It sounds small. But 1.5 °C is a global, 20-year average — and the difference between 1.5 °C and 2 °C is the difference between losing most coral reefs and losing virtually all of them.
By Andreas Marshall · Last reviewed 17 October 2026 · Every claim is linked to its source below.
Where are we now?
Over the last ten years (2016–2025) the world averaged1.32 °C above pre-industrial, and the past 12 months reached1.51 °C (Copernicus ERA5). The Paris Agreement's 1.5 °C refers to the long-term average, so one hot year does not mean the goal has formally been breached. But the gap is now very small.
Global temperature, annual average (°C above 1850–1900)
NASA GISTEMP (vs 1880–1900)Copernicus ERA5
ERA5 anomalies converted to 1850–1900 using Copernicus' standard +0.88 °C offset. GISTEMP rebased to its earliest years, 1880–1900.
Why half a degree matters: extremes get more frequent
The IPCC compared how often extreme events that used to happen once every 10 years (in a climate without human influence) occur at different levels of warming. Each step up multiplies the risk.
How many times more often a once-in-10-years event happens
Today's ~1 °C (IPCC baseline)+1.5 °C+2 °C+4 °C
Hot extremes over land
2.8×
4.1×
5.6×
9.4×
Heavy one-day rainfall
1.3×
1.5×
1.7×
2.7×
Agricultural drought (drying regions)
1.7×
2.0×
2.4×
4.1×
Source: IPCC AR6 WG1 SPM, Figure SPM.6. Median frequency vs 1850–1900. Once-in-50-years heat extremes rise even faster: 8.6× at 1.5 °C and 13.9× at 2 °C.
1.5 °C versus 2 °C
The IPCC's 2018 special report spelled out what the extra half degree would cost:
Share of species losing more than half their climatic range
+1.5 °C+2 °C
Insects
6%
18%
Plants
8%
16%
Vertebrates
4%
8%
Source: IPCC SR1.5 SPM B.3.1.
Coral reefs: projected to decline by a further 70–90% at 1.5 °C, and by more than 99% at 2 °C.
Arctic summer sea ice: an ice-free September about once per century at 1.5 °C, but at least once per decade at 2 °C.
Sea level: about 10 cm lower by 2100 at 1.5 °C than at 2 °C — meaning up to 10 million fewer people exposed to related risks.
Fisheries: global annual catch losses of about 1.5 million tonnes at 1.5 °C, versus more than 3 million tonnes at 2 °C.
Source: IPCC SR1.5 SPM B.2.1, B.4.2, B.4.4.
What it means
1.5 °C is not a line between safe and dangerous: people are already living with the consequences of today's warming. It is a point on a scale where every increment counts. Keeping as close to 1.5 °C as possible limits the damage; every tenth of a degree avoided means fewer extremes and fewer irreversible losses.
It means the planet's average surface temperature, averaged over about 20 years, is 1.5 °C higher than in 1850–1900. It is a global average: land warms faster than the ocean, and the Arctic several times faster than the world as a whole.
Why is 1.5 °C the limit?
Under the 2015 Paris Agreement, countries agreed to hold warming “well below 2 °C” and pursue efforts to limit it to 1.5 °C. The IPCC's 2018 special report showed that impacts — on heat extremes, coral reefs, sea ice, species and food — are substantially lower at 1.5 °C than at 2 °C.
Have we already crossed 1.5 °C?
Individual years have: 2024 in the Copernicus ERA5 record. But the Paris goal is about the long-term average, which is around 1.3–1.4 °C today. Scientists expect that to pass 1.5 °C around the early 2030s at current emission rates.
Is 1.5 °C a tipping point where everything collapses?
No. It is not a cliff edge — every tenth of a degree increases risks, and every tenth avoided reduces them. But several tipping elements, such as warm-water coral reefs and parts of the polar ice sheets, have thresholds estimated around 1–2 °C.
Is 1.5 °C still possible?
Physically, yes, but only with an extremely rapid cut in emissions. The remaining carbon budget for a 50% chance is about 53 billion tonnes of CO₂, around 1.3 years of current emissions. Most scenarios that limit warming to 1.5 °C now involve temporarily overshooting it and bringing temperatures back down later.