In a December 17th Fox News story (See full report here) Steven Milloy comments on a lecture by Lonnie Thompson at the Annual meeting of the American Geophysical Union in San Francisco. He uses a common ploy of truncating what Thompson said, to ensure that a quotation fits with his message. According to Milloy, Thompson said, “Any prudent person would agree that we don’t yet understand the complexities with the climate system.” But what he actually said was “Any prudent person would agree that we don’t yet understand the complexities with the climate system and, since we don’t, we should be extremely cautious in how much we ‘tweak’ the system.” (see full press release here). Such manipulations are designed so that Milloy can’t be accused of misquoting, but clearly, he completely contorts Thompson’s point. Milloy also misunderstands the science.
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How do we know that recent CO2 increases are due to human activities?
An updated version of this post is now available.
The fact that CO2 increases in the past 150 years are due virtually entirely to human activities is so well established that one rarely sees it questioned. Yet is is quite reasonable to ask how we know this.
There are actually multiple, largely independent lines of reasoning, discussed in some detail in the IPCC TAR report, Chapter 3. One of the best illustrations of this point, however, is not given in IPCC. Indeed, it seems not all that well appreciated in the scientific community, and is worth making more widely known.
Carbon is composed of three different isotopes 14C, 13C and 12C of which 12C is the most common and 14C (used for dating purposes) is only about 1 in 1 trillion atoms. 13C is about 1% of the total.
Over the last few decades, isotope geochemists have worked together with tree rings experts to construct a time series of atmospheric 14C variations over the last 10,000 years. This work is motivated by a variety of questions, most having to do with increasing the accuracy of the radiocarbon dating method. A byproduct of this work is that we also have a very nice record of atmospheric 13C variations through time, and what we find is that at no time in the last 10,000 years are the 13C/12C ratios in the atmosphere as low as they are today. Furthermore, the 13C/12C ratios begin to decline dramatically just as the CO2 starts to increase — around 1850 AD. This is no surprise because fossil fuels have lower 13C/12C ratios than the atmosphere.
The total change is about 0.15%, which sounds very small but is actually very large relative to natural variability. Although it has proved quite challenging to do the analyses, there are a limited number of measurements of the 13C/12C ratio in ice cores. The results show that the full glacial-to-interglacial change in 13C/12C of the atmosphere — which took many thousand years — was about 0.03% 00 or about 5 times less than that observed in the last 150 years. The ice core data also agree quite well with the tree ring data where these data sets overlap.
I will put a couple of plots up when I get a chance. For those who are interested, some relevant references are: Stuiver, M., Burk, R. L. and Quay, P. D. 1984. 13C/12C ratios and the transfer of biospheric carbon to the atmosphere. J. Geophys. Res. 89, 1731�1748. for tree rings, and
Francey, R.J., Allison, C.E., Etheridge, D.M., Trudinger, C.M., Enting, I.G., Leuenberger, M., Langenfelds, R.L., Michel, E., Steele, L.P., 1999. A 1000-year high precision record of d 13Cin atmospheric CO. Tellus 51B, 170�193.
Statistical analysis of consensus
) Is there really “consensus” in the scientific community on the reality of anthropogenic climate change? As N. Oreskes points out in a recent article in Science, that is itself a question that can be addressed scientificially. Oreskes took a sampling of 928 articles on climate change, selected objectively (using the key phrase “global climate change”) from the published peer-reviewed scientific literature. Oreskes concluded that of those articles (about 75% of them) that deal with the question at all, 100% (all of them) support the consensus view that a significant fraction of recent climate change is due to human activities. Of course, there are undoubtedly some articles that have been published in the peer-reviewed literature that disagree with this position and that Oreskes’s survey missed, but the fact that her sample didn’t [Read more…] about Statistical analysis of consensus
Michael Crichton’s State of Confusion II: Return of the Science
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.
[Read more…] about Michael Crichton’s State of Confusion II: Return of the Science
Michael Crichton’s State of Confusion
) 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.
Climate Change Disinformation
by Michael Mann and Gavin Schmidt
As highlighted in the introduction to the site, we seek to clarify the findings of scientists who study the earth’s climate, and have an informed view on the science of climate change. Additionally we will speak out where we feel that the public discourse surrounding the science is being detrimentally impacted by the shrill voices and disinformation campaigns of the “partisan think-tanks or other interested parties”.
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Weren’t temperatures warmer than today during the “Medieval Warm Period”?
) 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 disinguish 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.
OK, But we do know it was warmer than present 6000 years ago, don’t we?
) This is yet another oft-repeated but problematic assertion based in this case on the mis-characterization of the so-called Mid-Holocene Climatic Optimum” or “Mid-Holocene Warm Period”. Paleoclimate experts now know that the mid-Holocene warmth centered roughly 8000 to 6000 years ago was probably restricted to high latitudes and certain seasons (summer in the Northern Hemisphere and winter in the southern hemisphere). Because much of the early paleoclimate evidence that was available (for example, fossil pollen assemblages) came from the Northern Hemisphere extratropics, and is largely reflective of summer conditions, decades ago some scientists believed that this was a time of globally warmer conditions. More abundant evidence now demonstrates, for example, that the tropical regions were cooler over much of the year.
[Read more…] about OK, But we do know it was warmer than present 6000 years ago, don’t we?