Great Basin bristlecone pines, Pinus longaeva, are the Methuselahs of the living world. Many live trees are several thousand years old, and the record holder clocks in at around 4,840 years. The pines, which subsist high on the mountain slopes of the western United States, grow very slowly. But, old age be hanged, those at the highest elevations are now having the time of their lives, thanks to global warming.
Trees leave a record of their growth in their annual rings—the wider the ring, the greater the growth that year. A team of dendrochronologists four strong, headed by Matthew W. Salzer of the University of Arizona in Tucson, reports that pines high up near the tree line in California and Nevada developed wider rings during the second half of the twentieth century than during any other fifty-year period of the past 3,700 years.
That’s probably a consequence of milder temperatures, because only pines close to the tree line—those most limited by cold—exhibit the effect. If the growth spurt were caused by more-abundant carbon dioxide boosting photosynthesis, or by a wetter climate, then lower-elevation trees should have wider rings too. They don’t.
In fact, over the past century (for which good weather records exist), there is a significant correlation between tree-ring width at the tree line and mean air temperature—further support for the notion that the venerable trees are long-lived indicators of warming in western mountains. (PNAS)