A major conclusion of the critique is that Hansen often confuses, and intertwines his personal opinion unsupported by sound and accurate science. This is well -documented in the critique. I am only reproducing a portion of it here. The remainder can be viewed in html format, or downloaded and saved in pdf format.
The critique addresses the major scientific issues related to the complex subject of global warming. Since the subject is one of such importance, it is well worth studying.
In the materials that follow, we present such a comparison, focusing on a number of key subjects addressed by Hansen. These topics include:
(1) ice sheet disintegration,
(2) sea level trends,
(3) atmospheric methane concentrations,
(4) climates of the past,
(5) predicted warming-induced extinctions of terrestrial plants and animals,
(6) the CO2-induced preservation of terrestrial species, and
(7) predicted CO2-induced extinctions of calcifying marine organisms.
In addition, we discuss a number of other topics that Hansen addresses in less detail, including: (1) positive vs. negative climate feedbacks,
(2) effects of drought on agriculture in a CO2-enriched world,
(3) sea level rise over the next hundred years,
(4) the adaptability of living organisms to rising sea levels,
(5) the "dangerous" level of atmospheric CO2,
(6) the magnitude of climate forcing due to a doubling of the air's CO2 content,
(7) empirical evaluations of earth's climate sensitivity,
(8-10) the ability of man to control global climate,
(11-14) the need to act now to reduce CO2 emissions, and
(15) the role of morality in the debate over what to do, or not do, about anthropogenic CO2 emissions.
And when Hansen's testimony is compared with what has been revealed by the scientific investigations of a diverse assemblage of highly competent researchers in a wide variety of academic disciplines, we find that he paints a very different picture of the role of anthropogenic CO2 emissions in shaping the future fortunes of man and nature alike than what is suggested by that larger body of work.
The Basis for Hansen's Testimony
Hansen's testimony is divided into five parts: (1) Summary, (2) Basis for Testimony, (3) Crystallizing Science, (4) Metrics for Dangerous Climate Change, and (5) Four-Point Strategy to Stabilize Climate. We will begin our critique of the document with a brief analysis of what Hansen says is its foundation, i.e., his Section 2: Basis for Testimony.
Six papers in various stages of preparation for publication in peer-reviewed scientific journals form the basis for Hansen's testimony. The first, written by Hansen and 46 co-authors, is entitled "Dangerous human-made interference with climate: A GISS modelE study" and is listed as being "in press" in Atmospheric Chemistry and Physics.
The second paper, written by Hansen and five co-authors, is entitled "Climate change and trace gases" and is listed as being "in press" in the Philosophical Transactions of the Royal Society A. The third paper, also written by Hansen and 46 co-authors, is entitled "Climate simulations for 1880-2003 with GISS modelE" and is listed as being "in press" in Climate Dynamics.
The fourth paper, written by Hansen alone, is entitled "Scientific reticence and sea level rise" and is listed as being "accepted for publication" by Environmental Research Letters. The fifth paper, again by Hansen alone, is entitled "State of the wild: Perspective of a climatologist" and is listed as being "accepted" by an unnamed journal.
The sixth paper, where Hansen appears as the second of two authors, is entitled "Implications of 'peak oil' for atmospheric CO2 and climate" and is listed as being a "first draft" prepared for Geophysical Research Letters.
In perusing these manuscripts, it is readily apparent they either deal with, or are based upon, scenario-driven climate-model projections, which obviously can be no better than the physics, chemistry and biology upon which they are based, as well as the scenarios that drive them.
To be of any prognostic value, therefore, the models must include, and correctly characterize, all of the physical, chemical and biological phenomena that significantly impact the planet's climate, which is something most climate modelers would probably admit they have not yet achieved to the degree they would like. But are they close enough?
Our only way of answering this question is to see if what the models portend about the future compares favorably with what they suggest about the past. Of course, the models could accidentally give the "right answers," but there is no other course of action we can take at the present time; and, hence, this is what we will do in evaluating Hansen's testimony, for if the models give the wrong answers about the recent past, we can be confident they are not up to the task of correctly inferring the future.
Analyzing Hansen's "Crystallizing Science"
The core concept of Hansen's testimony is that the earth "is close to dangerous climate change, to tipping points of the system with the potential for irreversible deleterious effects." However, this contention, like the many other claims Hansen makes, is neither a self-evident verity nor a proven fact. It is merely an opinion. And to raise it to a loftier status requires that there be real-world evidence for the changes the climate models suggest should occur in response to increasing atmospheric CO2 concentrations and rising air temperatures.
