Weather Bee: Is it 2023 again for global temperatures?

May 2026 has recorded the second-highest global temperatures ever for the month, signaling a potentially significant year for climate trends. This data, released by the Copernicus Climate Change Service (C3S), marks the first time this year that any month has ranked among the top three warmest on record. This development, coupled with the ongoing El Niño phenomenon forecast to strengthen later this year, suggests that 2026 might mirror the global temperature trajectory observed in 2023.

Understanding how 2026 temperatures might align with 2023 requires examining typical annual temperature variations. Historically, global temperatures have often followed a U-shaped curve over a year, starting with higher warming relative to pre-industrial averages, decreasing during the Northern Hemisphere summer, and then rising again. However, this pattern is not constant. Some years, like 2021 and 2022, showed relatively flat warming trends, while others, such as 2016, 2017, and 2020, saw warming decrease as the year progressed. In contrast, 2023 exhibited an unusual trend where warming appeared to increase throughout the year.

The primary driver behind these interannual temperature variations is the state of the central-eastern equatorial Pacific Ocean, specifically tracked by the Oceanic Niño Index (ONI). El Niño conditions, indicated by an ONI of 0.5 or above, have a warming effect on global temperatures, while La Niña conditions (ONI of -0.5 or lower) have a cooling effect. Neutral conditions prevail when ONI values are between -0.5 and 0.5.

Analysis of past years reveals a correlation between Pacific conditions and temperature trends. For instance, the decrease in warming observed in 2016, 2017, and 2020 coincided with a shift from El Niño to La Niña. Stable Pacific conditions in 2021 and 2022 corresponded with consistent global warming trends. Crucially, the increase in warming throughout 2023 occurred as the Pacific shifted from neutral conditions to El Niño. The current intensification of El Niño suggests that 2026 could follow a similar warming trajectory, potentially matching or exceeding the temperature anomalies seen in 2023.