California Climate – Sep 2026September 2026 Update

Novarupta (Katmai) eruption

The largest volcanic eruption anywhere in the world in the 20th century - 13 km3 of magma, about thirty times the 1980 Mount St. Helens eruption - at Novarupta in Alaska on 6-8 June 1912. Ash reached 100,000 ft and cooled the Northern Hemisphere by roughly 0.3°C over 1912-13. Unlike a tropical eruption such as Pinatubo, a high-latitude eruption's haze stays in its own hemisphere, so it did little to the Southern Hemisphere.

Smithsonian Global Volcanism Program, Alaska Volcano Observatory, National Park Service, Oman et al. 2005

Post-WWII industrial expansion begins

After the Second World War, coal and oil use grew rapidly across Europe, North America and the Soviet Union. Global sulphur dioxide emissions rose from about 30 to about 130 million tonnes a year by 1980, and the sulphate haze they formed masked part of the greenhouse warming underneath - the effect known as 'global dimming'.

Klimont et al. 2013

Agung eruption

Agung's eruption in Bali put a veil of sulphate haze into the stratosphere that cooled global temperature by about 0.3°C over 1963-66.

Smithsonian Global Volcanism Program, NOAA Global Monitoring Laboratory

US Clean Air Act

The 1970 Clean Air Act set strict national standards for sulphur dioxide and particulates, and American skies got measurably cleaner over the decades that followed. There is a climate sting in that success: sulphate aerosols reflect sunlight, so removing them removed a cooling effect that had been partly masking greenhouse warming. Measured here, California averaged +1.16°C warmer across 2006-2025 than across the two decades before the Act, 1951-1970, the 20th-largest rise of the 49 states measured and above their median of +1.09°C. Cleaning the air was right for human health. It also uncovered warming that was already there.

US EPA

The 1973-74 La Niña

The strongest La Niña of the 1950-present record, part of a multi-year cool phase that also included a second, separate La Niña in 1975-76.

ONI -2.0°C · RONI -1.9°C

NOAA CPCENSO Tracker

The 1976-77 drought

1976 was California's 2nd-driest year on record here - 298 mm, 47% below its 1961-90 average. A caution specific to California: official accounts call 1977 the driest year in its history, but that is the WATER year, October 1976 to September 1977. On this site's calendar-year series 1977 ranks only 16th, because the wet winter that broke the drought falls inside the same calendar year. Across the two calendar years together California ran 34% below its 1961-90 average.

USGS, US GAO, USGS Water Data Labs

Pacific Decadal Oscillation flips to a warm phase

The 1976-77 flip of the Pacific Decadal Oscillation to its warm phase arrived in the middle of a severe California drought, and the two decades that followed tilted the odds towards wetter California winters, particularly when an El Niño coincided.

Learn more →

Global SO2 emissions peak

Global sulphur dioxide emissions peak at about 130 million tonnes a year, then begin a long decline as Europe, North America and Japan clean up their air. As the aerosol mask thins, the rate of global warming picks up through the 1980s.

Klimont et al. 2013

El Chichón eruption

A sulphur-rich eruption in Mexico whose aerosol cloud stayed in the stratosphere for more than two years, cooling the Northern Hemisphere by about 0.2°C.

Smithsonian Global Volcanism Program

1982-83 El Niño

El Niño has only a weak pull on California's winter rainfall - it is not one of the seven states where ENSO reliably moves it. In 1982-83 California's winter rainfall ran +63% against the 1961-90 average, with temperatures +0.3°C. On NOAA's RONI index, which strips out background ocean warming, this is the strongest El Niño since 1950.

ONI +2.1°C · RONI +2.4°C

NOAA CPC, NOAA CPC (2)ENSO Tracker

Daytime warming catches up with the night-led pattern

Across 1961-90, 81% of the world's land saw nights warming faster than days. Across 1991-2020 the pattern reversed: 70% saw days warming faster, as the industrial haze that had been dimming daytime sunshine was cleaned up. The study compares two fixed thirty-year windows; measured as a turning point, this site's own global series turns around 1982.

Zhong et al. 2023

Mount Pinatubo erupts

Pinatubo's cooling is only faintly visible in California's own record. 1993, two years after the June 1991 eruption, ranks 27th-coldest of the 76 years there, though 1998 and 2011 have since been colder. A single large eruption can hold temperatures down for two or three years; it cannot reverse the trend.

Learn more →

Atlantic Multidecadal Oscillation flips to a warm phase

The Atlantic Multidecadal Oscillation flipped to a warm phase in 1995. It is an Atlantic cycle, but its reach is not confined to the coast: a warm AMO alongside a cool Pacific has been tied to more frequent drought across the western and central United States, including the widespread droughts of 1996 and 1999-2002. It is a natural cycle of roughly 60-70 years, so it shifts the baseline rather than driving the long-term trend.

Learn more →

1997-98 El Niño

In 1997-98 California's winter rainfall ran +98% against the 1961-90 average, with temperatures -0.1°C - though ENSO's pull on rainfall here is weak. It is often treated as the textbook strong El Niño.

ONI +2.4°C · RONI +2.3°C

NOAA CPC, NOAA NCEIENSO Tracker

Pacific Decadal Oscillation flips back to a cool phase

The Pacific Decadal Oscillation flipped back to a cool phase around 1998-99. Cool phases tilt the odds towards dry winters across California and Nevada, and the period that followed includes the long 2012-16 and 2020-22 droughts.

