Key takeaways 

• Carbon dioxide, methane, and nitrous oxide reached record-high concentrations in 2023
• 2015 to 2023 were the nine warmest years on record 
• Approximately 94 percent of the ocean surface experienced at least one marine heatwave in 2023
• Global average sea levels were record-high for the 12th consecutive year
• The Arctic Ocean’s Northern Sea Route and Northwest Passage both became accessible to non-ice-hardened marine traffic 

CIRES' Lindsay Lan discusses the importance of emission reductions in this Q&A with CU Boulder. 

Greenhouse gas concentrations, global temperatures, sea levels, and ocean heat content all reached record highs in 2023, according to the 34th annual State of the Climate report released today by the Bulletin of the American Meteorological Society. 

The international annual review of the world’s climate, led by scientists from NOAA’s National Centers for Environmental Information with involvement from CIRES, CU Boulder, and other institutions, is based on contributions from more than 590 scientists in nearly 59 countries. The report provides the most comprehensive update on Earth’s climate indicators, notable weather events, and other data collected by environmental monitoring stations and instruments located on land, water, ice, and in space.

“The Bulletin of the American Meteorological Society State of the Climate in 2023 report is a truly international effort to more fully understand climate conditions around the globe and our capacity to observe them,” said NCEI Director Derek Arndt. “This annual physical of the Earth system serves present and future generations by documenting and sharing data that indicate increasingly extreme and changing conditions in our warming world.”

CIRES and CU Boulder researchers’ expertise in analyzing greenhouse gas levels, studying Arctic and Antarctic climate, managing Earth systems data, and other fields was crucial to compiling the report’s findings. Report authors include CIRES scientists from the National Snow and Ice Data Center and various NOAA labs.  

“It's a critical time for us to reduce greenhouse gas levels in the atmosphere,” said Xin (Lindsay) Lan, a CIRES scientist in NOAA’s Global Monitoring Laboratory who leads the reporting of greenhouse trends and is a co-author of the report. “Instead, we're still seeing a rapid increase of those key greenhouse gases, and we're definitely not on the right path to limit global warming.”

Notable findings from this year’s report include:

Earth’s greenhouse gas concentrations were the highest on record. 

Carbon dioxide, methane, and nitrous oxide ⁠— Earth’s major human-made greenhouse gases⁠ — once again reached record-high concentrations in 2023. The growth of carbon dioxide levels from 2022 to 2023 was 2.8 parts per million, the fourth-highest annual jump since the 1960s.

Record temperatures were notable across the globe and the last decade was incredibly warm. 

All seven major global temperature datasets used for analysis in the report agree that the last nine years (2015 to 2023) were the nine warmest on record. The annual global mean surface temperature has increased at an average rate of 0.08 to 0.09 of a degree Celsius (0.14 to 0.16 of a degree Fahrenheit) per decade since 1880, and at a rate more than twice as high since 1981.

In addition, 2023 was the warmest year since records began in the mid to late 1800s. The transition in the Pacific Ocean from La Niña conditions at the beginning of the year to a strong El Niño by the end of the year contributed to the record warmth. 

The Arctic was warm and wet and Antarctica sea ice set record lows throughout 2023. 

The Arctic had its fourth-warmest year in the 124-year record, with summer (July to September) record warm. Below-ground, permafrost temperatures were the highest on record at over half of the reporting sites across the Arctic. The seasonal Arctic minimum sea ice extent, typically reached in September, was the fifth-smallest in the 45-year record. The amount of multiyear ice — ice that survives at least one summer melt season in the Arctic — continued to decline. Since 2012, the Arctic has been nearly devoid of ice that is more than four years old. Both the Northern Sea Route and Northwest Passage became accessible to non-ice-hardened marine traffic. 

Eight months saw new monthly mean record lows in Antarctic sea ice extent and sea ice area, and 278 days in 2023 set new daily record-low sea ice extents. On February 21, Antarctic sea ice extent and sea ice area both reached record lows, surpassing the previous record lows that were set just a year earlier in February 2022. On July 6, a new record-low daily sea ice extent was 695,000 square miles (1.8 million square kilometers) lower than the previous record low for that day.

Ocean heat and global sea levels were the highest on record. 

Over the past half-century, the oceans have stored more than 90 percent of the excess energy trapped in Earth’s system by greenhouse gases and other factors. The global ocean heat content, measured from the ocean’s surface to a depth of 2,000 meters (more than 6,500 feet), continued to increase and reached new record highs in 2023. Global average sea levels were record-high for the 12th consecutive year, reaching about 4.0 inches (101.4 millimeters) above the 1993 average when satellite altimetry measurements began. 

El Niño contributed to the extreme heat. El Niño conditions in the equatorial Pacific Ocean emerged in spring 2023 and strengthened throughout the year. Each month from June to December 2023 was record-warm. On August 22, an all-time high globally averaged daily sea-surface temperature of 66.18 degrees F (18.99 degrees C) was recorded. Approximately 94 percent of the ocean surface experienced at least one marine heatwave in 2023. 

Heatwaves and droughts contributed to massive wildfires around the world.

During late spring and a record-warm summer, approximately 37 million acres burned across Canada, an area more than twice the size of Ireland and more than double the previous record from 1989. Approximately 232,000 people were evacuated due to the threat of wildfires, and smoke from the wildfires impacted regions across Canada and also affected the heavily populated cities of New York City and Chicago, and even areas of western Europe.