Wednesday, September 2, 2015

Sea level rise has been artificially low in Hawai`i—but it’s going to catch up

Sea levels are rising globally at an increasing rate—three inches in the last 25 years or so--but we’re not seeing that much in Hawai`i.

So what’s up?

One answer to this mystery is that our islands are in a kind of temporary sweet spot. Satellite imagery shows that while most of the globe has seen dramatic rises in sea levels—as much as 3 inches in the past 25 years—Hawai`i has been flat to actually lower.

(Image: The red shows areas of dramatic sea level rise. Blue shows areas where it’s flat or down. Hawai`i appears in the blue zone. But how long will that last? Credit: NASA.)

At a human scale, this makes no sense. If you fill a bathtub, clearly it fills all around the tub.

But global scales are different. There are humps and valleys in the oceans across the scale of thousands of miles. Winds can push water up against a coast, creating a hump. Eddies can change sea levels regionally. Currents and storms and tides and even temperatures can all impact the height of the ocean.

“In a nutshell it's due to changes in winds and ocean circulation that counteract the global sea level signal regionally. That should shift as part of a long-term fluctuation but no projections on when that is likely to occur. This big El Nino may herald the start of a shift, but we have to see how that plays out,” said University of Hawai`i oceanographer Mark Merrifield.

Here is NASA’s recent report on accelerating sea levels and related issues. 

“Sea levels are rising rapidly—much more rapidly than they have any time in the last several thousand years,” said NASA’s Joshua Willis, at the Jet Propulsion Laboratory. 

And the rate of increase has been increasing as well, he said. It was about 1 millimeter annually in 1900, rose to 2 millimeters annually in the mid 1900s, and is now at 3 millimeters annually. That works out to more than an inch a decade.

I wrote to Willis to ask whether our islands can continue to dodge this bullet.

“In the long run sea level rise will affect Hawaii as well. Because it is in the central Pacific, the impacts of the long-term natural cycles may not be quite as large. Eventually, however, the global rates of rise will be felt in Hawaii also,” he said.

University of Hawai`i coastal geologist Charles “Chip” Fletcher agreed.

“The global oceans cannot keep rising without us experiencing the rise as well - we just may be able to avoid the worst aspects of the variability. On the other hand, models show that the tropics as a region will experience the upper end of global sea level change, so that makes us part of a more dangerous region.

“I have held for several years that Hawaii should plan for one meter of sea level rise by end of century and as far as I can see that is still a valid number,” he said.

© Jan TenBruggencate 2015


Alex said...

Just my personal take because global warming is taking on religious like tones. This chart they produced is bunk. So long they can claim 'regional' effects they can always justify why sea levels are dropping and just like in a bathtub it absolutely should be uniform. It's part of this ongoing farce where long cold winters and plainly obvious cold effects are somehow mystically translated into proof of global warming-including this chart where they can explain away why the sea is dropping. Its rather convenient that the image shows a rise in the deep ocean where it would be impossible to measure yet where people live its conveniently dropping, very convenient.
Truth is the sun powers the climate here, that big glowing red hot ball of fire. In the 90's it was warming due to an active sun but we are now entering a prolonged cooling stage, where unfunded government scientist say were entering a Maunder minimum.
Australlia is dealing with multiple cold records and we are already seeing the signs of a brutal winter rolling in for the northern hemisphere.
And why all this effort to keep up the global warming fraud? Money for the government and control, pure and simple.
They don't even account for underwater thermal activity(making things like El-Nino) where plumes of warm water seem to originate directly over volcanic hotspots(Credit: Michael Rivero), these are nearly impossible to measure and gauge.
I used to be a member of the G.W. religion.

Mauibrad said...

The variation more specifically is due to the difference between high and low pressure air above the sea level. Higher pressure air pushes down the sea a little. Lower pressure air allows the sea level to rise temporarily. Hawaii's sea level has not risen appreciably. 1 millimeter a year here or there has not been adding up to inches per decade. Hawaii's sea level is not rising. Is it truly rising elsewhere?

Jan T said...

Hawaii sea levels are in fact rising, have been rising for more than a century. There may have been a recent apparent pause in the rise, but the long-term trend is clear. If you're interested in more, here's a specific paper.

Alex said...

How does the long term sinking islands trend play into all this?