Temperature is the measure of the average heat or thermal energy in a substance. Air and water temperatures are primarily determined by the amount of sunlight that is absorbed by the surface of the Earth, and the amount of heat that is re-radiated in the atmosphere by the greenhouse gases. Atmospheric and ocean circulation redistribute heat across the surface of the Earth and shape regional temperature patterns.
Various human activities and environmental phenomena influence air and water temperature, including:
- The increase in greenhouse gases from the burning of fossil fuels, agricultural activities, and deforestation, which has caused global average air temperatures to increase. Around 90% of this excess atmospheric heat is absorbed by the ocean, thereby increasing average ocean temperatures.
- The use of asphalt and other dark colored materials in urban areas can dramatically increase the amount of sunlight absorbed. This creates what are called urban heat islands, whereby cities experience higher temperatures than surrounding areas.
- The burning of fossil fuels as well as fires lit deliberately to remove trees to clear land for agricultural activities or ignited by accident, release airborne particles into the atmosphere. Dark colored particles that absorb sunlight have a warming effect, while light colored particles that reflect or scatter sunlight have a cooling effect.
- Over much longer time periods — tens of thousands to hundreds of thousands of years — changes in Earth’s spin, tilt, and orbit, periodically increase and decrease the amount of sunlight absorbed by different areas of the Earth’s surface.
- Over millions of years changes in the carbon cycle, including the rates of weathering and volcanic activity, alter the amount of carbon dioxide and other greenhouse gases in the atmosphere, which affect Earth’s average temperature.
- Over millions of years changes in the distribution of continents alters how much sunlight is absorbed by the land or ocean.
Air and water temperatures affect many Earth system processes and phenomena, including:
- Atmospheric and ocean circulation patterns, which affect how heat is distributed around the globe. Global warming has altered these patterns, affecting regional climate and the frequency and intensity of extreme weather.
- How water cycles through the Earth system, including where clouds form, precipitation occurs, and the extent of snow and ice cover. Changes in the water cycle, in turn, can affect the availability of freshwater for humans and other organisms.
- The rate of biological reactions, including the function of enzymes needed for photosynthesis, respiration, and other processes essential for survival. Most organisms can only survive within a particular temperature range, and thus their health will be affected if the environment gets too hot or too cold.
- The evolution of life cycles and traits, including physical, physiological, and behavioral characteristics that help organisms regulate their body temperatures and survive within their geographic ranges.
- The rate and direction of chemical reactions, including those in rocks, soil, water, and the atmosphere. For example, as the ocean warms, less carbon dioxide will be absorbed by the ocean.
- Water oxygen levels, as warm water holds less oxygen than cold water. Thus, global warming reduces oxygen in the ocean, lakes, rivers and streams, which can lead to changes in species populations.
- The frequency and intensity of fires. Increasing average temperatures have altered temperature and precipitation patterns, and decreased snow and ice cover, resulting in dryer, longer annual fire seasons.
Can you think of additional cause and effect relationships between air and water temperature and other parts of the Earth system?
Visit the absorption and reflection of sunlight, greenhouse effect, and the atmospheric circulation pages to explore more connections between the hydrosphere, atmosphere, and other global changes.