Climate change killing western forests, eroding Alaska coast
February 19th, 2009 by Jim JustRealClimate has a post by Jim Bouldin discussing a paper in Science showing that background levels of tree mortality have been increasing in undisturbed old-growth forests in the western United States without the accompanying increase in tree “recruitment” (new trees) necessary to maintain the forests. The paper’s lead author was Phil van Mantgem of the USGS.
Background mortality is the regular ongoing process of tree death, unrelated to the more visible, catastrophic mortality caused by such events as fires, insect attacks, and windstorms, and typically is less than 1% per year. Background mortality is that portion of tree death due to the direct and indirect effects of tree competition, climate (often manifest as water stress), and old age.
In each of three regions, the Pacific Northwest, California, and the Interior West, mortality rates have doubled in 17 to 29 years (depending on location), and have been doing so across all dominant species, all size classes, and all elevations.
Bouldin asks, are these changes attributable to human-induced global warming?
Bouldin’s answer is pretty unequivocal. The factors affecting forest productivity and demographic processes cannot be explained by either natural variability or non-human forcings.
Climate change is affecting Alaska, too. A new USGS study reports that erosion of Alaska’s Arctic coast has surged in recent years to more than double the average historical rate. A selection of photos show newly collapsed sections of permafrost coastline as well as decades-old artifacts that have slipped into the sea.
The study attributes the increasing erosion to declining Arctic sea ice extent, increasing summertime sea-surface temperatures, rising sea levels, and increases in storm power and corresponding wave action; and warns climate change “may be leading to a new era.”