Global warming

Topic: Environment and Sustainable Development · NCERT: Class 11, Ch 7 "Environment and Sustainable Development"

Meaning

Global warming is the slow rise in the average temperature of the earth's lower atmosphere since the Industrial Revolution. It happens because humans add more greenhouse gases (gases that trap heat) to the air, mainly by burning coal, oil and gas and by cutting forests.

It matters because warming leads to rising seas, water shortages, species loss, more storms and the spread of disease. It also raises a basic economic question for a country like India: who pays to cut emissions, and how much development room is left for poorer countries.

Explanation

How it works: the greenhouse effect

• Greenhouse effect is the natural process behind global warming:
• Sunlight passes through the air and warms the earth's surface.
• The warm surface gives off heat (infrared radiation).

• Greenhouse gases absorb part of this heat and send it back down, so the lower air stays warmer.

• The natural greenhouse effect is good. It keeps the earth fit for life.

• The problem is the extra greenhouse effect caused by human emissions. Global warming refers to this extra warming.

The main greenhouse gases (GHGs)

• Carbon dioxide (CO2) comes from burning coal, oil and gas, and from cutting forests.
• Methane (CH4) comes from animal waste, cattle digestion, rice paddies and landfills.
• Nitrous oxide (N2O) comes mainly from fertilisers.
• F-gases are factory-made gases used in cooling and industry:
• HFCs (hydrofluorocarbons)
• PFCs (perfluorocarbons)

• SF6 (sulphur hexafluoride)

• Latest levels (2024, WMO Greenhouse Gas Bulletin):

• CO2 was 423.9 ppm (parts per million) in 2024, up from 377.1 ppm in 2004 [2].
• CO2 is now about 52% above its pre-1750 level [2].
• CO2 rose by a record 3.5 ppm from 2023 to 2024. This is the biggest jump since measurements began in 1957 [2].
• Methane was 1,942 ppb (parts per billion), which is 166% above pre-industrial levels [2].
• N2O was 338 ppb, which is 25% above pre-industrial levels [2].

• NCERT gives older figures: CO2 +31% and CH4 +149% above 1750 levels.

• CO2 is rising faster than before:

• It grew by about 0.8 ppm a year in the 1960s.
• It grew by about 2.4 ppm a year in 2011-20 [2].

What causes it (NCERT Box 7.1)

• Burning coal and petroleum in power plants, vehicles and industry releases CO2.
• Deforestation adds CO2 in two ways:
• When trees are cut or burnt, the carbon stored in them goes into the air.

• Fewer trees are left to absorb CO2.

• Methane from animal waste.

• More cattle production works as a chain:
• More cattle need more grazing land, so forests are cleared.
• More cattle produce more methane.

• Rearing, feeding and transporting cattle burns more fossil fuel.

• Weaker natural sinks in 2024:

• Sinks are the land and oceans, which absorb CO2.
• These sinks absorbed less in 2024, and wildfires increased.
• Both pushed up the record CO2 rise [2].

What it does and how much the earth has warmed

• Impacts (NCERT Box 7.1):
• Polar ice melts, so the sea level rises and coasts flood.
• Drinking water is disrupted where it depends on snow-melt. Example: rivers fed by Himalayan glaciers.
• Species go extinct because the places they live in (ecological niches) disappear.
• Tropical storms become more frequent.

• Tropical diseases such as malaria and dengue spread more widely.

• How much warming so far:

• NCERT: +0.6°C in the last century.
• IPCC AR6 (2021-23): the average temperature in 2011-20 was about 1.1°C above 1850-1900.
• WMO (January 2025): 2024 was the warmest year on record, at about 1.55°C ± 0.13°C above the pre-industrial level [3].
• It was likely the first calendar year above 1.5°C, and the warmest year in the 175-year observation record [3].

• Record greenhouse gas levels were the main cause. El Niño played a smaller part [3].

• Carbon budget is the total CO2 that can still be emitted while keeping warming below a chosen limit, such as 1.5°C.

• AR6: about 500 GtCO2 from 2020 gives a 50% chance of staying at 1.5°C. (GtCO2 means gigatonnes of CO2. 1 Gt = 100 crore tonnes.)

• Worked example (using round numbers):

• Budget from 1 January 2020 = 500 GtCO2.
• World emissions ≈ 40 GtCO2 a year.
• Used in 2020-25 = 6 years × 40 = 240 GtCO2.
• Left at the start of 2026 ≈ 500 − 240 = 260 GtCO2.
• Years left at the current rate ≈ 260 ÷ 40 ≈ 6.5 years. This is an illustration, not an official estimate.

