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Natural Factors That Increase Greenhouse Gases

Throughout the Earth's history, greenhouse gases have played a vital role in keeping the planet's surface warm enough to support life. Without any greenhouse gas sources, the average global temperature would be almost 60 degrees Fahrenheit less than what it is now. Human industry over the past 150 years or so has increased atmospheric levels at unprecedented speed, but many major greenhouse gases are also produced naturally.

Carbon Dioxide
- The respiration of living organisms emits about 220 gigatonnes of carbon dioxide into the atmosphere every year. Rotting organic matter contributes another 220 gigatonnes, and a further 330 gigatonnes is released from the surface of the ocean. While this amount dwarfs the estimated 32.3 gigatonnes produced by humans, the natural emissions are balanced by carbon sinks that "soak up" the newly released carbon dioxide, along with about 40 percent of the extra carbon dioxide from human activity. The other 60 percent collects in the atmosphere, where it contributes to climate change.
Methane
- Anaerobic bacteria that break down organic matter and produce methane as a byproduct are the largest natural source of methane. Termites also produce significant amounts. Further releases stem from methane hydrates found on the ocean floor and in polar soils, as well as from geothermal activity, wildfires and wild animals, where it is a byproduct of digestion. Methane is a more powerful greenhouse gas than carbon dioxide, causing a larger greenhouse effect per unit volume. Human activity releases more methane per year than all natural sources combined.
Nitrous Oxide
- Nitrous oxide is produced naturally when microorganisms break down nitrogen-containing compounds in the soil and ocean. Smaller quantities are produced from the chemical breakdown of methane in the atmosphere and the release from oxygen-depleted surface water. The amount of nitrous oxide produced naturally and by humans is about the same, meaning humans approximately double the volume of nitrous oxide released into the Earth's atmosphere every year.
Water Vapor
- Water vapor is the most prevalent greenhouse gas, and virtually all of it is produced naturally from evaporation on the Earth's surface. Unlike other greenhouse gases, water vapor acts as a feedback mechanism, not an original source of global warming. As other factors raise the planet's temperature, evaporation increases and the warm air gains a greater capacity to hold water vapor. As the water vapor levels go up, they increase the greenhouse effect, raising temperatures even further.

Nature