The physical science of climate change

I’m late find­ing this Non­govern­men­tal Inter­na­tion­al Pan­el on Cli­mate Change (NIPCC) report. I include the sum­ma­ry of their find­ings on the phys­i­cal sci­ence here because they accord with my present assess­ment.

I would have added only one thing to the recita­tion below. I do not know why the NIPCC omit­ted it. That is: the IPCC’s the­o­ry of cat­a­stroph­ic warm­ing depends, not on CO2 alone — to which the atmos­pher­ic tem­per­a­ture is only mod­est­ly sen­si­tive — but still more on the effect of pos­i­tive-feed­back. They point to water vapour in the atmos­phere as the the prob­a­ble mech­a­nism that mul­ti­plies the sen­si­tiv­i­ty of tem­per­a­ture to CO2.

But net-pos­i­tive feed­backs are utter­ly implau­si­ble in nat­ur­al sys­tems that have endured for geo­log­i­cal aeons. If large pos­i­tive feed­backs were real, the cli­mate would have become hos­tile to any life as long ago as the pre-Cam­bri­an era. Net-pos­i­tive feed­backs are a self-destruct mech­a­nism. Why should we believe they char­ac­terise the cli­mate? What is so spe­cial about our era that we should have been respon­si­ble for cre­at­ing such a mech­a­nism where none exist­ed before? Where has the pos­i­tive feed­back been for the past 16 years (or so)?

I should add that my own views do not orig­i­nate with the NIPCC, although I have read mate­r­i­al from their “lead authors” else­where. My views were formed by read­ing as wide­ly as I can on this sub­ject for, now, almost a decade. I began with the assump­tion that the IPCC’s views were cor­rect. I was at first con­cerned main­ly by the naïve pro­pos­als for mul­ti­lat­er­al action. But I became more and more dis­sat­is­fied with the evi­dence for cli­mate alarm. A search on this site will turn up many more arti­cles.

The NIPCC Summary

  • Atmos­pher­ic car­bon diox­ide (CO2) is a mild green­house gas that exerts a dimin­ish­ing warm­ing effect as its con­cen­tra­tion increas­es.
  • Dou­bling the con­cen­tra­tion of atmos­pher­ic CO2 from its pre-indus­tri­al lev­el, in the absence of oth­er forc­ings and feed­backs, would like­ly cause a warm­ing of ~0.3 to 1.1°C, almost 50% of which must already have occurred.
  • A few tenths of a degree of addi­tion­al warm­ing, should it occur, would not rep­re­sent a cli­mate cri­sis.
  • Mod­el out­puts pub­lished in suc­ces­sive IPCC reports since 1990 project a dou­bling of CO2 could cause warm­ing of up to 6°C by 2100. Instead, glob­al warm­ing ceased around the end of the twen­ti­eth cen­tu­ry and was fol­lowed (since 1997) by 16 years of sta­ble tem­per­a­ture.
  • Over recent geo­log­i­cal time, Earth’s tem­per­a­ture has fluc­tu­at­ed nat­u­ral­ly between about +4°C and -6°C with respect to twen­ti­eth cen­tu­ry tem­per­a­ture. A warm­ing of 2°C above today, should it occur, falls with­in the bounds of nat­ur­al vari­abil­i­ty.
  • Though a future warm­ing of 2°C would cause geo­graph­i­cal­ly var­ied eco­log­i­cal respons­es, no evi­dence exists that those changes would be net harm­ful to the glob­al envi­ron­ment or to human well-being.
  • At the cur­rent lev­el of ~400 ppm we still live in a CO2-starved world. Atmos­pher­ic lev­els 15 times greater exist­ed dur­ing the Cam­bri­an Peri­od (about 550 mil­lion years ago) with­out known adverse effects.
  • The over­all warm­ing since about 1860 cor­re­sponds to a recov­ery from the Lit­tle Ice Age mod­u­lat­ed by nat­ur­al mul­ti­decadal cycles dri­ven by ocean-atmos­phere oscil­la­tions, or by solar vari­a­tions at the de Vries (~208 year) and Gleiss­berg (~80 year) and short­er peri­od­ic­i­ties.
  • Earth has not warmed sig­nif­i­cant­ly for the past 16 years despite an 8% increase in atmos­pher­ic CO2, which rep­re­sents 34% of all extra CO2 added to the atmos­phere since the start of the indus­tri­al rev­o­lu­tion.
  • CO2 is a vital nutri­ent used by plants in pho­to­syn­the­sis. Increas­ing CO2 in the atmos­phere “greens” the plan­et and helps feed the grow­ing human pop­u­la­tion.
  • No close cor­re­la­tion exists between tem­per­a­ture vari­a­tion over the past 150 years and human- relat­ed CO2 emis­sions. The par­al­lelism of tem­per­a­ture and CO2 increase between about 1980 and 2000 AD could be due to chance and does not nec­es­sar­i­ly indi­cate cau­sa­tion.
  • The caus­es of his­toric glob­al warm­ing remain uncer­tain, but sig­nif­i­cant cor­re­la­tions exist between cli­mate pat­tern­ing and mul­ti­decadal vari­a­tion and solar activ­i­ty over the past few hun­dred years.
  • For­ward pro­jec­tions of solar cyclic­i­ty imply the next few decades may be marked by glob­al cool­ing rather than warm­ing, despite con­tin­u­ing CO2 emis­sions.

Source: “Exec­u­tive Sum­ma­ry,” Cli­mate Change Recon­sid­ered II: Phys­i­cal Sci­ence (Chica­go, IL: The Heart­land Insti­tute, 2013).

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