Trees hold secrets of El Niño and hurricanes, scientists say

Scientists who study trees say that tree rings hold hidden records of past storms, droughts, and other weather events. As the 2026 hurricane season gets underway and a strong El Niño may shake up weather around the world, researchers are turning to trees for answers. By looking at thin slices of wood from some of the oldest trees on Earth, scientists can learn about weather events that happened long before satellites or modern weather tools existed.

Each year, a tree adds a new ring of wood as it grows. The width, density, and pattern of these rings tell scientists a lot about what the tree went through. Narrow rings mean a hard year — maybe a drought or a big storm. Wider rings usually mean the tree had plenty of water and sunlight. Scientists say reading these rings can be thrilling because each one is like a page in the tree's diary.

Researchers collect samples by drilling a tiny core — about the width of a pencil — from a living tree. These cores don't harm the tree, and they give scientists a long record of past weather. Some trees alive today were already growing in 1776, when the United States was founded. Scientist Nicole Davi, a professor at William Paterson University, calls these 'witness trees' because they were literally there during major moments in history.

Finding the right trees is an important part of the job. Valerie Trouet, a professor at the University of Arizona and author of the book 'Tree Story,' says she loves hiking into remote mountain forests to find ancient trees. 'You arrive and you see these ancient old trees, in a beautiful landscape,' she said. These old trees, sometimes called patriarchs, have been alive for hundreds of years and hold centuries of information in their rings.

Scientists choose which trees to study based on what they want to learn. If they are studying drought, they look at trees in dry areas, like the American Southwest. In places like Tucson, Arizona, trees grow a lot in wet years but barely at all in dry ones, leaving very narrow rings. That makes it easy for scientists to spot the dry years just by looking at the rings under a microscope.

Tree rings can even show the effects of volcanic eruptions. When a volcano erupts, ash and dust can block sunlight for months or even years, causing trees to grow more slowly. Davi said you can see these patterns in trees from places as far apart as Mongolia, Canada, and Alaska. The rings act like a worldwide record of major natural events.

One big reason scientists study tree rings is to learn more about El Niño, a weather pattern that happens every six or seven years and affects rain and storms around the globe. Satellites have only been around for about 50 to 60 years, which means scientists have data on fewer than ten El Niño cycles. That is not enough information to spot reliable patterns, Trouet said. Tree rings let scientists look back hundreds of years to study many more cycles.

Tree rings also help scientists track hurricanes. Rings from trees in areas hit by hurricanes can show how a storm affected growth in the years that followed. For example, research has shown that trees in Texas grew more slowly after Hurricane Harvey's heavy flooding. Trees that survived big storms often lost their leaves and branches, and the stress from that damage shows up clearly in their rings.

Scientists also use tree rings to study wildfires. The records show that wildfires in the Pacific Northwest tend to happen more often during El Niño years, while the Southwest sees more fires during La Niña years. By looking at old tree rings, researchers can see how large and common wildfires were in the past. This helps scientists understand how fire patterns may change as the climate continues to shift.

Davi says it is exciting to think about all the stories that trees are still waiting to tell. Trees are quietly recording history every single year, building up rings that future scientists will one day study. 'It's super exciting scientifically,' she said, to think about what more we might learn. The forests of the world are, in a way, the planet's oldest library.