Bob - from where I stand limits to growth does have a relevance, albeit a very unwelcome one.
It tells how we are 40 yrs late, and how, if it hadn't been for Reagan's treasonous deal with Iran to pervert the course of US democracy, things might have been very different.
Spilt milk.
Its relevance is that the core question is not what Near-zero GHG date would avoid 2.0C, but how swift is our best achievable termination of fossil fuel dependence ?
And 'achievable' to my mind means maintaining sufficient economic activity to maintain the crucial sense of common purpose and avoid rebellion, conflict and failure. Indeed, the scale of economic activity just in replacing the global energy production capacity is actually very great. As it is in the planting of sufficient native coppice forestry to supply the requisite new worldwide industry in "Carbon Recovery for Food Security".
Anyone who actually thinks that an early crash of society - due almost certainly to the onset of serial global crop failures and consequent geopolitical destabilization, would impose less damage in the way of genocide and ecocide than would striving by whatever means are necessary and sufficient to avoid that crash - in my view simply hasn't been paying attention to the science, let alone doing their homework.
The eight Major interactive Feedbacks [MIFs] are up and running. Besides being driven by anthro-warming, they are also being driven by numerous direct coupling mechanisms (I found over eighty reported in the literature in a few days study) of which the classic example is of arctic sea-ice decline and Albedo Loss warming mobile air masses over the Arctic ocean whose signature can then be traced in raised Permafrost Melt up to 1500kms inland. A third indirect driver is each MIF's own warming input adding to SAT after the timelag of ocean thermal inertia and thus adding to all MIFs' further escalation.
The most advanced MIF that I've seen reported is Albedo Loss which (in case anyone reading this hasn't seen it) was reported in the Jan 2014 paper by Ramanathan et al :
http://www.pnas.org/content/111/9/3322.abstract It evaluated the Arctic sea ice decline in the satellite record since '79, and found that the warming from Albedo Loss on average equalled 25% of the warming from anthro-CO2 stocks for the period. This is roughly equal to a new China's worth of annual CO2 output, and given the progress of ASI decline it is plainly on a rising trend.
The fact that ASI decline is only a part of Cryosphere decline, and that Albedo Loss is only one of eight MIFs, should be borne in mind in collating their potential with our best efforts at Emissions Control.
IF a best efforts target were set for
"Near-zero global GHG outputs by 2050", then beside the warming unveiled by the closure of the sulphate parasol we should also see anthro-warming timelagged potentially to the 2080s (there was a paper disputing the timelag, which Gavin S at RC shredded last year). This would allow around 70 years of continuous anthro-warming of the MIFs, as well as their own indirect warming, which indicates to me (and this is interpretation) that their CO2_e outputs on top of anthro-warming would more than fully offset our best efforts at Emissions Control. This prospect offers no chance of staying below 2.0C.
Nor does it do anything to reduce the prospect of major regional droughts coinciding during the 2020s to cause the onset of serial global crop failures. This possibility is drawn from a study by Prof Forster, an IPCC lead author, into the prognosis for extreme drought in Asia and shows that China, Pakistan and Turkey are the most seriously affected of the region’s major producers of wheat and maize.
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From the press release:
http://www.leeds.ac.uk/news/article/3291/food_security_effects_of_climate_change_will_be_felt_in_10_yearsOct 2012 “Food Security: Near future projections of the impact of drought in Asia” "Research released today shows that within the next 10 years large parts of Asia can expect increased risk of more severe droughts, which will impact regional and possibly even global food security. On average, across Asia, droughts lasting longer than three months will be more than twice as severe in terms of their soil moisture deficit compared to the 1990-2005 period. This is cause for concern as China and India have the world’s largest populations and are Asia’s largest food producers.
Dr Lawrence Jackson, a co-author of the report, said: "Our work surprised us when we saw that the threat to food security was so imminent; the increased risk of severe droughts is only 10 years away for China and India. These are the world’s largest populations and food producers; and, as such, this poses a real threat to food security.""So with 0.85C realized, and at least another 0.5C in the pipeline realized by 2050, and another ~0.6C of the fossil suphate parasol closure, and whatever the MIFs provide, and with Anthro GHG outputs crashing say in 2027 after a mere 12 years, by 2050 we are still at or above 2.0C even with the lower future anthro-CO2 inputs.
No less an authority than Michael Mann puts the passing of 2.0C under BAU at 2036 (on an ECS of 3.0) and at 2046 (on an ECS of 2.5). How much difference our best efforts before 2036 would make is unclear.
The question I've yet to see answered is just why fast crash proponents assume that with MIFs up and running at 0.85C, and SAT rising to at least 2.0C, they can then be expected to stop escalating, in direct contravention of their mutually self-reinforcing capacity ? What is to prevent their continued rise ? And what is the effect of that continued rise on human stragglers from a collapsed society and on the remaining vitality of the terrestrial and marine ecologies ?
The premis that a fast crash offers a better outcome in terms of genocide and ecocide than the all out attempt at mitigation is not borne out by the prognosis once the MIFs are included.
It may also be noted that the premis is the most wildly unsaleable proposal and so has zero prospect of preventing the coming global attempt at effective mitigation. The most it could do is to damage that attempt by demoralizing individuals - But, under a war-footing to address an existential challenge, most nations have the tradition of treating the promotion of defeatism as a serious crime, so those who choose to abstain from helping would do best to withdraw.
Regards,
Lewis
