Environment › Climate science
Climate science: records, attribution and tipping points
The science of a warming world: the records and reports that track it, the carbon cycle, how much likelier warming makes an extreme event, tipping points, and the climates of the past. Prelims has asked about the temperature goal of the Paris Agreement.
3 Sep 2026 · 5 Aug 2026 · Prelims and Mains
The 1.5°C goal
The line everything else is measured against is a decadal average rather than a reading taken in one hot year, and the world is closing on it faster than it was.
1.8°CPeak warming even if every national plan and net zero target is met
2.6°CWarming by 2100 on current policies
0.5°CPresent warming caused by methane
220 billion tonnesCO₂ to be removed to reverse 0.1°C of peak warming
- Article 2 of the Paris Agreement holds warming well below 2°C and pursues 1.5°C, goals first set in the Cancun Agreements at COP16 in 2010.
- The 1.5°C goal refers to warming averaged over decades, so a single year above the line does not breach it.
- A study in Geophysical Research Letters found that warming sped up from about 2015, once volcanic and solar noise was removed from five temperature datasets.
- At that pace the world breaches 1.5°C by 2030.
- Cleaner air is part of it, because fewer aerosols now reflect sunlight.
The Hindu, 3 Sep 2026 · The Hindu, 5 Aug 2026
3 Sep 2026 · Prelims and Mains
Overshoot, peak and decline
UNEP's Limiting Overshoot report is the first UN pathway to treat a breach of 1.5°C as unavoidable and to plan the way back down instead.
Overshoot
Warming crosses 1.5°C within a few years; slash emissions and protect vulnerable people and ecosystems
Peak
Reach at least net zero CO₂; every five years of high emissions adds about 0.1°C to the peak
Decline
Sustained net negative CO₂ emissions bring warming back below 1.5°C by 2100
- The pathway is neither acceptable nor preferred, the report says, only the best remaining option.
- Cutting methane, a short-lived climate pollutant, is the fastest way to slow near term warming.
- Carbon dioxide removal is unlikely to reverse more than a few tenths of a degree this century.
- Returning below 1.5°C will not stop sea level rise or undo extinctions.
- A longer overshoot raises the risk of tipping points in the Greenland and West Antarctic ice sheets, the Amazon and the Atlantic Meridional Overturning Circulation (AMOC).
- COP30's Global Mutirão decision of 2025 was the first COP text to concede a likely temporary overshoot.
- India has not joined the Global Methane Pledge, arguing that developed countries owe finance and affordable technology first.
- The report put developing countries' adaptation needs above $310 billion a year by 2035, a figure expected to divide COP31 in Türkiye in November.
The Hindu, 3 Sep 2026 · The Indian Express, 4 Sep 2026: UNEP says 1.5°C warming overshoot is now 'unavoidable'. What does it mean for climate action? (opens in a new tab)
30 Aug 2026 · Prelims and Mains
Extreme event attribution
Attribution science answers a narrower question than the one asked of it after every disaster: not whether climate change caused this flood, but how much likelier it made one.
What it can say
- How much likelier an event became
- How much more intense it became
- Enough to support adaptation and loss and damage claims
Where it breaks down
- A cloudburst is far harder to attribute than a heatwave
- Weather records are sparse and models too coarse to resolve them
- Extreme events can occur without human caused warming
- It compares model runs of a pre-industrial world, carbon dioxide at 280 parts per million, against today's 420 and more, and returns a probability rather than a cause.
- World Weather Attribution (WWA) found a South Asian heatwave this year three times likelier and up to 1°C warmer.
The Hindu, 30 Aug 2026: The limits of blaming extreme weather on climate change (opens in a new tab)
13 Sep 2026 · Prelims and Mains
The slow carbon cycle
Over millions of years it is the rate at which rock weathers, rather than anything anyone emits, that sets the carbon dioxide in the air.
Erosion
Glaciers and rapid erosion expose pyrite, an iron sulphide, to air and water
Oxidation
The pyrite oxidises to sulphuric acid
Dissolution
The acid dissolves carbonate rocks
Release
CO₂ escapes to the atmosphere
- In silicate weathering, freshly exposed silicate minerals react with CO₂, and the carbon ends up locked in seafloor sediments.
- Silicate weathering is thought to have helped cool the planet over the last 50 million years.
- This cycle works over millions of years rather than decades.
- A study of the upper Indus basin found that rapid Himalayan erosion releases about three times as much CO₂ through pyrite oxidation as silicate weathering there removes.
- Steep mountain catchments came out as net sources of CO₂, while the flatter floodplains downstream were sinks.
- Silicate weathering removes carbon as CaSiO₃ + 2CO₂ + H₂O → Ca²⁺ + 2HCO₃⁻ + SiO₂, and the carbon is later locked away as carbonate.
- Pyrite oxidation releases it as 2FeS₂ + 7O₂ + 2H₂O → 2FeSO₄ + 2H₂SO₄, and the acid then attacks carbonate rocks as CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂.
- Neither equation needs to be memorised; what matters is which way each reaction moves the carbon.
The Hindu, 13 Sep 2026
10 Sep 2026 · Prelims and Mains
Bakhira Lake and the monsoon record
A sediment core holds the only record of climate from before instruments, which is how natural variability is separated from human induced change.
- The Birbal Sahni Institute of Palaeosciences, Lucknow, an autonomous institute of the Department of Science and Technology, reconstructed about 25,000 years of the Indian Summer Monsoon from a core taken at Bakhira Lake.
- Bakhira, in Uttar Pradesh, is an oxbow wetland formed when the Rapti cut off a meander, and a Ramsar Site.
- Long records from the Central Ganga Plain are scarce, which is what makes this one useful to water resource management there.
UPSC has asked
- Prelims 2023: rivers and lakes, including Kanwar Lake, formed by a meander