Climate Change

Evidence for Climate Change

The scientific consensus, based on multiple independent lines of evidence, is that Earth's climate is warming rapidly, and that human activity is the primary cause since the mid-20th century.

Evidence:

• Temperature records: Global average surface temperature has risen by approximately 1.1°C since pre-industrial levels (1850–1900). The last decade (2011–2020) is the warmest on record.
• Ice cores: Bubbles trapped in Antarctic and Greenland ice contain ancient air. They show CO₂ levels are now higher than at any time in the past 800,000 years.
• Sea level rise: Global mean sea level has risen by approximately 20 cm since 1900 (satellite records since 1993 confirm this); current rate ~3.7 mm/year.
• Arctic sea ice: The extent and thickness of summer Arctic sea ice has declined dramatically — September 2012 set a record minimum.
• Glacial retreat: Glaciers worldwide are retreating (e.g., Franz Josef Glacier, New Zealand; Gangotri Glacier, India — source of the Ganges).
• Species migration: Plants and animals moving poleward and to higher altitudes; timing of seasons shifting (earlier spring).

Causes of Climate Change

Natural Causes

• Milankovitch cycles: Long-term variations in Earth's orbit and axial tilt cause ice ages and warm periods over 20,000–100,000 year cycles. Too slow to explain recent rapid warming.
• Solar variation: Changes in solar output — slight variation in energy output. Cannot explain post-1980 warming (solar output has been flat or declining since 1980 while temperatures rise).
• Volcanic eruptions: Large eruptions (e.g., Mt Pinatubo, 1991) release sulphur dioxide → stratospheric aerosols → temporary global cooling. Short-term effect (1–3 years).

Human (Anthropogenic) Causes

• Burning fossil fuels (coal, oil, gas): Releases CO₂. The single largest cause.
• Deforestation: Trees absorb CO₂ — cutting them releases stored carbon and removes carbon sinks.
• Agriculture: Livestock (cattle) produce methane (a powerful greenhouse gas); paddy fields; fertilisers produce nitrous oxide.
• Industrial processes: Cement production; chemical manufacturing.
• Land use change: Urbanisation; draining of peatlands.

The greenhouse effect: Greenhouse gases (CO₂, CH₄, N₂O, H₂O vapour) absorb outgoing long-wave radiation from Earth's surface and re-emit it → the atmosphere traps heat. The enhanced greenhouse effect = human activities increasing greenhouse gas concentrations → more heat trapped → warming.

Effects of Climate Change

Physical effects:

• Rising sea levels → coastal flooding and erosion; island states threatened (e.g., Maldives, Tuvalu)
• Increased frequency/intensity of extreme weather events — heatwaves, droughts, floods, tropical storms
• Melting ice → less reflectivity (albedo feedback), further warming; freshwater input to oceans affecting ocean circulation
• Ocean acidification (CO₂ dissolving in seawater → carbonic acid → harms coral reefs and shellfish)
• Changing precipitation patterns — some areas wetter, others drier

Human effects:

• Food security: changing growing seasons; droughts in some areas; flooding of farmland
• Water security: glacial retreat threatens freshwater supply for billions (Himalayas supply 1.3 billion people)
• Displacement: rising sea levels; extreme events; climate refugees
• Health: spread of tropical diseases (malaria, dengue) to new areas; heat-related mortality

Managing Climate Change

Mitigation (reducing emissions)

• Switching to renewable energy (solar, wind, tidal)
• Energy efficiency; insulation; electric vehicles
• Carbon capture and storage (CCS)
• Afforestation (planting trees) and avoiding deforestation
• International agreements: Kyoto Protocol (1997); Paris Agreement (2015) — aim to limit warming to 1.5°C

Adaptation (adjusting to the effects)

• Flood defences (Thames Barrier, sea walls)
• Drought-resistant crops; water conservation
• Early warning systems for extreme weather
• Managed retreat from vulnerable coastal areas

WJEC Exam Tips

• Questions on climate change often ask for evidence, causes, effects OR management — read carefully
• AO3 questions ask you to evaluate — "to what extent" or "how effective" require a judgement
• Always distinguish between mitigation (stopping it getting worse) and adaptation (coping with what's already happening)