Global Sea Surface Temperature breaks record as El Nino gains strength
The global average sea surface temperature reached a record daily high of 21.1°C on 21-22 August 2026, according to data released by the Copernicus Climate Change Service (C3S).
The new reading surpasses the previous all-time high of 21.09°C recorded in March 2024, and is well above the earlier August-specific high of 20.98°C recorded in 2023.
The record is attributed to a developing El Nino event overlaying long-term ocean warming; forecasters expect the El Nino to strengthen further in the coming months and potentially reach an intensity not seen in several decades.
The timing is unusual because global sea surface temperatures typically peak in March-April, following the Southern Hemisphere summer, making an August record an atypical seasonal pattern.
El Nino-Southern Oscillation (ENSO) and the Oceanic Nino Index (ONI)
ENSO is a recurring, irregular climate pattern involving coupled ocean-atmosphere fluctuations in sea surface temperature across the central and eastern equatorial Pacific Ocean. Its warm phase is called El Nino, its cool phase La Nina, and the intermediate state is ENSO-neutral. NOAA's Climate Prediction Center has traditionally tracked ENSO using the Oceanic Nino Index (ONI), a rolling three-month average of sea surface temperature anomalies in the Nino 3.4 region.
Key Details
- ONI threshold: a value of +0.5°C or higher for the Nino 3.4 region signals El Nino; -0.5°C or lower signals La Nina; values in between are ENSO-neutral
- ENSO cycles recur roughly every two to seven years and are monitored jointly by NOAA, the India Meteorological Department (IMD), and the World Meteorological Organization (WMO)
- In February 2026, NOAA's Climate Prediction Center adopted a Relative Oceanic Nino Index (RONI) to better characterise ENSO against a warming ocean baseline
- El Nino weakens the easterly trade winds over the Pacific, allowing warm water to spread eastward and elevate sea surface temperatures across large ocean regions
The August 2026 record reflects a developing El Nino phase captured by rising Nino 3.4 region temperatures, which — combined with background anthropogenic ocean warming — pushed the global daily average past the previous record.
El Nino's Impact on the Indian Summer Monsoon
El Nino is historically associated with a weaker and more erratic Indian Southwest Monsoon, since warming in the equatorial Pacific tends to suppress the low-pressure systems and cross-equatorial moisture flow that drive monsoon rainfall over the subcontinent. The IMD issues its monsoon forecasts each year factoring in ENSO status alongside the Indian Ocean Dipole (IOD).
Key Details
- IIMD's 2026 monsoon forecast anticipated below-normal rainfall (around 90% of the Long Period Average) with an elevated probability of a deficient season, linked to the developing El Nino
- Cumulative all-India monsoon rainfall for the 2026 season has run below the Long Period Average, with central, eastern, and north-eastern India worst affected
- El Nino does not guarantee drought in India; a positive Indian Ocean Dipole (IOD) can partly offset El Nino's suppressive effect on monsoon rainfall
- The Nino 3.4 region and the IOD (measured via the Dipole Mode Index) are the two Indian Ocean-Pacific indicators UPSC most frequently tests together for monsoon prediction
A strengthening El Nino, as signalled by the record sea surface temperatures, raises the risk of continued monsoon rainfall deficits over India for the remainder of the 2026 season, with direct implications for agricultural output and food-price inflation.
Ocean Heat Content and Sea-Level Rise
Oceans absorb the great majority of the excess heat trapped by greenhouse gases, making sea surface and sub-surface ocean temperature one of the most reliable indicators of global warming — more stable than atmospheric temperature, which fluctuates more with weather. Rising ocean heat content also drives thermal expansion of seawater, a major contributor to global sea-level rise alongside glacier and ice-sheet melt.
Key Details
- The IPCC's Sixth Assessment Report (AR6) estimates that the ocean has absorbed over 90% of the excess heat generated by human-driven greenhouse gas emissions since the industrial era
- Thermal expansion of ocean water, driven by rising heat content, is one of the two principal drivers of observed global mean sea-level rise, the other being land-ice melt
- Marine heatwaves — discrete periods of anomalously high sea surface temperature — have become more frequent as background ocean heat content rises, increasing risks to coral reefs and fisheries
- Record ocean temperatures are tracked as a headline indicator in the WMO's annual State of the Global Climate reports, alongside atmospheric CO2 concentration and global mean surface temperature
The record sea surface temperature is both a symptom of rising global ocean heat content and a contributing driver of the developing El Nino, illustrating the feedback between long-term anthropogenic ocean warming and shorter-term natural climate variability.
Global Mean Temperature Tracking and the Paris Agreement Threshold
Multiple international agencies — Copernicus C3S, NOAA, NASA, and the WMO — independently compile global temperature datasets used to assess progress against the Paris Agreement's temperature goals, which reference a pre-industrial baseline rather than any single record-breaking day.
Key Details
- The Paris Agreement (2015, COP21) commits parties to holding global average temperature rise "well below" 2°C above pre-industrial levels, with efforts to limit it to 1.5°C
- Individual daily or monthly sea surface temperature records, such as the August 2026 reading, are distinct from the Paris Agreement's benchmark, which is assessed as a multi-decadal average of global surface temperature, not ocean temperature alone
- Copernicus C3S is implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF) on behalf of the European Union and has published authoritative global climate bulletins since becoming fully operational in 2018
While the August 2026 sea surface temperature record does not by itself indicate a Paris Agreement breach, it adds to a cumulative body of ocean-temperature records that agencies like C3S and WMO track as evidence of the underlying warming trend against which the 1.5°C/2°C goals are measured.
- Record global average sea surface temperature: 21.1°C, recorded 21-22 August 2026 (Copernicus C3S)
- Previous all-time record: 21.09°C, set March 2024
- Previous August-specific record: 20.98°C, set in 2023
- ONI threshold for El Nino classification: +0.5°C or higher (Nino 3.4 region, three-month rolling average)
- IMD's 2026 monsoon forecast: approximately 90% of the Long Period Average, with an elevated chance of a deficient season
- IPCC AR6 estimate: oceans have absorbed over 90% of excess heat from human-driven global warming since the industrial era