The lithosphere

The lithosphere is the surface crust of the Earth, the mountains, rocks and ocean basins. While it does interact with the overlying atmosphere, by transfers of mass and energy, its very long response time means that except for geological time-scales, the lithosphere can be regarded as unchanging. On geological time-scales continental drift, uplift and subsidence may all play a role in the modulating the climate.

Interactions: feedbacks and sensitivity

The sub-systems of the climate are not always in equilibrium with each other or in internal equilibrium. The sub-systems also have feedback loops. Feedback is a term coined from electronics where a change in the original signal results in a change in output which then feeds back into the signal again. It is these feedbacks which make the climate system so complex as an original forcing to the system will be considerably altered by these feedback loops. Feedbacks can be positive or negative. Positive feedbacks are where the original signal is amplified. In negative feedbacks the signal is damped. Positive feedbacks are much more common in natural systems than negative feedbacks. A good example of a positive feedback in the climate system is the ice-albedo feedback. The distribution of snow and ice cover depends primarily on the near surface air temperature. If a perturbation occurs which decreases the temperature, more snow and ice will be able to form. Snow and ice are highly reflective and so increased snow cover will reflect more solar radiation leading to decreased near surface air temperatures. Similarly, as the temperature increases so the amount of snow and ice will decrease and the amount of solar radiation absorbed will increase and the temperature will rise. By contrast, one of the few negative feedbacks to be identified relates to the Stefan-Boltzmann Law. If the temperature of the atmosphere increases, then it will lose more radiation to space (by the Stefan-Boltzmann law). This will reduce the temperature and ameliorate the original change (Peixoto and Oort, 1992).

Sometimes it is not always clear which feedback dominates. A good example of this are clouds. Clouds reflect and scatter incoming solar radiation. As much as 80 per cent of incoming solar radiation may be reflected back into space by clouds (Coley and Jonas, 1999). This albedo effect of clouds leads to a cooling of the Earth, an apparently negative feedback. Clouds, however, are composed of water which is a very good absorber of long-wave radiation, therefore clouds have a greenhouse effect. Clouds warm the Earth by trapping the outgoing long-wave radiation which is a positive feedback. On a global annual average clouds act to cool the Earth. Generally low clouds act to cool the Earth while high thin cirrus clouds act to warm the Earth (Coley and Jonas, 1999). The large control that clouds have on the radiation balance means that clouds are an important area of study for climatologists. It is fairly easy to see that a change in cloud amount will affect the Earth's radiation budget and clouds may well change in response to global warming. This aspect of cloudiness will be discussed further in Chapter 6.

Due to feedback even for a forcing, which could be measured quite accurately, it is very difficult to predict how the climate system will respond. Through the various feedback mechanisms the climate might be quite stable to large forcings or it might be extremely unstable and change in response to very small forcings. Climatologists therefore talk in terms of the sensitivity of the climate to a forcing. Sensitivity is (as defined by Houghton et al., 1990) the change in surface air temperature in response to a radiative forcing.

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  • carisio
    How lithosphere change climate?
    4 months ago
  • asmara
    How does global warming affect the lithosphere?
    3 months ago

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