What If Everything You Knew About Projected Global Warming Was Wrong?
One of the dirty secrets in the climate change community is that the IPCC consensus is widely seen as the lower bound of likely warming because the models do not incorporate the slower and much more powerful positive feedbacks such as increased methane release from permafrost and bogs. In the years since it was released, every study that has looked at the issue has concluded that the models are far far more likely to drastically understate warming and sea level rise than overstating. One reason for this is the growing work on past climate that shows we’re not even in the same ballpark:
The atmospheric CO2 concentration currently is 390 parts per million by volume (ppmv), and continuing on a business-as-usual path of energy use based on fossil fuels will raise it to ?900 to 1100 ppmv by the end of this century (see the first figure) (1). When was the last time the atmosphere contained ?1000 ppmv of CO2? Recent reconstructions (2–4) of atmospheric CO2 concentrations through history indicate that it has been ?30 to 100 million years since this concentration existed in the atmosphere (the range in time is due to uncertainty in proxy values of CO2). The data also reveal that the reduction of CO2 from this high level to the lower levels of the recent past took tens of millions of years. Through the burning of fossil fuels, the atmosphere will return to this concentration in a matter of a century. Thus, the rate of increase in atmospheric CO2 is unprecedented in Earth’s history.
What was Earth’s climate like at the time of past elevated CO2? Consider one example when CO2 was ?1000 ppmv at ?35 million years ago (Ma) (2). Temperature data (5, 6) for this time period indicate that tropical to subtropical sea surface temperatures were in the range of 35° to 40°C (versus present-day temperatures of ?30°C) and that sea surface temperatures at polar latitudes in the South Pacific were 20° to 25°C (versus modern temperatures of ?5°C). The paleogeography of this time was not radically different from present-day geography, so it is difficult to argue that this difference could explain these large differences in temperature. Also, solar physics findings show that the Sun was less luminous by ?0.4% at that time (7)….
Thus, Earth was 16°C warmer at 30 to 40 Ma. … The conclusion from this analysis—resting on data for CO2 levels, paleotemperatures, and radiative transfer knowledge—is that Earth’s sensitivity to CO2 radiative forcing may be much greater than that obtained from climate models (12–14).
As Joe Romm notes:
Methane release from the not-so-perma-frost is the most dangerous amplifying feedback in the entire carbon cycle. The permafrost contains a staggering “1.5 trillion tons of frozen carbon, about twice as much carbon as contained in the atmosphere,” much of which would be released as methane. Methane is is 25 times as potent a heat-trapping gas as CO2 over a 100 year time horizon, but 72 times as potent over 20 years! The carbon is locked in a freezer in the part of the planet warming up the fastest (see “Tundra 4: Permafrost loss linked to Arctic sea ice loss“). Half the land-based permafrost would vanish by mid-century on our current emissions path (see “Tundra, Part 2: The point of no return” and below). No climate model currently incorporates the amplifying feedback from methane released by a defrosting tundra.
OK so the question to the people that don’t think this is a major is simple: why? But before you answer, I will note something about the possible methane release dynamics. In a paper that I regrettably cannot find again (although it was so mathematical that I would expect only a couple of TMV readers would get anything out of it) they point out that based on what we know about permafrost and decomposition, there is a high chance of a random “detonation” of methane. Here is why:
The majority of organic matter waiting to be decomposed is trapped below the surface. As the tundra heats up, the upper layers of this matter are warmed to the point that they thaw out and anaerobic processes start decomposition, which produces methane and heat. This methane and heat are largely trapped under the surface because the top level is compressed in a way that it can’t vent, so the heat warms the matter more, increasing the reaction rate and widening the reaction depth. At some point the pressure underground becomes so high that it fractures the top level and vents. This isn’t speculation, it is a widely observed fact.
What IS speculation is how widespread this is occurring and what it means. Scientists on site are noticing an uptick in the amount of venting locations and we are detecting an increase in methane release through satellite measurements, but so far it is a linear increase (meaning predictable…it’s rising but slowly and steadily). However this paper was a mathematical modelling of the dynamics in a compartmentalized model, which basically means that there are different basins of decomposition that are relatively separate but have some connections, and is a relatively realistic assumption. They show that the dynamics of the whole system will exhibit local stability (small increases in venting) but that the region as a whole will be vulnerable to simultaneously massive methane release, a so called “methane bomb.” Oh, and there would be absolutely no way to predict when it would occur until it does, all we can say is that the warmer the Arctic gets the greater the risk. [For those that know about neuron firing, this is the exact dynamics of action potentials in neuronal firing….you have a quiescent period that holds until the resting potential rises near the threshold and then you have an indeterminate amount of time until the coordinated feedback kicks in and you have the unstoppable action potential. This model even produces the same refractionary period after the methane release that neurons display after APs.]
So in summary, we know we have enough methane trapped in the arctic regions to increase radiative forcing by an extreme amount, we are increasingly confident that in the past that level of GHGs produced temperatures that even if you take the lower bounds are still several times worse than the IPCC projections and there is a very convincing argument that the nature of the Arctic and chemistry means that it could explode without warning at a fundamentally unknowable time…which increases in probability (exponentially) with temperature and all evidence suggests that the last few decades of warming are almost certainly anthropogenic and will continue to increase.
Can we ever “prove” any of this stuff? No, we can’t, but at this point the evidence that supports the fears encompasses an extraordinary amount of scientific fields and the dynamics that suggest we need to be really careful are seen widely in biology, electronics, the stock market/economy, weather formation patterns, crowd behavior, chemical reaction dynamics, ecology, etc etc etc.
We cannot know with certainty what will happen but we seem to be damn close (actually past) the danger point when we may not have any control no matter what we do. People that argue “well I believe in AGW but we need to do a risk analysis to make a rational approach weighing cost and risk” better understand the massive tail risk that is getting wider with our increased understanding…something that wasn’t taken into account for the financial system and the reason why literally “impossible” events transpired. The “impossibility” of rapid warming may prove just as shortsighted.