Natural climate drivers act over different timescales. Check how each changes Earth's energy balance before using it to explain a trend.
Changes in Earth's orbit and axial tilt alter how solar energy is distributed by latitude and season. They act over tens of thousands of years or longer. These orbital cycles help pace glacial changes, with ice and greenhouse-gas feedbacks amplifying their effects. They are different from the annual seasons produced by Earth's existing tilt during one orbit.
The Sun's energy output varies slightly over an activity cycle of about 11 years. Sunspots are one indicator of this cycle. Although the spots themselves are dark, accompanying bright regions mean that greater solar activity can slightly increase total output. The climate effect depends on the energy reaching Earth.
Large explosive eruptions can temporarily cool the surface. Sulfur dioxide reaching the stratosphere forms sulfate aerosols that reflect sunlight. Less solar energy then reaches the surface. Ash often falls out sooner. Volcanoes also release carbon dioxide, but this warming influence is a separate process from short-lived aerosol cooling.
A proposed cause must match the timing, duration and geographical pattern of the change. Slow orbital cycles and brief volcanic cooling cannot explain the sustained recent warming, which is mainly caused by human greenhouse-gas emissions. Natural variability still affects individual years and regions.
Step by step
Orbit and tilt
Slow changes redistribute sunlight between seasons and latitudes.
Solar activity
Changes in the Sun's output alter incoming energy.
Volcanic aerosols
Reflective particles from large eruptions can reduce surface heating temporarily.
Worked example: A cause must fit the observation
If temperatures dip for a few years after an explosive eruption, reflective stratospheric aerosols are a plausible explanation to test. A persistent warming over many decades needs a cause that fits that longer pattern, alongside other evidence.
Watch out for this
Climate changed naturally before, so recent warming must be natural.
Past variability does not identify the cause of a new change. Test all relevant mechanisms against the observed evidence.
Check your understanding
How can a large explosive eruption temporarily cool Earth's surface?
- Reflective stratospheric aerosols reduce incoming solar energy.
- Lava absorbs all atmospheric carbon dioxide.
- The eruption stops Earth's annual revolution.