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हिन्दी — Read in HindiClimate science: records, attribution and tipping points
The science of a warming world: the IPCC and its reports, the temperature and greenhouse gas records, the attribution of extreme events, and the tipping points the climate may cross. Prelims has asked about the temperature goal of the Paris Agreement.
Foundation note: Climate science and the greenhouse effect
UPSC has asked
- Prelims 2023: rivers and lakes, including Kanwar Lake, formed by a meander
The 1.5°C goal and overshoot
Copy link to The 1.5°C goal and overshootPrelims and Mains
The 1.5°C goal is the limit on global warming above pre industrial levels that the Paris Agreement pursues, the line everything else is measured against.
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 goal
- Article 2 of the Paris Agreement holds warming well below 2°C above pre industrial levels and pursues 1.5°C, goals first set in the Cancun Agreements at COP16 in 2010.
- It refers to warming averaged over decades, so a single year above the line does not breach it; a breach is declared when the running average crosses it.
- Methane is the fastest lever on near term warming; India has not joined the Global Methane Pledge, arguing that developed countries owe finance and technology first.
Overshoot
- Overshoot is a period in which warming passes 1.5°C before being brought back below it by deep cuts and carbon removal.
- A pathway that plans for overshoot is different in kind from one that avoids it.
- Tipping points in the Greenland and West Antarctic ice sheets, the Amazon and the Atlantic overturning circulation are why the length of the overshoot matters.
What changed
3 Sep 2026
- The UN Environment Programme's Limiting Overshoot report is the first UN pathway to treat a breach of 1.5°C as unavoidable and plan the way back down.
- It projects peak warming of 1.8°C even if every national plan is met, and 2.6°C by 2100 on current policies.
- Reversing 0.1°C of peak warming needs 220 billion tonnes of CO₂ to be removed.
- Carbon dioxide removal is unlikely to reverse more than a few tenths of a degree this century, and returning below 1.5°C will not stop sea level rise or undo extinctions.
- It puts developing countries' adaptation needs above $310 billion a year by 2035, a figure expected to divide COP31 in Türkiye.
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)
Extreme event attribution
Copy link to Extreme event attributionPrelims and Mains
Extreme event attribution is the science that estimates how much likelier, or how much more intense, climate change made a particular weather event.
- Attribution science answers a narrower question than the one asked after every disaster: not whether climate change caused this flood, but how much likelier it made one.
- It compares model runs of a pre industrial world, with carbon dioxide at 280 parts per million, against today's 420 and more, and returns a probability rather than a cause.
- It works best for heat, less well for rain, and hardly at all for a single cloudburst, which is where its limits lie.
- For India, a study of rainfall from 1905 to 2014 finds greenhouse gas forcing the dominant driver of rising extreme rainfall in the core monsoon zone.
- Planning can therefore no longer assume that extremes are stationary.
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
What changed
30 Aug 2026
- World Weather Attribution found a South Asian heatwave this year three times likelier and up to 1°C warmer because of climate change.
- The Hindu set out the limits of blaming any one event on it.
The Hindu, 30 Aug 2026: The limits of blaming extreme weather on climate change (opens in a new tab)
27 Jun 2026BriefWorld Weather Attribution found Europe's most severe recorded heatwave impossible without climate change. Record nights were almost 100 times and daytime peaks almost 10 times more likely than in 2003, under a heat dome held in place by an omega block. The Indian Express, 27 Jun 2026: Europe's worst heatwave would have been impossible without climate change (opens in a new tab) · The Hindu, 25 Jun 2026: Why is Europe baking this summer? | Explained (opens in a new tab) · The Indian Express, 30 Jun 2026: As Europe reels from record heatwave, why air-conditioning has become a political flashpoint (opens in a new tab)
The 4.2 ka event
Copy link to The 4.2 ka eventPrelims
The 4.2 ka event was an abrupt drought and cooling about 4,200 years ago recorded across continents, and it marks the start of the Meghalayan Age, the youngest stage of the Holocene.
- Indian records of it come from sediment cores, whose layers hold pollen that records past vegetation and grain sizes that record river energy.
What changed
29 Jul 2026BriefA pollen record from Deoria Tal in the Garhwal Himalaya, dated by the Birbal Sahni Institute of Palaeosciences, shows a sharp dry phase around 4,250 years before present. The researchers link the weak monsoon of roughly 5,100 to 4,000 years before present to the contraction of the Harappan civilisation, as seasonal flooding of the Indus and the Ghaggar-Hakra failed. The weakening is attributed to a southward shift of the Inter Tropical Convergence Zone, a stronger El Niño phase and a negative Indian Ocean Dipole. PIB, 29 Jul 2026: Pollens help trace why the Harappan Civilization shrank (opens in a new tab)
Emission scenarios: from RCP8.5 to CMIP7
Copy link to Emission scenarios: from RCP8.5 to CMIP7Prelims and Mains
LeadClimate science in 2026: new scenarios, tipping points and the next IPCC reportJune 2026
Why in news
The new emissions scenarios for the next assessment of the Intergovernmental Panel on Climate Change (IPCC), published in April 2026, retire the worst case scenario, known as RCP8.5. In June a global report put human caused warming at 1.37°C in 2025, with the carbon budget for 1.5°C nearly spent.
