September 2026 was Earth's second warmest on record as oceans set all time heat mark

Earth just came off its second warmest September on record, and the planet's oceans set a new high for any month in more than a century and a half of record keeping. The findings, released by NOAA's National Centers for Environmental Information, paint a picture of a climate system that continues to push into uncharted territory, driven in part by an exceptionally strong El Nino.

The global surface temperature for September 2026 averaged 2.39 degrees Fahrenheit (1.33 degrees Celsius) above the 20th century average, according to the NOAA NCEI report published on October 8. That ranks as the second warmest September since 1850, trailing only September 2023 by 0.13 degrees Fahrenheit (0.07 degrees Celsius). The month also marked the 51st consecutive September with global temperatures above the 20th century average, and all 10 of the warmest Septembers on record have occurred since 2015.

While the atmosphere was historically warm, the oceans were even more exceptional. The global ocean surface temperature departure hit 1.98 degrees Fahrenheit (1.10 degrees Celsius) above average, the highest monthly departure ever recorded, edging out the previous all time record set just one month earlier in August 2026 by 0.04 degrees Fahrenheit (0.02 degrees Celsius). It was the fourth consecutive month with record warm global oceans.

In a separate report also published on October 8, NOAA's National Centers for Environmental Information reported that the contiguous United States had its warmest September on record. The average temperature was 69.4 degrees Fahrenheit, 4.6 degrees Fahrenheit above the 20th century average, surpassing the previous record set in 1998. The U.S. monthly average has now been above the 20th century average for 20 consecutive months, from February 2025 through September 2026.

Key Facts

NOAA's National Centers for Environmental Information reported on October 8 that the global surface temperature in September 2026 was 2.39 degrees Fahrenheit (1.33 degrees Celsius) above the 20th century average, the second warmest September in the 1850 to 2026 record. The agency noted that this was the 51st consecutive September with above average temperatures and that all 10 warmest Septembers have occurred since 2015.

The same report stated that the global ocean surface temperature departure averaged 1.98 degrees Fahrenheit (1.10 degrees Celsius) above average for September, the highest for any month on record. It edged out the previous all time record from August 2026 by 0.04 degrees Fahrenheit (0.02 degrees Celsius), marking a fourth straight month of record warm oceans. Persistent El Nino conditions drove record warmth across the central and eastern tropical Pacific.

Global land surface temperature averaged 3.29 degrees Fahrenheit (1.83 degrees Celsius) above average, the third highest for September in the 177 year record. September 2026 was the warmest September on record for the Arctic region, North America and Asia. For the year to date, the January through September global surface temperature was the second highest on record behind 2024.

Global sea ice extent was the third smallest for September in the 48 year record, covering 8.54 million square miles, which is 800,000 square miles below the 1991 to 2020 average. Nineteen tropical cyclones formed globally during September. The Eastern North Pacific tied its September record for total storms and set new basin records for the number of hurricanes and major hurricanes. The most notable storm, Hurricane Polo, rapidly intensified to Category 5.

Analysis

What this really means is that the planet's climate is not just warming gradually; it is repeatedly shattering records that were set only recently. The fact that the global ocean heat record was broken in August and then broken again in September, just one month later, signals an acceleration that goes beyond typical year to year variability. El Nino is a natural phenomenon, but its impact is being amplified by the long term buildup of greenhouse gases. The result is a cascade of extremes, from record warm nights in the United States to a record warm Arctic September.

The U.S. data illustrate how climate change can manifest in ways that are less visible but no less dangerous. ABC News reported on October 8 that the contiguous United States had its warmest September on record, driven primarily by exceptionally warm overnight low temperatures rather than extreme daytime highs. More than 30 percent of the country's area, home to an estimated 80 million people, experienced their warmest September nighttime temperatures on record. Warm nights prevent the body from recovering from daytime heat, and they also increase energy demand for cooling, stressing power grids.

Yale Climate Connections reported on October 9 that NASA and the European Copernicus Climate Change Service also rated September 2026 as the second hottest September, behind 2023. That independent corroboration strengthens the finding. The same article noted that the developing El Nino has been confirmed as the strongest on record, with the Nino 3.4 sea surface temperature breaking the November 2015 benchmark. The Japanese Meteorological Agency and the Met Office reported daily Nino 3.4 values around plus 3.0 degrees Celsius. University of Chicago's Climate Impact Lab estimated that heat linked to the event could cause as many as 451,000 excess deaths worldwide between June 2026 and February 2027.

Why It Matters

The record ocean heat has profound implications for marine ecosystems, fisheries and coastal communities. Warmer oceans fuel stronger hurricanes and typhoons, and they contribute to coral bleaching and the migration of fish stocks. NOAA reported that the Eastern North Pacific tied its September record for total storms and set new records for hurricanes and major hurricanes, a direct link between ocean heat and extreme weather. The Atlantic basin, meanwhile, had eight named storms through September but none reached hurricane strength, the latest point in the season without an Atlantic hurricane in the satellite era, which began in 1966. This contrast shows that climate change does not produce uniform effects; it shifts patterns in complex ways.

On land, the warmth exacerbated drought. Drought conditions expanded to cover 89 percent of the South region, the largest extent for the region since October 2000, according to NOAA. ABC News noted that roughly 55 percent of the contiguous United States was in drought as of October 8. At the same time, the Southwest received more than twice its average September rainfall, with Arizona recording its wettest September since 1983 and New Mexico its wettest since 1941. These whiplash events, from drought to deluge, are consistent with a warmer atmosphere that can hold more moisture. The human toll is already being measured: the Climate Impact Lab estimate of up to 451,000 excess deaths underscores that climate change is not a distant threat but a present danger.

Another critical data point is the shrinking sea ice. The third smallest September sea ice extent on record, at 8.54 million square miles, is 800,000 square miles below the 1991 to 2020 average. Sea ice loss amplifies warming through the albedo effect, as darker ocean water absorbs more solar energy. This feedback loop means that the Arctic, which just had its warmest September on record, is warming faster than the global average, with consequences for weather patterns far to the south.

Next Up

With El Nino conditions expected to persist, NOAA and other agencies will continue to monitor monthly temperature and ocean heat records. The next major update will come in November, when NOAA NCEI releases its October 2026 global climate report. Given that August and September both set all time ocean heat records, and that the year to date is running second only to 2024, there is a strong chance that 2026 will rank among the hottest years on record. Scientists will also be watching whether the Atlantic hurricane season, which has so far produced no hurricanes, remains unusually quiet, and how the record warm ocean temperatures affect marine life and coastal communities in the months ahead.

Additionally, the Copernicus Climate Change Service and NASA will release their own October analyses, providing further corroboration or nuance. The University of Chicago's Climate Impact Lab estimate of excess deaths will be tracked as the El Nino event continues through early 2027. For now, the September data serve as a stark reminder that the climate is changing faster than many expected, and that the oceans, which absorb most of the excess heat, are at the forefront of that transformation.