Kirk Smith, a colleague also participating in the Global Energy Assessment argues that only about half the warming that has occurred up to now is due to CO2. The rest is caused by other greenhouse gases, particularly methane. Similarly, less than half of the total warming expected over the next 20 years will be caused by CO2.
Recent modelling shows the way to have the biggest impact on warming over this century is to immediately reduce emission of these gases, and keep them low.
Methane is a much more powerful greenhouse gas than CO2. A tonne of methane is responsible for nearly 100 times more warming over the first five years of its lifetime in the atmosphere than a tonne of CO2. Methane is removed from the atmosphere much more rapidly than CO2, with a half-life of 8.5 years compared with many decades for CO2, but a tonne of methane eventually turns to 2.75 extra tonnes of CO2 in the atmosphere. Even without taking this into consideration, a tonne of methane emitted today will exert more annual warming than a tonne of CO2 emitted today until 2075. Not until the year 7300 will the cumulative warming exerted by the two become equal. It is truly carbon on steroids.
Reduction of methane can occur in developing countries and bring numerous health and economic benefits.
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