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Climate is usually described in terms of...

the mean and variability of temperature, precipitation and wind over a period of time, ranging from months to millions of years.


What are external factors that affect climate called?



How does climate evolve?

Internal dynamics and forcings


What are some examples of external forcings?

Natural phenomena such as volcanic eruptions and solar variations, as well as human-induced changes in atmospheric composition.


What powers the climate system?

Solar radiation


There are three fundamental ways to change the radiation balance of the Earth:

1) by changing the incoming solar radiation (e.g., by changes in Earth’s orbit or in the Sun itself)
2) by changing the fraction of solar radiation that is reflected (called ‘albedo’; e.g., by changes in cloud cover, atmospheric particles or vegetation)
3) by altering the longwave radiation from Earth back towards space (e.g., by changing greenhouse gas concentrations).


About 30% of the sunlight that reaches the top of the atmosphere is reflected back to space. Roughly two-thirds of this reflectivity is due to...

Clouds and small particles in the atmosphere known as ‘aerosols’.


To balance the incoming energy what must happen?

The Earth itself must radiate, on average, the same amount of energy back to space.
The Earth does this by emitting outgoing longwave radiation.


What does and does not contribute to the greenhouse effect?

The most important greenhouse gases are water vapour and carbon dioxide. The two most abundant constituents of the atmosphere – nitrogen and oxygen – have no such effect.


Because the Earth is a sphere, more solar energy arrives for a given surface area in the tropics than at higher latitudes, where sunlight strikes the atmosphere at a lower angle. Energy is transported from the equatorial areas to higher latitudes via...

atmospheric and oceanic circulations, including storm systems.


Due to the rotation of the Earth, the atmospheric circulation patterns tend to be...

more east-west than north-south.


Give an example of a positive feedback.

For example, as rising concentrations of greenhouse gases warm Earth’s climate, snow and ice begin to melt. This melting reveals darker land and water surfaces that were beneath the snow and ice, and these darker surfaces absorb more of the Sun’s heat, causing more warming, which causes more melting, and so on, in a self-reinforcing cycle.