Short note: Causes and impacts of climate change

Climate change is a long-term change (over decades or more) in the average weather pattern – temperature, rainfall, wind, extreme events – of a region or the whole Earth. The present change is mainly due to human activities that increase greenhouse gases (GHGs) in the atmosphere. Global average temperature has already risen by about 1.1 °C above pre-industrial levels (IPCC).

Causes

Natural: changes in solar output, volcanic eruptions, changes in Earth's orbit, ocean currents (El Niño).

Human (anthropogenic) – the main cause today:

1. Burning of fossil fuels (coal, oil, gas) for power, industry and transport – CO₂.
2. Deforestation and land-use change – fewer trees to absorb CO₂.
3. Agriculture – methane from livestock and rice paddies; N₂O from fertilisers.
4. Industrial processes – cement (CO₂), refrigerants (HFCs, CFCs).
5. Waste – methane from landfills.
6. Black carbon – soot from diesel, kilns and cook stoves.

These gases trap heat radiated by the Earth (enhanced greenhouse effect).

Impacts (consequences)

• Rising temperature and more heat waves.
• Melting glaciers and snow – Himalayan glaciers are retreating; risk of GLOF (e.g. Imja and Tsho Rolpa lakes in Nepal).
• Sea level rise – flooding of coastal cities and islands.
• Erratic rainfall – more floods, landslides and droughts; changed monsoon.
• Agriculture – lower yields, crop failure, food insecurity.
• Health – spread of dengue and malaria to new (hill) areas, heat stress.
• Biodiversity loss – species shift upwards or go extinct; coral bleaching.
• Water scarcity – drying springs in Nepal's hills.
• Economic and social – damage to infrastructure and hydropower, migration, poverty.