Climate change gases and symptoms in Nepal

Climate change is a long-term change (over decades or longer) in the average weather pattern of the Earth or a region, such as temperature, rainfall and wind. The present climate change is mainly caused by human activities that increase greenhouse gases (GHGs) in the atmosphere, leading to global warming. The Earth is already about 1.1–1.2 °C warmer than in pre-industrial times (IPCC AR6).

Gases that cause climate change

Greenhouse gases let sunlight pass through but absorb the long-wave heat radiated back by the Earth, and re-emit part of it towards the surface. This is the greenhouse effect. A natural greenhouse effect keeps the Earth at about 15 °C instead of −18 °C; extra GHGs from human activity make it stronger.

           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.

Major symptoms of climate change in Nepal

Nepal is a mountain country with fragile geology, so it shows the signs of climate change clearly:

• Rising temperature: DHM data show average maximum temperature rising by about 0.06 °C per year, faster in the mountains than in the Terai.
• Glacier retreat and snow loss: Himalayan glaciers are thinning and retreating; snow lines are moving up and snow-capped peaks are turning into bare rock.
• Glacial lake growth and GLOF risk: lakes such as Tsho Rolpa and Imja Tsho are expanding. ICIMOD (2020) listed 47 potentially dangerous glacial lakes in the Koshi, Gandaki and Karnali basins (21 of them in Nepal).
• Erratic monsoon: late onset, fewer rainy days but more intense rain, causing both floods and drought in the same year.
• More floods, landslides and debris flows: e.g. the 2021 Melamchi flood and the 2024 Kathmandu valley floods.
• Drying of springs and water sources in the middle hills, forcing people to migrate.
• Agricultural changes: crop failure, new pests and diseases, upward shift of crops (apple farming moving to higher altitudes such as Mustang).
• Health effects: spread of malaria, dengue and other vector-borne diseases to hill areas (dengue now reaches Kathmandu and above).
• Biodiversity shift: species and tree lines moving upward; invasive species spreading.
• Forest fires in dry winter and pre-monsoon seasons are becoming more frequent.

These symptoms threaten Nepal's water resources, hydropower, agriculture, tourism and the lives of people living in the hills and mountains.