The United States and China — the world's top two greenhouse gas-emitting countries, which together account for about 40% of the world's annual carbon output — announced Wednesday they have agreed to cooperate on limiting emissions to address the global climate crisis.

The agreement, announced at the United Nations climate change conference in Glasgow, Scotland, known as COP26, aims to accelerate emissions reductions toward the goals set in the 2015 Paris agreement, which include keeping the global temperature rise "well below" 2 degrees Celsius (3.6 degrees Fahrenheit), with a target of 1.5 degrees Celsius (2.7 degrees Fahrenheit).

Despite the encouraging news, experts predict that most countries are currently not on track to meet the commitments they agreed to in Paris. In the U.S., the West Coast is already experiencing more frequent and severe weather, and rising seas are already putting some Bay Area communities at risk.

In Southern California in September, Amtrak suspended service on their Pacific Surfliner route for a few weeks between Orange and San Diego counties for emergency repairs due to beach erosion. The scenic coastline route connects San Diego and other cities on its way to San Luis Obispo.

https://twitter.com/PacSurfliners/status/1438320674506821632

Beach erosion, the process in which the sand and rocks that make up a coastline are carried away by rising seas and stronger waves, presents an ongoing threat to the tracks of the Pacific Surfliner and the oceanfront homes, roads, piers and power plants in the vicinity.

Rick Behl, professor of geological sciences at Cal State Long Beach, points out that even in normal times, California’s coast can be a hazardous place to build things.

"The coastline is a super-dynamic place naturally," he said. "It’s where everything comes together: the ocean, the atmosphere, the land, the rivers. It’s constantly changing."

An aerial shot of a long, silver-and-blue train on tracks, with only a few yards of beach between it and ocean waves, with low, green hills on the immediate opposite side. — Amtrak's Pacific Surfliner train travels along the Southern California coast. (Courtesy of Amtrak)

He adds that climate change is supercharging these changes, making storms stronger, tides higher and the coastal erosion of beaches and cliffs worse.

Riding the Pacific Surfliner provides a unique vantage point to this transformation. As the train crosses San Diego County into Orange County, the tracks come really close to the Pacific Ocean, making it clear how vulnerable the train and nearby homes are to climate change.

View inside the interior of a train car taken from the back, with rows of four seats and an aisle up the middle. The bright sun makes the interior mostly dark. A man with short hair, glasses, and a mask takes a photo with his phone out through the window, where a receding wave seems to come up almost to the train itself. — A passenger takes a photo as an Amtrak train passes near the Pacific Ocean on Nov. 9, 2021, near Oceanside, California. (Mario Tama/Getty Images)

In nearby towns like San Clemente and Oceanside, seawalls have been built in front of many homes, and giant boulders have been placed between the ocean and the train tracks.

But Behl warns that “coastal armoring” actually makes erosion worse in the long term by starving beaches of new sources of sand.

"It increases the energy on the beach, causes more erosion, drops the sand and makes less beach," he said.

The cycle can possibly reach a point where "there really is no beach left."

[aside postID="science_1973805" hero="https://ww2.kqed.org/app/uploads/sites/35/2021/04/RS48686_EPA_image_selects_fullsize-3-qut.jpg"]Looking ahead, Behl says Californians will likely face the expensive challenge of moving some homes and critical infrastructure, including parts of this train route, away from the coast. That’s called “planned retreat.”

Behl also says we have to stop thinking about sea level rise as something that’s happening so slowly we just don’t have to worry about it yet.

"Beach erosion, cliff retreat is not a gradual process, it's episodic," he said. "So when someone says that’s long in the future, far in the future, it may be, or it may not be."

This post includes reporting from KQED's Carlos Cabrera-Lomelí and NPR.

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