Emery Letter

Chaotic events and nonlinearities in climatic evolution.

Alan Emery is a frequent contributor to a discussion forum I scan; not to put too fine a point on it, he’s the one there most worth reading. Here is a recent post, responding to a question [a challenge, really] as to how it is possible to say what can happen in climate is there are chaotic events and nonlinearities to be expected?  Emery explains James Hansen’s method for dealing with the problem as regards ice melting and sea level rise. –zj 

Emery writes:

You are quite correct…. Examination of the natural factors that could cause dramatic non-linear events further underscores that these are quite possible.

In 1990, Tom Goreau (Jr) (PDF View…) proposed using paleo evidence as the basis for realistic projections of the effects of increased CO2. One paleo model used by both Goreau in the 1990s and Hansen very recently is the Eemian (the last interglacial period) when the atmospheric CO2 level was slightly elevated above the norm to about 280 ppm and the global temperature averaged about 2C-3C above today’s average global temperatures. The present calculations suggest that a forcing of 3C for CO2 doubling is about right for the rapid feedbacks (water vapour, clouds, aerosols, and sea ice).

Non-linear events are not included in the current mathematical models… . For example if the Antarctic and Greenland ice sheets begin to disintegrate at a rate such that the dynamics and momentum itself are in control, then no amount of greenhouse gas emission reduction will stop the process. Hansen points out there are no [historic] examples of such rapid changes in warming, so the behaviour of the ice sheets is unpredictable and the ultimate rates of sea level rise are unknown, but could be in meters per century or even per decade.

Hansen also remarks that methane hydrates and organic matter trapped in permafrost can rapidly amplify warming effects. Paleo climate examples include rapid spikes of 5C-6C. Goreau predicts temperatures as much as 30C above the norm for the Arctic and tropical temperature regimes in the now temperate zones for CO2 levels of 350ppm – well below what we are now and way below what we will reach with current plans for transitioning away from fossil fuels. Unless that speeds up dramatically we will likely reach 500ppm to 550 ppm by 2100. Another confusing factor was that the apparent temperature regime of the deep ocean changed dramatically with the deep ocean temperatures rising to 12C-14C. These predictions are consistent with the paleo evidence.

Both Goreau and Hansen suggest policies to halt the problems. Goreau emphasizes a wide range of approaches but stresses an approach so far largely ignored; that of using the natural processes of soil and plant absorption of CO2. Hansen also agrees with a wide range of ideas, including soil sequestration, but he states emphatically that the only energy source that can scale up fast enough is nuclear.

One of the dangers of the short time frame of the IPCC and political planning is that it essentially ignores the longer term oceanic process that will lock in many meters of sea level rise and far more temperature rise than the fast forcings* suggest.

*The only forcings included in the IPCC model—zj

What rate of change would be not be too fast for humans to react appropriately? People in the Florida Keys even now have to wade the streets at king tides. Surely they know what is going to happen? But shoreline properties are still selling well. (Have to admit, I am not tempted). Imagine hundreds of millions or even a billion people retreating slowly from sea shorelines creeping landward inexorably destroying infrastructure and salinating freshwater aquifers, and having to abandon farmlands in Mexico and the southern US, large tracts of Africa and Asia in the face of persistent drought. If a mere 8 million people on the move as refugees [as now] causes world emergencies, the impact of a hundred times as many refugees is unthinkable and could easily destabilize civilization as people scramble for survival.

Is that picture a ridiculously overblown piece of hyperbole? I don’t know, but at least right now the best minds who have thought and calculated carefully using past examples as their reference points don’t think it is alarmist.