This requirement is all the more justified in light of the fact that air temperatures of the last quarter-century are typically claimed by climate alarmists to have been unprecedented for at least the past two thousand years (Mann and Jones, 2003; Mann et al., 2003) - and possibly for close to a million years, if one believes Hansen et al. (2006) - while the atmosphere's current CO2 concentration is greater than it may have been for tens of millions of years (Pagani et al., 1999).
So what are the major climate changes and associated catastrophic consequences that are suggested by the climate models? And are there any signs they may already be in process of developing? The "sharpest criterion" for defining dangerous climate change, in the words of Hansen, "is probably maintenance of long-term sea level close to the present level," and in this regard he says that "sea level is already rising at a rate of 3.5 cm per decade and the rate is accelerating [our italics]," due, he would have us believe, to "ice sheet disintegration."
But are there any real-world data to support this claim?
Ice Sheet Disintegration
A good perspective on this issue is provided in the 16 March 2007 issue of Science by Shepherd and Wingham (2007), who review what is known about sea-level contributions arising from wastage of the Antarctic and Greenland Ice Sheets, focusing on the results of 14 different satellite-based estimates of the imbalances of the polar ice sheets that have been derived since 1998. These studies have been of three major types - standard mass budget analyses, altimetry measurements of ice-sheet volume changes, and measurements of the ice sheets' changing gravitational attraction - and they have yielded a diversity of values, ranging from an implied sea-level rise of 1.0 mm/year to a sea-level fall of 0.15 mm/year. Based on their evaluation of these diverse findings, the two researchers come to the conclusion that the current "best estimate" of the contribution of polar ice wastage to global sea level change is a rise of 0.35 millimeters per year, which over a century amounts to only 35 millimeters, or less than an inch and a half.
Yet even this small sea level rise may be unrealistically large, for although two of Greenland's biggest outlet glaciers doubled their mass-loss rates in 2004, causing many to claim that the Greenland Ice Sheet was responding more rapidly to global warming than expected, Howat et al. (2007) report that the glaciers' mass-loss rates "decreased in 2006 to near the previous rates." And these observations, in their words, "suggest that special care must be taken in how mass-balance estimates are evaluated, particularly when extrapolating into the future, because short-term spikes could yield erroneous long-term trends."
Other findings also contradict Hansen's claim that "increasingly rapid changes on West Antarctica and Greenland ... are truly alarming." Writing in the 30 March 2007 issue of Science, for example, Anandakrishnan et al. (2007) describe a sedimentary wedge or "till delta" deposited by and under West Antarctica's Whillans Ice Stream that they detected via radar surveys made from the floating Ross Ice Shelf. This grounding-line buildup of sedimentary material, as they describe it, "serves to thicken the ice and stabilize the position of the grounding line," so that "the ice just up-glacier of the grounding line is substantially thicker than that needed to allow floatation." Consequently, they say that "the grounding-line will tend to remain in the same location ... until sea level rises enough to overcome the excess thickness that is due to the wedge."
So how high would the sea need to rise to "unground" the Whillans Ice Stream and wrest it from the continent? In a study that analyzes this question in detail, Alley et al. (2007) find that "sea-level changes of a few meters are unlikely to substantially affect ice-sheet behavior," and they conclude that a rise on the order of 100 meters might be needed to "overwhelm the stabilizing feedback from sedimentation." In fact, Anderson (2007) states that "at the current rate of sea-level rise, it would take several thousand years [our italics] to float the ice sheet off [its] bed." What is more, Alley et al. say that the ice sheet's extra thickness up-glacier from the grounding-line wedge will tend to stabilize it against "any other environmental perturbation."
With respect to the range of applicability of the findings of Anandakrishnan et al. and Alley et al., Anderson notes that "grounding-zone wedges are common features on the continental shelf, including the Ross Sea Shelf," and that "all ice streams of the Siple Coast have an anomalous elevation and stop at the grounding line," which leads him to conclude that "this mechanism for stabilization of the grounding-line is likely to be widespread." Consequently, Anderson concludes that "sea-level rise may not destabilize ice sheets as much as previously feared," which in turn suggests that sea level itself may not rise as fast or as high as previously feared. So what do actual sea level data suggest?
(continued here: http://scienceandpublicpolicy.org/current_issue.html