Climate change gases and mitigation interventions

Climate change is a significant long-term change in the average weather (temperature, rainfall, wind, seasons) of a place or of the Earth as a whole. The present change is mainly due to human emission of greenhouse gases, which trap extra heat and cause global warming.

Gases causing climate change

Greenhouse gases are transparent to incoming sunlight but absorb outgoing infrared heat from the Earth and send part of it back, warming the lower atmosphere.

           Sun (short-wave radiation)
                  |
                  v
   ======== atmosphere with GHGs ========
     ^   some heat escapes     |  GHGs absorb and
     |                         v  re-emit heat back
   ----------- Earth's surface ------------
     (absorbs light, emits long-wave heat)

• Carbon dioxide (CO₂) is the most important gas because of its huge quantity. Its concentration has risen from about 280 ppm before the Industrial Revolution to over 420 ppm today, mainly from fossil fuels and loss of forests.
• Methane (CH₄) comes from anaerobic decomposition in rice fields, livestock digestion, landfills and leaks from gas wells. It traps about 28 times more heat than CO₂ per kg over 100 years.
• Nitrous oxide (N₂O) is released from chemical fertilisers, animal waste and biomass burning. It is long-lived and also damages the ozone layer.
• Halocarbons (CFCs, HCFCs, HFCs) are man-made gases from refrigeration and air conditioning. CFCs also destroy stratospheric ozone; they are controlled by the Montreal Protocol (1987) and HFCs by its Kigali Amendment (2016).
• Water vapour is the most abundant natural greenhouse gas. It is not emitted directly by people, but warmer air holds more of it, so it amplifies warming (positive feedback).
• Ozone and black carbon (soot from brick kilns, diesel and firewood) are short-lived climate pollutants. Black carbon deposited on snow makes it darker, so glaciers melt faster.

Possible interventions to mitigate climate change

1. Energy sector (largest source of CO₂)

• Shift from coal, oil and gas to renewable energy: hydropower, solar, wind, geothermal, biogas.
• Improve efficiency in power plants, buildings, appliances and industry.

2. Transport

• Electric vehicles and electric mass transit (e.g. Nepal's electric buses and reduced customs duty on EVs).
• Better urban planning, cycling lanes, footpaths.

3. Forestry and land use

• Stop deforestation, afforestation and reforestation; community forestry (Nepal's forest cover has risen to about 45%).
• REDD+ payments for keeping forests standing.

4. Agriculture

• Organic farming and balanced fertiliser use to cut N₂O.
• Improved rice cultivation (alternate wetting and drying) to cut methane; biogas from dung.

5. Industry and waste

• Cleaner brick kilns, low-clinker cement, recycling.
• Landfill gas capture, composting, waste-to-energy.

6. Policy and economic tools

• Carbon tax, emission trading, removal of fossil-fuel subsidies, green building codes.
• Climate finance and technology transfer to developing countries.

7. International cooperation

• UNFCCC, Kyoto Protocol, Paris Agreement and NDCs; Montreal Protocol and Kigali Amendment for halocarbons.

8. Research and technology

• Carbon capture and storage, green hydrogen, better batteries.

9. Awareness and behaviour

• Saving energy, using public transport, reducing food waste, sustainable consumption.

Mitigation should go together with adaptation, especially in vulnerable countries like Nepal.