Overshoot

Geography glossary

Also called: 1.5°C overshoot, temperature overshoot · Topic: Climate Change: Causes, Evidence and the Global Response · NCERT: Beyond NCERT

Meaning

Overshoot (also called 1.5°C overshoot or temperature overshoot) means global warming goes above a set limit such as 1.5°C for some years and then comes back down to it by the end of this century. It matters because a return to 1.5°C depends on taking large amounts of CO2 back out of the air later. The extra warming in between also causes harm, and some of that harm can never be undone.

Explanation

How it works: cause → process → result

  • Cause: the world emits more CO2 than the budget allows
  • A carbon budget is the total CO2 the world can still emit for a given warming limit.
  • The AR6 estimate was 500 GtCO2 (billion tonnes of CO2) from the start of 2020, for a 50% chance of staying under 1.5°C.

  • In IPCC SR15 pathways, gross CO2 emissions usually go over the remaining budget by several hundred GtCO2.

  • Process: temperature rises past the limit, peaks, then is pulled back

  • Warming crosses 1.5°C in the near term.
  • Carbon dioxide removal (CDR) means taking CO2 out of the air and storing it. To bring temperature down, the world must remove more CO2 than it emits after the peak.

  • SR15 notes that CDR is limited before 2050. So the return depends on removal in the later decades.

  • Result: the temperature number comes back, but the damage does not

  • The IPCC says overshoot brings harm, and some of it is irreversible.
  • A 2024 Nature study says that, for a range of climate impacts, we should not expect them to reverse straight after an overshoot.

What decides how bad an overshoot is

  • Height: how far temperature goes above the limit.
  • Length: how long it stays above the limit.
  • Risk grows with both. A bigger overshoot also needs more CDR.
  • UNEP says emission cuts of 26% by 2030 and 46% by 2035 would hold the overshoot to about 0.3°C.
  • One UNEP scenario peaks near 1.8°C and falls back below 1.5°C by the end of the century.

Why the hot period makes the return harder

  • Feedback during the overshoot
  • Overshoot can bring wildfires, mass tree deaths and the drying of peatlands (wet lands that store very large amounts of old carbon).
  • These weaken carbon sinks (forests and soils that take in CO2) and release more greenhouse gases.

  • So the hot years add to the CO2 that must later be removed.

  • The removal itself is doubtful

  • UNEP's 2026 report says even the lowest-overshoot scenario still available depends on storing about 320 GtCO2 over this century.
  • UNEP calls the methods needed for a return by 2100 uncertain, risky and costly.
  • Technical, economic and sustainability limits may stop CDR from reaching this scale.

Where the idea came from and where it stands now

  • The term comes from climate modelling research. It is now used in political talks.
  • IPCC SR15 found that most 1.5°C-consistent pathways it assessed were overshoot pathways.
  • UNEP's 2026 report says the chance of limiting warming to 1.5°C with no or limited overshoot has been lost.
  • UNEP's 2025 report said a multi-decade average above 1.5°C is very likely within the next decade.

Where it occurs

  • Global temperature goal: overshoot is measured against the Paris Agreement goal (COP21, 2015) to keep warming "well below 2°C" and to try for 1.5°C.
  • Ecosystems hit first: the IPCC names polar, mountain and coastal ecosystems as the places that suffer irreversible harm from going above 1.5°C.
  • Arctic: it has warmed nearly four times faster than the globe since 1979. September sea ice is shrinking by about 12–13% per decade.
  • Hindu Kush Himalaya: ICIMOD (2023) found the glaciers may lose 30–50% of their volume by 2100 even at 1.5–2°C. This threatens the Indus, Ganga and Brahmaputra.
  • Glacial lake floods: new glacial lakes can burst, as at Kedarnath (2013) and South Lhonak, Sikkim (2023).

  • Warm-water coral reefs: the 2025 Global Tipping Points Report judged that they have likely crossed their tipping point.

  • Coasts at risk: deltas (Ganga-Brahmaputra, Mekong, Nile), the Maldives, Tuvalu, Kiribati, and Mumbai, Kolkata and Chennai.

  • CDR and storage examples: direct-air-capture plants in Iceland, and CO2 storage at Sleipner, Norway (since 1996). NITI Aayog published a CCUS report in 2022.
  • India's position: India contributed only about 4% of cumulative global emissions (all emissions added up over time) from 1850 to 2019, with about one-sixth of humanity. India argues that its emissions can keep rising and peak after the global peak. A steep return path leaves less room for countries like this.

Don't confuse with

  • One warm year above 1.5°C: 2024 was about 1.55°C above pre-industrial levels and was the first calendar year above 1.5°C. This is not an overshoot of the Paris goal, because Paris uses 20-year averages.
  • Carbon budget: the budget tells you how much CO2 can still be emitted. Overshoot describes the temperature path over time. A budget can be split among countries. Overshoot is one global curve and names no country.
  • Net zero: net zero means emissions are balanced by removals, so warming stops rising. A return from overshoot needs net-negative emissions, where removals are larger than emissions.
  • Tipping point: a tipping point is a threshold after which a system changes suddenly and often cannot recover. Overshoot is the temperature going above a limit. If it goes high enough, it can push systems past tipping points.

Prelims Hooks

  • In "1.5°C overshoot", temperature goes above 1.5°C in the near term and comes back to it by the end of this century.
  • IPCC SR15: most 1.5°C-consistent pathways it assessed were overshoot pathways, and CDR is limited before 2050.
  • IPCC AR6 Synthesis Report (2023): overshoot risk grows with its size and length, and some harm is irreversible.
  • UNEP Emissions Gap Report 2026 (The Point of Return): 1.5°C with no or limited overshoot is no longer possible. The lowest-overshoot scenario relies on storing about 320 GtCO2.
  • Trap: "2024 crossed 1.5°C, so the Paris goal has been breached." FALSE. Paris uses 20-year averages, not one year.
  • Trap: the budget figures 420 GtCO2 (SR15, two-thirds chance, from 2018) and 500 GtCO2 (AR6, 50% chance, from 2020) use different odds and start years. The difference is not a simple revision.

Mains Points

  • Coming back to 1.5°C does not undo the damage: glacier loss in the Himalaya, coral reef decline and the loss of polar and coastal ecosystems are irreversible. The hot period also weakens carbon sinks, so the return gets harder. Policy should therefore cap how high and how long the overshoot goes. UNEP's figure of about 0.3°C is a starting point.
  • Climate justice and India (GS-III): overshoot is one global curve and hides who used the carbon budget. India, with about 4% of cumulative emissions and one-sixth of humanity, links finance to historical emissions. India also rejected the NCQG as against equity and CBDR-RC (those who polluted more and can afford more should do more).
  • A promise, not a plan: a return by 2100 depends on CDR that is uncertain, risky and costly. If removal fails, the emissions cannot be taken back. NDCs should report removals separately from real emission cuts. The Global Stocktake should show the budget next to each country's share of past emissions.

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