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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