New measurements from a pair of satellites nicknamed Tom and Jerry have provided a first time look into the planet’s average ocean level increase.
Measuring gravity everywhere around the globe, Tom and Jerry have provided researchers with data showing that the annual world average sea level rise is about 1 millimetre.
Naturally, this is not a general 1 millimetre spread across the entire planet. In some areas such as the Pacific Ocean near the equator and the waters offshore from India and north of the Amazon river, the increase in sea level is larger; whereas in some areas such as off the east coast of the United States the sea levels have actually dropped.
Scientists, in an effort to get an accurate measurement of sea levels across the planet, have started measuring the gravity in any one place, determining how much mass lies in that region and whether it is the result of mountains, glaciers, mineral deposits or oceans.
When the gravity changes, that refers to a loss of or increase in mass, which in the case of the oceans correlates to a rise or drop in ocean level.
Tom and Jerry are a pair of satellites that are part of the Gravity Recovery and Climate Experiment, thankfully known as GRACE. According to the press release;
The two craft … send constant signals to each other to determine their relative spacing to about 10 microns — one-tenth the width of a human hair — over a distance of 130 miles. If the first craft flies above a slightly more weighty area of the Earths’ surface — like a mountain range — it will be tugged a bit out of place, an effect picked up by a change in the relative spacing of the craft.
Riccardo Riva, one of the authors of the report looking at years 2003-09, said that the average rise in sea levels is mostly due to meltwater entering the oceans, but that an additional rise may come from the increase in ocean temperature: as the oceans warm, they will expand, thus encroaching upon our land.
“GRACE is definitely the ‘real deal’ when it comes from measuring climate change from space,” said Joshua Willis, an ocean expert at the Jet Propulsion Laboratory in Pasadena, Calif. “This work by Dr. Riva and company reminds us that the world’s oceans don’t behave like a giant bathtub. As the ice melts and the water finds its way back to the ocean, the resulting sea level rise won’t be the same all over the world.”
“These effects are still small in today’s rising ocean, but as we look out over the next century, the patterns of sea level change due to melting ice will be magnified many times over as the ice sheets thin and melt,” Willis said.