29.2: What is Climate?
Climate refers to the prevailing weather conditions in a specific area over an extended period. As the saying goes, “Climate is what you expect. Weather is what you get.” Climate is influenced by geographic factors, such as latitude, terrain, and proximity to bodies of water.
Weather and Climate
Weather and climate are related, though they differ in terms of time scale and predictability. Weather refers to the state of the atmosphere at a specific time and place, whereas climate encompasses the “average” weather conditions over a much longer time. In terms of predictability, weather forecasts are limited to days, but the climate can be modeled and predicted over substantial periods, such as years or even decades.
The Climate System
The Earth’s climate system consists of several smaller, interacting sub-systems. The atmosphere is an envelope of gases surrounding the Earth. The hydrosphere consists of all the water on, above, or below the Earth’s surface. Oceans cover more than two-thirds of the Earth’s surface. Ice, including sea ice, glaciers, ice sheets, and snow, comprises the cryosphere, which is also part of the hydrosphere. The geosphere, or lithosphere, consists of the Earth’s crust. Finally, the biosphere includes all the ecosystems on Earth, including all living organisms and their interactions with the atmosphere, hydrosphere, cryosphere, and lithosphere. These sub-systems exchange energy, water, and momentum. The power source driving all of these complex interactions is radiation from the sun.
Planetary Energy Balance
The climate system is powered by radiation from the sun; however, solar radiation does not even provide enough energy to keep the Earth above freezing temperatures. The Earth’s temperature, which has a significant impact on climate, depends on the amplification of thermal energy from solar radiation. The Earth’s surface absorbs approximately 49% of solar radiation, and ~20% is absorbed by the atmosphere. This radiation warms the planet, which in turn causes the Earth to radiate energy back into space. Thus, the ultimate temperature of the planet is determined by the balance between the energy that as absorbed and lost.
Climate Change and Society
Compared to patterns revealed by historical data, Earth’s climate is currently changing rapidly. While these changes are too minute to notice on a day-to-day basis, the accumulation of these minute changes could have devastating impacts on society. Agriculture and food production industries are particularly vulnerable to climate change, and several models have been created to predict the potential effects of climate change. While the effects of climate change on food production vary by crop and region, one model predicts that South Asia and Southern Africa are likely to suffer negative impacts on several crops that are important to large, food-insecure populations.