The summer of 2023 was the hottest in the Northern Hemisphere in over two millennia, according to a study published in Nature on Tuesday. Despite the extreme heat of 2023, the coming summer is expected to be even hotter, driven by human-induced climate change and exacerbated by an El Niño weather pattern reported Bloomberg.
Previous research established 2023 as the hottest year since 1850 when modern global temperature records began. By combining instrumental measurements with climate reconstructions, researchers created a 2,000-year temperature record. They discovered that the extreme heat of last summer not only broke modern records but also surpassed the warmest summer before the instrumental record in the year 246 by over half a degree Celsius. It was nearly 4°C warmer than the coldest summer in 536.
“When examining the long sweep of history, the dramatic nature of recent global warming becomes evident,” stated Ulf Büntgen, a study co-author from the University of Cambridge. “2023 was exceptionally hot, and this trend will persist unless we significantly reduce greenhouse gas emissions.”
Büntgen and his team focused their analysis on landmasses between the 30th parallel north and the North Pole, where most long-standing meteorological stations are located. They reconstructed historical climate conditions by examining thousands of tree rings from nine regions in the Northern Hemisphere. Tree rings, influenced by weather conditions, provide crucial insights into past temperatures, particularly between June and August.
The study noted inconsistencies between tree-ring-based climate reconstructions and instrument-based measurements in the latter half of the 19th century. This discrepancy suggests older thermometers may have recorded inaccurately high temperatures, resulting in a “systematic warm bias” in early instrumental records, which are widely used as baselines in climate science. The tree-ring data also showed that most cooler periods over the past 2,000 years followed major volcanic eruptions, which released large amounts of aerosols into the stratosphere, causing rapid surface cooling. Conversely, most warmer periods were linked to El Niño events, a phase of the El Niño-Southern Oscillation that disrupts global weather patterns and typically increases summer temperatures in the Northern Hemisphere.
While El Niño is a natural climate phenomenon, scientists warn that global warming from fossil fuel combustion and other human activities is amplifying its effects, leading to more extreme summer heat. The ongoing El Niño, which began in June 2023, is expected to end soon, but its impact continues to drive up temperatures.
“Indeed, the climate is always changing, but the warming in 2023, driven by greenhouse gases, is further intensified by El Niño, resulting in longer, more severe heat waves and prolonged droughts,” explained Jan Esper, the study’s lead author and a professor of climate geography at Johannes Gutenberg University Mainz.
The study indicates that the 2015 Paris Agreement goal to limit temperature rises to 1.5°C above pre-industrial levels has already been surpassed in the Northern Hemisphere. Although this conclusion cannot be applied globally due to varying warming rates across different latitudes and between land and sea surfaces, the findings clearly demonstrate the unparalleled nature of current warming on a large scale. This reaffirms warnings from climate scientists that as climate change is amplified by El Niño, 2024 is likely to set new temperature records. Recently, extraordinary heat waves have affected many countries in Asia, with Myanmar experiencing its highest-ever April temperature of 48.2°C.
