Runaway Feedback

Ending greenhouse gas emissions may not stop global warming: study

Marlowe Hood 11/12/2020 Phys.Org

Even if humanity stopped emitting greenhouse gases tomorrow, Earth will warm for centuries to come and oceans will rise by metres, according to a controversial modelling study published Thursday.

Natural drivers of global warming—more heat-trapping clouds, thawing permafrost, and shrinking sea ice—already set in motion by carbon pollution will take on their own momentum, researchers from Norway reported in the Nature journal Scientific Reports.

The Rumbling ESAS Methane Enigma

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Unfortunately, recent events in the high Arctic lean toward option number one ((1) high risk -- methane bursts will bury civilization with runaway global warming – a dreadful, deadly risk) as the more likely outcome. In that regard, I recently met with Dr. Peter Wadhams, world-renowned Arctic expert, to discuss the issue (more on that follows). 

As it happens, only recently, inordinately high levels of methane emissions have been reported, to wit:  

(1) Methane Observation -- October 2019 -- “This is the most powerful seep I have ever been able to observe. . .No one has ever recorded anything similar.” (Source: Research Vessel Encounters Giant Methane Seep in Arctic Waters, The Maritime Executive, Oct. 10, 2019) The quote is from Professor Igor Semiletov, Tomsk Polytechnic University, on the research vessel Academic M.A. Lavrentyev on a 40-day Arctic mission. 

(2) Methane Observation -- December 2019 -- Three months later at COP25 in Madrid, Dr. Peter Carter, an IPCC expert reviewer, in an interview d/d December 10, 2019, referenced an ongoing eruption of methane above Barrow, Alaska, saying: “We’ve never seen anything like it. And, it has stayed at elevated levels to the present week. Looking at the 2.2 million-year ice core, the maximum methane concentration ever was 800 ppb. In Barrow, Alaska it is 2,050 ppb and staying there. It’s been up there for four months.” 

Trajectories of the Earth System in the Anthropocene

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Risk of a Hothouse Earth Pathway

Limit Cycles and Planetary Thresholds.

The trajectory of the Earth System through the Late Quaternary, particularly the Holocene, provides the context for exploring the human-driven changes of the Anthropocene and the future trajectories of the system (SI Appendix has more detail). Fig. 1 shows a simplified representation of complex Earth System dynamics, where the physical climate system is subjected to the effects of slow changes in Earth’s orbit and inclination. Over the Late Quaternary (past 1.2 million years), the system has remained bounded between glacial and interglacial extremes. Not every glacial–interglacial cycle of the past million years follows precisely the same trajectory (7), but the cycles follow the same overall pathway (a term that we use to refer to a family of broadly similar trajectories). The full glacial and interglacial states and the ca. 100,000-years oscillations between them in the Late Quaternary loosely constitute limit cycles (technically, the asymptotic dynamics of ice ages are best modeled as pullback attractors in a nonautonomous dynamical system). This limit cycle is shown in a schematic fashion in blue in Fig. 1, Lower Left using temperature and sea level as the axes. The Holocene is represented by the top of the limit cycle loop near the label A.

Our analysis suggests that the Earth System may be approaching a planetary threshold that could lock in a continuing rapid pathway toward much hotter conditions—Hothouse Earth. This pathway would be propelled by strong, intrinsic, biogeophysical feedbacks difficult to influence by human actions, a pathway that could not be reversed, steered, or substantially slowed.

Where such a threshold might be is uncertain, but it could be only decades ahead at a temperature rise of ∼2.0 °C above preindustrial, and thus, it could be within the range of the Paris Accord temperature targets.

The impacts of a Hothouse Earth pathway on human societies would likely be massive, sometimes abrupt, and undoubtedly disruptive.