Introduction to Climate Change
Key concepts, causes, impacts, and responses
1. What Is Climate Change?
| Term |
Definition |
| Climate |
Long‑term (30‑year average) patterns of temperature, precipitation, wind, etc., for a region or the globe. |
| Weather |
Short‑term atmospheric conditions (hours to days). |
| Climate Change |
A statistically significant shift in average climate conditions or their variability over decades to centuries, caused by natural processes, human activities, or a combination of both. |
| Global Warming |
The observed rise in Earth’s average surface temperature, primarily due to increased concentrations of greenhouse gases (GHGs). |
2. The Science Behind Climate Change
2.1 The Greenhouse Effect
- Solar radiation reaches Earth → some is reflected, most is absorbed by the surface.
- The warm surface emits infrared (IR) radiation.
- Greenhouse gases (CO₂, CH₄, N₂O, water vapor, etc.) absorb and re‑emit IR, trapping heat in the lower atmosphere.
- This natural “blanket” keeps the planet ~15 °C warmer than it would be without it.
2.2 Why the Climate Is Warming Now
| Driver |
Mechanism |
Current Trend |
| Carbon Dioxide (CO₂) |
Fossil‑fuel combustion, cement production, land‑use change |
↑ ~50 % since pre‑industrial (≈ 415 ppm in 2023) |
| Methane (CH₄) |
Agriculture (rice, ruminants), fossil‑fuel extraction, waste |
↑ ~150 % since pre‑industrial (≈ 1,900 ppb) |
| Nitrous Oxide (N₂O) |
Fertilizer use, industrial processes |
↑ ~20 % since pre‑industrial |
| Aerosols |
Particulate matter from combustion, dust |
Can cool (reflect sunlight) or warm (absorb heat); net effect currently negative but decreasing with air‑quality regulations |
2.3 Climate Feedbacks
- Positive feedbacks amplify warming (e.g., ice‑albedo loss, permafrost thaw releasing CH₄).
- Negative feedbacks dampen warming (e.g., increased cloud albedo, enhanced plant growth).
- Overall, Earth system models indicate net positive feedback, leading to further warming if GHG emissions continue.
3. Evidence of Climate Change
| Indicator |
Observed Change (≈ 1880‑2020) |
Data Sources |
| Global mean surface temperature |
+1.1 °C relative to pre‑industrial |
NASA GISS, NOAA, HadCRUT |
| Ocean heat content |
↑ ~25 % in upper 2 km |
Argo floats, IPCC |
| Sea‑level rise |
+20 cm (average) |
Satellite altimetry, tide gauges |
| Arctic sea‑ice extent |
↓ ~40 % (summer minimum) |
NSIDC |
| Glacial mass balance |
Net loss of ~10 % of global ice volume |
GRACE, field surveys |
| Extreme events |
Increased frequency/intensity of heatwaves, heavy precipitation, droughts |
EM-DAT, IPCC AR6 |
4. Impacts of Climate Change
4.1 Environmental Impacts
- Ecosystem shifts – species migrate poleward/upward; coral bleaching; forest die‑back.
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