One thousand ppm might be better

The Aus­tralian gov­ern­ment is bent on enact­ing a car­bon-emis­sions tax that has no respon­si­ble jus­ti­fi­ca­tion oth­er than recent­ly re-hashed advice designed to jus­ti­fy an emis­sions tax. Lit­tle won­der, then, that polling shows vot­ers are strong­ly opposed to the tax, despite wide­spread their appar­ent con­vic­tion that the cli­mate is warm­ing and their accep­tance that warm­ing is at least part­ly caused by human action .

The “Newspoll” does not ask the most impor­tant ques­tion: is cli­mate warm­ing an immi­nent threat that calls for gov­ern­ment action. The gov­ern­ment itself has not pro­duced a con­vinc­ing answer to that ques­tion. The most dili­gent of its advi­sors, Ross Gar­naut, has failed to sup­port the hypoth­e­sis of dan­ger­ous man-made warm­ing except by a leap of faith: a “bal­ance of prob­a­bil­i­ties” that rests, ulti­mate­ly, on appeal to an author­i­ty (the IPCC) whose cred­i­bil­i­ty is in shreds.

No sound argu­ment relies on an appeal to author­i­ty, but a deep under­stand­ing of a com­plex prob­lem some­times pro­duces insights that can be com­mu­ni­cat­ed with sur­pris­ing sim­plic­i­ty. One recent exam­ple is this arti­cle on the con­tri­bu­tion of green­house gasses to cli­mate change by Prince­ton Uni­ver­si­ty pro­fes­sor of Physics, William Hap­per from the jour­nal First Things.

Hap­per makes sev­er­al famil­iar crit­i­cisms of the “moral epi­dem­ic” of cli­mate-dread that has infat­u­at­ed pub­lic sci­ence and polit­i­cal insti­tu­tions in the Unit­ed States, Europe and Aus­tralia. But he also calls atten­tion to some sim­ple ques­tions that are not being asked. For exam­ple: what is the desir­able and tol­er­a­ble lev­el of atmos­pher­ic CO2, giv­en its essen­tial role in pho­to­syn­the­sis.

The min­i­mum accept­able val­ue for plants is not that much below the 270 ppm prein­dus­tri­al val­ue. It is pos­si­ble that this is not enough, that we are bet­ter off with our cur­rent lev­el, and would be bet­ter off with more still. There is evi­dence that Cal­i­for­nia orange groves are about 30 per­cent more pro­duc­tive today than they were 150 years ago because of the increase of atmos­pher­ic CO2.

Although human beings and many oth­er ani­mals would do well with no CO2 at all in the air… the Navy rec­om­mends an upper lim­it of about 8000 ppm for cruis­es of nine­ty days, and nasa rec­om­mends an upper lim­it of 5000 ppm for mis­sions of one thou­sand days, both assum­ing a total pres­sure of one atmos­phere. High­er lev­els are accept­able for mis­sions of only a few days.

We con­clude that atmos­pher­ic CO2 lev­els should be above 150 ppm to avoid harm­ing green plants and below about 5000 ppm to avoid harm­ing peo­ple. That is a very wide range, and our atmos­phere is much clos­er to the low­er end than to the upper end [PWG: about 390ppm]. The cur­rent rate of burn­ing fos­sil fuels adds about 2 ppm per year to the atmos­phere, so that get­ting from the cur­rent lev­el to 1000 ppm would take about 300 years—and 1000 ppm is still less than what most plants would pre­fer, and much less than either the nasa or the Navy lim­it for human beings.

Happer’s full paper is well worth read­ing for the per­spec­tive of a physi­cist whose inde­pen­dence of cli­mate-sci­ence fund­ing means that he joined with about 200 oth­er mem­bers of the Amer­i­can Phys­i­cal Soci­ety in their suc­cess­ful 2009 peti­tion against the extra­or­di­nary (pos­si­bly, self-inter­est­ed) obei­sance of the Society’s Coun­cil to the “incon­tro­vert­ible” con­clu­sion that man is respon­si­ble for recent warm­ing.

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