November 2026 Climate Baseline: Record Ocean Heat, 426.07 ppm CO₂, and an Arctic Freeze-Up Ahead of 2025

The 5 November 2026 cut-off, at 10:00 UTC, finds the four indicators at different points in their release cycles. NOAA NCEI and Copernicus have both published September 2026 as their newest complete month, and so has NOAA's Mauna Loa CO₂ series. NASA's public sea-level indicator has moved to October 2026, while NSIDC has posted a September monthly average and is tracking a freeze-up that is already well under way.

NOAA's September 2026 global surface temperature was 1.33 °C above the 20th-century average, the second-warmest September in the 1850–2026 record and 0.07 °C behind 2023. All ten warmest Septembers on record have come since 2015. 1

Within the same series, August 2026 was 1.32 °C above the average and September 2025 was 1.12 °C, so September 2026 finished 0.01 °C warmer than the month before and 0.21 °C warmer than a year earlier. January–September 2026 ranks second behind 2024. NOAA's annual outlook puts 2026 very likely among the five warmest years, with the highest probability on second place. 123

The ocean set the month's largest mark. Its September departure of 1.10 °C above average was the highest for any month in the record, beating the previous all-time value set in August 2026 by 0.02 °C. That made September the fourth consecutive month to set a record ocean departure. Record warmth covered a wide stretch of the central and eastern tropical Pacific, which NOAA links to the El Niño in place, and parts of the Atlantic, Indian and Southern Oceans. 1

Land averaged 1.83 °C above the 20th-century average, the third-highest September figure in the record. Record September warmth appeared across parts of North and South America, Europe, Asia, Africa and Australia. Below-average readings were confined to Antarctica, parts of the Arctic, western North America, southern South America and southern Africa. No land or ocean area logged a record-cold September. 1

Copernicus, using ERA5, puts September 2026 at 16.27 °C, or 0.82 °C above the 1991–2020 average — its second-warmest September, 0.11 °C cooler than September 2023. Measured against the 1850–1900 pre-industrial estimate, the month reached 1.63 °C, the first time since November 2025 that two consecutive months have run above 1.5 °C. 4

European land averaged 16.26 °C in September, 1.54 °C above the 1991–2020 average and the third-warmest September on the continent in the ERA5 record. Dry conditions widened across Iberia, France, Italy, the western Balkans and Greece through the month, extending the summer's pattern. 4

The NOAA and Copernicus anomalies use different reference periods and different datasets, so the two sets of figures stay apart.

NOAA's Global Monitoring Laboratory reports a 426.07 ppm monthly mean at Mauna Loa for September 2026, the latest value on its trend page, which was last updated on 9 October 2026. September 2025 stood at 424.37 ppm, so the year-on-year increase is 1.70 ppm. 5

The downloadable monthly series puts August 2026 at 427.55 ppm, which makes September 1.48 ppm lower than August. That decline is the ordinary seasonal drawdown: Northern Hemisphere vegetation takes up CO₂ through the growing season, and the Mauna Loa series peaks each year in May. The 2026 sequence ran 432.34 ppm in May, 431.43 ppm in June, 429.13 ppm in July, then 427.55 ppm in August. 6

The growth rate behind the seasonal swing slowed a little. September 2025 sat 2.34 ppm above September 2024, against this year's 1.70 ppm step. 6

Mauna Loa is a high-altitude station in the northern subtropics, and the globally averaged surface concentration is tracked as a separate series. NOAA flags the most recent year of values as preliminary, pending recalibration and quality-control checks, with revisions expected to be small. 5

NASA's public Earth Indicator reports 115.8 ± 4.0 mm for October 2026, measured against the 1993 satellite baseline. The same indicator stood at 109.8 mm for September 2026 when this channel read it on 5 October, so the newest point sits 6.0 mm higher. 7

The page describes an overall rise carrying a seasonal cycle, visible as a rise and fall each year, and attributes the cycle to water moving between the oceans and the land: rain and snow fall on land, and the water takes time to run back to the sea. The page gives about two-thirds of the rise to melting land ice and one-third to the expansion of warming seawater. 7

The public dashboard publishes its latest point alone, so the year-earlier comparison has no value in the same product to sit beside. The underlying PO.DAAC collection, NASA_SSH_GMSL_INDICATOR, is Version 1, spans 4 January 1993 to the present, and carries DOI 10.5067/NSIND-GMSV1. PO.DAAC quotes 3–5 mm of uncertainty on global estimates across the 30-plus-year record. 78

The indicator's summary text still says global sea level has risen around 91 mm since 1993, a figure that sits below the dashboard's own latest measurement. A reader citing this indicator should take the monthly value and its date from the measurement field. 7

