While much of climate science is pretty firmly established, whatever Donald Trump may think, climatologists are still puzzling out some of the details. And some of those details are turning out to be very important.
Feedback is one such critical detail. Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. In positive feedback, the chain amplifies itself. The chain of cause and effect increases the outputs of the system, which flow back in and further amplify that system.
It’s becoming clear that permafrost thawing is a positive feedback in global warming. As the atmosphere warms, permafrost thaws and the microbes in the carbon-dense soils decompose the organic materials, increasing the amount of CO2 and methane (CH4) stored there. That additional CO2 and CH4 contributes to the greenhouse effect, accelerating the rate of permafrost thawing. The outputs from global warming – more heat – operate as inputs to permafrost thawing, which promotes microbial growth, creating more greenhouse gases. A positive feedback loop.
Positive feedback loops are dicey. They can run away, greatly accelerating the underlying process. Sometimes it leads to a yeast growth effect, where in a brief time the system can explode out of control. Climatologists are just now puzzling out the probable effect of permafrost thawing as a positive feedback effect on climate change.
Northern permafrost soils represent the largest terrestrial organic carbon pool (1330–1580 petagrams, Pg) on Earth. While frozen, this soil carbon reservoir is stable. When it thaws, however, things change:
Future soil warming and permafrost thaw suggest that permafrost soil carbon will be increasingly vulnerable to decomposition by microbes that generate the greenhouse gases carbon dioxide (CO2) and methane (CH4). This release of permafrost carbon as greenhouse gases constitutes a positive feedback likely to amplify climate warming beyond most current earth system model projections
It turns out that how it melts is critical to the rate at which the microbe decompose all those organics. Current projections assume simple thawing. Recent studies, including one by University of Alaska Fairbanks’ Katey Walter Anthony and others, published in Nature Communications, make it pretty clear that at least for the next 10-15 years, water will be the thawing agent, and water’s greater thermal conductivity greatly increases the rate of thaw and, as a result, the strength of the positive feedback. A recent study concluded:
Abrupt thaw lake emissions are similar under moderate and high representative concentration pathways (RCP4.5 and RCP8.5), but their relative contribution to the [permafrost carbon feedback] is much larger under the moderate warming scenario. Abrupt thaw accelerates mobilization of deeply frozen, ancient carbon, increasing 14C-depleted permafrost soil carbon emissions by ~125–190% compared to gradual thaw alone.
At the high end, CO2 and CH4 emission from melted permafrost may be nearly twice as high as previously thought.
It’s positive feedback with a vengeance. The net effect is to increase the rate of atmospheric warming and the other effects of those additional greenhouse gases in the atmosphere. It also means the existing models are wrong: they understate the rate the world’s temperatures are going to increase, and the world’s oceans acidify. It’s going to get warmer faster; the oceans are going to get more acidic faster.
It’s worth mentioning that these recent studies are likely conservative assessments.
So tell WC again why Alaska continues to base its economy on fossil fuels?