Environment › Climate science › Warming and temperature records
Climate change: records, attribution and impacts
Warming will cross 1.5°C above pre-industrial levels within a few years, and the UN now plans to come back down to that line rather than stay below it: even if every pledge is delivered, warming peaks near 1.8°C. Two sciences test that headline. Attribution says how much likelier climate change made a flood or a heatwave, not that it caused one, and the long record read from lake sediment and mountain rock sets today's change against what the Earth does on its own.
UPSC has asked
- Prelims 2023: rivers and lakes, including Kanwar Lake, formed by a meander
- Prelims 2016: the Paris Agreement and its temperature goal
The temperature goal, and what breaching it means
- 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.
Where warming is headed
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
Overshoot, peak and decline
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
- 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).
The politics of an overshoot world
- 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.
Attributing an extreme event
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
- Extreme event attribution 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 slow carbon cycle
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.
The reactions, which need not be memorised
Removes CO₂
- Silicate weathering: CaSiO₃ + 2CO₂ + H₂O → Ca²⁺ + 2HCO₃⁻ + SiO₂
- The carbon is later locked away as carbonate
Releases CO₂
- Pyrite oxidation: 2FeS₂ + 7O₂ + 2H₂O → 2FeSO₄ + 2H₂SO₄
- Acid on carbonate rock: CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂
Reading the record before instruments
- A sediment core holds the only record of climate from before instruments, which is how natural variability is separated from human induced change.
- Long records from the Central Ganga Plain are scarce.
What has happened
13 Sep 2026
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.
The Hindu, 13 Sep 2026
10 Sep 2026
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 sediment 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.
2 Sep 2026
UNEP's Limiting Overshoot report set out the UN's first overshoot, peak and decline pathway, treating a breach of 1.5°C as unavoidable.
- The pathway is neither acceptable nor preferred, the report says, only the best remaining option.
- It 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)
5 Aug 2026
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, 5 Aug 2026