From Emissions to Warming
The presence of an atmosphere containing greenhouse gases (especially carbon dioxide, CO2) is crucial for keeping the Earth's temperature mild enough for human existence. Without greenhouse gases in the atmosphere, Earth's daily temperature would vary between -15 and 150 ºF (-25 and 65 ºC)!
Greenhouse gases are produced in nature and by humans, and emitted into the atmosphere – where they can store infrared radiation (many people think of this as “heat.”). Greenhouse gas emissions increase in both A2 and B2 scenarios. However, they are expected to increase more rapidly under scenario A2 compared with B2. (The figures show that A2 and B2 each are from a “family” of scenarios.) This can be explained by the A2 assumptions compared with B2. Population grows faster under A2, consuming more than a smaller population. Under A2 the larger population emphasizes self-reliance, and relatively slow improvements in technology imply faster use of energy—hence more CO2 emissions.
The amount of warming depends on the concentration of greenhouse gases, particularly CO2. Unless removed, CO2 emissions will accumulate and continue to warm the atmosphere.
SRES stands for IPCC’s Special Report on Emissions Scenarios.
- “ppm” is a measure of concentration and stands for “parts per million.” For example, “300 ppm” means “for every 1 million molecules in the atmosphere, 300 of them are expected to be CO2.”
- A “gigaton of carbon per year” is a measure of carbon dioxide emitted into the atmosphere each year. A gigaton is one billion tons (109 tons). One ton is about the weight of a passenger car.
For more details, go to: Climate Change Scenarios and Projections