Central Japan Was 3°C (And Up To 7°C) Warmer Than Today Throughout The Early To Mid Holocene

“Based on the records of the δ¹⁸O stalagmite , the [Holocene Thermal Maximum] occurred between 10.9 and 6.7 ka [Honshu, Japan], reaching its peak temperature (15.0°C) around 7.0 ka. At this time, temperatures were approximately 3°C warmer than present.” – Murata et al., 2025

In a new study, scientists have used oxygen and carbonate isotope proxy evidence to determine millennia of temperature variations at Kiriana Cave in central Japan.

Today, the average temperature at Kiriana Cave “can be estimated at 11.8°C.” But from 13.7 ka (thousand years before 1950) to 12.4 ka, when CO2 was still only about 250 ppm, the “calculated temperature…ranges from 11.5°C to 15.0°C,” peaking at more than 3°C warmer than today.

Furthermore, the rate of warming reached 1°C per century in this region, as temperatures rose from “around 12°C until 12.9 ka and then increased to ~15°C at 12.6 ka.” Over the next 200 years temperatures fell by 2.2°C, or from 15°C at 12.6 ka to 12.8°C by 12.4 ka.

The scientists also point out the Maboroshi Cave near Hiroshima had Mid-Holocene temperatures ranging “from 21°C to 15°C, clearly warmer than the present temperature (14.1°C) by 7°C − 1°C.”

Image Source: Murata et al., 2025