Global Warming and Ozone Depletion
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Direct answer
Carbon dioxide contributes the largest share of human-driven greenhouse warming, with methane, nitrous oxide and chlorofluorocarbons alongside it; these gases trap outgoing infrared radiation, and their accumulation from fossil-fuel burning and deforestation is raising global mean temperature, melting polar ice, lifting sea levels and widening the reach of vector-borne diseases. Ozone depletion is a different wound in a different layer: chlorofluorocarbons from refrigerants and sprays drift to the stratosphere, where their released chlorine destroys ozone catalytically, thinning the shield that filters harmful ultraviolet rays — most dramatically as the springtime ozone hole over Antarctica. The policy pair to remember is Kyoto 1997 for greenhouse-gas emissions and Montreal 1987 for ozone-depleting substances, two protocols NEET never tires of swapping in options.
What you must remember
- Greenhouse gas roster: carbon dioxide (the dominant contributor to warming), methane, nitrous oxide and CFCs — water vapour also acts as a greenhouse agent.
- Warming arithmetic: the global mean temperature of the planet has risen measurably since pre-industrial times, with NCERT-era estimates around half a degree Celsius over the twentieth century and ongoing accumulation.
- Warming consequences: melting polar ice and rising sea levels submerging coastlines, altered evaporation-precipitation patterns, subtropical arid-zone expansion, and poleward spread of tropical vector-borne diseases.
- Ozone's job: stratospheric ozone absorbs the bulk of harmful UV-B, which otherwise damages DNA (thymine dimers), induces skin cancers and cataracts, and can cause snow-blindness.
- The villain: CFCs — chemically inert in the troposphere — photodissociate in the stratosphere to release chlorine radicals, each destroying many ozone molecules catalytically.
- The hole: maximal ozone thinning appears over Antarctica in the southern spring (September-October), first reported in the mid-1980s.
- Protocol pairing: Kyoto Protocol (1997) targets greenhouse-gas emission reductions; Montreal Protocol (1987) controls emission of ozone-depleting substances such as CFCs.
- Common thread: both problems are caused by stable synthetic (or over-emitted) molecules altering atmospheric chemistry faster than natural cycles can absorb.
Two atmospheric problems, one chlorine atom
Follow a CFC molecule's biography. Released from a leaking refrigerator or an old spray can, it is too stable to break down in the lower atmosphere, so it drifts upward for years until hard ultraviolet light in the stratosphere finally cracks it, freeing a chlorine atom. That atom reacts with ozone to form chlorine monoxide and ordinary oxygen, and when chlorine monoxide meets a free oxygen atom the chlorine is released again — undamaged and ready to repeat the cycle thousands of times. Over Antarctica, winter polar circulation isolates stratospheric air, and when sunlight returns in spring the trapped chlorine devastates ozone, opening the famous hole. Contrast this with global warming: there the culprit molecules do not react at all — they simply vibrate under infrared and re-radiate heat downward, so the Earth radiates less energy than it receives. One problem is chemistry destroying a shield; the other is physics thickening a blanket. Both answers, though, begin with stopping emissions at the source — the logic of both protocols.
Where candidates slip
The protocols swap is the classic trap: Kyoto for climate, Montreal for ozone — anchor the years by the fact that Montreal (1987) came a decade before Kyoto (1997). The second slip conflates the two issues themselves, imagining ozone thinning lets heat in to cause warming; they are mechanistically separate, though CFCs happen to contribute to both. Statement traps also test that UV-B damages DNA, that the ozone hole is Antarctic and seasonal (spring), and that carbon dioxide remains the single largest contributor to warming. Note too that the standalone environmental chapter was trimmed from the rationalised NEET syllabus, so these facts now surface as assertion-reason and general-knowledge statements rather than full chapters.
Frequently asked questions
Which gases are chiefly responsible for the greenhouse effect?
Carbon dioxide, methane, nitrous oxide and chlorofluorocarbons, with carbon dioxide the largest single contributor to current warming.
How do CFCs destroy stratospheric ozone?
Ultraviolet light splits CFCs in the stratosphere, releasing chlorine radicals that catalytically convert ozone to oxygen, one chlorine atom destroying many ozone molecules.
Why is the ozone hole most severe over Antarctica in spring?
Winter circulation traps chlorine-containing air over the pole; returning sunlight then drives rapid catalytic ozone loss, peaking in September-October.
What health effects follow increased UV-B reaching the earth?
DNA damage with thymine dimer formation, more skin cancers, cataracts and snow-blindness, plus harm to crops and plankton.
What do the Kyoto and Montreal Protocols each regulate?
Kyoto (1997) commits nations to greenhouse-gas emission cuts; Montreal (1987) phases out ozone-depleting substances such as CFCs.