In India

• Equity position (CBDR):
• Developed countries used most of the historical carbon budget while they industrialised.
• So India argues that rich countries should cut emissions first and should provide money and technology.
• This is the basis of CBDR (Common But Differentiated Responsibilities: every country must act, but not in the same way or to the same degree).

• The Kyoto conference (1997) asked industrialised nations to cut their emissions.

• Kigali Amendment (controls HFCs):

• HFCs replaced ozone-harming CFCs. HFCs do not harm ozone, but they are strong greenhouse gases.
• Kigali was adopted at the 28th Meeting of the Parties to the Montreal Protocol, in Kigali, Rwanda (October 2016) [4].
• The Union Cabinet approved India's ratification in August 2021, and India ratified in September 2021 [4].
• India's HFC path: freeze in 2028, then cumulative cuts of 10% by 2032, 20% by 2037, 30% by 2042 and 85% by 2047 [4].

• The global HFC phase-down may prevent up to 105 million tonnes of CO2-equivalent emissions and avoid up to 0.5°C of warming by 2100 [4].

• India Cooling Action Plan (ICAP, 2019):

• It was the world's first cooling action plan, with a 20-year outlook [5].
• Targets by 2037-38: cut cooling demand by 20-25%, energy used for cooling by 25-40% and refrigerant demand by 25-30% [5].

• It supports India's HFC phase-down through better energy efficiency and climate-friendly refrigerants [5].

• Local impact: Himalayan glacier-fed rivers are a direct Indian example of how warming disrupts drinking water that depends on snow-melt.

Don't confuse with

• Greenhouse effect vs global warming: the greenhouse effect is natural and keeps the earth fit for life. Global warming is the extra warming caused by human emissions on top of it.
• Ozone depletion: this is the thinning of the stratospheric ozone layer by chlorine and bromine compounds (CFCs, halons). It lets in more UV-B radiation. It is a separate problem, handled by the Montreal Protocol (1987). Global warming is about heat trapped in the lower atmosphere.
• One year above 1.5°C vs breaching the Paris limit: 2024 was about 1.55°C above pre-industrial [3]. But the Paris 1.5°C limit refers to the average over about 20 years, so the limit has not been breached yet.
• Carbon budget vs annual emission cap: a carbon budget is the total (cumulative) CO2 still allowed for a temperature limit. It is not a limit for each year.

Prelims Hooks

• CO2 was 423.9 ppm in 2024, about 52% above pre-industrial. Methane was 166% above pre-industrial and N2O 25% above (WMO GHG Bulletin) [2].
• CO2 rose by a record 3.5 ppm in 2023-24, the biggest jump since measurements began in 1957 [2].
• 2024 was the warmest year on record and likely the first calendar year above 1.5°C, at about 1.55°C ± 0.13°C above pre-industrial [3]. This is not yet a breach of the Paris goal.
• HFCs do not deplete ozone but are powerful greenhouse gases. They are controlled by the Kigali Amendment (2016) to the Montreal Protocol, not by the Kyoto Protocol or the Vienna Convention.
• India's HFC steps: freeze 2028, then 10% (2032), 20% (2037), 30% (2042), 85% (2047) [4]. ICAP (2019) was the world's first cooling action plan, with a target year of 2037-38 [5].
• NCERT causes of global warming include methane from animal waste and cattle production, not just fossil fuels and deforestation. NCERT puts warming at +0.6°C in the last century.

Mains Points

• Carbon budget and climate justice: only about 500 GtCO2 from 2020 was left for 1.5°C (AR6), and rich countries have already used most of the historical budget. So India asks for CBDR, climate finance and "carbon space" for its development. At the same time, it acts on its own through Kigali and ICAP [4][5].
• Lessons from Montreal for climate deals:
• The Montreal Protocol worked because substitutes were available and every country ratified it.
• Developing countries got delayed deadlines and money through the Multilateral Fund (1990).
• By cutting ozone-depleting substances, which are also greenhouse gases, it helped avoid about 0.5°C of warming [6].

• Climate deals still lack an equally credible package of money and technology.

• Cooling as a development need: heat waves and urbanisation will push up India's cooling demand. HFC cuts must go together with energy efficiency, so cooling stays affordable for the poor. This links SDG 13 (Climate Action) with the Brundtland idea of sustainable development [5][4].

Related concepts

• Greenhouse gases
• Carbon budget
• Ozone depletion
• Chlorofluorocarbons

Read more

• Global environmental issues: global warming, greenhouse gases and ozone depletion