The dominant climate process is radiation to and from the Earth-ocean-atmosphere system. Increased absorption of solar (shortwave) radiation causes the climate to warm, which is compensated by increased infrared (IR, longwave) radiation out to space. This strong negative feedback has allowed the absolute temperature at Earth’s surface to vary by only 4% over millions of years.
But small changes have indeed occurred. Recent changes are associated with human activity such as greenhouse-gas emissions and land-surface modification. Other changes are natural — influenced by astronomical and tectonic factors. These primary influences can be amplified or damped by changes in clouds, ice, vegetation, and other feedbacks.
To illustrate dominant processes, consider the following highly simplified “toy” models.
- 21.8: Natural Oscillations
- The 30-year-average climate is called the normal climate. Any shorter-term (e.g., monthly) average weather that differs or varies from the climate norm is called an anomaly. Natural climate “oscillations” are recurring, multi-year anomalies with irregular amplitude and period, and hence are not true oscillations.