Scenario Overview Severe Climate Change

The recently released Intergovernmental Panel on Climate Change (IPCC) studies are a substantial improvement over their predecessors: they now assign probabilities to alternative physical outcomes of climate change, and they express these alternatives within a time frame. That said, it is important to keep in mind that the IPCC models still provide only a starting point for estimating the national security implications of climate change.

Much more needs to be done before it will be possible to convert broad-gauged forecasts of climate change into relatively precise forecasts of local climatic changes, from which it would then be possible to assess the economic, social, and political consequences. Nevertheless, climate change itself is no longer debatable and prospective: it is under way, and every week brings word that rates of change are much faster than had been anticipated.

The IPCC reports make it possible to chart at least a notional timeline for significant environmental and ecological change over the next century. There are considerable uncertainties as to the timing and magnitude of events along this line, but we have enough data to warrant making at least approximate correlations between these events and their policy and security implications.

The projection of severe climate change employed in this chapter is based on IPCC findings,1 with an adjustment to account for possible "tipping point" events such as the abrupt release of massive quantities of methane from melting tundra or of carbon dioxide as the sea warms up. Under these conditions, adverse trends could accelerate abruptly, as follows:

—Over the next thirty years, average global surface temperature rises unexpectedly to 2.6°C (4.7°F) above 1990 levels, with larger warming over land and at high latitudes. Dynamic changes in polar ice sheets accelerate rapidly, resulting in about 52 centimeters (20 inches) of sea level rise. On the basis of these observations and of improved understanding of ice sheet dynamics, climate scientists express high confidence that the Greenland and West Antarctic ice sheets have been destabilized and that 4 to 6 meters (13 to 20 feet) of sea level rise are now inevitable over the next few centuries, bringing intense international focus to this problem.

—Water availability decreases strongly in the most affected regions at lower latitudes (dry tropics and subtropics), affecting 1 billion to 2 billion people worldwide. The North Atlantic meridional overturning circulation (MOC) slows significantly, with consequences for marine ecosystem productivity and fisheries.

—Crop yields decline significantly in the fertile river deltas because of sea level rise and damage from increased storm surges. Agriculture becomes essentially nonviable in the dry subtropics, where irrigation becomes exceptionally difficult because of dwindling water supplies, and soil salinization is exacerbated by more rapid evaporation of water from irrigated fields. Arid regions in the low latitudes have spread significantly by desertification, taking previously marginally productive crop lands out of production.

—Global fisheries are affected by widespread coral bleaching, ocean acidification, substantial loss of coastal nursery wetlands, and warming and dry ing of tributaries that serve as breeding grounds for anadromous fish (ocean fish that breed in freshwater streams).

—The Arctic Ocean is now navigable for much of the year because of decreased Arctic sea ice, and the Arctic marine ecosystem is dramatically altered. Developing nations at lower latitudes are impacted most severely because of climate sensitivity and high vulnerability. Industrialized nations to the north experience net harm from warming and must expend greater proportions of GDP adapting to climate change at home.

This projection serves as the basis for a scenario depicting the possible societal consequences of severe climate change over the course of thirty years. These consequences are not to be taken as predictions: they represent a selected construct of the future, intended to encourage reflection about the consequences of continued inaction.

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