Many of the articles that discuss the projected temperature change from global warming do not explain crucial points in a clear fashion. Since Climate Progress will be discussing temperature a great deal–why the planet must avoid 3°C (5.4°F) warming and how we can do so–a clarifying note is in order.
Americans use the Fahrenheit scale of temperature and have the most intuitive familiarity with it. CP will also use the Centigrade scale because most scientific research uses it. Anyone who wants to become knowledgeable about global warming research needs to become familiar with thinking in centigrade terms. Since our focus is on temperature change, here is the key conversion:
A 1°C change equals a 1.8°F change.
Thus a 5°C change equals a 9°F change
Different parts of the globe are expected to warm up at faster or slower rates than the global average. The land typically warms up faster than the oceans, and higher latitudes warm up faster than the tropics. Most of the inland continental United States is expected to warm up roughly 50 percent faster than the global average. Greenland has been warming up 2.2 times faster than the planet. So an additional average global warming of 2°C (3.6°F) means much of this country would be expected to warm 3°C (4.8°F) and Greenland would warm 4.4°C (7.9°F).
A third confusion can arise when scientists report how much warming will result from a rise in greenhouse gas concentrations. Some report how much the temperature will rise from pre-industrial temperature levels while others talk about how much additional or further warming will occur from present-day levels. The Earth has already warmed 0.8°C through 2005, so the difference is significant. CP will try to state which it is using each time.
Most analyses suggest that a doubling of greenhouse gas concentrations from pre-industrial levels will increase global temperatures about 3°C from pre-industrial levels as Science magazine noted in August 2004 [subs. req'd], which is 2.2°C warming from current levels (although many studies suggest the climate could be even more sensitive to a doubling of CO2 concentrations, as future posts will discuss).
A final, related confusion: Some scientists report how much the temperature will rise ultimately (due to a given rise in greenhouse gas concentrations) while others report only how much the temperature will rise by 2100. Because of the lags in the climate system, those figures can be quite different. CP will usually describe how much temperature will rise by 2100.