Massive tides, dragged up the shore by the gravitational pull of the sun and the moon, will wash up on the Oregon coast this weekend, giving researchers a glimpse of what threats climate change might pose to coastal communities.

The high tides forecast for Friday, Saturday and Sunday, informally known as king tides, occur a few times a year when the Earth is closest to the moon and sun. The gravitational pull of the celestial bodies can bring water up to 4 feet higher than an average high tide.

As the planet warms, mostly due to the increased levels of carbon dioxide in the atmosphere from burning fossil fuels, ice sheets in Antarctica and Greenland melt. Water also takes up more space as it warms in a process known as thermal expansion. Melting ice and thermal expansion are expected to drive up sea levels across the globe, including on the Oregon coast, where problems like erosion and flooding would be be exacerbated.

“In areas where dunes and bluffs are getting impacted every winter, that will get worse,” said Peter Ruggiero, interim director of the Oregon Climate Change Research Institute. Flooding of roads, homes, businesses and other types of coastal infrastructure, which happens periodically today, will become more common, he said.

“These kinds of things that we experience every now and then will happen much more frequently,” Ruggiero said.

Global mean sea level rose by more than 7 inches between 1901 and 2010, according to a 2017 report from the institute. Of that, some 75 percent is thought to be caused by the melting of ice sheets and thermal expansion of ocean waters.

Looking forward, Newport, one of the Oregon coast’s biggest population and tourism centers, could see somewhere between 12 and 47 inches of sea level rise by the end of the century if carbon dioxide emissions continue unabated. At Astoria in the north, the coast could see between 2.4 and 35 inches of sea level rise. At the southern end of Oregon in Port Orford, sea levels could go up between 6.7 and 42.5 inches.

Researchers are using what are referred to as citizen scientists to bolster their efforts at learning where sea level rise will pose the biggest threats.

An army of volunteers with the King Tide Project, toting cameras and smartphones, will fan out across the coast this weekend to document where the high water is having its most substantial impacts. The project began in Australia in 2009 and quickly spread around the world. The effort to document king tides on the Oregon coast got its start in 2011 and now boasts a trove of photographs from high tides over the past decade. Deanna Caracciolo, a worker with the Oregon Coastal Management Program who helps oversee the project, said they get as many as 100 submissions per king tide. She said the pictures help researchers validate flooding and erosion models.

“A picture is worth 1,000 words,” she said, “and king tide photos highlight how a rising sea or increased storm surge may impact familiar and recognizable places in our communities.”

Anyone can participate by simply uploading their pictures to the project’s website and tagging them with the location where they were taken.

This weekend’s king tides are expected to be accompanied by strong winds, rain and large waves, so anyone looking to participate should exercise caution when near the ocean.

By next week, the king tides will have come and gone, but flooding and erosion are expected to become more frequent threats in the long-term as global temperatures increase, Ruggiero said.

“With sea levels rising, there’s no possibility of anything happening other than those things getting worse,” he said.

-- Kale Williams

kwilliams@oregonian.com

503-294-4048

@sfkale

Subscribe to Oregonian/OregonLive newsletters and podcasts for the latest news and top stories.