IPCC's High-impact, low-probability risk media talking points

 ‘Abrupt Climate Change’ may turn out to be an IPCC own goal

Guest essay by Barry Brill

It’s one thing to terrify the populace with apocalyptic rhetoric and images of collapsing ice sheets or tsunamis. It’s quite another to gain ratification of a treaty obligation imposing huge costs on both the future economy and the individual voters.

The 2015 COP in Paris is scheduled to finalise a climate change treaty which imposes CO2-mitigation obligations on all 194 member countries. Members have four years to ratify  the whole agreement before it supposedly comes into force in 2020.

The process has many aspects of the prisoner’s dilemma, in that no country will want to ratify unless it believes others will do likewise. Nobody believes the majority will sign up in the absence of a benefit-cost analysis which can at least make sense to an alarmist.

These analyses are undertaken in economic models, which ascertain the present value of net impacts of expected temperatures, determined by climate models that are driven by CO2-e concentrations and sensitivities. The impacts will be taken from AR5 WG2 which should reflect the basic science in the WG1 draft released this week.

The prognosis for alarmists is not good. Richard Tol’s literature survey produced a well-known graph of 14 estimates of the global economic impact of climate change, expressed as the welfare-equivalent income gain or loss.

www.aeaweb.org/articles.php?doi=10.1257/jep.23.2.29

This graph shows that net damages from warming don’t accrue until temperatures increase about 2.2°C from 2009, or 3°C from the usual 1850 baseline. However, after a very benign start, it is true that incremental welfare losses do begin to appear after temperatures have risen about 2°C from 1850 levels.

Tol’s graph accounts for the 2°C upper limit adopted by the G8, which was proposed to the UNFCCC at Copenhagen, and adopted at Cancun (2010; COP16).

However, that 2°C target is becoming further and further out of reach. No progress at all has been made in the past 17 years and these doldrums may continue indefinitely. The SREX report has knocked over swathes of impact possibilities. And now there’s an inescapable need to reduce ECS by half, or at least a third!

This was a terribly dispiriting outlook for the climate industry – so it was essential that AR5 pull something out of the hat.

One area had potential for improvement. The “tipping point” or “irreversible” events that all previous reports had treated as too far-fetched to warrant much attention could be added into impact valuations if they were accorded a percentage probability. Insurance underwriters suggested “high-impact, low-probability risks” (eg http://eprints.lse.ac.uk/37612) might supply the best hope to justify imposition of an expensive premium payment under a global risk management plan.

AR5 duly introduced some new definitions and came up with the Table 12.4 discussed at the Royal Society meeting reported by Bishop Hill:

http://www.bishop-hill.net/blog/2013/10/2/a-report-from-the-royal.html?lastPage=true&postSubmitted=true

Here we see a familiar list – collapse of ice-sheets, release of permafrost and clathrate methane, forest die-back and loss of monsoons. Sure they have low probabilities and varying confidence levels, but the impacts will run to trillions of dollars. Even 5% of one of these events is a very large number.

A great deal depends upon whether the probabilities are temperature-factored. If, for example, monsoonal collapse is included as a small risk from a low threshhold temperature, it might avoid much of the time-discounting effect. This could make it a major NPV player in future economic models. Such prospects explain why Table 12.4 held such an important place in the agenda of the Royal Society meeting.

There is also a (weak) philosophical argument that irreversibilty should overcome the usual effect of time-discounting. No doubt this will be a topic addressed by Oxford moral philosopher, John Broome, who is to be a lead author  of WG3.

But Table 12.4 might be a double-edged sword. The IPCC has given full rein to its penchant for sweeping and unusual definitions. Thus, TFE.5 says:

“Abrupt climate change is defined in AR5 as a large-scale change in the climate system that takes place over a few decades or less, persists (or is anticipated to persist) for at least a few decades, and causes substantial disruptions in human and natural systems.”

A change is said to be irreversible if the recovery timescale from this state due to natural processes is significantly longer than the time it takes for the system to reach this perturbed state.

“A few decades” is apparently capable of relating to each phase in a long-term process, because, for example, it does not omit the near-complete disintegration of the Greenland ice sheet. “Or less” covers things that take place instantaneously. So the occurrence time element seems to be a red herring.

The persistence time element won’t exclude much either, as the ‘commitment’ concept assumes the continuance of any damaging impact. “Large-scale change” only allows small regional effects to fall outside the ambit of the definition.

So, by and large, this Table 12.4 should include every expected large-scale change in the climate system that “causes substantial disruptions in human and natural systems”. If a feared impact is not mentioned in the table, it is reasonable to conclude that the IPCC does not expect that its “disruption” potential is “substantial”.

‘Abrupt climate change’, as defined, is a useful concept.

Lukewarmers (the majority of skeptics) do not generally hold dogmatic views that anthropogenic global warming (AGW) could never cause small-scale or medium-term changes capable of causing minor disruptions in existing systems. Where they differ from the IPCC is in disagreeing that any such disruptions would be “substantial”. This is usually expressed by saying that skeptics don’t believe in catastrophic (CAGW) or dangerous (DAGW) warming.

With the introduction of these innovative definitions, the lexicon can be re-framed. “Skeptics don’t accept that fossil fuel usage gives rise to any realistic or actionable threat of Abrupt Climate Change (ACC)”  is a statement that even the mainstream media might come to understand.

The items missing from Table 12.4 are like  Sherlock Holmes’ “curious incident of the dog in the night-time”. They are not even “exceptionally unlikely” or “low confidence” possibilities. They just don’t exist as real threats.

Few of the large number of previously accused items are expected by the IPCC to cause “substantial disruption”. Some excluded favourites are:

• persistent tornadoes or flooding or hurricanes (only droughts make the cut);

• non-ice-fed (thermic) sea level rise;

• productivity of food-producing land;

• spread of vector diseases;

• stoppage of Gulfstream flow;

• climate migration and warfare;

• melting of Antarctic sea ice;

• melting of the East Antarctic ice-sheet;

• interference with thermohaline circulation; and

• large-scale species extinction.

And the other good news is that every one of the “substantial disruption” possibilities are seen as “unlikely” by the IPCC except* Arctic Sea Ice melting. This is mainly positive in opening up new sea lanes – while albedo effects have low significance in a slow-warming world.

(*The low-confidence possibility of “permafrost carbon release” has been rendered toothless by its definition as ‘a net source of emissions’. I thought it already was.)

So, now remind me:  why do some see AGW as ‘the greatest moral challenge of our times’?

Related articles

• Judith Curry: Despite hysteric claims, IPCC models incapable of producing abrupt climate change (junkscience.com)
• IPCC says abrupt irreversible clathrate methane, ice sheet collapse are unlikely. (joannenova.com.au)