Introduction to Climate Change
Key concepts, causes, impacts, and responses
1. What Is Climate Change?
| Term |
Definition |
| Climate |
Long‑term (30‑year+) average of temperature, precipitation, wind, etc., for a region. |
| Weather |
Short‑term atmospheric conditions (hours to days). |
| Climate Change |
A statistically significant shift in climate patterns over decades to centuries, driven by natural processes and human activities. |
| Global Warming |
The increase in Earth’s average surface temperature, a major component of climate change. |
2. Scientific Basis
2.1 The Greenhouse Effect
- Solar radiation reaches Earth → some is reflected, most is absorbed and re‑emitted as infrared (IR) radiation.
- Greenhouse gases (GHGs) (CO₂, CH₄, N₂O, water vapor, etc.) absorb IR, trapping heat and warming the lower atmosphere.
- Without GHGs, average surface temperature would be ~‑18 °C; with them it is ~+15 °C.
2.2 Radiative Forcing
- Positive forcing → warming (e.g., increased CO₂).
- Negative forcing → cooling (e.g., volcanic aerosols).
- The Intergovernmental Panel on Climate Change (IPCC) quantifies forcing in watts per square meter (W m⁻²).
2.3 Evidence of Change
| Indicator |
Observation |
Time Scale |
| Global mean surface temperature |
↑ ≈ 1.2 °C since pre‑industrial (1850‑1900) |
1850‑present |
| Ocean heat content |
↑ ≈ 0.5 °C in upper 200 m |
1950‑present |
| Sea‑level rise |
↑ ≈ 20 cm (1900‑present) |
1900‑present |
| Glacial retreat |
Majority of world’s glaciers shrinking |
20th century‑present |
| Arctic sea‑ice extent |
↓ ≈ 13 % per decade (satellite era) |
1979‑present |
| Extreme weather frequency |
More heatwaves, heavy precipitation events |
Recent decades |
3. Primary Drivers
| Driver |
Source |
Approx. Share of Anthropogenic GHG Emissions |
| Carbon Dioxide (CO₂) |
Fossil‑fuel combustion, cement production, land‑use change |
~75 % |
| Methane (CH₄) |
Agriculture (livestock, rice), landfills, fossil‑fuel extraction |
~15 % |
| Nitrous Oxide (N₂O) |
Fertilizer use, industrial processes |
~6 % |
| Fluorinated gases (F‑gases) |
Refrigerants, electronics, fire‑suppression |
~4 % |
3.1 Natural vs. Anthropogenic
- Natural variability (solar cycles, volcanic eruptions, El Niño/La Niña) still influences climate but cannot explain the observed long‑term warming trend.
- Anthropogenic forcing (mainly CO₂) accounts for > 95 % of the warming since the mid‑20th century (IPCC AR6).
4. Impacts
4.1 Physical Environment
- Temperature: More frequent heat extremes, longer warm seasons.
- Hydrology: Altered precipitation patterns