Saturday, August 20, 2016

Sea level can drive temperature change--this is weird but it explains a lot.

Scientists have long tried to calculate sea level rise from estimates of temperature rise, but now researchers believe they can work the other way.

They think they can predict global temperatures from sea level change.

Based on their calculations, they figure air temperatures will be up half a degree, Fahrenheit, by the end of this year (2016) from 2014. Half a degree in two years; that’s a lot.

It indicates a higher-than usual rise in global atmospheric temperatures, which is bad news. But the research also helps explain a long period of low temperature rise a decade ago--a slowdown that critics of climate theory used to suggest global warming was a hoax. More on that at the end of this post.

The new paper. Pacific sea level rise patterns and global surface temperature variability, is published in the journal Geophysical Research Letters. It was written by Cheryl Peyser, Jianjun Yin and Julia Cole of the Department of Geosciences, University of Arizona, and Felix Landerer of NASA’s Jet Propulsion Laboratory in Pasadena. 

“We find a significant and robust correlation between the east-west contrast of dynamic sea level in the Pacific and global mean surface temperature variability on both interannual and decadal time scales,” they wrote, with typical scientific impenetrability.

The fact that sea level rise and atmospheric temperatures are linked is no surprise. Warmer weather causes polar ice and glaciers to melt, adding water to the seas. Rising atmospheric temperature transmits energy into the ocean, and warmer water expands. Both thing make sea levels go up.

But apparently it works the other way, too. Changes in ocean temperature patterns impact the atmosphere. When you think about it, that makes perfect sense. 

Science Daily summarizes the new paper here.

“We're using sea level in a different way, by using the pattern of sea level changes in the Pacific to look at global surface temperatures -- and this hasn't been done before," Peyser said.

They found that when sea levels in the western Pacific rise more than usual, worldwide surface temperature rise slows. And when sea levels drop in the Western Pacific but go up in the eastern Pacific, global air temperatures jump. Apparently that’s because a lot of ocean heat is lost back to the atmosphere.

Water appears to slosh back and forth across the Pacific east to west and west to east. Strong tradewinds pushing water westward is part of that sloshing phenomenon. (Sloshing back and forth may not be the best analogy, since some of the sea level rise isn’t from movement of water but from the expansion in volume of warmed water. But it helps visualize the activity.)

There was a period from about 1998 to 2012 when conservative pundits were touting a slowdown in global temperature rise as proof that climate change wasn’t happening. It now turns out that slowdown was associated with a dramatic slosh to the west, when sea levels in the western tropical Pacific were significantly higher than average global sea level change.

Now it’s sloshing back, and atmospheric temperatures are rising faster again. 

The research helps explain why atmospheric temperature rise slows and speeds up at various times.

“Our research shows that the internal variability of the global climate system can conceal anthropogenic global warming, and at other times the internal variability of the system can enhance anthropogenic warming,” said paper co-author Yin.

© Jan TenBruggencate 2016

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