What’s causing the West Coast warming? It’s naturally occurring changes in wind patterns that are responsible for most of the warming, not man-caused climate change, according to a new study. Findings of a study conducted by the National Oceanic and Atmospheric Administration (NOAA) and University of Washington have challenged a long-standing assumption that greenhouse gases have been driving the temperatures on West Coast over the past several decades.
Wind-driven climate patterns influence temperatures
The study appeared Monday in the journal Proceedings of the National Academy of Sciences. The northeast Pacific Ocean and nearby coastal land have witnessed about one degree Fahrenheit of temperature rise between 1990 and 2012. Researchers blamed changes in ocean circulation due to weaker winds for warming.
It’s well-known that wind-driven, natural climate patterns such as the Pacific Decadal Oscillation and El Niño exert influence on sea and land temperatures for decades. The new study shows that similar changes in ocean and atmospheric circulation trigger trends that last over a century. James Johnstone, lead author of the study, said that changing winds explain a large fraction of warming on the West Coast.
Weak winds responsible for 80% warming on the West Coast
He said weakening coastal wind speeds decrease evaporation from the sea surface and lead to unusually low pressure. It changes ocean currents and result into temperature rise over time. Scientists found that weaker wind trends accounted for more than 80% of temperature rise between Washington and Northern California. Weak winds were blamed for 60% of the increased warming in Southern California.
If human-caused climate change had been responsible for warming along the West Coast, the temperatures would have been drastically different, scientists said. They found that most of the temperature rise in the region occurred before 1940, when winds were weaker and greenhouse gas concentrations were far lower.
NOAA and the University of Washington scientists studied the trends only at the regional level. They did not offer conclusions about the impact of changing wind patterns on warming across the globe.