Scenarios
Much of the literature about climate involves scenarios. These are highly educated speculations about what might happen in the future under various circumstances. While it is true that no one knows for sure what the future holds, we do have a good idea about what happened yesterday, what is happening today and what will probably happen tomorrow.
Scenarios are mental exercises in drawing a line connecting the known past to the known present and then extending that line through the immediate future to a more distant future.
What makes it a scenario is varying the assumptions about future conditions. If global average temperature compared to 1990 has risen 1 degree by the year 2040 that’s one thing. If it has risen by 2-3 degrees then that is quite another thing.
In the book Climatic Cataclysm, the authors present three scenarios:
Expected Climate Change Over the Next 30 Years: Average global temperature rises 1.3 C (2.3 F) as compared to 1990. Global mean sea level rises 0.23 meter (.75 foot). This is bad news for folks in low-lying coastal areas and anyone already experiencing water shortages or extreme weather events, both of which will worsen.
Severe Climate Change Over the Next 30 Years: Average global temperature rises 2.6 C (4.7 F) as compared to 1990. Global mean sea level rises 0.52 meter (1.7 feet). This is really bad news for just about everyone. Melting ice sheets guarantee enormous rises in sea levels over the next few centuries. Water shortages will affect about 2 billion people. Agriculture and fisheries are adversely affected. The developing nations are the most severely affected, but even the developed world feels the strain of diverting resources to deal with the problems.
Catastrophic Climate Change Over The Next 100 Years: Average global temperature rises 5.6 C (10.1 F) as compared to 1990. Global mean sea level rises 2 meters (6.6 feet). This is really ugly. Many low-lying areas are uninhabitable. The Gulf Stream has collapsed. Weather extremes prevail. Agriculture is severely compromised by reduced rainfall. The southwestern United States, much of South America, Central America and northern Mexico are no longer livable.
What defines each scenario is the rate at which Earth gets warmer, which in turn is derived from varying assumptions about future levels of carbon emissions. The higher the levels of carbon emissions, the greater the rise in temperature, which in turn has consequences ranging from moderate to severe to well, cataclysmic.
A lot of people are very uncomfortable with the whole notion of scenarios. It is after all nothing more than highly educated guessing that is very much affected by the assumptions that underlay the analysis. It is not unknown for political or ideological agendas to influence the assumptions and variables that go into scenarios.
On the other hand, if you are a policy-maker trying to come up with a sensible plan to deal with a future problem, scenarios are very helpful in framing the debate. Properly constructed scenarios can help the deciders choose the lesser of the many evils that confront us on any given day.
Note: For more information on how scenarios are framed, check out the UN Intergovernmental Panel on Climate Change Data Distibution Center Environmental Data and Scenarios page.
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