THE HOTTEST 12 MONTHS  in 150 years of recordkeeping — and probably in the last 125,000 years — are due to human-caused climate change. From November 2022 through October 2023, the Earth’s average temperature was about 1.3 degrees Celsius higher than the average temperature from 1850 to 1900, say researchers.

The report also quantifies temperatures that people around the world are actually experiencing day-to-day, and how much those are due to climate change.

To that end, the analysis used Climate Central’s Climate Shift Index, or CSI. CSI is a daily local temperature attribution system that uses a combination of observational data and climate simulations to determine the likelihood that local temperature variations are attributable to climate change.

Extreme heat is a relative term, dependent on both place and time. So, the researchers considered extreme heat for a given location to be daily temperatures that would have been in the 99th percentile for that place from 1991 to 2020 — temperatures, in other words, that locals would recognize as extremely hot.

Using that index with data from hundreds of countries, states, provinces and major cities, the researchers found that about 90% of the world’s population, or 7.3 billion people, experienced at least 10 days of extreme temperatures in the last year that were very strongly affected by climate change.

Those days had a CSI rating of at least 3, indicating that human-caused climate change made those temperatures at least three times as likely. Nearly 3 out of 4 people experienced over a month of those temperatures.

The report also reveals unfairness in the burden of climate change around the world. Earth’s least developed countries, including many nations in sub-Saharan Africa and in Southeast Asia, had a relatively high average CSI of 2, the report notes, though they have contributed the least amount of fossil fuel emissions.

But climate impacts are also increasing in many of the world’s richest countries, including the United States. Heat waves across much of the southern United States have occurred more frequently. Houston sweltered through a 22-day streak of extreme heat, where each consecutive day topped 38° C (100° Fahrenheit). That was the longest such extreme heat streak of the 700 cities examined with a population of at least 1 million people.

The CSI analysis is similar to the analyses performed by the consortium World Weather Attribution, or WWA, which looks for the fingerprints of human-caused climate change in specific extreme events around the world.

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. OMG! Heat strokes even in tropical Philippines might be more common by then. By Manny Palomar, PhD (EV Mail Feb. 5-11, 2024 issue)