The summer of 2023 was hotter than any season since the Chola Empire 2000 years ago!

No one would have expected it, but 2024 finally boasted the summer that made Bengalureans hesitant to talk about their city’s weather. The UN has already warned that this year could shape up to be even hotter than 2023, which has already gained enough well-deserved notoriety for its string of broken heat records. But how does it compare to more ancient times in human history, where weather bookkeeping wasn’t really a thing?

As per a new study, 2023’s records hold up pretty well actually — for two millennia in the Northern Hemisphere, at least.

Even though modern humans and society have been around for quite a while now, our personal records on the weather remain patchy at best. In fact, instrumental and reliable weather data only reaches back as far as the 1850s, meaning scientists had to find a new way of comparing the current situation to the centuries and millennia past.

To accomplish this monumental task, scientists looked at trees. Trees can live anywhere from 100 to 1000 years, with the living oldest tree being nearly 10,000 years old. Using the age rings inside tree trunks, scientists were able to extract climatic data spanning the past 2,000 years. They found that, even when factoring in natural climate variations, 2023 surpassed all previous records, including those dating back to Ashoka and the Chola Empire.

“When you look at the long sweep of history, you can see just how dramatic recent global warming is," explains study author Professor Ulf Büntgen.

2023 was also 3.93°C hotter than the coolest summer since the first century, which took place in 536 CE after a volcanic eruption plunged the world into a little ice age. The mercury was half a notch above the most extreme natural climate variability during the past two millennia, the study found.

In fact, volcanic eruptions coincided very well with cooler times, while warmer periods were linked to the El Niño climate pattern. However, the researchers noted a concerning trend: over the past six decades, greenhouse gas-induced global warming has intensified El Niño events, leading to more frequent and severe heatwaves.

"It's true that the climate is always changing, but the warming in 2023, caused by greenhouse gases, is additionally amplified by El Niño conditions, so we end up with longer and more severe heat waves and extended periods of drought," explains another study author Jan Esper. "When you look at the big picture, it shows just how urgent it is that we reduce greenhouse gas emissions immediately."

Despite the robustness of their findings for the Northern Hemisphere, obtaining global averages remains challenging due to sparse data in the Southern Hemisphere. Nonetheless, the study underscores the critical need for concerted efforts to reduce greenhouse gas emissions to mitigate the devastating impacts of climate change.

The findings of this research have been published in Nature and can be accessed here.