Summers in the nation’s first and oldest national park are rapidly heating up, new research finds. For the last two decades, Yellowstone National Park has been warming at its most intense rates in at least 1,250 years. Tree rings can provide a variety of information about the climate and weather conditions a tree has experienced over the course of its lifetime. The samples helped scientists construct a timeline of the Yellowstone climate, focusing on August temperatures — the hottest time of the year. Yellowstone has had its ups and downs over the past millennium, they found, including periods of both warming and cooling.