Climate Change
Climate change refers to long-term shifts in global temperatures and weather patterns. While climate has changed throughout Earth's history due to natural factors, the term today primarily refers to human-caused (anthropogenic) climate change resulting from the burning of fossil fuels and other activities that release greenhouse gases into the atmosphere.
Understanding Climate
Weather vs. Climate
- Weather: Short-term atmospheric conditions (days to weeks)
- Climate: Long-term average weather patterns (decades to millennia)
- Climate change: Statistically significant variations in climate over extended periods
Earth's Energy Balance
Earth's temperature depends on:
- Incoming solar radiation (shortwave)
- Outgoing infrared radiation (longwave)
- Greenhouse gases trapping heat
- Reflectivity (albedo) of surfaces
The Greenhouse Effect
Natural Greenhouse Effect
Without greenhouse gases, Earth's average temperature would be approximately -18°C instead of +15°C:
| Gas | Pre-industrial Level | Current Level | Contribution |
|---|---|---|---|
| Water vapor | Variable | Variable | 36-72% |
| Carbon dioxide | 280 ppm | ~420 ppm | 9-26% |
| Methane | 700 ppb | ~1,900 ppb | 4-9% |
| Nitrous oxide | 270 ppb | ~335 ppb | ~6% |
| Ozone | Variable | Variable | 3-7% |
Enhanced Greenhouse Effect
Human activities have increased greenhouse gas concentrations:
- CO₂ increased 50% since pre-industrial era
- Methane increased 150%
- Nitrous oxide increased 23%
- New synthetic gases (CFCs, HFCs) introduced
Evidence for Climate Change
Temperature Records
Global average temperature has risen approximately 1.1°C since pre-industrial times:
- Instrumental records since 1850
- 2023 was the warmest year on record
- Each of the last four decades warmer than any previous decade since 1850
- Arctic warming at 2-3 times global average
Ice Core Data
Ice cores reveal past climate:
- Trapped air bubbles preserve atmospheric composition
- Antarctic cores extend back 800,000 years
- Show correlation between CO₂ and temperature
- Current CO₂ levels unprecedented in this period
Sea Level Rise
| Period | Rate | Contributing Factors |
|---|---|---|
| 1901-1990 | 1.4 mm/year | Thermal expansion, glaciers |
| 1993-2018 | 3.3 mm/year | Ice sheets accelerating |
| 2006-2018 | 3.7 mm/year | Greenland, Antarctica |
Other Indicators
- Glaciers retreating worldwide
- Arctic sea ice declining (13% per decade)
- Ocean acidification (30% increase in acidity)
- Shifting plant and animal ranges
- Earlier spring events (flowering, migration)
Causes
Fossil Fuel Combustion
The primary source of anthropogenic CO₂:
| Source | CO₂ Emissions (%) |
|---|---|
| Coal | 40% |
| Oil | 34% |
| Natural gas | 20% |
| Cement/other | 6% |
Deforestation
Forest loss contributes ~10% of emissions:
- Trees store carbon (carbon sink)
- Burning releases stored carbon
- Reduces future absorption capacity
- Tropical deforestation most significant
Agriculture
Agricultural emissions include:
- Livestock: Methane from digestion
- Rice paddies: Methane from flooded fields
- Fertilizers: Nitrous oxide release
- Land use change: Converting forests to farmland
Industrial Processes
Non-energy industrial emissions:
- Cement production
- Steel manufacturing
- Chemical production
- Refrigerants and aerosols
Climate System Responses
Feedback Mechanisms
Positive Feedbacks (Amplifying)
- Ice-albedo: Less ice → more absorption → more warming → less ice
- Water vapor: Warming → more evaporation → stronger greenhouse effect
- Permafrost: Thawing releases methane and CO₂
Negative Feedbacks (Dampening)
- Plant growth: More CO₂ → increased photosynthesis → CO₂ uptake
- Weathering: Warmer temperatures → faster rock weathering → CO₂ removal
Tipping Points
Critical thresholds that may cause irreversible changes:
| Tipping Point | Threshold | Impact |
|---|---|---|
| Greenland ice sheet | ~1.5-2°C | 7 m sea level rise |