NSIDC puts the September 2026 Arctic monthly average at 4.81 million km², thirteenth lowest in the satellite record and 1.6 million km² below the 1981–2010 average. The annual minimum of 4.60 million km² came on 12 September and tied 2008, 2010 and 2025 for tenth lowest. 10

October turned the other way. The monthly average reached 6.69 million km², up 1.88 million km² on September and 0.37 million km² above October 2025. That is still 1.66 million km² below the 1981–2010 October average of 8.35 million km², and the twelfth-lowest October in the 48-year record. 910

The daily record shows the pace of it. Extent reached 8.153 million km² on 3 November 2026, against 7.845 million km² on the same date in 2025 and a 1981–2010 average for that date of 9.85 million km². The 2026 value ranks fifth lowest for a 3 November across the 45 years with a reading. 11

NSIDC's account of the season explains both halves. Low sea-level pressure held over the Arctic Ocean through summer and September, with air temperatures 0–1 °C below average at the 925 hPa level. Cyclonic winds spread a loose ice pack toward the pole, and cool, cloudy conditions slowed melt. Ice along the Beaufort and Chukchi coasts lasted into August before going quickly; first-year ice dominated the area, and thinner ice melts out more completely. 10

The long-term trend runs underneath the month-to-month weather. September extent has fallen 74,100 km² per year, or 11.6% per decade against the 1981–2010 average, and the month has lost 3.24 million km² since 1979. Since 2012, ice older than four years has shrunk to 250,000 km² or less at the end of each melt season, down from roughly 1.5 million km² before 2005. 10

The other agencies rank the same month with their own products. NOAA counts September 2026 as the Arctic's thirteenth-lowest September, the Antarctic's third-smallest and the globe's third-smallest. Copernicus puts the monthly Arctic extent 16th lowest at about 10% below average and the daily minimum 14th lowest. Each rank belongs with the product that produced it. 14

Antarctic sea ice moved the other way. Its maximum of 17.59 million km² came on 14 September, the third-lowest in the record, and daily extents have set record lows for the date since 2 October, overtaking 2023. 10

NOAA's Climate Prediction Center issued its ENSO Diagnostic Discussion on 8 October 2026 under an El Niño Advisory. Indices for the past month reached +2.1 °C in Niño-3.4, +3.0 °C in Niño-3 and +3.9 °C in Niño-1+2, and sea surface temperature anomalies exceeded +4.0 °C in parts of the eastern equatorial Pacific. 12

The Center gives a 54% chance that September–November reaches a three-month RONI of at least +2.5 °C, which it defines as a historic event exceeding prior El Niños back to 1950. That chance rises to 83% for October–December and 70% for November–January, and the Center expects a strong to very strong event through January–March 2027 with more than 83% probability. The next discussion is scheduled for 12 November. 12

Those probabilities describe a forecast. The four rows above describe observations, and the ocean's record September departure is the clearest place El Niño already shows in them. 1

September also set tropical cyclone records in the eastern North Pacific: eight tropical storms, tying 1994, 1997 and 2015 for the month, seven hurricanes and five major hurricanes, both September records for the basin. Hurricane Polo reached Category 5 and ranks second by pressure among eastern North Pacific hurricanes. The Atlantic produced no hurricane before October for the first time in the satellite era. 1

IPCC AR6 Working Group III Figure 2.7 collects the remaining carbon budgets for 1.5 °C and 2 °C from 1 January 2020, each carrying an uncertainty of ±220 GtCO₂-equivalent at the 67th percentile. The budget is a cumulative quantity: it counts tonnes emitted from that date, whatever any single month's temperature does. 13

The Global Carbon Budget's newer estimate, dated January 2026, allows 170 GtCO₂ for 1.5 °C, 525 GtCO₂ for 1.7 °C and 1,055 GtCO₂ for 2 °C. At current emission levels those translate to roughly four, 12 and 25 years. The estimate carries different dating and methodology from the IPCC framework, so it supplements the IPCC figures. 14

Copernicus's global temperature trend monitor reads the trajectory from the other end. It now places the 1.5 °C long-term threshold about 24 years closer than its own 2015 estimate did — 27 years away when the Paris Agreement was signed, about three years away now. The application extrapolates the recent ERA5 trend in a straight line, which its authors describe as an illustration of pace rather than a prediction. 15

The November baseline therefore pairs September readings for temperature and CO₂ with an October sea-level point and an October sea-ice average. Three indicators carry direct month-on-month and year-on-year comparisons; sea level carries the month-on-month step alone, because NASA's public dashboard publishes a single value. Each figure stays attached to its named product, date and baseline.