Major Factors That Affect Earth’s Climate
Earth’s climate is determined by the balance between incoming solar energy and outgoing infrared radiation. Several natural and anthropogenic factors alter this balance, producing climate variability and change.
Earth’s Energy Balance
The energy balance describes the equilibrium between:
- Incoming short-wave solar radiation (visible light + UV)
- Outgoing long-wave infrared radiation (heat)
When these are balanced, global average temperature is stable. Any factor that alters either side disrupts the balance and drives warming or cooling.
$$\text{Energy In} = \text{Energy Out (equilibrium)}$$
When Energy In > Energy Out, the planet warms until a new equilibrium is reached.
Natural Factors
Volcanic Eruptions
- Large eruptions inject sulfur dioxide ($SO_2$) and aerosols into the stratosphere
- Aerosols reflect incoming solar radiation → temporary global cooling
- The 1991 eruption of Mt Pinatubo (Philippines) lowered global average temperatures by ~0.5°C for 2 years
- Large flood basalt events (e.g. Siberian Traps, 252 MYA) released massive CO$_2$ over millennia → long-term warming
Solar Variability
- The Sun’s output is not constant — it varies on 11-year (solar cycle) and longer time scales
- Solar maximum: more sunspot activity, slightly higher energy output
- Changes in solar output are small (~0.1%) and cannot explain observed 20th–21st century warming
- Significant solar variations over very long timescales (Milankovitch cycles — Earth’s orbital geometry) drive glacial-interglacial cycles
Orbital Mechanics (Milankovitch Cycles)
- Eccentricity (100,000 year cycle): Shape of Earth’s orbit around the Sun varies
- Obliquity (41,000 year cycle): Tilt of Earth’s axis changes (21.5°–24.5°)
- Precession (26,000 year cycle): Wobble of Earth’s axis orientation
- Together, these cycles distribute solar energy differently across latitudes and seasons, triggering ice ages
Anthropogenic Factors
Changes in Atmospheric Gas Composition
Human activities have increased concentrations of greenhouse gases since the Industrial Revolution (~1850):
| Gas |
Pre-industrial (ppm) |
Current (~2024) |
Primary Human Sources |
| CO$_2$ |
~280 |
~424 |
Fossil fuels, deforestation, cement |
| CH$_4$ |
~0.72 |
~1.92 |
Agriculture, landfill, fossil fuels |
| N$_2$O |
~0.27 |
~0.34 |
Agriculture, industry |
| F-gases |
Near zero |
Various |
Refrigerants, industrial processes |
These gases enhance the greenhouse effect, trapping more infrared radiation in the atmosphere.
Key Climate Mechanisms
Albedo Effect
Albedo is the fraction of incoming solar radiation reflected back to space.
| Surface |
Approximate Albedo |
| Fresh snow |
0.80–0.90 |
| Desert sand |
0.35–0.45 |
| Forest |
0.10–0.20 |
| Ocean |
0.06–0.10 |
| Bare soil |
0.15–0.35 |
- Melting ice and snow (due to warming) exposes lower-albedo ocean and land → less reflection → more absorption → further warming (ice-albedo positive feedback)
- Deforestation replaces darker forest with lighter crops/pasture → increases albedo → slight local cooling effect
Ocean Circulation
- Oceans store 90% of the excess heat from the enhanced greenhouse effect
- Thermohaline circulation (‘ocean conveyor belt’) distributes heat globally
- Disruption of circulation (e.g. from freshwater input due to ice sheet melt) could alter regional climates dramatically, including cooling Europe
REMEMBER: Natural climate forcings (volcanic, solar, orbital) explain past climate variation but do NOT explain observed rapid 20th–21st century warming. The scientific consensus is that the dominant driver since ~1950 is the increase in greenhouse gas concentrations from human activities.
