What makes climate?

The climate of a place is the average over a number of years of the day-to-day variations in temperature, precipitation, cloud cover, wind and other atmospheric conditions that normally occur there. Climate also includes the variability of individual climate elements, such as temperature and precipitation, and the frequency with which various weather conditions occur. In other words, climate is the combination of average weather conditions and weather patterns over time for a particular location.

The climate of the earth is a balanced system of interconnected, interacting elements powered by incoming energy from the sun. The main factors affecting climate can be distinguished as either internal or external processes. The internal processes include the circulation of the air and currents of the ocean; the effects of clouds and large masses of snow and ice; the influence of topography, surface soils and vegetation; the impact of processes and activities within the biosphere; and regional, seasonal and daily difference in solar heating. The external factors are solar energy output, atmospheric composition, land features, and ocean characteristics.

Global scale climatic changes occur when the balance between the rate at which energy enters or leaves the global climate system is upset by changes in one or more of its major elements. Possible primary causes for such changes include variations in the aerosol and gaseous content of the atmosphere, changes in the reflective properties of the earth's surface, and alterations in the intensity of sunlight reaching the earth's surface. Complex reactions in other factors are likely as the system adjusts to establish a new balance of input and output energy. Positive feedback refers to the reactions by climatic factors that increase the initial change, such as additional surface warming due to reduced reflected radiation by less snow cover. Negative feedback by other factors would oppose and partially offset change, such as storage by oceans of excess atmospheric heat caused by increased greenhouse gas concentrations.

The change in climate expected within the next four or five decades is believed to be a result of mainly human activities that are causing changes in atmospheric composition (increasing greenhouse gases and aerosols) and changes in land features (reducing natural vegetation).

Source: Henry Hengeveld, March 1995, "Understanding Atmospheric Change", (A State of the Environment (SOE) Report No. 95-2), Atmospheric Environment Service, Environment Canada (pp. 13-18).

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