Best Effort Global Warming Trajectories


	This is a "what if" tool for global warming policy makers. The policy contains just two parameters: the approximate number of (transition) years needed by the world to firmly decrease its annual carbon emissions, and the maximum annual emission reduction effort after that time, expressed in terms of Pacala–Socolow "wedges". Here "effort" is the additional emission reduction effort after all increases of future energy demands have already been met by carbon-free technologies. (So the Pacala-Socolow immediate/seven-wedge strategy is a strategy of zero transitions/zero wedges for the next 50 years). The purple curve is the world's annual carbon emission rate, the blue curve is the trajectory, and the black dashed line is the popular "doubling" target ceiling. All three curves share the same ordinate. The unit GtC stands for billions of metric tons of carbon.


	Contributed by: Harvey Lam (Princeton University)
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The world carbon cycle model is based on the one-tank model of Socolow–Lam:

, where

is time (years) offset from the start of the 21st century,

is atmospheric

in GtC (divide by 2.1 to get ppmv, parts per million by volume), and

is the annual emission rate (GtC/yr). The value of

is constrained to be larger than -0.02 times the number of wedges ("wedge" as defined by Pacala–Socolow), and the maximum effort is reached after "transition years" (the approximate number of years needed by the world to make

firmly negative). For more information, see