Background
- The IPCC is an intergovernmental body of 195 members. It does no research of its own; scientists assess published studies for it.
- It reports in cycles through three Working Groups: I on the physical science, II on impacts and adaptation, III on mitigation, joined by a Synthesis Report.
- An emissions scenario is a storyline of how greenhouse gas emissions may run this century, which climate models turn into projected warming.
- The 2011 scenarios were the Representative Concentration Pathways (RCPs); in 2016 the Shared Socioeconomic Pathways added population and economic growth.
What changed in the scenarios
- RCP8.5 assumed coal use rising four to five times. It was meant as an edge case but came to be treated as "business as usual".
- The seven new scenarios, prepared under CMIP7, drop it as implausible.
- The new highest scenario gives about 3.5°C by 2100, against about 5°C under RCP8.5.
- The world's present path is near the middle scenario, up to 2.8°C.
- No new scenario holds warming to 1.5°C by 2100 without overshoot.
The carbon budget
- The carbon budget is the carbon dioxide that can still be emitted if warming is to stay below a limit.
- The Indicators of Global Climate Change report put human caused warming at 1.37°C in 2025.
- At present emissions, the budget for 1.5°C runs out in about three years.
Tipping points
- A tipping point is a threshold beyond which part of the climate system shifts to a new state that is hard to reverse, even if the cause is removed.
- Candidates include the Greenland ice sheet, the Amazon forest, coral reefs and the Atlantic Meridional Overturning Circulation (AMOC).
- At the Bonn talks India asked for care and clarity in using the term, cautioning against oversimplifying uncertain science.
The dispute over the next IPCC report
- The Global Stocktake under the Paris Agreement runs every five years; an IPCC cycle takes six to seven. The second stocktake concludes in 2028.
- Many developed countries want all the reports except the Synthesis Report ready before then.
- India, with China, Saudi Arabia and Kenya, opposes advancing them; experts who share this view argue that haste would leave out research from the Global South.
The way forward
- Plan adaptation against the middle scenario, not the retired worst case, so that money is not spent on the wrong risk.
- Keep pressing for deep cuts by developed countries, under common but differentiated responsibilities.
- Build India's own climate models and data, so that its science is represented in the assessments.
Prelims facts
- The IPCC does no research of its own; it assesses published studies.
- Working Group I is physical science, II impacts and adaptation, III mitigation.
- RCP8.5 was the highest of the 2011 scenarios and is now retired.
- CMIP is the Coupled Model Intercomparison Project.
- The Global Stocktake is held every five years.
Emission scenarios project greenhouse gas trends with technology and socioeconomic assumptions and are revised every six to eight years for the modelling community. The four Representative Concentration Pathways (RCPs) of 2011 included RCP8.5, which assumed CO2 tripling to 850 to 900 ppm and coal use rising four to fivefold; meant as an edge case, it came to be treated as business as usual. In 2016 the RCPs were joined by Shared Socioeconomic Pathways, which add economic growth and population. Returning from an overshoot of 1.5°C needs large scale carbon dioxide removal.
Three generations of scenarios
2011
Four Representative Concentration Pathways; the worst case, RCP8.5, gives about 5°C by 2100
2016
Shared Socioeconomic Pathways add economic growth and population
2026
Seven CMIP7 scenarios; the worst case gives about 3.5°C by 2100
What changed
See also: The 1.5°C goal and overshoot
Climate tipping points
Copy link to Climate tipping pointsPrelims and Mains
A tipping point is a threshold beyond which part of the climate system shifts to a new state that is hard to reverse even if the cause is removed. The behaviour is non linear: small warming can trigger self amplifying feedback, as when melting Arctic ice exposes dark ocean that absorbs more heat. Candidates include Amazon dieback, collapse of the Atlantic meridional overturning circulation (AMOC), mass coral bleaching, monsoon shifts and Greenland ice loss.
The Arctic ice feedback
Warming
The Arctic warms
Melt
Sea ice melts
Dark water
Dark ocean is exposed where bright ice was
More heat
The ocean absorbs more heat
More warming
The warming speeds up, and melts more ice
See also: The 64th sessions of the Subsidiary Bodies (SB64), Bonn