From: Allison Winter, ENN
Published October 12, 2012 09:51 AM

Increased Rainfall Causes Drop in Sea Level?

Current perception of climate change leads us to believe that sea levels are constantly rising due to thermal expansion and melting ice caps. However, from the beginning of 2010 until mid-2011, the average level of the world's oceans dropped by 0.2 inches.

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According to a recent study in the journal Geophysical Research Letters, this sea level decline was due to an increase in the amount of rainfall in Australia, northern South America and Southeast Asia.

This increase in rainfall led to La Niña conditions, a period marked by lower sea surface temperatures in the Eastern Central Pacific Ocean which consequently affects global weather patterns. While much of the globe's rainfall happens over the ocean and evaporated seawater returns from where it came from, during La Niña, much of that rain fell over land instead.

The temporary fall in sea levels challenged climatologists and other scientists to question whether or not sea level rise may be of concern. However, this study found that the drop in sea level was only temporary, and levels are already rising at the same average rate as before.

"It is important to recognize that this was a temporary effect," said John Church, an Australian climate scientist who wasn't involved in the study. "Much of this flood water has returned to the ocean and sea level has now returned to the trend line and globally the ocean volume is increasing at a rate of (0.1 inches) 3.1 millimeters per year," the same as before the decline.

Study author Carmen Boening, a researcher at NASA's Jet Propulsion Laboratory describes that we can measure global average sea levels by bouncing microwaves off of the ocean at many points around the globe. Satellites can also measure masses of water over land. The GRACE satellites, as they're known, follow an identical orbit around the Earth, and are tugged by minute changes in Earth's gravity fields, which are affected by large changes in mass like those caused by floods and droughts. To detect a drop of 0.2 inches in global sea levels may seem questionable, but by constantly measuring the distance between each other, the satellites can measure these small changes in mass and gravity and detect the location and abundance of water on Earth's surface.

Measuring ocean rise and fall will help researchers better recognize the temporary changes in sea level that are caused by land-bound rainfall.

For more information see Our Amazing Planet.

Ocean waves image via Shutterstock.

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