Chlorofluorocarbons

Also called: CFCs · Topic: Climate Change: Causes, Evidence and the Global Response · NCERT: Class 11, Ch 11 "World Climate and Climate Change"

Meaning

Chlorofluorocarbons (CFCs) are factory-made gases built from chlorine, fluorine and carbon. They were once used in refrigerators, air conditioners and aerosol sprays. They trap heat as greenhouse gases, and they also destroy the ozone layer in the stratosphere.

They matter because they do two kinds of harm. They warm the planet, and they caused the Antarctic ozone hole. The response was the Montreal Protocol (1987), the world treaty that phased them out.

Explanation

How CFCs destroy ozone (cause → process → result)

• CFCs are very stable
• They do not break down in the lower air.

• So they slowly rise into the stratosphere (the air layer about 10–50 km up).

• Ultraviolet light breaks them apart

• In the stratosphere, strong ultraviolet light splits CFC molecules.

• This sets free chlorine.

• Chlorine eats ozone in a chain reaction

• One chlorine atom can destroy many ozone molecules, one after another.
• Over Antarctica, very cold polar stratospheric clouds (thin clouds that form only in extreme cold high up) speed this up.

• It happens every spring, in September–October. The result is the Antarctic ozone hole.

• Why this is dangerous: stratospheric ozone ("good ozone", about 15–35 km up) absorbs harmful ultraviolet-B rays. Less ozone lets more of these rays reach life on the ground.

CFCs as greenhouse gases

• NCERT (Class 11) names CFCs among the main greenhouse gases, along with CO2, methane, nitrous oxide and ozone.
• Global warming potential (GWP) compares how much heat 1 kg of a gas traps over 100 years with 1 kg of CO2 (CO2 = 1).

• The GWPs of CFCs run into the thousands. This is the highest of the main greenhouse gases.

• Lifetime: long, from decades to a century. So CFCs released long ago still trap heat today.

• Share of warming: in 2024, CFCs and related gases caused about 8% of the warming push from long-lived greenhouse gases. CO2 caused 66% and methane 16% [2].
• Warming push here means radiative forcing: the extra heat energy a gas traps over each square metre of the Earth's surface.

The global response: from CFCs to HFCs

• Montreal Protocol (1987): phased out CFCs. Their levels have been falling since then.
• The replacement problem:
• CFCs were replaced by HFCs (hydrofluorocarbons).

• HFCs do not harm ozone, but they are strong greenhouse gases.

• Kigali Amendment (2016): this addition to the Montreal Protocol phases down HFCs.

• So the ozone treaty has also become a climate treaty.

Where it occurs

• Stratosphere, worldwide: CFCs release their chlorine here, about 10–50 km above the Earth.
• Antarctica: the ozone hole forms every spring (September–October), because polar stratospheric clouds form in the extreme cold there.
• Sources (past use): refrigerators, air conditioners and aerosol sprays in homes and industry all over the world.
• India and the HFC phase-down:
• India ratified the Kigali Amendment in September 2021 [3].
• India will freeze HFC use in 2028.
• It will then cut HFCs in four steps: 10% by 2032, 20% by 2037, 30% by 2042 and 85% by 2047 [3].
• India finalised a National Strategy for HFC phase-down in 2023 [3].

Don't confuse with

• HFCs (hydrofluorocarbons): HFCs replaced CFCs. They do not destroy ozone, but they are strong greenhouse gases. CFCs do both kinds of harm. Treaties: CFCs → Montreal (1987). HFCs → Kigali (2016).
• Tropospheric ozone ("bad ozone"): it forms near the ground when vehicle and factory pollution reacts in sunlight. It causes photochemical smog (smog made by sunlight acting on pollution). CFCs work in the opposite direction: they destroy the good ozone high up in the stratosphere.
• Nitrous oxide (N2O): it is also both a greenhouse gas and an ozone-depleting gas, but it comes from nitrogen fertilisers and manure. It has a GWP of about 270, far below the CFCs' thousands. N2O is not covered by the Montreal phase-out.
• Carbon dioxide (CO2): it has the lowest GWP (1) but the largest share of warming (66%) [2]. CFCs are the reverse: a very high GWP but a small share (about 8%) [2].

Prelims Hooks

• GWP order, lowest to highest (100 yr): CO2 (1) < methane (~28) < nitrous oxide (~270) < CFCs (thousands).
• Share of long-lived greenhouse gas forcing, 2024: CO2 66% > methane 16% > CFCs ~8% > N2O ~6% [2].
• Trap: HFCs harm the climate but not the ozone layer. CFCs harm both.
• Montreal Protocol, 1987 (CFCs) → Kigali Amendment, 2016 (HFCs). India ratified Kigali in Sept 2021, will freeze HFC use in 2028 and cut it 85% by 2047 [3].
• Antarctic ozone hole: caused by chlorine from CFCs. It is sped up by polar stratospheric clouds and appears every spring (September–October).
• Stratospheric ozone (about 15–35 km) absorbs ultraviolet-B rays. Ozone near the ground is a pollutant and a greenhouse gas.

Mains Points

• One gas, two kinds of harm (GS-I/III):
• CFCs thin the stratospheric ozone layer, which lets more harmful ultraviolet-B rays reach the surface.

• They also trap heat, with GWPs in the thousands and lifetimes of decades to a century. So past emissions keep doing harm long after the phase-out.

• Montreal Protocol as a model of global cooperation:

• It phased out CFCs, and their levels have been falling since.

• The switch to HFCs created a new climate problem. The Kigali Amendment (2016) corrected it, which shows that environmental treaties must look at the side effects of the substitutes they bring in.

• India's approach (GS-III environment):

• India joined Kigali in September 2021 with a later timeline: a freeze in 2028 and an 85% cut by 2047 [3]. This gives its cooling and refrigeration industries time to shift to safer gases.
• The National Strategy for HFC phase-down (2023) [3] links climate goals with industrial planning, through a phase-down backed by technology.

Related concepts

• Greenhouse effect
• Greenhouse gases
• Global warming potential
• Methane
• Nitrous oxide
• Tropospheric ozone
• Carbon sink
• Climate sensitivity
• Carbon budget

Read more

• The greenhouse effect and greenhouse gases