"At the close of the growing season of 2004, Goetz was seeing changes in the forest. The blackened skeletons of trees extended into the distance after fires consumed a record six million acres. Up close, the gold and green leaves of the rustling aspen trees were marbled with white squiggly lines where leaf miners had eaten through them. While both fires and insects were a natural part of the forest’s lifecycle, Goetz hadn’t seen either have such a wide impact on the forest before. But the most disturbing and unexpected change, he had observed months earlier back in his office at the Woods Hole Research Center in Woods Hole, Massachusetts."
"In addition to his research in the forest, Goetz was using satellite data to study how the spruce-rich forests of northern Canada and Alaska recover after large fires. The burned forest was re-growing as he expected, but the unburned forest was behaving strangely. Since the 1990s, scientists have known that increasing global temperatures have lengthened the growing season in the Arctic. With carbon dioxide, one of the key ingredients in photosynthesis, also on the rise, the forest should have been thriving. But it wasn’t. The forest was getting browner, not greener."
"On the other side of the United States, Alon Angert, a scientist at the University of California, Berkeley, noticed a strange trend in the forest, too. Angert was tracking carbon dioxide in the atmosphere over the Arctic from 1985 to 1994 when he saw that trees weren’t soaking up as much of the gas at the end of the period as at the beginning. It was as if the whole forest had slowed its breathing during that single decade.
“Something big is happening in the high latitudes,” says Rama Nemani, a research scientist at NASA Ames Research Center, in response to the papers that Goetz and Angert published within weeks of each other. Nemani was on the research team that initially noticed that the Arctic was beginning to green in response to global warming in the 1990s. Despite the previous discovery, Nemani wasn’t surprised that Northern forests now seem to have slowed their growth. After all, the same theories that predicted that global warming would increase forest growth in the Arctic, theories that Nemani helped prove, also predicted that the forests would eventually reach the limits of the water supply and go into decline. “We knew something like this would happen,” Nemani says. “We didn’t expect that it was going to happen so quickly.”