The heating up of America’s west coast over the last century has been mostly caused by natural alterations in wind patterns rather than climate change brought about by humans, according to a new study.

Between 1900 and 2012 temperatures have increased by about one degree Fahrenheit in coastal areas along the Pacific Ocean.

In California, 2014 is on course to be the hottest year since records began and almost the entire coastline is in a state of “exceptional drought”.

But a new study carried out by researchers at the National Oceanic and Atmospheric Administration and the University of Washington concluded that this was not caused by a build up of greenhouse gases.

Instead, they found it was mainly due to changes in ocean and wind circulation patterns which could affect temperatures over periods lasting longer than a century. When the winds drop less water evaporates and temperatures rise.

Most of the warming actually took place before 1940 when concentrations of greenhouse gases were lower, the study found.

Nate Mantua, co-author of the study, told the Seattle Times: “It’s a simple story but the results are very surprising. We do not see a human hand in the warming of the west coast, That is taking people by surprise, and may generate some blow back.”

He added: “This doesn’t say that global warming is not happening. It doesn’t say human-caused climate change isn’t happening globally. It’s a regional story. The climate system isn’t that simple. History has been playing tricks on us.”

Read more about California coastal warming ‘due to wind not humans’.