Man-made climate change reduced US wildfires to lowest levels in 400 years

Congressional testimony demonstrates that man-made intensive livestock grazing since 1879 has reduced the size and intensity of U.S. wildfires to lowest levels since the 1600s. 

In congressional testimony regarding "Natural Disasters in the Wake of Climate Change" hearings, Dr. Judith Curry, former chair of Earth and atmospheric sciences at Georgia Tech, agreed that "climate variations have been important drivers of wildfire occurrence in ponderosa pine forests across western North America for at least 400 years."  But she demonstrates that human land use associated with "intensive livestock grazing disrupted fuels continuity and fire spread and then active fire suppression maintained the absence of widespread surface fires during most of the 20th century."

The 2014 "National Climate Assessment Report" claimed that the Southwest would be the most vulnerable U.S. region to CO2 emissions' generated climate change, causing:

... [i]ncreased heat, drought, and insect outbreaks, all linked to climate change, have increased wildfires." Its models predicted a "doubling of burned area in the southern Rockies, and up to a 74% increase in burned area in California" would result in a "conversion of forests to woodland or grassland.

But rather than the perma-drought reduced mountain snowfalls forecasted by NCAR, California in its 2018–2019 water year reported a record 200 percent of average Sierra snowpack, the second highest precipitation for May, and the Department of Water Resources reported river run-off at about 165 percent of average for this time of year.

Directly contradicting NCAR, Dr. Curry demonstrated that for the past 400 years, the link between widespread wildfires has been ocean circulation patterns associated with El Niño–Southern Oscillation, the Pacific Decadal Oscillation, and the Atlantic Multidecadal Oscillation influence on temperature and moisture patterns.

In the Southwest, El Niño ocean warming cycles cause increased wet year production of grass and needle litter.  These events tend to be followed by La Niña ocean cooling, causing dry years associated with "fires synchronized across this region."

Dr. Curry highlights that climate change advocates are focused only on recent temperature and wildfire records since 1950s.  This ignores that U.S. wildfire intensity has consistently trended down during the "era of livestock grazing and fire suppression" that began in about 1879, an era prior to use of coal for electricity and oil for transportation.

Records within the narrow livestock grazing era reveal that cyclical wildfire activity with the most elevated period being from 1916 through to the 1930s.  Wildfires stayed uniformly low during the 1950s through the 1970s, then became elevated again after 1985.

The 1930s still hold the modern era records for many of the worst U.S. weather disasters.  Notable events include the Labor Day Hurricane of 1935 as the strongest landfalling hurricane, the worst drought in 1934, and the largest number of severe heat waves in 1934.

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