Low Sierra snow seen as piece of alarming climate picture

This image from the NOAA/NASA Suomi NPP satellite on May 30, 2016, highlights the Arctic ice retreat off the northwest coast of Alaska. According to the National Snow and Ice Data Center, the average Arctic sea ice extent set a new record that month, becoming the lowest extent for May since satellite observations began. less This image from the NOAA/NASA Suomi NPP satellite on May 30, 2016, highlights the Arctic ice retreat off the northwest coast of Alaska. According to the National Snow and Ice Data Center, the average Arctic sea ... more Image 1 of / 3 Caption Close Low Sierra snow seen as piece of alarming climate picture 1 / 3 Back to Gallery

A fifth year of disappointing snow in the Sierra is part of a much larger predicament of record-low snow across the Northern Hemisphere, a setback that scientists identified Wednesday as another reminder of the alarming pace of human-caused global warming.

A panel of climate experts organized by SEARCH, or the Study of Environmental Arctic Change, met in Washington, D.C., to draw attention to the historic melt-off of snow and ice during the first six months of 2016 — and the resulting problems.

“We lost the snow earlier than anytime on record, and it wasn’t just in one part of the snow-covered universe,” said Dave Robinson, New Jersey state climatologist at Rutgers University, noting that as much as 30 percent of the land in the Northern Hemisphere is typically white. “This is the lowest spring snow extent on record.”

The lack of snow, a result of record-high temperatures across the planet, not only intensifies water shortages and the threat of wildfires in California and other parts of the country, but also amplifies global warming. Because snow helps reflect the sun’s hot rays, less of it means the Earth only heats up more, the scientists said.

Sea ice, which is also vanishing, is similarly losing its potency as a repellent. More of the sun’s warmth is being absorbed by the increasingly unfrozen ocean.

The extent of snow covering the Northern Hemisphere so far this year rivals only 2012 as the most paltry in recent decades, according to Robinson, and the National Snow and Ice Data Center in Boulder, Colo., shows the extent of sea ice in the Arctic at record lows during most of the first half of the year. Both are part of longer-term trends.

“It’s really unusual to have melt on the North Pole on New Year’s Day,” noted Walt Meier, a research scientist at NASA who spoke Wednesday. “The heat and the warm temperatures (have) stayed in the Arctic.”

In California, the warm temperatures, combined with historic drought, resulted in snowpack at 87 percent of average in the Sierra this year at the traditional peak time of April 1. This was followed by a swift melt-off of snow that is expected to produce only three-quarters of the water that normally flows from the mountains through July.

Brendan Kelly, executive director of SEARCH, acknowledged that declining levels of ice and snow are a tough problem to reverse but should serve as a call to action for the industrialized world. Reducing greenhouse gas emissions is essential, he and Wednesday’s panelists agreed.

“It’s sort of like having the diagnosis that you have a really aggressive cancer,” Kelly said. “You’re going to try really hard to be the success case that beats the odds.”

Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander