Here is the second new piece of scientific evidence in two days that President Obama should take notice off. The first was news of warming in Antarctica, but today’s news is much closer to home.

The majestic old-growth forests of western North America that stretch from Arizona to British Columbia are more vulnerable to climate change than scientists previously believed. A study published yesterday in the journal Science found that tree death rates have more than doubled in old-growth forests over the last 30 years.

Temperatures in the forests have increased by on average over 0.5 degrees C over the period, reducing snowfall accumulations, prolonging summer droughts and raising the insect population, including tree-killing bark beetles.

The study found that the increase in dying trees has been pervasive. Tree death rates have increased across a wide variety of forest types, at all elevations, in trees of all sizes, and in pines, firs, hemlocks, and other kinds of trees. Moreover, the scientists believe that the accelerated forest loss could trigger an environmental domino effect on the region’s wildlife and climate.

“Tree death rates have more than doubled,” says study co-author Phillip van Mantgem, a research ecologist with the U.S. Geological Survey (USGS). “The same way that in any group of people a small number will die each year, in any forest a small number of trees die each year. But our long-term monitoring shows that tree mortality has been climbing, while the establishment of replacement trees has not.”

“Tree death rates are like interest on a bank account – the effects compound over time,” adds Nate Stephenson, the research team co-leader. “A doubling of death rates eventually could reduce average tree age in a forest by half, thus reducing average tree size.”

“If anything, it’s a warning bell,” concludes van Mantgem. “A lot of people like to think of these majestic old-growth forests as unchanging, but this showed us that they do in fact respond rather quickly to the environment.”