Understanding Climate-2

How is the climate determined? (Earths energy budget)

All the parameters of the Earth’s climate (wind, rain, clouds, temperature…) are the result of energy transfer and transformations within the atmosphere at the Earth’s surface and in the oceans. Over time, the Earth’s climate remains largely stable because the energy received is equal to that lost (the energy budget is balanced). The sunlight hitting earth (solar radiance) is on average, 1370 watts per square meter (W/m²).

The temperature of the Earth results from a balance between energy coming into the Earth from the Sun (solar radiation) and the energy leaving the Earth into outer space.  About half the solar radiation striking the Earth and its atmosphere is absorbed at the surface. The other half is absorbed by the atmosphere or reflected back into space by clouds, small particles in the atmosphere, snow, ice and deserts at the Earth’s surface.

Part of the energy absorbed at the Earth’s surface is radiated back (or re-admitted) to the atmosphere and space in the form of heat energy. The temperature we feel is a measure of this heat energy. In the atmosphere, not all radiation emitted by the Earth reaches outer space. Part of it is reflected back to the Earth’s surface by the atmosphere (the green house effect) leading to a global average of around 14°C, well above the -19°C which would be felt without the natural greenhouse effect. This effect is illustrated in the diagram.

Because the Earth is round and its position in the solar system, more solar energy is absorbed in the tropics creating temperature differences from the equator to the poles. Atmospheric and oceanic circulation contributes to reducing these differences by transporting heat from the tropics to the mid-latitudes and the polar regions. These

equator to pole exchanges are the main driving force of the climate system.

The energy budget of the Earth can be changed, which in turn can affect the Earth’s temperature. An increase in the greenhouse effect, feedbacks in the climate system, or other changes can modify the energy budget of the Earth.