| West Antarctic ice sheet | ~1.5-2°C | 3 m sea level rise |
| Amazon dieback | ~3-4°C | Carbon source, biodiversity loss |
| Permafrost collapse | ~4-5°C | Massive methane release |
| Coral reef die-off | ~1.5°C | 70-90% loss |
Impacts
Physical Impacts
Temperature Extremes
- More frequent heat waves
- Fewer cold extremes
- Longer heat wave duration
- Urban heat island amplification
Precipitation Changes
- Wet regions generally getting wetter
- Dry regions generally getting drier
- More intense precipitation events
- Changes in monsoon patterns
Sea Level Rise Consequences
By 2100 (depending on emissions scenario):
- 0.3-1.1 meters rise
- Coastal flooding increases
- Storm surge amplification
- Saltwater intrusion
- Island nations threatened
Ecological Impacts
Biodiversity
- Species range shifts poleward and upward
- Phenological mismatches
- Coral bleaching events
- Ocean dead zones expansion
- Extinction risk increase (20-30% of species at risk)
Ecosystems
- Forest composition changes
- Wetland loss
- Tundra shrinking
- Ocean circulation changes
Human Impacts
Health
- Heat-related mortality
- Vector-borne disease spread
- Air quality degradation
- Food security threats
- Mental health impacts
Economy
Estimated costs:
- 2°C warming: 2-4% global GDP loss annually
- 4°C warming: 10%+ global GDP loss
- Developing nations most affected
- Infrastructure damage
- Agricultural losses
Security
- Climate migration
- Resource conflicts
- Food and water scarcity
- Political instability
Projections
IPCC Scenarios
The Intergovernmental Panel on Climate Change models different futures:
| Scenario | 2100 Warming | CO₂ Level | Likelihood |
|---|---|---|---|
| SSP1-1.9 | 1.4°C | 350 ppm | Very low emissions |
| SSP1-2.6 | 1.8°C | 400 ppm | Low emissions |
| SSP2-4.5 | 2.7°C | 600 ppm | Intermediate |
| SSP3-7.0 | 3.6°C | 850 ppm | High emissions |
| SSP5-8.5 | 4.4°C | 1100 ppm | Very high emissions |
Regional Projections
- Arctic: Warming 2-3× global average
- Mediterranean: Increased drought
- South Asia: Monsoon intensification
- Small islands: Existential threat from sea level rise
- Africa: Water stress, crop failures
Solutions
Mitigation
Reducing greenhouse gas emissions:
Energy Transition
- Renewable energy (solar, wind, hydro)
- Nuclear power
- Energy efficiency improvements
- Electrification of transport
- Grid modernization
Carbon Capture
- Direct air capture
- Bioenergy with carbon capture and storage (BECCS)
- Enhanced weathering
- Ocean-based approaches
Nature-Based Solutions
- Reforestation and afforestation
- Wetland restoration
- Sustainable agriculture
- Blue carbon ecosystems
Adaptation
Adjusting to climate impacts:
- Coastal defenses and managed retreat
- Drought-resistant crops
- Early warning systems
- Urban cooling strategies
- Water management improvements
Policy Framework
International Agreements
- UNFCCC (1992): Framework convention
- Kyoto Protocol (1997): First binding commitments
- Paris Agreement (2015): 1.5-2°C target
- Annual COPs for negotiations
Carbon Pricing
- Carbon taxes
- Emissions trading systems
- Border carbon adjustments
Climate Science
Attribution Science
Connecting specific events to climate change:
- Extreme weather attribution studies
- Statistical analysis of event probability
- Human fingerprint detection
Climate Models
Computer simulations of the climate system:
- General Circulation Models (GCMs)
- Earth System Models (ESMs)
- Coupled atmosphere-ocean models
- Regional downscaling
Remaining Uncertainties
- Cloud feedback magnitude
- Ice sheet dynamics
- Tipping point thresholds
- Carbon cycle responses
- Regional precipitation changes
See Also
References
- IPCC (2023). Climate Change 2023: Synthesis Report. Intergovernmental Panel on Climate Change.
- Mann, M.E. (2021). The New Climate War. PublicAffairs.
- Archer, D. (2011). Global Warming: Understanding the Forecast. Wiley.