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Dark surface

Dark surface

Descending air 'caps' the rising air — no rain

Descending air 'caps' the rising air — no rain

. 2 km altitude

Weaker convection

Less heating

Light surface

Figure 5.1. If we take two equally moist surfaces with different albedo values, the darker low-albedo one is more likely to give rain, (a) Ascending air over a dark surface rises high, then cools and condenses out water droplets that can form rain, (b) Air does not rise as high above a light-coloured surface and so is less likely to condense out water droplets.

aridity, making things more arid than they would have been to start off with. This process of reinforcement is known as positive feedback (see Box 5.1).

So, there is a positive feedback process involving surface reflectivity in deserts, and this can intensify the arid desert climate. However, the mechanism is also liable to break down sometimes and produce a sudden flip between moist and dry climates, if a slight triggering change in the environment occurs. This triggering change could be something natural, or something caused by humans.

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Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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