Learn more →

Southwest megadrought (2000-2021+)

California's 2000-2021 rainfall averaged 6% below its 1961-90 average - a smaller shortfall than Arizona's, though California's own severe 2012-16 and 2020-22 droughts both sit inside this period. Warming matters as much as rainfall here: higher temperatures pull more moisture out of soil and snowpack for the same rain.

Williams et al. 2022

Colorado River flow decline / Lake Mead crisis

California holds the largest and most senior allocation on the Colorado, and Imperial Valley agriculture is the single biggest user of the river's water. Seniority means California is legally last to be cut - which has made it central to every negotiation since Lake Mead began setting record lows in 2021. The river also supplies part of southern California's urban supply through the Colorado River Aqueduct.

Udall & Overpeck 2017

2006: a national heat record that lasted six years

California took the worst of the July 2006 heat wave in the West: the Central Valley reached 110-115°F, and NOAA's storm record lists 46 heat deaths in the San Joaquin Valley episode of 16-27 July alone. The same summer made 2006 the contiguous United States' warmest year on record at the time.

NOAA NCEI, Science

Start of the sustained rise in US heatwave frequency

California's own Heatwave Days (WSDI) count rose from a 1961-90 average of 9.0 days a year to 24.9 in 2016-25 - more than doubling, close to the 2.4x averaged across the 50 states.

World Bank CCKP (CCKP), NOAA Climate at a Glance

California droughts, 2012-16 and 2020-22

2012-16: the most severe drought in California's instrumental record - 2014 and 2015 statewide snowpack hit record lows (25% then 5% of average); $3.8bn in agricultural losses 2014-16. 2020-22: a second episode reaching comparably severe conditions over a larger area, $1.3bn-$1.7bn in annual crop losses.

California DWR / PPIC

Post-2013 acceleration in US temperatures

Every one of California's ten warmest years on record has occurred since 2013 - the only state in the country where the post-2013 acceleration is that complete, with 2014 the warmest of all.

NOAA Climate at a Glance

2015-16 El Niño

In 2015-16 California's winter rainfall ran +14% against the 1961-90 average, with temperatures +1.2°C - though ENSO's pull on rainfall here is weak. By the raw ONI index it was the strongest El Niño ever measured - a reminder that a strong index does not guarantee a strong local outcome.

ONI +2.6°C · RONI +2.3°C

NOAA CPCENSO Tracker

2015-2025: the eleven warmest years on record

Globally, the eleven warmest years on record have all happened since 2015. California tracks that closely - nine of its own eleven warmest fall in the same span, with only 2014 and 1996 outside. California and Florida are the closest-matching states in the country, and California's warmest year is 2014.

Learn more →

California's 500-year-record-low Sierra snowpack, 2015

Snowpack measured at just 5% of average on April 1, 2015 (the historic peak-measurement date). A tree-ring reconstruction back to 1500 CE (Nature Climate Change) confirmed this was the lowest Sierra Nevada snowpack in over 500 years.

The Conversation / Nature Climate Change

The West's air gets drier

California's relative humidity has fallen 3.4 percentage points comparing 2015-2025 with 1950-2014 - the 4th-largest fall of any US state - while its annual temperature rose +1.09°C over the same comparison. California's fire seasons, its snowpack losses and its 2012-16 and 2020-22 droughts all sit inside this drying.

World Bank CCKP (CCKP), NOAA Climate at a Glance

The 2015 western snow drought

California's own 2015 snowpack was 5% of average on 1 April, the lowest in a tree-ring reconstruction going back to 1500 CE. It sits inside this wider western event: 81% of the West's monitored snow sites hit record lows that year, and the cause was warmth rather than a shortage of precipitation. Uniquely among the western states, the North Pacific 'Blob' did NOT drive California's snow drought - greenhouse warming and the ongoing drought pattern did.

Mote et al. 2016, NOAA Drought.gov, USDA

The Camp Fire

The Camp Fire began in Butte County on 8 November 2018 and destroyed almost all of the town of Paradise within hours. It killed 85 people - the deadliest wildfire in California's history - burned 153,000 acres, destroyed around 19,000 structures including some 11,000 homes, and caused economic losses above $16.5bn.

Cal OES, NIST

Low-sulphur shipping fuel rule (IMO 2020)

New international shipping rules cut the sulphur allowed in ship fuel from 3.5% to 0.5% almost overnight, removing about 8 million tonnes of sulphur dioxide a year. With less sulphate haze over the oceans, it may have added around 0.1°C of warming by 2023-24.

Gettelman et al. 2024

California's 2020 fire siege

8,648 fires burned 4,304,379 acres in California in 2020 - the largest wildfire season in the state's modern record. The August Complex passed a million acres to become the first fire in California history described as a 'gigafire', crossing seven counties and covering more ground than Rhode Island. On 16 August Furnace Creek in Death Valley recorded 130°F, potentially the highest reliably measured temperature anywhere on Earth.

CAL FIRE, CalMatters, NOAA NESDIS

2023-24 El Niño

A strong El Niño arriving on top of long-term greenhouse warming, with the cut in shipping sulphur from the 2020 fuel rule adding a little more. Together they produced the record global temperatures of 2023 and 2024.

ONI +2.0°C · RONI +1.4°C

NOAA CPCENSO Tracker

The January 2025 Los Angeles fires

The Palisades and Eaton fires broke out on 7 January 2025 and burned into Los Angeles itself. Together they killed 31 people and destroyed more than 16,000 structures - 6,837 in Pacific Palisades and 9,414 in Altadena and Pasadena. A rapid attribution study found climate change made the fire-prone conditions about 35% more likely, and responsible for roughly a quarter of the available fuel.

World Weather Attribution, NOAA Climate.gov, CarbonBrief