Climate change forcings are factors that alter the Earth's energy balance, pushing the climate toward warming or cooling. They are broadly divided into:
Internal variations (also called internal forcings or internal climate variability) are changes that arise from interactions among the components of the climate system — the atmosphere, oceans, land surface, cryosphere, and biosphere — without any change in external inputs.
ENSO is the most significant internal climate variation on interannual timescales (2–7 years).
This is a powerful positive internal feedback:
The ocean's thermohaline circulation (the "global conveyor belt") redistributes heat around the planet. Internal changes in ocean temperature and salinity can:
These changes arise internally from the ocean–atmosphere system.
While large explosive volcanic eruptions are sometimes classified as external forcings, internal volcanic activity (e.g., long-term outgassing of from mid-ocean ridges) can slowly alter atmospheric composition over geological timescales, acting as an internal component of the Earth system.
Natural shifts in large-scale atmospheric circulation — such as the North Atlantic Oscillation (NAO) or the Pacific Decadal Oscillation (PDO) — redistribute heat and moisture internally, causing regional climate variability over years to decades.
| Feature | Internal Forcing | External Forcing |
|---|---|---|
| Origin | Within the climate system | Outside the climate system |
| Examples | ENSO, ice-albedo feedback, thermohaline changes | Solar variability, Milankovitch cycles, anthropogenic GHGs |
| Timescale | Years to centuries | Years to millions of years |
| Net energy input | No change in total energy input | Changes total energy input to system |
Key point for SLO P-12-F-55: Internal forcings do not change the total amount of energy entering the climate system — they redistribute energy within it. External forcings change the energy input itself.
Internal climate variations arise from natural interactions within Earth's climate components. They can cause significant regional and global temperature changes over interannual to decadal timescales. Understanding internal variability is essential for distinguishing natural climate fluctuations from human-caused (anthropogenic) climate change.