our originally published error margin assigned to v5.1. In the tropics, the effect was to increase the trend from +0.00 to +0.05 °C/decade. We corrected the error in May 2005 and with the publication of Mears and Wentz put the data on a public website in August 2005, though it was provided to several scientists before that date. This new version, v5.2, has been publicly available since that time. So there are two LT datasets with somewhat differing trends, UAH's and RSS's. Of interest to the committee is the fact I will have two papers to be published shortly which indicate UAH v5.2 is highly consistent with independent temperature measurements of the LT layer. These papers show that it is very likely that the tropical atmosphere is warming at a rate equal to or less than that of the surface, a characteristic no climate model that we have examined replicates. Thus, there is evidence that the theoretical ideas of how the large-scale atmosphere should be responding to the enhanced greenhouse effect, as embodied in climate models, still have shortcomings. As to the first question, we provide only the latest version of our data to the public. And, since 1998 any version of our lower tropospheric dataset would have shown a positive global trend. Thus, if someone is using UAH data to claim no global warming, I would speculate they are likely using pre-1998 data or are somehow altering the data to make that conclusion. I don't know of any current claims to that effect, and UAH has been forthright in reporting positive trends (and the likelihood that at least part of that positive trend is due to enhanced greenhouse gases) these past 8 years. In answering the second question, the discussion above describes the events that led to the correction of the drift error and UAH's corrected data have been publicly available since August 2005. However, one should be aware that datasets are always subject to revision, and we look forward to v6.0 of our current dataset, though there will be little change in the outcome relative to v5.2. RESPONSE FOR THE RECORD OF DR. RALPH J. CICERONE, PRESIDENT, NATIONAL ACADEMY OF SCIENCES Responses to questions following the July 27, 2006 hearing before the U.S. House of Representatives Ralph J. Cicerone, Ph.D. President, National Academy of Sciences The Honorable Bart Stupak 1. We have heard the view expressed that the global warming that we are experiencing today is part of a sinusoidal wave that reflects the earth's normal warming and cooling patterns. Do you agree with that view? If not, please explain why. No, I do not agree. Let me explain. In geological history, there are some examples of quasi-periodic variations in the Earth's climate that must have been natural. Changes in the Earth's orbit around the Sun, known as Milankovitch cycles, are associated with climate variations over long timescales, such as the ice ages that have occurred over the last few million years. Also, the internal dynamics of the tropical ocean and atmosphere give rise to the El Niño phenomenon, a warming of the central and eastern tropical Pacific Ocean that is associated with climate impacts across the globe every 2 to 5 years. However, while the El Niños affect large regions, they are not global. In contrast, no known natural phenomenon can explain the observed warming of the past 30 years, which has been continuous, rapid and widespread. Furthermore, the magnitude and pattern of this recent warming matches what we expect based on the observed increase in greenhouse gas concentrations and other human activities. 2. Please describe the peer review process that was used for the National Academy of Sciences (NAS) report on global temperature reconstruction. Every report prepared by a National Research Council committee is reviewed by a group other than its authors. This independent review distinguishes the NRC from many other organizations offering scientific and technical advice on important national issues. The purpose of review is to assist the authoring committee in making its report as accurate and effective as possible. The review of the report Surface Temperature Reconstructions for the Last 2000 Years followed the National Academies' normal, rigorous peer-review process. The review was overseen by the Report Review Committee (RRC), made up of approximately 30 members of the National Academy of Sciences, National Academy of Engineering, and Institute of Medicine. The Board on Atmospheric Sciences and Climate (BASC), in consultation with the RRC, appointed a group of 13 independent reviewers with a broad range of expertise and diverse perspectives on the issues addressed in the report. The identity of reviewers is considered to be privileged information during the review process. Anonymous review is intended to encourage individual reviewers to express their views freely and to permit the authoring committee to evaluate each comment on its merits without regard for the position or status of the reviewer. The names and affiliations of the reviewers were made public when the report was released, but their comments remain confidential. The draft report was sent to the 13 reviewers only after all authors indicated that they were satisfied with its form and content. Reviewers received the complete report (including front matter, preface, executive summary, and appendices) along with the committee's statement of task and the NRC review guidelines. Reviewers were asked to provide written comments on any and all aspects of the draft report, including the accuracy of the committee's analysis and the responsiveness of the committee to its charge. The authors were required to respond in writing to every review comment, revising the report where appropriate. These responses were evaluated by a review monitor appointed by the RRC and by a review coordinator appointed by the NRC Division on Earth and Life Studies. The report was not released until after the review monitor, the review coordinator, and all members of the authoring committee approved the revised draft. Once the review process was successfully completed, no changes (other than minor editorial corrections) were made to the approved text. 3. Please describe the key elements of academic peer review, such as who picks the reviewers, whether comments can be submitted anonymously, and who decides whether the paper can be published if there are negative comments that the authors do not accept. Each scientific journal has its own policies for peer review, but there are some standard features among them. Generally, submitted manuscripts are assigned to an editor who has