A changing context for life on Earth.

79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 O R R E C My wife and children have allergies and asthma. From time to time, we discuss whether their discomfort is worsening. One reason to believe this to be the case is the reality of anthropogenic climate change. As discussed elsewhere in this theme issue (eg, Shea et al), firm links have been established between climate change and changes in prevalence and severity of asthma and related allergic disease. My family and I live in the Rocky Mountain West, and evidence of climate change is all around us. Perhaps most people don’t notice many of the signs—for instance, that spring is coming a week earlier, or that the high elevation snowpack is considerably reduced by late spring. After all, many of us welcome a longer gardening season, and the earlier mountain snowmelt makes for great white water rafting by the time the summer vacation season begins. But as you drive through the mountains, an unmistakable sign of climate change is the extremely large clusters of dead pine trees, not only in my home state of Colorado but from the southern Rockies into vast parts of Canada and Alaska. Forest managers throughout the West have called the diebacks ‘‘catastrophic’’ and ‘‘unprecedented.’’ The area affected is 50 times larger than the area affected by forest fire, with an economic impact nearly 5 times as great. The trees are succumbing to the relentless attack of the mountain pine beetle. Warming temperatures not only have removed the natural line of defense against such infestations, sufficiently cold temperatures in winter, but also are speeding up the life cycle of the beetle. In the contiguous United States, for example, warmer summer temperatures are enabling the beetle to produce 2 generations in a year, when previously they reproduced once a year. Even centuries-old lodgepole pines at the highest elevations of the Rockies, once seen as impregnable because of the extremely cold temperatures at such altitudes, are dying. Pine beetle infestations are certainly part of the natural cycle; however, it is highly unlikely this current environmental change, like so many others we are witnessing, is entirely natural in origin. Significant advances in the scientific understanding of climate change now make it clear that there has been a change in climate