Global warming is real; The death rates of trees in western U.S. doubled over the past decades

A new study spearheaded by the U.S. Geological Survey has found that the death rates of trees in western U.S. forests have doubled over the past two to three decades, driven in large part by warmer temperatures and water scarcity linked to climate change.

The research, examined changes in 76 long-term forest plots in three broad regions across the West, and found similar shifts regardless of the areas' elevation, fire history, dominant species and tree sizes. It is the largest research project based on old-growth forests in North America. 

After examining a range of possible causes for the region-wide pattern, the researhcer find out that the West’s warming trend and warming’s effect on the amount of water available in these areas. hence effect the tree growth.  Summer dry spells are longer. Snows melt earlier. More winter precipitation falls as rain, rather than snow, and the snow that falls has a lower water content than it once did. This all contribute and effect the to the ground water level.

If current tree mortality rates continue and even accelerate,  there is a chance that U.S. forests could shift from being a carbon sink that takes greenhouse gases out of the atmosphere to becoming a net emitter of carbon dioxide. 

Washington Post