Climate

Study Reveals Scary New Facts About Sea Level Rise

CREDIT: AP Photo/Eranga Jayawardena

A Sri Lankan man throws his bait as he fishes in Colombo, Sri Lanka, Monday, July 1, 2013.

A new study from scientists at Harvard and Rutgers Universities has been sweeping the internet, and for good reason: it shows, quite alarmingly, that the planet’s seas have been rising much faster than we thought.

The research can be confusing on its face. At first glance, it shows that scientists have actually been overstating the rate of sea level rise for the first 90 years of the 20th century. Instead of rising about six inches over that period of time, the Harvard and Rutgers scientists discovered that the sea actually only rose by about five inches. That’s a big overstatement — a two quadrillion gallon overstatement, in fact — enough to fill three billion Olympic-size swimming pools, the New York Times reported.

But here’s the thing. If the sea wasn’t rising as steadily as we believed from 1900 to 1990, that means that it has been rising much more quickly than we thought from 1990 to the present day. In other words, we used to think the rate of acceleration of sea level rise in the last 25 years was only a little worse compared to the past — now that we know the rate used to be much slower, we know that it’s much worse.

This chart shows as estimate of global sea level side from four different analyses, shown in red, blue, purple, and black. Shaded regions show uncertainty.

This chart shows as estimate of global sea level side from four different analyses, shown in red, blue, purple, and black. Shaded regions show uncertainty.

CREDIT: Nature

“What this paper shows is that the sea-level acceleration over the past century has been greater than had been estimated by others,” lead writer Eric Morrow said in a statement. “It’s a larger problem than we initially thought.”

Specifically, previous research had stated the seas rose about two-thirds of an inch per decade between 1900 and 1990. But with the new study, that rate was recalculated to less than half an inch a decade. Both old and new research say that since 1990, the ocean has been rising at about 1.2 inches a decade, meaning the gap is much wider than previously thought.

Most scientists believe that the main driver of sea level rise is the thermal expansion of warming oceans and the melting of the world’s ice sheets and mountain glaciers, two phenomena driven by global warming. Antarctica, for example, is losing land ice at an accelerating rate. In December, scientists discovered that a West Antarctic ice sheet roughly the size of Texas is losing the amount of ice equivalent to Mount Everest every two years, representing a melt rate that has tripled over the last decade.

The common skeptic argument is that while Antarctica is losing land ice, it is actually gaining sea ice. While that’s true, sea ice melt does not affect sea level rise. It’s like an ice cube in a glass — if it melts, nothing happens. Up north in the Arctic, however, the loss of sea ice is just as important to look at, because when it melts, more sunlight is absorbed by the oceans. In Antarctica, sea ice melt is less of a problem for ocean warmth.

In addition, tropical glaciers in the Andes Mountains are melting, threatening freshwater supplies in South America. Some scientists have also predicted that the Greenland Ice Sheet — which covers about 80 percent of the massive country — is approaching a “tipping point” that could also have “huge implications” for global sea levels and ocean carbon dioxide absorption.

“We know the sea level is changing for a variety of reasons,” study co-author Carling Hay said. “There are ongoing effects due to the last ice age, heating and expansion of the ocean due to global warming, changes in ocean circulation, and present-day melting of land-ice, all of which result in unique patterns of sea-level change.”

All that may seem pretty grim, but there is a least one good thing to come out of the research — a new and hopefully more accurate method for measuring sea level rise. Before this study, scientists estimated global sea level by essentially dropping long yard sticks into different points of the ocean, and then averaging out the measurements to see if the ocean rose or fell.

For this study, Morrow and Hay attempted to use the data from how individual ice sheets contribute to global sea-level rise, and how ocean circulation is changing to inform their measurements. If the method proves to be better, it could serve to, as the New York Times put it, “increase scientists’ confidence that they understand precisely why the ocean is rising — and therefore shore up their ability to project future increases.”