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Greenhouse gases

How do we know that recent CO2 increases are due to human activities?

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Translations: (Svenska) (Español) (Français)

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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Michael Crichton’s State of Confusion II: Return of the Science

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Our first post on Crichton’s new novel “State of Fear” hits most of the key points, though there are a few more errors in the book that we hope to expand upon in future posts.

But for those of you uninterested in buying and reading the book, you can actually find a similar-minded opinion piece by Crichton criticizing climate science (and everything from SETI and the “Drake Equation” to Carl Sagan in the process) here in the public domain.

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Michael Crichton’s State of Confusion

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Translations: (Français)

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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Temperature Variations in Past Centuries and the so-called "Hockey Stick"

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Translations: (Français)

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temperature changes further back in time must therefore make use of the few long available instrumental records or historical documents and natural archives or ‘climate proxy’ indicators, such as tree rings, corals, ice cores and lake sediments, and historical documents to reconstruct patterns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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Antarctic cooling, global warming?

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Translations: (Français)

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?

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Translations: (Français)

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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Michaels misquotes Hansen

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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:

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Climate model scenarios

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Translations: (Français)

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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