expertise on the general topic. These editors conduct a first level review of the manuscript to determine if it meets basic criteria for publication in the journal (e.g., length, appropriateness of subject matter, etc.). Some manuscripts are rejected outright at this stage. If a manuscript is considered suitable for the journal, it will be sent out for peer review. Usually, two or more reviewers are chosen by the editor. In some cases, the journal may ask the author(s) to suggest potential reviewers who have the appropriate expertise, but the editor or an associate editor will make the ultimate decision. Reviewers are typically asked to submit comments on the manuscript and to make a recommendation on its suitability for publication in the journal. Once the reviewers' comments have been submitted, the editor decides whether to accept the manuscript for publication (perhaps with some minor revisions), ask the author(s) to make significant revisions and submit the paper for re-review (in which case the process is repeated), or reject the paper. In the case that two reviewers disagree about the suitability of a manuscript for publications, the editor may solicit an additional tie-breaking review or ask the author(s) to prepare a rebuttal to the critical reviews. Usually all of the review comments are shared with the author(s), regardless of the decision to publish, but the identity of the reviewers is kept anonymous throughout the process, even after publication, unless a reviewer specifically requests for their anonymity to be waived. In prestigious journals such as Science and Nature, the vast majority of manuscripts (up to 95%) are rejected at some point in this process. Acceptance rates in other journals vary considerably but are usually higher. For example, acceptance rates at the various journals published by the American Geophysical Union, including the Journal of Geophysical ~ Research, range from about 50-80%. 4. During the hearing, you referenced information on CO2 concentrations in Antarctica going back 650,000 years. Is this information quantitative or qualitative? High quality, quantitative measurements of CO2 concentrations are available from ice cores in Antarctica extending back to about 650,000 years before present (Siegenthaler, U. et al., 2005. Stable Carbon Cycle-Climate Relationship During the Late Pleistocene. Science, 310, p. 1313-1317). These measurements are obtained by analyzing the air extracted from small bubbles trapped in the ice, which reflect atmospheric composition at the time when the snow that formed each layer was compacted into ice. Because CO2 is well-mixed in the atmosphere, the CO2 concentration at Antarctica is representative of the globally-averaged atmospheric concentration. The measurements by Siegenthaler et al. show that CO2 did not exceed 300 ppmv (parts per million by volume) during the 650,000 years that preceded the industrial era. Present concentrations of CO2 in the atmosphere are about 380 ppmv, and current projections indicate that the level will reach 450 ppmv by mid-century. When evaluating CO2 data from ice cores, there are two types of uncertainties to consider: (1) uncertainty in the concentration of CO2 for any particular measurement, which tends to be small, perhaps a range of a few ppmv; and (2) uncertainty about dating the measurements, which can be as large as 1300 years for the earliest part of the record. This second source of uncertainty complicates efforts to synchronize measurements of CO2 (and other gases, such as methane) with ice core measurements of temperature, which are calculated based on the properties of the ice rather than the trapped air bubbles. Thus, an open research question is whether the rises and falls in greenhouse gas concentrations lead or lag the rises and falls of temperature associated with glacialinterglacial cycles (e.g., Mudelsee, M. 2001. The phase relations among atmospheric CO2 content, temperature, and global ice volume over the past 420 ka. Quaternary Science Reviews, 20. 583-589). This question is especially pertinent for the temperature increases after ice ages, which often occurred over only a few thousand years. Most analyses indicate that temperature increases have preceded increases in CO2 when the Earth warms after an ice age (e.g., Hansen and Sato, 2004. Greenhouse gas growth rates. Proceedings of the National Academy of Sciences, 101(46), p. 16109-16114.). However, this should not be interpreted to suggest that the current increase in CO2 concentrations will not produce further global warming, only that other processes (such as orbital forcing or changes in ocean circulation) may have initiated the rebound in global-mean temperature after ice ages. 5. Did the NAS Surface Temperature Reconstruction Committee find any temperature reconstructions that show global or Northern Hemisphere temperatures in the medieval period higher than recorded temperatures today? The paucity of proxy data for periods prior to about 1600 A.D., especially in the tropics and the Southern Hemisphere, limited the committee's confidence in statements regarding the global mean temperature of the past few decades compared to medieval times. Several proxies indicate that the area around Greenland was warmer between about 1000 and 1200 A.D. than it is today. There is also evidence for warm temperatures during medieval times from other regions of the world. However, several studies suggest that these warm anomalies appear to have occurred at different times and at different places rather than being hemispherically or globally synchronous, and also appear to have been offset by cold anomalies in other regions. Although it is difficult to quantify the full uncertainty associated with estimates of surface temperature prior to about 1600 A.D., all of the large-scale surface temperature reconstructions that the committee examined support the assertion that global-mean temperatures during the last few decades of the 20th century were unprecedented over at least the past 1,000 years, and a larger fraction of geographically diverse proxy records experienced exceptional warmth during the late 20th century than during any other extended period from 900 A.D. onward. Hence the committee found it plausible (or in other words, no evidence exists to refute the claim) that "the last few decades of the 20th century were warmer than any comparable period over the last millennium." This statement can be more strongly applied to the Northern Hemisphere than to the globe because there is very little proxy data from the Southern Hemisphere before about 1600 A.D. |