GATE — Environmental Science and Engineering (ES) · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersThe physical basis of climate change as assessed by the IPCC: the greenhouse effect, radiative forcing, the global carbon cycle, feedbacks, climate sensitivity, and the evidence for observed change. It goes well beyond the 'climate change and livestock' unit of veterinary environmental hygiene.
In the exams: GATE ES Section 8 (greenhouse gases, global warming); UGC NET Environmental Sciences Unit 10; GARP SCR 'Foundations of Climate Change'; UPSC CSE environment
GATE — Environmental Science and Engineering (ES), Section 8
Greenhouse gases and their sources and sinks, GWP comparisons, the greenhouse effect and energy balance arithmetic (effective temperature, S/4), carbon cycle pools and fluxes, ozone and aerosols, and IPCC facts. Numerical answer type questions favour Stefan–Boltzmann, CO2-equivalent and ppm-to-mass conversions.
How our questions for GATE spread across the units of Climate System Science. Difficulty: 20 easy, 23 medium, 2 hard.
| The global carbon cycle: pools, fluxes and the airborne fraction | 5 | |
| Observed changes: temperature, precipitation, sea level, cryosphere | 5 | |
| Ocean warming, deoxygenation and acidification | 5 | |
| Radiative forcing and global warming potential (GWP, GTP, GWP*) | 4 | |
| Methane and nitrous oxide budgets | 4 | |
| IPCC assessment process and confidence language | 4 | |
| The natural greenhouse effect and the energy budget | 3 | |
| Aerosols and their climate effects | 3 | |
| Climate feedbacks and equilibrium climate sensitivity | 3 | |
| Carbon budgets and the link between cumulative emissions and warming | 3 | |
| The climate system and its components | 2 | |
| Detection and attribution, including extreme-event attribution | 2 | |
| Tipping points and irreversibility | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Why does orbital (Milankovitch) forcing trigger large glacial–interglacial changes even though it changes the annual global mean sunlight only slightly?
B. It redistributes sunlight by season and latitude, and ice-albedo and carbon dioxide feedbacks amplify the response
Orbital changes mostly redistribute insolation between seasons and latitudes, especially northern summer sunlight that decides whether snow survives. Ice-sheet albedo and CO2 feedbacks then amplify the change. Orbital variation does not change total irradiance by tens of W m⁻², does not move the Earth beyond habitable distance, and does not alter rotation rate in this way.
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
For 2010–2019, take fossil CO₂ emissions as 9.6 PgC yr⁻¹, land-use change emissions as 1.6 PgC yr⁻¹ and atmospheric growth as 5.1 PgC yr⁻¹. What is the airborne fraction?
A. 0.46
Airborne fraction = growth ÷ total emissions = 5.1 ÷ (9.6 + 1.6) = 0.46. 0.53 leaves out land-use emissions; 0.54 is the fraction taken by sinks; 0.22 is the ocean sink's share.
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
Atmospheric CO₂ rises by 2.4 ppm in a year. Taking 1 ppm = 2.124 PgC, what mass of carbon dioxide (not carbon) does this represent?
A. 18.7 Gt CO₂
Carbon = 2.4 × 2.124 = 5.10 PgC; CO2 = 5.10 × 44/12 = 18.7 Gt CO2. 5.1 is the carbon mass mislabelled; 8.8 drops the ppm factor; 1.4 divides by 44/12 instead of multiplying.
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
Which reservoir is the largest pool of carbon that exchanges with the atmosphere on time scales of up to a few thousand years?
A. The ocean, mostly as dissolved inorganic carbon
The ocean holds about 38,000 PgC, overwhelmingly as dissolved inorganic carbon, far more than the atmosphere (~870 PgC), vegetation (~450–650 PgC) or soils (~1500–2400 PgC).
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
Which evidence shows that the rise in atmospheric CO₂ since industrialisation comes mainly from fossil carbon?
D. A falling ¹³C/¹²C ratio in atmospheric CO₂ together with falling atmospheric oxygen
Fossil carbon is depleted in ¹³C and free of ¹⁴C, so its addition lowers ¹³C/¹²C (the Suess effect), and combustion consumes oxygen. Ocean pH is falling, not rising, and CO2 is higher in the Northern Hemisphere where most emissions occur.
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
Why is the water vapour feedback positive?
D. Saturation vapour pressure rises about 7 per cent per kelvin and relative humidity stays near constant
By Clausius–Clapeyron the air's capacity for water vapour rises about 7% per kelvin; with near-constant relative humidity the amount of this strong greenhouse gas rises with warming. Cloud feedback is a separate term with mixed signs; ocean CO2 release is a carbon-cycle feedback; humid air is lighter, not heavier.
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
Global mean sea level rose at 3.7 mm yr⁻¹ over 2006–2018. If that rate held for 30 years, how much would sea level rise?
A. 0.11 m
3.7 mm yr⁻¹ × 30 yr = 111 mm = 0.11 m. 1.11 m is a factor-of-ten slip (dividing mm by 100 instead of 1000); 0.0037 m is a single year; 0.37 m is a full century at that rate. Actual rise is accelerating, so a constant rate underestimates.
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
About what share of the extra energy accumulated in the climate system has gone into the ocean, according to AR6?
D. 91 per cent
AR6: about 91% to the ocean, 5% to land, 3% to ice and 1% to the atmosphere. 25% is close to the ocean's share of CO2 emissions, a different quantity.
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
Marine heatwaves are periods of extreme high sea surface temperature. What did AR6 report about their frequency?
D. They have roughly doubled in frequency since the 1980s
AR6 assessed with high confidence that marine heatwaves have approximately doubled in frequency since the 1980s, with human influence very likely contributing to most since 2006. They occur in all ocean basins and in non-El Niño years.
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
Which publication sequence matches the IPCC Sixth Assessment cycle?
D. WGI 2021; WGII and WGIII 2022; Synthesis Report 2023
AR6: WGI August 2021, WGII February 2022, WGIII April 2022, Synthesis Report March 2023. 2014 belongs to AR5; 2018–2019 was the period of the AR6 special reports.
Further reading: IPCC AR6 WGI (2021) and the IPCC 2006 Guidelines / 2019 Refinement where cited
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