MPSC 2021 Prelims Paper-I · Question 35 of 100

Correct — option (4), All the above. The question asks which of the four listed effects follow from ozone depletion, and each of the four can be defended, so the row that accepts all of them is the answer. Take them in turn. Statement (a): the stratospheric ozone layer absorbs most incoming ultraviolet-B radiation, and when it thins more UV-B reaches the surface; the United States Environmental Protection Agency states that excessive exposure to UV-B radiation increases the risks of skin cancer, cataracts and a suppressed immune system in humans, so damage to the immune system is a recognised consequence. Statement (d) is settled by the same sentence — cataracts, a clouding of the lens of the eye, are among the effects the agency names explicitly, and it estimates that full implementation of the Montreal Protocol will prevent some 63 million cataract cases among Americans born between 1890 and 2100, alongside about 443 million skin cancer cases. Statement (b): the same agency states that plant growth can be directly affected by UV-B radiation, and that indirect effects on plant form, nutrient distribution and developmental timing may matter as much as the direct damage; reduced or stunted growth of plants is therefore a standard listed effect. Statement (c): a rise in temperature is bound up with ozone depletion because the substances that destroy the ozone layer are themselves powerful greenhouse gases — chlorofluorocarbons have global warming potentials in the thousands, and the hydrofluorocarbons brought in to replace them can be up to ten thousand times as potent as carbon dioxide molecule for molecule — and because a thinner ozone layer lets more ultraviolet energy through to the lower atmosphere and the surface. With all four statements standing, only the row that accepts all of them can be right, and that is option (4).

• (1)Only (a) and (b) — This row accepts only the damage to the human immune system and the stunted growth of plants, and rejects the temperature effect and cataracts. Cataracts are among the best-established consequences of increased ultraviolet-B exposure and are named directly by environmental agencies alongside skin cancer and immune suppression; the projected saving of tens of millions of cataract cases is one of the standard arguments for the Montreal Protocol. Rejecting a temperature effect is also unsafe, since the ozone-depleting substances are themselves potent greenhouse gases. A row that accepts two effects out of four is only correct if two of the four genuinely fail, and here none of them does; the row is there for a candidate who stops looking as soon as the first two statements check out.
• (2)Only (c) and (d) — This row accepts only the temperature effect and cataracts, and rejects the immune-system damage and the effect on plants. Both rejections are wrong. Immune suppression is listed by environmental agencies in the same breath as skin cancer and cataracts as a consequence of excessive UV-B exposure, and it matters particularly in populations where infectious disease is common, because a weakened immune response reduces the effectiveness of both natural resistance and vaccination. Damage to plants is equally well established: UV-B affects growth directly, and it also alters plant form, the distribution of nutrients within the plant and the timing of its development, with consequences for crop yield. This row is the mirror image of the previous one and fails for the same reason.
• (3)Only (b), (c) and (d) — This row accepts the stunted growth of plants, the rise of temperature and the cataracts, and rejects only the damage to the human immune system. It is the near-miss of the question, and it is dangerous precisely because it excludes just one statement — the one a candidate is least likely to have met, since immune suppression is the least publicised of the ultraviolet effects compared with skin cancer and cataracts. But it is not obscure: environmental agencies name a suppressed immune system explicitly among the risks of excessive UV-B exposure, and the mechanism is well studied, ultraviolet radiation acting on the skin's immune cells. A row that omits one true statement is the commonest construction in a question whose answer is an all-inclusive option, and the defence is to give every statement its own verdict before looking at the rows.

Ozone is a molecule of three oxygen atoms, and about ninety per cent of the earth's ozone sits in the stratosphere between roughly fifteen and thirty-five kilometres up, where it absorbs most of the sun's ultraviolet-B radiation and nearly all of the more energetic UV-C. Chlorofluorocarbons, halons, carbon tetrachloride, methyl chloroform and other halogen compounds released at the surface drift up into the stratosphere, where ultraviolet light breaks them apart and frees chlorine and bromine atoms; each of these can destroy many thousands of ozone molecules in a catalytic cycle before it is removed. The loss is greatest over Antarctica in the southern spring, where polar stratospheric clouds and the isolation of the polar vortex create the conditions for the ozone hole. The consequences at the surface follow from the extra ultraviolet: more non-melanoma skin cancer and a greater role in malignant melanoma, more cataracts, suppressed immunity, direct and indirect damage to plants and reduced crop yield, and harm to phytoplankton and to the marine food chain that rests on them. The international response is the Vienna Convention of 1985, a framework treaty signed by twenty nations, and the Montreal Protocol agreed on 16 September 1987 and in force from 1 January 1989, whose Kigali Amendment of October 2016 extends it to hydrofluorocarbons, requiring a cut of at least eighty-five per cent from the 2011 to 2013 average.

