Introduction to Climate Change
Key concepts, causes, impacts, and responses
1. What Is Climate Change?
| Aspect |
Description |
| Definition |
Long‑term alteration of temperature, precipitation, wind patterns, and other aspects of the Earth’s climate system. |
| Timescale |
Measured over decades to millions of years (distinguishes it from short‑term weather variability). |
| Natural vs. Anthropogenic |
Natural drivers (volcanic eruptions, solar cycles) have always operated, but the current rapid warming is overwhelmingly driven by human activities. |
2. The Science Behind It
2.1 The Greenhouse Effect
- Solar radiation reaches Earth as short‑wave (visible) light.
- Surface absorbs energy, warms, and re‑emits it as long‑wave (infrared) radiation.
- Greenhouse gases (GHGs)—CO₂, CH₄, N₂O, water vapor—absorb and re‑emit infrared radiation, trapping heat.
- Result: Average surface temperature is ~33 °C warmer than it would be without GHGs.
2.2 Key Greenhouse Gases & Sources
| Gas |
Atmospheric Lifetime |
Primary Human Sources |
| Carbon dioxide (CO₂) |
~100 yr |
Fossil‑fuel combustion, cement production, deforestation |
| Methane (CH₄) |
12 yr |
Livestock, rice paddies, landfills, natural gas extraction |
| Nitrous oxide (N₂O) |
114 yr |
Synthetic fertilizers, industrial processes |
| Fluorinated gases (SF₆, HFCs) |
1 – 10 000 yr |
Refrigeration, electronics, fire‑suppression systems |
2.3 Climate Feedbacks
| Feedback Type |
Mechanism |
Effect on Warming |
| Positive |
Ice‑albedo loss → less reflection → more absorption |
Amplifies warming |
|
Permafrost thaw → CH₄ release |
Amplifies warming |
|
Water‑vapor increase → stronger greenhouse effect |
Amplifies warming |
| Negative |
Increased cloud cover reflecting sunlight (region‑specific) |
Can dampen warming, but overall weaker than positive feedbacks |
3. Evidence of Current Climate Change
| Indicator |
Observed Trend (1850‑present) |
| Global mean surface temperature |
+1.2 °C (relative to pre‑industrial) |
| Ocean heat content |
↑ ~30 % of excess heat stored |
| Sea‑level rise |
≈ 20 cm (1900‑2020) |
| Arctic sea‑ice extent |
↓ ~ 13 % per decade (summer) |
| Glacial mass loss |
> 9 000 Gt of ice lost since 1961 |
| Frequency of extreme events |
More intense heatwaves, droughts, heavy precipitation |
4. Impacts of Climate Change
4.1 Environmental
- Ecosystem shifts: Species migrate poleward/upward; biodiversity loss.
- Coral bleaching: Ocean warming + acidification → reef degradation.
- Ocean acidification: 30 % increase in CO₂ uptake → pH drop, affecting calcifying organisms.
4.2 Societal
- Human health: Heat‑related mortality, vector‑borne diseases, air‑quality decline.
- Food security: Crop yield reductions in tropical/sub