CSIR-UGC NET Climate System Science: practice questions

1 · The climate system and its components · medium

Antarctic ice cores covering the last 800,000 years show atmospheric carbon dioxide varying with the glacial cycles. Which range matches the record before industrialisation?

1. Steady near 280 ppm, with the glacial changes driven by methane only
2. Between near 280 ppm in glacials and near 410 ppm in interglacials
3. Between near 180 ppm in glacials and near 280 ppm in interglacials
4. Between near 100 ppm in glacials and near 180 ppm in interglacials

2 · The natural greenhouse effect and the energy budget · medium

In the 'emission height' explanation of the enhanced greenhouse effect, what happens immediately after carbon dioxide is added to the atmosphere?

1. The surface instantly emits more longwave radiation, so the planet loses energy and cools until rebalanced
2. Emission to space shifts to a higher, colder level, so outgoing longwave falls and energy accumulates
3. The ozone layer thickens and absorbs more sunlight, which warms the surface directly by raising absorption
4. The lapse rate reverses so that temperature rises with height, trapping heat beneath an inversion layer

3 · The natural greenhouse effect and the energy budget · hard

Take an Earth energy imbalance of 0.79 W m⁻², Earth surface area 5.1 × 10¹⁴ m² and one year as 3.156 × 10⁷ s. What is the energy accumulated by the climate system in one year?

1. 1.27 × 10²² J
2. 4.03 × 10¹⁴ J
3. 2.49 × 10⁷ J
4. 3.18 × 10²¹ J

4 · The global carbon cycle: pools, fluxes and the airborne fraction · hard

AR6 projects how land and ocean sinks behave under higher-emission scenarios. Which statement matches its assessment?

1. Sinks reverse and become net sources this century in every scenario, including the lowest-emission ones
2. Sinks stay fixed in absolute size, so every extra tonne of emissions remains entirely in the atmosphere
3. Sinks take up more carbon in total but a smaller fraction of emissions, so the airborne fraction rises
4. Sinks take up a larger fraction of emissions because CO₂ fertilisation grows faster than emissions rise

5 · Methane and nitrous oxide budgets · hard

Why is methane's perturbation lifetime (about 12 years) longer than its total atmospheric lifetime (about 9 years)?

1. Added methane is partly converted into carbon monoxide, which re-forms methane later
2. Added methane consumes OH, its own main sink, so a pulse slows its own removal
3. Added methane is stored temporarily in the ocean and released back over the decades
4. Added methane rises into the stratosphere, where no removal process operates at all

6 · Climate feedbacks and equilibrium climate sensitivity · medium

Why is the water vapour feedback positive?

1. Higher humidity makes the air heavier, so it sinks and compresses, warming the lower atmosphere
2. Warmer oceans release dissolved carbon dioxide, which raises the greenhouse effect of the air
3. Warming increases cloud cover everywhere, and clouds always trap more heat than they reflect
4. Saturation vapour pressure rises about 7 per cent per kelvin and relative humidity stays near constant

7 · Climate feedbacks and equilibrium climate sensitivity · medium

Which feedback contributes most to the spread in estimates of climate sensitivity?

1. The cloud feedback
2. The lapse-rate feedback
3. The sea-ice albedo feedback
4. The Planck feedback

8 · Climate feedbacks and equilibrium climate sensitivity · hard

An energy-budget estimate uses: warming ΔT = 1.1 K, total forcing F = 2.72 W m⁻², energy imbalance N = 0.79 W m⁻², and F₂ₓ = 3.93 W m⁻². Using N = F + λΔT, what climate sensitivity does it imply?

1. 2.2 °C
2. 1.6 °C
3. 1.2 °C
4. 2.0 °C

9 · Detection and attribution, including extreme-event attribution · medium

In optimal fingerprinting, what does a regression scaling factor for the greenhouse-gas signal that is significantly above zero and consistent with one indicate?

1. The greenhouse signal is detected, and its observed amplitude agrees with what the models simulate
2. The models overestimate the greenhouse response by a factor of two, so observations must be adjusted
3. The greenhouse signal is absent, and the observed change is attributed entirely to internal variability
4. The observations are consistent with any forcing, so no attribution statement can be made at all

10 · Carbon budgets and the link between cumulative emissions and warming · medium

What did AR6 conclude about the zero emissions commitment (ZEC) after CO₂ emissions reach net zero?

1. It is unknowable, so AR6 excluded it from remaining carbon budget estimates
2. It is close to zero, as continued ocean heat uptake balances CO₂ drawdown
3. It is a further warming of 1.5 °C, because the ocean releases all its stored heat
4. It is a cooling of 1.0 °C within a decade, because CO₂ is rapidly reabsorbed