The ozone layer is one of the most frequently examined topics in the MPSC environment section, because it combines a clean physical mechanism, a well-known set of consequences and a treaty regime that is often called the most successful in environmental history. This question uses the statement-cluster form, and its answer is the all-inclusive row. That form has a particular discipline attached to it: a candidate must judge each statement separately and completely before looking at the options, because the wrong rows are built by omitting one or two true statements rather than by including a false one. A candidate who reasons from a feeling that an all-inclusive option is somehow too easy will talk themselves out of a correct answer. It is also worth separating ozone depletion from global warming in your own notes even while accepting the connection this question asserts, because the two are distinct phenomena, and the Commission has been known to test the distinction directly.

• Excessive exposure to ultraviolet-B radiation increases the risks of skin cancer, cataracts and a suppressed immune system in humans, and ozone depletion is what allows more UV-B to reach the surface.
• Plant growth can be directly affected by UV-B radiation, and the indirect changes it causes in plant form, nutrient distribution and developmental timing may be as important as the direct damage.
• Full implementation of the Montreal Protocol is estimated to prevent about 443 million skin cancer cases, 2.3 million skin cancer deaths and 63 million cataract cases among Americans born between 1890 and 2100.
• The chemicals that destroy stratospheric ozone are themselves powerful greenhouse gases: chlorofluorocarbons carry global warming potentials of roughly 4,680 to 10,720, and hydrofluorocarbons can be up to ten thousand times as potent as carbon dioxide.
• The Vienna Convention of 1985 set the framework and the Montreal Protocol, agreed on 16 September 1987 and in force from 1 January 1989, set the controls; the Kigali Amendment of October 2016 requires an eighty-five per cent cut in hydrofluorocarbons from the 2011 to 2013 average.

• Confusing stratospheric ozone, which shields the earth from ultraviolet radiation, with tropospheric ozone, which is a pollutant and a greenhouse gas at ground level
• Treating ozone depletion and global warming as the same phenomenon; they have different mechanisms, and while the ozone-depleting substances are potent greenhouse gases, the loss of ozone itself cools the stratosphere
• Rejecting an all-inclusive option because it seems too easy, when the wrong rows in such a question are built by omitting true statements rather than by adding false ones
• Overlooking immune suppression among the effects of ultraviolet exposure because skin cancer and cataracts are better publicised; agencies list all three together

Ozone questions in MPSC papers take three forms. The first is the effects cluster, as here, listing consequences and asking which hold. The second is the treaty question — the year, the city, which substances a given amendment covers, and which body administers it. The third is a chemistry or mechanism question about how chlorine destroys ozone or why the hole forms over Antarctica rather than the Arctic. A single sheet covering the mechanism in five lines, the treaty chronology, the substances controlled and the effects on humans, plants and marine life answers all three. Keep the distinction between the ozone problem and the greenhouse problem written down explicitly, because it is the point on which a well-read candidate is most often caught.

No directly related past PYQ was found.

• practice — not a real PYQ

  Increased ultraviolet-B radiation reaching the earth's surface as a result of stratospheric ozone depletion is associated with which of the following in human beings?

  • (a)skin cancer only
  • (b)cataracts only
  • (c)skin cancer, cataracts and suppression of the immune system
  • (d)none of these

  Answer(c) skin cancer, cataracts and suppression of the immune system — environmental agencies list all three together as consequences of excessive UV-B exposure, UV-B being responsible for non-melanoma skin cancer and playing a major role in malignant melanoma. Full implementation of the Montreal Protocol is estimated to prevent about 443 million skin cancer cases and 63 million cataract cases among Americans born between 1890 and 2100.

• practice — not a real PYQ

  The Kigali Amendment of 2016 to the Montreal Protocol deals with the phasing down of which substances?

  • (a)chlorofluorocarbons
  • (b)hydrofluorocarbons
  • (c)halons
  • (d)carbon tetrachloride

  Answer(b) hydrofluorocarbons — adopted in October 2016, the amendment requires parties to cut HFC production and consumption by at least eighty-five per cent from the annual average of 2011 to 2013, with later timelines for several groups of developing countries. HFCs do not deplete the ozone layer, which is why they were adopted as substitutes, but they are powerful greenhouse gases, up to ten thousand times as potent as carbon dioxide, which is why they were brought under the protocol.