A scientist central to early alarm about global warming now recommends that remedies focus on greenhouse gases other than carbon dioxide. His move does not represent retreat from an aggressive position in global-warming politics. It nevertheless demonstrates uncertainty in the complex science behind the issue. And it underscores an unfortunate tendency of international politics to lurch toward costly error.
The scientist is James E. Hansen, head of the National Aeronautics and Space Administration's Goddard Institute for Space Studies, who during the warm summer of 1988 told a congressional hearing chaired by then-Sen. Al Gore that the planet was warming due to an accumulation of greenhouse gases and urged officials to "stop waffling" about it.
Since then, of course, Gore has adopted global warming as a signature mission. As vice-president, he signed the Kyoto Protocol calling for national commitments to sacrificial cuts in carbon emissions. During his campaign for the presidency, he has shown no sign of moderating his position.
Evolving view
Hansen's view has evolved since his "stop waffling" testimony and the run of celebrity that followed. In 1998, he and colleagues published an article in the Proceedings of the National Academy of Sciences (PNAS) acknowledging that greenhouse warming might be offset by other effects of human origin. As a result, they wrote, changes in solar heat-over which humans have no control-might be the larger influence. Calling this insight a "paradigm change for long-term climate projections," Hansen concluded, "...Uncertainties in climate forcings have supplanted global climate sensitivity as the predominant issue."
That finding somehow escaped the notice of Gore and other anti-warming crusaders. By 1998, they had congealed a political movement out of a simple syllogism: measured temperatures and CO2 concentrations have risen in the past century; the apparent coincidence must have causal implications; therefore, CO2 emissions must be cut to prevent catastrophic warming, even if that means taxing people away from fossil energy. CO2 receives all the attention because of its volume in the atmosphere and its relationship to human activity. Suggestions even have arisen that it be treated as a toxic pollutant.
In a PNAS article last month, Hansen and coauthors suggest that whatever effect CO2 might have on global temperature gets lost in climate mechanics, which are complex and poorly understood. Although Hansen doesn't go this far in his analysis, cutting emissions of CO2 might well have no discernable effect on average temperature.
Hansen remains committed to the need for a political response to observed warming. In last month's article, therefore, he urges only that CO2 be moved out of its role as main target. He cites recent climate simulations showing that Kyoto's carbon-emission reductions will have little effect in the current century and that "30 Kyotos" would be needed "to reduce warming to an acceptable level." Better targets, he says, are other greenhouse gases and soot.
"This scenario derives from our interpretation that observed global warming has been caused mainly by non-CO2 (greenhouse gases)," Hansen writes. "Although this interpretation does not alter the desirability of slowing CO2 emissions, it does suggest that it is more practical to slow global warming than is sometimes assumed."
Hello? Observed warming has been caused by gases other than CO2? So much for the simplistic syllogism.
Precautionary principle
Hansen heeds the so-called precautionary principle, which says that the mere possibility of catastrophic warming warrants response prior to anything approaching certainty about the nature and existence of the threat. Hence his willingness to keep cuts in CO2-which he does see as a long-term warming cause-on the agenda.
And his alternative targets include methane, ozone, and other substances associated with fossil energy. So Hansen's view doesn't liberate oil and gas from global warming concern.
Still, the emphasis change would coordinate global warming response with antipollution efforts already under way in much of the world. Realistically implemented, they could be much less onerous than the carbon taxation on which Kyoto prescriptions ultimately rely. And the scientific swerve from which they emerge reasserts legitimacy of questions about whether any response to observed warming is needed at all.
Will this new message influence politics? The answer depends on whether politicians really care about planetary temperature or just want to tax individuals into changing the way they live.
