While the warming conditions in the Arctic and the continuing seasonal melting of the permafrost will produce increased rates of global warming, the amounts particularly in the latter case are very uncertain. Our best guess is that it will take, perhaps, centuries for the permafrost to fully decay and produce its effects. We really don’t know how long it will take and what its effects will be. The permafrost is like a giant compost heap, not worked at all in the summer months, but active on its hard-to-work surface during the summer when it slowly releases some of its greenhouse gases. Below the surface a foot or so or even as far as 2-3 feet down everything is frozen solid. We’ve no ideas how to work the pile so far, and thus we cannot influence the rate at which microorganisms will affect it and its conversion to a compost that might even be useful in farming. The best we can say is that as decomposition occurs we will add to the greenhouse gas burden of the atmosphere in ways and at levels that are hard to predict. The tree line around the Arctic is starting to advance significantly and may be expected to take up significant carbon dioxide through photosynthesis, but is unlikely to to compensate for permafrost decomposition as it accelerates. We are developing some permafrost experts who will consider the problem more thoroughly; however, for now permafrost decay is a significant wild card in the potential contributors to global warming we can expect to see going forward.
Second and third wild cards are the continuing melting of ice at the poles and in the release of significant block of above sea-level glacial ice in both Greenland and the Antarctic.
Much of the ice in the Arctic will more than likely melt over the next several decades. We will see more open water in summer in the Arctic and a gradual slow increase in average temperature over the Arctic region. This process will also slowly affect temperature and weather globally since the open water and thermal redistribution of the heated atmosphere and heated oceans over the entire planet will be affected. As I noted in a previous post, we understand this process will change weather patterns, but we don’t understand the particulars well enough to predict how and where even the most obvious changes will occur and with what ferocity (if any). In general, when new patterns of temperature equilibration occur in large complex systems, we should expect some unusual and even wildly violent weather to accompany it. But we don’t know when, where or how such patterns will be produced. Thus, we have the chance to be surprised by new kinds of weather patterns which will likely be transient and not represent long-term recurring formations.
Additional north polar sea ice is mostly surface ice and its melting will not significantly alter sea levels. However, an abrupt loss of the Greenland glacier and/or the glacial shelf in the Western Antarctic would be expected to produce major effects. These large above-sea-level edifices would both increase sea level and produce potentially serious though short term effects on ocean salinity as they melt. The salinity changes have the potential to disrupt the ocean conveyer belt currents and thus the efficiency with which heat is transferred off the equator. Such effects could substantially change coastal weather patterns globally, and put coastal regions where major population centers exist under the sudden more extreme effects of storm surges and a permanent flooding treat. While in some cases sea walls may provide protection, the timeline between when it becomes obvious that such protections are needed and when needs are critical may not be very wide.
In general, by slowing the rate of global warming through reduced power generation using fossil fuels, we can diminish or delay the risks of the several wild cards in play. We can slow the melting of Arctic ice and also slow the release of the Greenland or West Antarctic glaciers. Glacial release should be delayed as long as possible. Best case scenarios suggest that increases in sea level by the end of the century will be of the order of 1-2 meters. If either the high end permafrost evolution of greenhouse gases occurs together with the release of one or both of the major glaciers, then all bets are off. Sea level will rise substantially more than predicted, and coastal regions including island nations with abundant population centers may be at substantially increased risk due to violent and unpredictable weather patterns either from further alterations in the more open Arctic or to changes in local ocean salinity due to released glaciers melting in open seas.
The two glaciers and the permafrost decomposition rate are the three major wild cards affecting planet wide changes from global warming in this century.