Tipping Points for Processes that Can Accelerate Climate Change
Larry Kane
It is impossible to ignore that climate change is already having significant impacts in the U.S. and other countries of the world. The mean global surface temperature has already increased 1° C above pre-industrial levels, and the corresponding increase is greater over land masses.[i] At its worst, some areas of the world, such as in the Middle East and Pakistan, for example, are experiencing weeks or more of peak daily temperatures over 50° C (122° F), at the very extreme of human tolerance. Many more areas are incurring temperature increases that, though lower than such extremes, are high enough to seriously diminish crop productivity. The increasing temperatures and acidity of ocean waters are seriously damaging coral reefs, which are critical for biodiversity and fecundity of much ocean life. Temperature increases are relatively higher in the polar regions, leading to rapid melting of summer ice in the Arctic Ocean and in land-based glaciers, which in turn are contributing to sea level rise. Violent storms of increased frequency and force are battering coastal areas in many parts of the world.
Most of these impacts are worsening more quickly than had been previously projected by climatologists. While these developments depend on the direct relationship between increasing atmospheric carbon dioxide concentrations and climate impacts, there are categorically worse potential changes that are becoming more worrisome as carbon dioxide (CO2) concentrations are reaching levels not seen in over a million years. The phenomena of particular concern are known as “tipping points,” which are the ultimate result of other phenomena called “self-reinforcing processes.”
Self-reinforcing processes. This term refers to interactions among related physical processes in which a change in one process positively reinforces a second process so as to speed up or increase the magnitude of the second process. Following are some examples of such self-reinforcing processes that can accelerate or otherwise exacerbate climate change.[ii]
· Thawing of Arctic permafrost: permafrost soils in the Arctic are estimated to confine a quantity of methane that is 50 to 60 times the amount of CO2 emitted annually worldwide from the combustion of fossil fuels. As mean global temperatures rise, Arctic temperatures rise even higher and are threatening to thaw permafrost. To the extent permafrost does thaw, the methane trapped in those soils — a much more potent greenhouse gas than CO2 — will be released into the atmosphere, contributing to yet higher increases in mean global temperatures.
· Melting of ice and snow. Light-colored snow and ice in the Arctic and Antarctic regions help reduce the amount of surface warming from solar radiation by reflecting the incoming solar radiation back into space. However, as surface temperatures rise as a result of global warming, more ice and snow will melt in the polar regions, revealing darker sea water or soils which have lower reflectivity and thus will absorb more heat from solar radiation. Thus, increased exposure of darker surfaces will accelerate the melting of snow and ice cover and lead to more rapid surface warming. This self-reinforcing process is further amplified by the fact, as alluded to above, that higher surface temperatures occurring from climate change are not uniformly distributed across the Earth’s land surfaces but are more pronounced in the polar regions.
Tipping Points. A tipping point is a threshold level in a certain self-reinforcing process that, once surpassed, results in a runaway or irreversible reaction or change. The following potential tipping points have been identified by scientists in the context of climate change:[iii]
· The breakup of the West Antarctic ice sheet;
· The melting of the entire Greenland ice sheet;
· Massive release of methane from thawing Arctic permafrost;
· Termination of the Atlantic Meridional Overturning Circulation system
· Severe reduction or collapse of the Amazon rainforest; and
· Severe damage or death of coral reefs.
Exceedance of any of these thresholds is believed by climate scientists to seriously threaten a rapid acceleration of climate disruption that could not be alleviated for many centuries or even millennia. There is a further prospect that the triggering of adverse impacts from exceedance of such a tipping point could in turn accelerate the reaching of another tipping point, resulting in cascading tipping points — a type of domino effect.
Current Status. Trends in climate change impacts that threaten triggering a tipping point include:
o West Antarctic Ice Sheet: this portion of Antarctic ice could raise sea level by up to 10 feet if it were to melt. It is more vulnerable since it sits in large part upon bedrock whose upper surface is below sea level. Some scientists question whether a tipping point has already past for the instability of this ice sheet. Others consider it to be dependent on whether mean annual air temperature will exceed 2° C above current levels. If a tipping point were reached, the melting of this immense ice sheet will irrevocably proceed, although its completion may take centuries.[iv]
o Greenland Ice Sheet: there is an estimated 684,000 cubic miles of ice residing on Greenland, totaling over 2,500,000 gigatons. Were all this ice to melt, it would raise sea level by more than 20 feet. A recent study reports that climate change has accelerated the rate of melting of Greenland’s ice by a factor of 10 times over the period from 1992 to 2017 to a rate of roughly 250 gigatons per year.[v] Recent estimates put the likely threshold for the tipping point for the melting of this vast ice reservoir as 1.6–1.8° C above pre-industrial levels, which most likely will be reached in this century. Once the tipping point is reached, there is no stopping the process although many centuries are likely to be required for all Greenland ice to melt.[vi]
o Arctic Permafrost: Reports of thawing permafrost in some Arctic areas are already surfacing and the forest fires that occurred in Siberia in the early summer of 2020 will exacerbate thawing of permafrost. Approximately 25% of the land area of the northern hemisphere overlies permafrost containing huge quantities of frozen organic matter. In total, permafrost is estimated to contain roughly twice the quantity of carbon that presently exists in the atmosphere. While some researchers have suggested that there may be an abrupt tipping point for irreversible thawing of the permafrost, the broader sentiment appears to be that there will be an ongoing positive feedback to climate change as more CO2 and methane are released from thawing permafrost.
