First, in spite of the fact that the authors' estimates of global climate forcings "indicate that it is the non-CO2 GHGs [greenhouse gases] that have caused most observed global warming," they state that "this interpretation does not alter the desirability of limiting CO2 emissions."  We totally disagree; for as our web site clearly indicates, there are untold benefits to be accrued by the biosphere as a consequence of the aerial fertilization effect of the ongoing rise in the air's CO2 content and the host of other positive effects that atmospheric CO2 enrichment have on the planet's vegetation.  In addition, if the planet were to experience some degree of global warming in the future, due to continued increases in non-CO2 GHGs or intensification of some other heat-inducing phenomenon, higher levels of atmospheric CO2 would actually be needed, in order to counteract the detrimental effects that further warming may have on that portion of earth's plant life that is already growing near the limits of its thermal tolerance.

This concept of CO2-induced plant "environmental protection" is described in our Editorial of 15 October 1999 - The Fortunate Coupling of Atmospheric CO2 and Temperature Trends- where we highlight the work of Sharon Cowling of the Climate Impacts Group of the Institute of Ecology at Lund University in Sweden.  Specifically, we review Cowling's revealing analysis published last year in Science (Cowling, 1999), where she shows for the IPCC's high-climate-change-rate scenario that by the time the globe has warmed by 4°C, the net assimilation or growth rate of the planet's C3 vegetation (which comprises 95% of all plants) falls by something on the order of 10 to 15% with no change in the air's CO2 content, but that if the atmosphere's CO2 concentration rises concurrently by a mere 76 ppm - which is what it did over the past century - the planet's vegetation experiences a 40% increase in growth.  The difference between these two scenarios is enormous; and we have recently demonstrated that the boost to agricultural productivity provided by the expected increase in the air's CO2 content over the next half century will be absolutely essential for maintaining the food security of the human population of the globe at that future date (Idso and Idso, 2000).

The second of our "quibbling points" is Hansen et al.'s contention that "attainment of a decreasing CO2 growth rate" - which, of course, we feel is undesirable, if not actually detrimental - "will require greater use of energy sources that produce little or no CO2."  Their own data, in fact, clearly indicate that this requirement is not a prerequisite to meeting the stated, though flawed, objective.  Between the late 1970s and late 1990s, for example, the growth rate of CO2-induced radiative climate forcing was, by their own admission, flat, and this "despite a 30% increase in fossil fuel use."  This flat growth rate of CO2 forcing, they rightfully acknowledge, "is at least in part a reflection of increased terrestrial sequestration of carbon."  They then claim, however, that "continuation of high terrestrial sequestration of CO2 is uncertain," but a quick perusal of our Editorials of 15 November 1998 and 1 December 1999 - CO2 Sequestration: Our Father was Right and Biospheric Carbon Sequestration: Does It Really Work?- reveals that, yes, this phenomenon really does work, as is also indicated by a wealth of research, the most recent few years of which are reviewed in our Subject Index under the heading Carbon Sequestration.

In spite of these two major shortcomings, the paper of Hansen et al. is a welcome addition to the scientific literature on the CO2/Global Warming debate.  It is not often that one sees a high-profile scientist do a 180-degree turnabout on an issue of such tremendous global significance.  We express admiration to him and his colleagues for their courage in this regard and hope that others that had previously thought as they did would be able to do likewise.