Prelims · Environment & ecology · 53 questions

Climate change & agreements

Every UPSC Prelims question on this topic, 2016–2026, newest first. Tap an option to check yourself; the answer and explanation open below it.

Asked in 11 of 11 years · most in 2016 (6)

UPSC syllabus: “General issues on Environmental ecology, Bio-diversity and Climate Change - that do not require subject specialization.” See the full syllabus →

Prelims 2019 · Q25

Easy

In the context of which of the following do some scientists suggest the use of cirrus cloud thinning technique and the injection of sulphate aerosol into stratosphere?

Answer & explanation

Answer: (d) Reducing the global warming

Both are proposed geoengineering methods of 'solar radiation modification', meant to cool the planet. Stratospheric sulphate aerosols would reflect sunlight back to space, copying the cooling seen after big volcanic eruptions; thinning heat-trapping cirrus clouds would let more of the Earth's heat escape.

✓ (d) The IPCC lists stratospheric aerosol injection and cirrus cloud thinning among the most-studied SRM methods, whose aim is to reduce warming.
✗ (a) Artificial rain uses cloud seeding with silver iodide or salt in rain-bearing clouds, not stratospheric sulphate.
✗ (b) These methods target the planet's overall heat budget; they are not cyclone-suppression tools.

Remember · Solar radiation modification (geoengineering to cut warming): stratospheric aerosol injection, marine cloud brightening, cirrus cloud thinning, surface albedo change. Carbon dioxide removal is the other branch.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 11 (practise this chapter)

Sources

IPCC Special Report on Global Warming of 1.5 °C, Glossary ↗ “Solar radiation modification refers to the intentional modification of the Earth’s shortwave radiative budget with the aim of reducing warming. Artificial injection of stratospheric aerosols , marine cloud brightening and land surface albedo modification are examples of proposed SRM methods.”
IPCC Special Report on Global Warming of 1.5 °C, Chapter 4 ↗ “Table 4.7 Overview of the main characteristics of the most-studied SRM methods SRM indicator Stratospheric Aerosol injection (SAI) Marine Cloud Brightening (MCB) Cirrus Cloud Thinning (CCT)”
NCERT Class 11 · Fundamentals of Physical Geography, Chapter 11 “Volcanic eruption throws up lots of aerosols into the atmosphere. These aerosols remain in the atmosphere for a considerable period of time reducing the sun's radiation reaching the Earth's surface.”

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

Prelims 2019 · Q32

Easy

For the measurement/estimation of which of the following are satellite images/remote sensing data used?

1.Chlorophyll content in the vegetation of a specific location
2.Greenhouse gas emissions from rice paddies of a specific location
3.Land surface temperatures of a specific location

Select the correct answer using the code given below.

Answer & explanation

Answer: (d) 1, 2 and 3

All three can be measured or estimated from satellite data: leaf greenness and chlorophyll from visible and near-infrared reflectance, land surface temperature from thermal infrared, and paddy methane by combining satellite-derived rice area and temperature with models.

✓ 1. Chlorophyll strongly absorbs visible light and leaves reflect near-infrared, so satellite vegetation indices (such as MODIS NDVI and EVI) track canopy greenness, which depends on leaf area, chlorophyll and canopy structure.
✓ 2. Methane from rice paddies has been estimated with a model driven by satellite-mapped rice area, land surface temperature and evapotranspiration, for example over China's Sanjiang Plain.
✓ 3. Land surface temperature is retrieved from thermal infrared measurements, for example the MODIS daily product at 1 km pixels.

Remember · Remote sensing gives vegetation greenness and chlorophyll (NDVI), land surface temperature (thermal infrared), and, with models, methane from rice fields.

Sources

NASA MODIS: Vegetation Index Products (NDVI and EVI) ↗ “MODIS vegetation indices, produced on 16-day intervals and at multiple spatial resolutions, provide consistent spatial and temporal comparisons of vegetation canopy greenness, a composite property of leaf area, chlorophyll and canopy structure.”
NASA MODIS: Land Surface Temperature and Emissivity (MOD11) ↗ “The Land Surface Temperature (LST) and Emissivity daily data are retrieved at 1km pixels by the generalized split-window algorithm and at 6km grids by the day/night algorithm.”
Sun et al. (2017), PLoS ONE: satellite-data-based estimation of methane emissions from rice paddies, Sanjiang Plain, China (open-access copy on PubMed Central, NIH) ↗ “we estimated CH 4 emissions using a process-based model derived by rice area, CH 4 flux, land surface temperature (LST), and the ratio of precipitation (P) and evapotranspiration (ET) in rice paddies in the SJP”

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

Prelims 2019 · Q34

Medium

Which of the following statements are correct about the deposits of ‘methane hydrate’?

1.Global warming might trigger the release of methane gas from these deposits.
2.Large deposits of ‘methane hydrate’ are found in Arctic Tundra and under the seafloor.
3.Methane in atmosphere oxidizes to carbon dioxide after a decade or two.

Select the correct answer using the code given below.

Answer & explanation

Answer: (d) 1, 2 and 3

All three statements are correct. Methane hydrate is an ice-like solid holding methane, found in Arctic permafrost and in sea-floor sediments; it releases methane when it warms, and methane that reaches the air lasts about a decade before it is oxidised to carbon dioxide.

✓ 1. Methane hydrate is stable only at low temperature and high pressure. Warming makes the hydrate release its methane, which is why global warming could trigger releases.
✓ 2. Gas hydrates occur in huge quantities in marine sediments just below the sea floor and in association with permafrost in the Arctic.
✓ 3. Methane is short-lived in the air: it lasts about a decade on average (IPCC AR6 gives 11.8 years). It is broken down by oxidation, ending as carbon dioxide and water.

Remember · Methane hydrate = methane locked in ice-like crystals under permafrost and seabed. Warming can release it; airborne methane lasts about 12 years and then oxidises to CO2.

Sources

US Geological Survey: Where are gas hydrates found? (Internet Archive copy) ↗ “it exists in huge quantities in marine sediments in a layer several hundred meters thick directly below the sea floor and in association with permafrost in the Arctic.”
US Geological Survey: What are gas hydrates? (Internet Archive copy) ↗ “Gas hydrate is sometimes called “the ice that burns” because the warming hydrates release enough methane to sustain a flame.”
US EPA: Understanding Global Warming Potentials ↗ “CH 4 emitted today lasts about a decade on average, which is much less time than CO 2 .”
IPCC AR6 Working Group I, Chapter 7: lifetime of methane (Table 7.15) ↗ “Species Lifetime (Years) Radiative Efficiency (W m –2 ppb –1 ) GWP-20 GWP-100 GWP-500 GTP-50 GTP-100 CGTP-50 (years) CGTP-100 (years) CO 2 Multiple 1.33 ± 0.16 ×10 –5 1. 1.000 1.000 1.000 1.000 CH 4 -fossil 11.8 ± 1.8”

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

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Conservation, pollution & EIAGS 3 syllabus

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Class 11 Fundamentals of Physical Geography, Chapter 11cited in 1 explanation

Climate change & agreements

Prelims 2019 · Q25

Prelims 2019 · Q32

Prelims 2019 · Q34

The same topic in Mains

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