Uncertainty in the global energy budget “imbalance”

The graph­ic is from “The ener­gy bal­ance over land and oceans: an assess­ment based on direct obser­va­tions and CMIP5 cli­mate mod­els” (Mar­tin Wild et al, 2015). You can find the paper here.

The paper dis­cuss­es the progress in under­stand­ing over­all ener­gy flows between the sur­face of the earth and the top of the atmos­phere (TOA) that are the motor of the earth’s cli­mate. It con­sid­ers the extent to which the cli­mate mod­els that are the basis for the find­ings of the lat­est, 5th, IPCC Assess­ment Report (AR5), match up with obser­va­tions. In brief, the paper shows that most of the mod­els sig­nif­i­cant­ly over­es­ti­mate the warm­ing con­tri­bu­tion of the sun at the sur­face of the earth (Fig 7 and the asso­ci­at­ed dis­cus­sion).

The graph­ic shows the IPCCs mod­el of ener­gy flows at the start of the 21st cen­tu­ry based on obser­va­tions by satel­lites at the top of the atmos­phere and at the sur­face of the earth, includ­ing the oceans, by a net­work of sen­sors. Notice that the net incom­ing ener­gy flows (yel­low) and the out­go­ing flow (orange) near­ly bal­ance at about 240 watts per square meter (w/m2 ). The dif­fer­ence in the inward and out­ward flows is illus­trat­ed by a small green arrow in the bot­tom-left of the graph­ic show­ing an “imbal­ance” of about 0.6 w/m2. This imbal­ance — which the IPCC says is due to the ‘green­house’ effect of CO2 (plus var­i­ous unspec­i­fied ‘feed­backs’) — is respon­si­ble for glob­al warm­ing. In their account, the feed­back-aug­ment­ed green­house effect pre­vents the full re-radi­a­tion of ener­gy to space and the dif­fer­ence is incre­men­tal­ly warm­ing the sur­face of the earth includ­ing the oceans.

What struck me about this graph­ic is the size of the uncer­tain­ty ranges in the mea­sure­ment of the ener­gy flows. Wild et. al. report that the ran­dom error in the observed val­ue of down­welling radi­a­tion at the sur­face of the earth is of the order of 5 per­cent on a month­ly basis and 2 per­cent on an annu­al basis. Accord­ing­ly, we see uncer­tain­ty ranges of about 2.5 per­cent in the major ener­gy flows at the top of the atmos­phere (in paren­the­ses in the graph­ic).

But what does this mean for the that rel­a­tive­ly small claimed ‘imbal­ance’ respon­si­ble for glob­al warm­ing? The imbal­ance is ten times small­er than the uncer­tain­ty in the mea­sure­ment of the major flows (incom­ing and out­go­ing): 0.6 w/m2 in a flow of 240 w/m2 or about two-tenths of a per­cent. 

What it means is that the IPCC claims to iden­ti­fy and and attribute (to CO2) a glob­al ener­gy imbal­ance of a mag­ni­tude that is so small that — if it exists — it is ful­ly explained by our ignorance/uncertainty about the pre­cise val­ues of the ener­gy flows we are try­ing to bal­ance. 

This is one (of sev­er­al) rea­sons I find the IPCC sto­ries about glob­al warm­ing uncon­vinc­ing. Some­thing is respon­si­ble for the mild, grad­ual warm­ing of the earth since the end of the sev­en­teenth cen­tu­ry.  I accept that it could be rep­re­sent­ed by an imbal­ance in the earth’s ener­gy budged. But the iden­ti­fi­ca­tion and attri­bu­tion (to CO2 by the IPCC) of the cause is impos­si­ble when the imbal­ance rep­re­sents only a small frac­tion of our uncer­tain­ty in the mea­sure­ment of the ener­gy flows.

As far as I can see from this paper (and oth­ers like it) there is no way to dis­tin­guish the con­tri­bu­tion of CO2 from oth­er fac­tors that, from igno­rance, we have to call ‘sec­u­lar nat­ur­al vari­abil­i­ty’ in the cli­mate.

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