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More Near-Record Warm Years Are Likely On Horizon

NOAA study: Most of the years in next decade very likely to rank as Top 10 warmest years

Photo of highway in desert looking toward mountain range
Courtesy of, Nextvoyage

Using data from tens of thousands of stations worldwide, NOAA scientists have developed a method to estimate how the average global temperature may rank year-to-year in subsequent years. The method indicates a strong probability that future years will continue to be among the hottest on record.

The method, described in a paper co-authored by scientists at NCEI, the North Carolina Institute for Climate Studies (NCICS), and California State University, Long Beach, is published by the Bulletin of the American Meteorological Society. The title of the article poses the question, “Should we expect each year in the next decade (2019–2028) to be ranked among the top 10 warmest years globally?” 

“In other words,” the authors wrote, “given historical observations (including the most recent ones), can we assume that near-record annual rankings are already ‘baked into the cake’ for the next several years?” 

Their refined method assesses the probability that future yearly temperatures might also follow a pattern established over the last twenty years. The calculations, which use forty years of land-only and ocean-only global temperature data, show there’s a strong probability that future years will rank among the top ten.

Ranking Global Temperature

In monthly climate monitoring activities, NOAA routinely tracks the status of the average global temperature. Global temperature data document a warming trend since the mid-1970s. The warmest years globally have all occurred since 2005, with the top ten being 2016, 2020, 2019, 2015, 2017, 2018, 2014, 2010, 2013 and 2005 (tied), respectively. 

Line graph of top ten hottest years on record as of 2020
Year-to-date global temperature comparison from the 2020 Annual Global Climate Report. Courtesy of NOAA NCEI.

The greatest departure from the 20th century average temperature has been +1.00°C (+1.80°F) in 2016. Last year, 2020, came in second with +0.98°C (1.76°F).

Infographic of seven warmest years in the global record based on temperature departure from average
The seven hottest years on record include 2016, 2020, 2019, 2015, 2017, 2018, and 2014, ranked by their departure from the 20th century average temperature. Courtesy of NOAA NCEI, Barbara Ambrose.

The new algorithm to compute the ranking probabilities, tested for more than a year, responded to growing questions by the public and data users about climate change impacts and the likelihood of continued global temperature increases. Besides NOAA, NASA also produces a global temperature ranking and probability. NOAA’s calculation uses the monthly version of NOAAGlobalTemp dataset, whose methodology was updated in June 2019. NOAAGlobalTemp is slated for another update in 2021.

NCEI produces State of the Climate reports, both national and global, that assess temperature trends. The reports are referred to by many decision makers in both public and private sectors, ranging from agriculture, marine resources, weather forecasting, insurance, urban planning, retail, shipping, emergency management, and transportation. 

Understanding the Ranking

Although the new methodology suggests a greater than ninety-nine percent probability that most of the years between 2019 and 2028 will rank within the ten warmest, variation is possible. Fluctuations could occur due to natural variability, variations in the extent of greenhouse gas emissions, or events like volcanic eruptions. However, the authors cautioned, it would “likely take an abrupt climate shift for even a few years within the next decade to register outside the top 10 warmest years.”

“This is a testament to the exceptional warmth experienced over the last few decades, punctuated by the last 4 years (2015–2018) which have separated themselves from ‘the pack,”’ they concluded. The study, written and submitted prior to the end of 2019, was in editorial review before 2019 was determined to be among the warmest years on record by NCEI.