Record-Breaking Heat: The Hottest 12 Months Ever Recorded

A new report suggests that the past year has been the hottest in 150 years of record keeping, and likely the hottest in the last 125,000 years, largely due to human-induced climate change.

From November 2022 to October 2023, the researchers at Climate Central, a nonprofit organization, recorded that the planet's average temperature was approximately 1.3 degrees Celsius higher than the historical average temperature from 1850 to 1900. This puts it dangerously close to the critical benchmark of 1.5 degrees Celsius which signifies irreversible climate change impacts.

According to the scientists, approximately a quarter of the global population experienced a heat wave driven by climate change, which persisted for at least five days, over the course of the last year.

The release of the report was intentionally timed just prior to the 28th United Nations Climate Change Conference of the Parties on November 30, Andrew Pershing, vice president for science at Climate Central, explains. The hope is that the findings, which indicate that fossil fuels are driving the increased heat, will be taken into serious consideration by global leaders.

The report delineates not only global averages but also breaks down everyday temperatures experienced by individuals around the globe and how much these temperatures are impacted by climate change. This presents a localized image of climate change's effects, giving people a clearer understanding of how it impacts daily temperatures.

Climate Central employed their Climate Shift Index (CSI) in this report, a system that gauges the impact of climate change on local temperature variations by combining observational data and climate simulations.

The report defines extreme heat differently across varying locations and timespans. For each location, extreme heat corresponds to daily temperatures sitting in the 99th percentile from the period between 1991 to 2020.

By using this index and corresponding data from hundreds of countries, states, provinces, and cities, the researchers concluded that around 90% of the world's population, or 7.3 billion people, experienced a minimum of 10 days of extremely high temperatures strongly impacted by climate change in the past year.

The report revealed substantial disparities in the climate change burden worldwide. The least developed nations bore some of the brunt despite contributing the least to fossil fuel emissions. However, even the wealthiest countries, including the United States, experienced increased climate impacts with the occurrence of severe heat waves.

The approach operative in the CSI analysis mirrors that of the World Weather Attribution (WWA) consortium, which investigates the role of human-induced climate change in specific extreme weather events worldwide.

WWA's findings from the past year, based on investigations of a few extreme heat waves, also concluded a strong link to climate change, according to Friederike Otto, a climate scientist at Imperial College London.

Otto explains that while an immediate reduction in fossil fuels won't counteract the current effects of the past century's emissions, it could stop the rise of global temperatures and prevent intensification of heatwaves. Maintaining global warming below the critical 1.5 degrees Celsius threshold, she claims, is achievable if done intentionally.

The past year also saw the beginning of an El Ni&o climate pattern, which usually results in higher global temperatures in addition to the ongoing trend of global warming. However, the impacts from El Ni&o generally take a year to unfold as the heat distributes globally, says Pershing.

The previous 12-month record was set from October 2015 to September 2016, as heat from a strong El Niño event spread around the globe. That record — where the global average was 1.29 degrees Celsius higher than the average preindustrial temperature — was tied earlier this year, for the period ending in September 2023.

That means that, as the El Niño pattern continues to develop into next year, 2024 will probably smash records once again.

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