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

Detail

1. What global warming is

• Global warming is the slow rise in the average temperature of the earth's lower atmosphere since the Industrial Revolution.
• Humans cause it by adding more greenhouse gases to the air.
• Greenhouse effect (the natural process behind it):
• 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 keeps the earth fit for life. The problem is the extra effect caused by human emissions.

2. Greenhouse gases (GHGs)

• Greenhouse gases are gases that trap heat in the atmosphere. The main ones are:
• 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: HFCs (hydrofluorocarbons), PFCs (perfluorocarbons) and SF6 (sulphur hexafluoride). These are factory-made gases used in cooling and industry.

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

• CO2 was 423.9 ppm (parts per million) in 2024. It was 377.1 ppm in 2004 [2].
• CO2 rose by a record 3.5 ppm from 2023 to 2024, 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].
• CO2 is now about 52% above its pre-1750 level [2].

• (NCERT: CO2 +31% and CH4 +149% above 1750 levels.)

• CO2 is growing 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].

3. Causes (NCERT Box 7.1)

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

• Fewer trees are left to absorb CO2.

• Methane from animal waste.

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

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

• Nature's CO2 "sinks" (the land and oceans, which absorb CO2) became weaker in 2024. Wildfires also increased. Both pushed up the record CO2 rise [2].

4. 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: Himalayan glacier-fed rivers.
• 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.

5. How much the earth has warmed

• 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 [3].
• It was 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].

• (NCERT: +0.6°C in the last century.)

• Exam trap: one year above 1.5°C does not mean the Paris 1.5°C limit has been breached. That limit refers to the average over about 20 years.

6. Carbon budget

• 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 the scaffold's 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 (verify the current figure).

• Equity angle:

• Developed countries used most of the historical budget during their industrialisation.
• So developing countries argue that the rich should cut emissions first and 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). See Section 10.

• Kyoto conference (1997): it asked industrialised nations to cut their emissions. Details are in Section 10.

7. Ozone depletion: the science

• Ozone (O3) is a gas. In the stratosphere (about 10-50 km above the earth), it forms a layer that absorbs harmful ultraviolet (UV) rays from the sun.
• Ozone depletion is the thinning of this layer. It is caused by high levels of chlorine and bromine compounds in the stratosphere.
• Ozone-depleting substances (ODS):
• Chlorofluorocarbons (CFCs): used as coolants in refrigerators and ACs, and as aerosol propellants (the gas that pushes spray out of a can).
• Halons (bromofluorocarbons): used in fire extinguishers.

• Carbon tetrachloride and methyl chloroform (trichloroethane): used as industrial solvents.

• How the damage happens:

• UV light breaks CFCs apart high in the stratosphere, which frees chlorine atoms.
• One chlorine atom can destroy thousands of ozone molecules in a chain reaction.

• Over Antarctica, very cold polar clouds speed up this reaction, so an "ozone hole" forms every spring (September-October).

• Effects: more UV-B radiation reaches the earth.

• Humans get more skin cancer. (Eye cataracts also increase.)
• Phytoplankton (tiny floating plants at the base of the ocean food chain) produce less, which harms aquatic food chains.

• Land plants grow less well, which hurts crop yields.

• NCERT records a ~5% fall in the ozone layer between 1979 and 1990.

• Key difference: ozone is "good" in the stratosphere because it shields us from UV. Near the ground (troposphere), ozone is a pollutant and a greenhouse gas.

8. The ozone regime

Step	Year	What it did
Vienna Convention	1985	Framework for cooperation (no binding cuts)
Montreal Protocol	1987	Phases out ODS (CFCs, halons, CCl4, methyl chloroform); ratified by every country
Multilateral Fund	1990	Pays developing countries' extra costs of phasing out ODS
Kigali Amendment	2016	Phases down HFCs

• Results of Montreal:
• Nearly 99% of banned ODS have been phased out [6].

• By cutting ODS, which are also greenhouse gases, the Protocol has helped avoid about 0.5°C of global warming [6].

• Expected recovery to 1980 ozone levels (UNEP/WMO Scientific Assessment 2022, released January 2023):

• Near-global average (60°N-60°S): around 2040 [7][6].
• Arctic: around 2045 [7].

• Antarctic: around 2066 [7][6].

• The Montreal Protocol is often called the most successful environmental treaty. The reasons:

• It was ratified by every country.
• Substitutes for ODS were available.
• Developing countries got delayed deadlines and money through the Multilateral Fund. This is CBDR in practice.

9. Kigali Amendment and India

• Why Kigali was needed:
• HFCs replaced CFCs. They do not harm ozone.
• But they are strong greenhouse gases. Their Global Warming Potential (GWP: how much heat a gas traps compared with the same mass of CO2) runs into hundreds or thousands.

• So the ozone solution became a climate problem, and Kigali fixed that.

• Kigali was adopted at the 28th Meeting of the Parties in Kigali, Rwanda (October 2016) [4].

• The Union Cabinet approved India's ratification in August 2021. India then ratified in September 2021 [4].
• India's HFC path:
• Freeze in 2028.

• Then cuts in 4 steps: 10% by 2032, 20% by 2037, 30% by 2042 and 85% by 2047 (cumulative) [4].

• Benefit: 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: reduce 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].

Prelims Hooks

• Methane was 166% above pre-industrial in 2024; CO2 was 423.9 ppm, about 52% above pre-industrial (WMO GHG Bulletin) [2].
• 2024 was the first calendar year about 1.55°C above pre-industrial. This is not yet a breach of the Paris 1.5°C goal, which is a long-term average [3].
• HFCs do not deplete ozone but are powerful GHGs. They are controlled by the Kigali Amendment (2016) to the Montreal Protocol, not by the Vienna Convention.
• Halons contain bromine and are used in fire extinguishers. CFCs contain chlorine.
• Ozone depletion increases UV-B radiation. It is a stratospheric problem, not a tropospheric one.
• Vienna 1985 was a framework; Montreal 1987 set binding phase-outs; the Multilateral Fund was created in 1990.
• 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. Its target year is 2037-38 [5].
• Ozone recovery to 1980 levels: global ~2040, Arctic ~2045, Antarctic ~2066 [7].
• Carbon budget means the cumulative CO2 still allowed for a given temperature limit. It is not an annual emission cap.

Mains Points

• Montreal as a model for climate diplomacy: it succeeded because substitutes were available, it had a dedicated fund, developing countries got delayed timelines, and it was ratified by every country. It also avoided about 0.5°C of warming [6]. Climate deals lack an equally credible finance and technology package.
• Carbon budget and equity: the remaining 1.5°C budget is small, and rich countries have already used most of the historical budget. So India argues for CBDR, climate finance and "carbon space" for its development, while still acting on its own (ICAP, Kigali).
• Cooling demand as a development need: India's cooling demand will rise with heat waves and urbanisation. ICAP links energy efficiency, refrigerant control and heat-related health. HFC cuts must not make cooling unaffordable for the poor [5][4].
• Linked problems, linked solutions: HFCs show how fixing one environmental problem (ozone) can worsen another (climate). Policy should be integrated, which fits SDG 13 (Climate Action) and the Brundtland idea of sustainable development.