SEATTLE – Changing wind patterns are the primary cause of warming temperatures in the Northwest, according to a study published Monday.
The authors lined up historical wind data with coastal sea surface temperature in the Northeastern section of the Pacific Ocean since the beginning of the 20th century. They found that up to 90% of the warming in the Pacific Northwest and Northern California is driven by changes in wind patterns.
“When people look at century long warming trends, it’s typically assumed that they’re caused by humans, at least over the last century or so. What we’ve shown is that the same wind mechanisms that regulate wind variability can also generate a warming trend as well,” said James Johnstone, the lead author of the paper, which was published in the Proceedings of the National Academy of Sciences.
Johnstone says that in this region, the data shows that winds over the Pacific have slowed down. Slower winds mean less evaporation and warmer water.
This natural process, Johnstone says, outstrips the contribution of global CO2 emissions to the warming trend in this region. But he says he does not dispute the contribution of greenhouse gas emissions, globally, to rising average temperatures.
“We tried to be very careful about what [the paper] says and what it doesn’t say, trying to keep the focus on the regional study that we’ve done. It doesn’t say anything about global temperatures,” said Johnstone, who just finished his post doctorate at the University of Washington’s Joint Institute for the Study of Atmosphere and Ocean.
One might think of climate change modeling like photographing supermodels. The models look great from far away, but when you zoom in, things aren’t so glossy and clean cut. Johnstone’s findings highlight the need for better climate modeling on the regional level, say other climate scientists.
“We’ve long known that climate models are the strongest at the global scale and the finer you go, the less you can believe them,” says Amy Snover, head of the Climate Impacts Group at the University of Washington. “So what this paper does is it gives us some things that we can suggest be improved in the global models.”
Wind patterns certainly deserve a place at the table in conversations about climate change at the regional level, as do other natural variations, like Pacific Decadal Oscillation, El Nino/La Nina, solar variability and volcanic forcing. One might think of warming temperatures as a symphony, says John Abatzoglou, associate professor of geography at the University of Idaho.
He says it's helpful to think of different instruments – volcanic forcing is your oboe, Pacific decadal oscillation your flute, wind patterns your French horns.
“But what we found is that when you look, over the long haul, the drum of anthropogenic warming is the instrument that continues to play louder and louder through time,” Abatzoglou said, referring to a recent study of his that was published in the Journal of Geophysical Research. “Most of the warming that we have seen, seems to be linked to the increases in greenhouse gases.”
This is, after all, how science works. New hypotheses get introduced. Some stick. Some are thrown out. Abatzoglou says Johnstone’s research will add to the conversation about how natural patterns influence climate change in the Northwest.
But, he says, blaming it on the wind could enable some to continue to deny that greenhouse gas emissions are the leading cause of climate change in the Northwest and around the world.
“I think this study in particular is one that might help people say ‘hey, we’re not changing the climate. It’s all natural,'” Abatzoglou said.
By mid-century, Washington is likely to regularly experience average annual temperatures that exceed the warmest conditions observed in the 20th century. Washington is also expected to experience more heat waves and more severe heavy rainfall events, despite relatively small changes in annual and seasonal precipitation amounts, according to a report from the Climate Impacts Group at the University of Washington.