The Greenhouse Gamble
("WITH POLICY" Scenario)
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This wheel depicts the MIT Joint Program's estimation of the range of probability of potential global warming over the next hundred years, under the following
policy scenario.
HYPOTHETICAL POLICY:
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- Assumes the Koto Protocol is implemented in 2010 by all countries that agreed to caps in the original protocol.
- The cap is lowered by 5% every 15 years (i.e., 35% below 1990 for all countries under cap by 2100).
- For countries not capped, they assume a cap in 2025 at 5% below their 2010 emissions levels, and reduced at 5% every 15 years thereafter (30% below 2010 by 2100).
- Assumes the Koto Protocol is implemented in 2010 by all countries that agreed to caps in the original protocol.
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For further discussion of this type of uncertainty and probability prediction, see Forest et al., 2004, Webster et al., 2003, Webster, 2003, Forest et al., 2002, Reilly et al., 2001, and Reilly et al., 1999.
In this example, the size of the slice for greater than 3 degrees Celsius warming (shown in orange), which represents the largest temperature increase predicted under this policy scenario, has a probability of 3.5%, or odds of about 1 in 29. The slice representing the smallest predicted change, less than 1 °C (shown in blue), becomes much more likely than in the reference (no policy) case, with a probability of 15.8% (1 in 6 odds).Note that compared to the reference case, this policy scenario not only increases the chances that the warming will be less (the cooler-range slices are larger), but it also removes the warmest two (red and pink) slices from the no-policy pie.
The MOST LIKELY values predicted by the MIT Program for warming under this sample policy scenario are in the lower-range: 1 to 1.5 °C (36%, aqua: 1 in 3 odds), and 1.5 to 2 °C (26.2%, light green: 1 in 4 odds) . The likelihood of the temperature change falling in the other ranges are the following: 2 to 2.5 °C (13%, yellow: 1 in 8 odds), and 2.5 to 3 °C (5.5%, yellow-orange: 1 in 18 odds).
The temperature change is the difference in the global average surface temperature predicted for 2100, with respect to the 1990 value.
