Overshoot Pathways in Climate Science

An overshoot happens when global warming goes above a chosen limit, such as 1.5°C, for some time and then is brought back below it later. An overshoot pathway is a plan for how the world's emissions could move so that warming first crosses the limit, reaches a peak, and then falls back. Think of a car that crosses a speed limit on a downhill road, then has to brake hard to come back to the right speed. The longer and faster it goes over the limit, the greater the danger.

Why does it matter now?

For many years, the hope was to stay below 1.5°C without ever crossing it. Emissions did not fall fast enough, so this is no longer possible. The debate has now shifted to two questions: how high will warming go above 1.5°C, and how long will it stay there? Both matter, because damage depends on the peak and on the time spent at high temperatures.

Where did the idea come from?

Climate modellers have used overshoot scenarios for many years. The IPCC's Special Report on 1.5°C (2018) made it a central idea. It sorted 1.5°C pathways by how much they overshoot. The IPCC's Sixth Assessment Report (AR6, 2021 to 2023) used formal categories:

• C1: "1.5°C with no or limited overshoot": warming goes above 1.5°C by at most about 0.1°C, for no more than a few decades, before coming back.
• C2: "return to 1.5°C after a high overshoot": warming goes above 1.5°C by about 0.1 to 0.3°C before being brought back down by 2100.

In 2026, UNEP's Emissions Gap Report concluded that the C1 type of pathway is no longer reachable.

How does warming stop and then fall?

This needs two simple ideas.

1. Warming stops rising only when CO2 emissions reach net zero. CO2 stays in the air for centuries, so as long as we keep adding it, temperatures keep climbing. Net zero CO2 is like turning off the tap: the water level stops rising.
2. Warming falls only with net-negative CO2 emissions. To bring the temperature down, we must take out more CO2 than we put in. This is like opening a drain after turning off the tap.

Scientists estimate that warming rises by roughly 0.45°C for every 1,000 billion tonnes of CO2 released (IPCC AR6 best estimate). By the same rule, bringing temperature down by just 0.1°C would need roughly 220 billion tonnes of CO2 to be removed from the air, after reaching net zero. That is about five or six years of today's total world CO2 emissions.

What is Carbon Dioxide Removal (CDR)?

CDR means human activities that take CO2 out of the air and store it for a long time. It is the main tool for any return from overshoot. There are two groups:

• Conventional CDR: planting new forests (afforestation), regrowing cut forests (reforestation), and storing more carbon in soils. These provide almost all of today's removals, about 2 billion tonnes of CO2 a year (State of CDR report, 2024).
• Novel CDR: newer technologies such as BECCS (growing plants, burning them for energy, and storing the CO2 underground), DACCS (machines that suck CO2 directly from the air and store it), biochar (turning crop waste into charcoal that is added to soil) and enhanced rock weathering (spreading crushed rock that slowly absorbs CO2). Together these removed only about 1.3 million tonnes a year in 2024, less than 0.1% of all removals.

The same report estimated that about 7 to 9 billion tonnes of CO2 a year may need to be removed by the middle of the century in pathways that meet the Paris goal.

What risks come with overshoot?

Some damage cannot be undone even if the temperature later falls.

• Extinctions: a species that dies out does not come back.
• Ice sheets and sea level: ice lost from Greenland and Antarctica takes centuries or thousands of years to regrow, and seas keep rising long after warming stops.
• Tipping points: some systems may switch suddenly into a new state. The Global Tipping Points Report (October 2025) said warm-water coral reefs have already crossed their tipping point, which has a central estimate of about 1.2°C.
• Feedbacks: thawing permafrost and weaker forests may release more carbon, making a return harder.

India's position and Indian examples

India's NDCs include a forest carbon sink: an additional 2.5 to 3 billion tonnes of CO2-equivalent by 2030, and 3.5 to 4.0 billion tonnes by 2035 in its 2035 NDC. Programmes such as the Green India Mission support this. NITI Aayog released a CCUS (Carbon Capture, Utilisation and Storage) policy framework in 2022 for hard-to-cut sectors like steel and cement. India argues that developed countries, with more money and technology, should lead on large-scale carbon removal and reach net-negative emissions first.

Commonly confused concepts

• Overshoot vs exceeding 1.5°C in one year: A single hot year above 1.5°C is not an overshoot. Overshoot refers to the long-term average (about 20 years) going above the limit.
• CDR vs CCS: CCS (Carbon Capture and Storage) catches CO2 at a factory chimney before it enters the air. It reduces new emissions but does not remove old CO2. CDR takes CO2 that is already in the air out of it. (BECCS and DACCS count as CDR because the carbon comes from the air.)
• CDR vs Solar Radiation Modification (SRM): SRM means trying to cool the Earth by reflecting sunlight, for example with particles in the upper atmosphere. It does not remove any CO2 and does not stop ocean acidification.
• Net zero vs net negative: Net zero stops further warming from CO2. Net negative brings warming down.
• Peak warming vs warming in 2100: An overshoot pathway may end at 1.5°C in 2100 but peak much higher in between. The peak decides much of the damage.

Issues, criticism and the way forward

• Moral hazard: Critics warn that promises of future removal may be used as an excuse to delay cutting emissions today. Scientists stress that removal is an addition to deep cuts, not a replacement.
• Land and food: Large-scale BECCS and tree planting need huge areas of land. This could compete with food crops and harm biodiversity and forest-dwelling communities.
• Cost and scale: Direct air capture is still very expensive and tiny in scale today.
• Permanence: Carbon stored in forests can be released again by fires or felling. Removals must be stored safely for a very long time.
• Fairness: Who pays for removal, and who suffers the losses during the overshoot? Poor and vulnerable countries face the worst impacts while having done least to cause the problem.
• The way forward: experts say the best way to limit overshoot is to cut emissions as fast as possible now, so that the peak is lower and less removal is needed later.

Concepts to Know

• Pathway (emissions pathway): A possible path that world emissions could follow year by year in the future, used in climate models to see what warming it would lead to.
• Tipping point: A level beyond which a part of the Earth system changes suddenly and often cannot easily return, like a glass pushed past the edge of a table.
• Permafrost: Ground that stays frozen for at least two years in a row. It holds large amounts of old carbon.
• Ocean acidification: Seawater becoming more acidic as it absorbs CO2. It harms corals and shellfish.
• Carbon sink: Anything (forest, soil, ocean) that takes in more CO2 than it gives out.