsequent amendments. Another factor is the fact that stratospheric temperatures are generally cooling as greenhouse gases increase (see MSU Temperature Record, also Why does the stratosphere cool when the troposphere warms?). Due to the temperature dependence on the rates of chemical reactions involving ozone, cooler temperatures also lead to more ozone destruction. Stratospheric temperatures, particularly near the pole are also significantly influenced by dynamical changes, and in particular, the strength of the polar vortex that is set up every winter at the edge of the polar night. Note as well that the strength of the vortex itself depends on the temperatures, which in turn (more…)


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.
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Myth vs. Fact Regarding the "Hockey Stick"

Filed under: — mike @ 5:15 pm

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:

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False Claims by McIntyre and McKitrick regarding the Mann et al. (1998) reconstruction

Filed under: — mike @ 4:03 pm

A number of spurious criticisms regarding the Mann et al (1998) proxy-based temperature reconstruction have been made by two individuals McIntyre and McKitrick ( McIntyre works in the mining industry, while McKitrick is an economist). These criticisms are contained in two manuscripts (McIntyre and McKitrick 2003 and 2004–the latter manuscript was rejected by Nature; both are collectively henceforth referred to as “MM"). MM claim that the main features of the Mann et al (1998–henceforth MBH98) reconstruction, including the “hockey stick” shape of the reconstruction, are artifacts of a) the centering convention used by MBH98 in their Principal Components Analysis (PCA) of the North American International Tree Ring Data Bank (’ITRDB’) data, b) the use of 4 infilled missing annual values (AD 1400-1403) in one tree-ring series (the ‘St. Anne’ Northern Treeline series), and c) the infilling of missing values in some proxy data between 1972 and 1980. Each of these claims are demonstrated to be false below.

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3 Dec 2004

Antarctic cooling, global warming?

Filed under: — gavin @ 9:17 pm

by Eric Steig and Gavin Schmidt
Long term temperature data from the Southern Hemisphere are hard to find, and by the time you get to the Antarctic continent, the data are extremely sparse. Nonetheless, some patterns do emerge from the limited data available. The Antarctic Peninsula, site of the now-defunct Larsen-B ice shelf, has warmed substantially. On the other hand, the few stations on the continent and in the interior appear to have cooled slightly (Doran et al, 2002; GISTEMP). At first glance this seems to contradict the idea of “global” warming, but one needs to be careful before jumping to this conclusion.

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What does the lag of CO2 behind temperature in ice cores tell us about global warming?

Filed under: — jeff @ 9:42 am

This 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.

Does this prove that CO2 doesn’t cause global warming? The answer is no.
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2 Dec 2004

Michaels misquotes Hansen

Filed under: — gavin @ 12:42 pm

Pat Michaels (under the guise of the Greening Earth society) is particularly fond of misquoting Jim Hansen, director of the NASA GISS laboratory (and in the interests of full disclosure, GS’s boss).

Recently he claimed that Dr. Hansen has now come around to the ’skeptics’ (i.e. Pat Michaels) way of thinking and suggests that they agree on the (small) amount of warming to be expected in the future. Michaels quotes Hansen from a 2001 PNAS paper:

Future global warming can be predicted much more accurately than is generally realized … we predict additional warming in the next 50 years of 3/4 +/- 1/4°C, a warming rate of 0.15 +/- 0.05°C per decade.

However, as is usual in these cases, the ‘…’ hides most of the point. The full quote is:

Given these constraints on climate forcing trends, we predict additional warming in the next 50 years of 3/4 +/- 1/4°C, a warming rate of 0.15+/- 0.05°C per decade.

What are these constraints that Hansen mentions? Precisely the control of CO2, methane and black carbon emissions that Michaels insists are unnecessary!

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1 Dec 2004

Climate model scenarios

Filed under: — gavin @ 6:59 pm

A couple of commentators (Pat Michaels, Roy Spencer) recently raised an issue about the standard scenarios used to compare climate models, in this case related to a study on the potential increase in hurricane activity.

The biggest uncertainty in what will happen to climate in the future (say 30 years or more) is the course that the global economy will take and the changes in technology that may accompany that. Since climate scientists certainly don’t have a crystal ball, we generally take a range of scenarios or projections of future emissions of CO2 and other important forcings such as methane and aerosols.

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