Short note: Global warming

Global warming is the gradual rise of the average temperature of the earth's surface and lower atmosphere due to the increased concentration of greenhouse gases (CO₂, CH₄, N₂O, CFCs, water vapour, O₃). The rise has been about 1.1 °C since the pre-industrial era.

Mechanism (greenhouse effect): Short-wave solar radiation passes through the atmosphere and warms the earth. The earth re-emits this energy as long-wave infrared radiation. Greenhouse gases absorb part of this infrared and send it back towards the earth, so the lower atmosphere is warmer than it would otherwise be (greenhouse effect). Human activities add more of these gases, so the effect is enhanced.

   Sun
    │ short-wave
    ▼
 ─────────────── GHG layer (CO₂, CH₄ ...)
    ▲     │ absorbs and returns IR
    │ IR  ▼
 =============== Earth surface (warms)

Major gases: CO₂ (fossil fuels, deforestation), CH₄ (paddy fields, cattle, landfills), N₂O (fertilisers), CFCs and tropospheric ozone.

Consequences

• Melting of glaciers and polar ice, and rise of sea level (flooding of coastal regions, island nations). In Nepal, Himalayan glaciers are retreating and glacial lake outburst floods are a threat.
• Changed rainfall patterns: more floods, droughts, storms and heat waves.
• Loss of crop yield, food and water shortage; shifting of climatic zones.
• Extinction of species and loss of biodiversity; coral bleaching.
• Spread of diseases such as malaria and dengue to new areas.

Remedies

• Reduce use of fossil fuels; use renewable energy (hydro, solar, wind), improve energy efficiency.
• Afforestation and stopping deforestation (trees absorb CO₂).
• Use public transport, electric vehicles and biogas.
• Control methane from landfills and agriculture; reduce use of nitrogen fertiliser.
• Stop using CFCs; follow international agreements: UNFCCC (1992), Kyoto Protocol (1997), Paris Agreement (2015).