At his laboratory in a wooded grove in northern Kyoto, Takeshi Nakatsuka holds up a vacuum sealed bag. Inside, bobbing in a bath of brown water, is a glistening disk the size of a dinner plate and the color of rich gravy. This soggy circle is the remnants of a 2,800-3,000-year-old tree, recovered from a wetland – water included, so the spongy wood does not deform – in Japan’s Shimane Prefecture, just north of Hiroshima. Within this ancient trunk lie secrets that can help us prepare for the future.

Nakatsuka, a palaeoclimatologist at Japan’s Research Institute for Humanity and Nature, along with a diverse team of 68 collaborators, has spent the last decade developing a novel method to reveal bygone precipitation patterns and interpret their effect on society. The results offer unprecedented insight into 2,600 years of Japanese rainfall patterns. By teasing out information locked inside the preserved wood of ancient forests, they are able to reveal just how much rain fell around the country over the past two and half millennia. It is an extraordinary record.

About every 400 years, the researchers found, the amount of rain falling on Japan would suddenly become extremely variable for a period. The nation would toggle between multi-decadal bouts of flood-inducing wetness and warmer, drier years that were favorable for rice cultivation. As the rains came and went, Japanese society prospered or suffered accordingly.

Takeshi Nakatsuka with a 2,800-3,000 year old tree stump (Credit: Rachel Nuwer) Palaeoclimatologist Takeshi Nakatsuka is using information preserved inside ancient tree stumps to learn about Japan’s climate in the past (Credit: Rachel Nuwer) “Multi-decadal variability provides us with the chance to transform as well as the chance to collapse,” Nakatsuka says. Regardless of the outcome, he emphasises that such change caused large amounts of stress for the people who lived through it. As weather patterns today increasingly defy expectations, this window into past climate variability hints at what may be in store for us in the coming years

As weather patterns today increasingly defy expectations and extreme events become more frequent and severe, this window into past climate variability hints at what may be in store for us in the coming years. “Today is not different than 1,000 or 2,000 years ago,” Nakatsuka says. “We still have the same lifespans and we are still facing large, stressful multi-decadal variation.” Nakatsuka builds a picture of what happened in the past using a number of proxies, including tree rings, corals, stalagmites, ice cores and sediment. But his latest findings, which he and his colleagues are currently preparing for publication, primarily rely on a new method that uses isotope ratios contained within wood to estimate precipitation patterns.