Dessler Ch 6 Flashcards
What is radiative forcing?
The change in Ein − Eout for the planet as a result of some change imposed on the planet before the temperature of the planet has adjusted in response.
The advantage of using radiative forcing is that it allows us to express diverse changes to the climate system by using a common metric.
Combining all types of aerosols (those discussed above and several not discussed), the direct radiative effect of aerosols is to…
However, aerosols also have an indirect effect on the climate..
cool the climate
If you add aerosols to a cloud, then you will increase the number of cloud-condensation nuclei- a cloud containing a larger number of smaller droplets is more reflective and slow down the coagulation process whereby cloud droplets combine to form raindrops. This in turn means that the clouds don’t rain, so they last longer.
Over all, human land-use changes have tended to…
cool the climate
Agricultural land typically has a higher albedo than does the natural landscape, especially if the latter is
forest. Thus, cutting down a forest and replacing it with grassland for grazing cattle will increase the surface’s albedo.
However black soot deposited on snow = positive radiative forcing
A final radiative forcing – and one that’s entirely unrelated to humans – comes from…
changes in the amount of solar energy reaching the Earth.
The Sun’s output also varies slightly with a period of
27 days, which is the time it takes the Sun to rotate once on its axis.
Difference between feedback and forcing
Radiative forcings, in contrast, affect the climate but are themselves unaffected by the climate.
How is climate sensitivity expressed?
is a metric used to characterise the response of the global climate system to a given forcing. It is broadly defined as the equilibrium global mean surface temperature change following a doubling of atmospheric CO2 concentration
How long does the earths temperature take to respond to an imposed radiative forcing (e.g., increase in greenhouse gases, change in the solar constant).
Because of the Earth’s thermal mass, the Earth’s temperature takes several decades to
respond.
Positive feedbacks amplify and negative feedbacks ameliorate an initial warming. For the
problem of modern climate change, we are mainly concerned with the following fast feedbacks:
Water vapor, ice–albedo, lapse rate, and clouds. Together, they double to triple an initial warming.
What are feedbacks?
Feedbacks are processes that respond to changes in the surface temperature, whereas forcings are unrelated to the surface temperature. Thus, feedbacks do not initiate
climate change, but forcings do.
