Projections of Future Climate Change
Coupled ocean–atmosphere GCMs use transient climate simulations to project/predict future temperature changes under various scenarios. These can be idealised scenarios (most commonly, CO2 increasing at 1%/yr) or more realistic (usually the "IS92a" or more recently the SRES scenarios). Which scenarios should be considered most realistic is currently uncertain, as the projections of future CO2 (and sulphate) emission are themselves uncertain.
The 2001 IPCC Third Assessment Report figure 9.3 shows the global mean response of 19 different coupled models to an idealised experiment in which CO2 is increased at 1% per year. Figure 9.5 shows the response of a smaller number of models to more realistic forcing. For the 7 climate models shown there, the temperature change to 2100 varies from 2 to 4.5 °C with a median of about 3 °C.
Future scenarios do not include unknowable events – for example, volcanic eruptions or changes in solar forcing. These effects are believed to be small in comparison to GHG forcing in the long term, but large volcanic eruptions, for example, are known to exert a temporary cooling effect.
Human emissions of GHGs are an external input to the models, although it would be possible to couple in an economic model to provide these as well. Atmospheric GHG levels are usually supplied as an input, though it is possible to include a carbon cycle model including land vegetation and oceanic processes to calculate GHG levels.
Read more about this topic: Global Climate Model
Famous quotes containing the words projections of, projections, future, climate and/or change:
“Predictions of the future are never anything but projections of present automatic processes and procedures, that is, of occurrences that are likely to come to pass if men do not act and if nothing unexpected happens; every action, for better or worse, and every accident necessarily destroys the whole pattern in whose frame the prediction moves and where it finds its evidence.”
—Hannah Arendt (1906–1975)
“Western man represents himself, on the political or psychological stage, in a spectacular world-theater. Our personality is innately cinematic, light-charged projections flickering on the screen of Western consciousness.”
—Camille Paglia (b. 1947)
“I am not naturally ... “A bag of wind”; yet ... I mean deliberately and decidedly “to cut” in future all my old ideas on this head. I don’t think modesty “pays.” It is a good quality in a family, it is a domestic virtue, it makes a home happy after you have got a home, but it is not potent in getting homes. It is not a money-maker, neither is it lucky in gaining a reputation. I am of the impression that gaseous bodies do better.”
—Rutherford Birchard Hayes (1822–1893)
“If often he was wrong and at times absurd,
To us he is no more a person
Now but a whole climate of opinion.”
—W.H. (Wystan Hugh)
“My love is fair, my love is gay,
As fresh as bin the flowers in May
And of my love my roundelay,
My merry, merry, merry roundelay,
Concludes with Cupid’s curse,—
‘They that do change old love for new
Pray gods they change for worse!’”
—George Peele (1559–1596)