o Atlantic Meridional Overturning Circulation system: this mouthful (abbreviated as AMOC) is the technical name for the system of ocean currents that: (i) transport warm semitropical ocean water via the shallow Gulf Stream and North Atlantic Current to western Europe and (ii) transport cool water from the far north Atlantic via deeper currents to equatorial regions of the Atlantic. Climate change has the potential to disrupt this oceanic circulatory system as it melts ice in the northern reaches of the Atlantic and the fresh water resulting from the melting dilutes the denser salt water that otherwise would sink to greater depth for the return trip to the equatorial region. Research indicates that the AMOC has already been weakened by about 15% since 1950. There is considerable uncertainty whether there is a threshold point of climate warming that would totally interrupt the AMOC, although most researchers appear to agree that an increase in mean global temperature of 3° C to 4° C above pre-industrial levels would be necessary to shut down the AMOC.[vii]
o Amazon Rainforest: This vast rainforest is the largest in the world. Its importance as a natural resource includes being: (1) one of the world’s greatest sources of biodiversity; and (2) an important sink for atmospheric carbon dioxide. But the Amazon rainforest is under direct attack by humans who are clearing sections of the forest for crop production and cattle grazing. It is estimated that approximately 17% of the rainforest has already been cleared. Such deforestation is a threat to the survival of the rainforest for at least two reasons. One is the obvious direct physical loss of trees from deforestation. The second is the loss of moisture input to the atmosphere that otherwise occurs from tree leaves through transpiration. Ironically, the survival of rainforests depends on large part on the moisture given off by plant transpiration. A rainforest supplies half of the rainfall it receives through transpiration and evaporation of surface water. As the number of trees dwindles, there is less moisture given off and the climate becomes drier. It appears that there is a critical (minimum) mass of tropical trees that are necessary to sustain a rainforest. Some scientists have estimated that a 40% loss of tree cover due to deforestation could be a tipping point for conversion of the rainforest to a drier savannah ecosystem. When increased heat from climate change and forest fires (the main deforestation method) are considered, some scientists posit that the tipping point could be as low as 20% to 25% loss of forest, which is perilously close to the loss that has already occurred.[viii]
o Coral Reefs: The health of coral reefs depends on a symbiotic relationship between coral polyps and one-celled algae that reside within each polyp. A polyp is a simple, immobile animal with a cup-like structure and tentacles surrounding its mouth. Polyps secrete calcium carbonate that forms a hard “skeleton” surrounding each polyp. Reefs are formed by a large colony of coral polyps. The algae provide oxygen and nutrients to the polyps while the polyps in turn provide carbon dioxide needed by the algae for photosynthesis. The algae also provide colored pigment to the coral. Climate change becomes a serious threat to coral reefs because heat stress can cause coral polyps to expel the algae from their bodies. Since the presence of the algae are needed for the polyps’ survival, the expulsion of the algae, if it persists for a long enough time, will result in starvation of the polyps. Thus, long-term heat stress of a coral reef will lead to death of the coral polyps, also referred to as the “bleaching” of the reef (since the coloration by the algae is missing). Increased warming and acidification of ocean waters, particularly in the near shore areas in which reefs exist, is occurring from climate change and has already caused extensive damage to coral reefs throughout the world. Investigation has shown that the majority of reefs exhibit severe bleaching, including those in the Caribbean and the northern half of the Great Barrier Reef. Some researchers have proposed that 90% of tropical reefs will be at severe risk with climate warming of 1.5° C and 98% of reefs at 2° C warming. At this point, maintaining climate change to an increase of 1.5° C appears dubious at best, so the world may be on the very threshold of a tipping point for tropical coral reefs. If so, this will be a serious loss since coral reefs provide habitats for over 25% of all marine fish species and fisheries associated with reefs have supported hundreds of millions of people.[ix] Overfishing of these fisheries has become another chronic stress endangering the survival of these natural resources.
Conclusions. Self-reinforcing processes can be a significant factor in accelerating the impacts of climate change that we are already beginning to experience. Although there is some degree of uncertainty concerning the threshold that would trigger one or more of the tipping points listed above or the timeframe it would take to reach that threshold, the severity of the impacts if a tipping point is reached make them worthy of serious concern. Clearly, it must be a critical objective for any climate change mitigation strategy to prevent, to the extent humanly possible, any of these tipping points from being reached.
Endnotes
[i] If fossil fuel emissions were to continue at present rates, it is projected by climate scientists that mean global temperatures could increase another 4.5° C (8.1° F) by 2100. See IPCC’s Fifth Assessment Report.
[ii] Living in the Environment, pp. 503–506, G. Tyler Miller, et al., 2012 Brooks/Cole.
[iii] Ibid, pp. 510–511; “Nine ‘tipping points’ that could be triggered by climate change”, Carbon Brief, February 2020.
[iv] “Nine ‘tipping points’ that could be triggered by climate change”, Carbon Brief, February 2020.
[v] “Mass balance of the Greenland Ice Sheet from 1992 to 2018”. Shepherd, Andrew, et al., 2020, Nature. 579.
[vi] “Nine ‘tipping points’ that could be triggered by climate change”, op.cit
[vii] Ibid.
[viii] Ibid.
[ix] “Symbiotic Relationships in Coral Reefs,” Frontier — Into the Wild, October 2018; “Nine ‘tipping points’ that could be triggered by climate change”, op.cit.
