02 Apr 2012

Data was collected in the 1870s by the Challenger vessel and compared to modern data from the Argo project, which uses 3500 free-drifting floats like the one shown here to show oceans have been warming for over 100 years.  (CREDIT:  Argo Project)
Data was collected in the 1870s by the Challenger vessel and compared to modern data from the Argo project, which uses 3500 free-drifting floats like the one shown here to show oceans have been warming for over 100 years. (CREDIT: Argo Project)

It had been previously suggested by climate models and other data that the world's oceans have been warming for 50 years.  Now new research seems to indicate that the oceans have been warming for more than 100 years.

Scientists have been trying to understand the Earth's sea-level rise, that has been partly due to the heating of the water and consequently its expansion as a result.  Now these new findings may help scientists better understand this process. 

HMS Challenger - Adds Another Piece to the Climate Puzzle

Dean Roemmich, an oceanographer at the University of California, San Diego says "Temperature is one of the most fundamental descriptors of the physical state of the ocean, beyond simply knowing that the oceans are warming, [the results] will help us answer a few climate questions."

Researchers used data from a ship called the HMS Challenger that sailed the world's oceans from 1872 to 1876 along a 69,000 nautical-mile track in the Atlantic, Indian and Pacific oceans.  The ship had a 200 person crew and took 300 ocean-temperature profiles at several depths with pressure-protected thermometers.

Today's Argo project compared to Challenger Data

Data from the Challenger temperatures was compared to the modern-day Argo project.  The Argo project uses 3,500 free-drifting devices to measure various things like temperature and salinity every 10 days.  The result of the comparison was a 1.1 degree Fahrenheit (0.59 Celsius) temperature increase at the surface of the ocean over the last 135 years.

Roemmich said that "That is a substantial amount of warming."  Ocean warming has been shown to be linked with glacial melting and mass coral bleaching.

Accounting for Challenger Errors

The research team did take into account sources of error in the Challenger readings.  The one issue was that the crew didn't directly measure the depth of the thermometers, instead they measured only the length of the line.  Since the ocean has currents, its hard to get a line completely vertical in the water, making the actual depth less than the line length.  Having a shallower line can lead to warmer water temperature readings because the water is warmer as the depth becomes less.

Roemmich and his team accounted for this error and came up with the average of a temperature increase of 0.59 degrees Farenheit (0.33 degrees Celsius) in the upper ocean down to 2,300 feet (700 meters).

This study was published on April 1st in the journal Nature Climate Change.

The Tech-Stew Take Home

Overall, the readings from this new study suggest that the global ocean temperature change is twice what has been observed in the last 50 years.  This suggests the oceans have been warming for much more than just a few decades.  Other research to help try to understand the imbalance of the Earth's energy budget, has shown that the Earth is absorbing more heat than it is radiating and much of that excess gets stored in the oceans.  This makes the ocean temperature a good candidate for a direct measure of the energy imbalance of the climate system.  While this research doesn't state that human generated pollution and CO2 are (or are not) directly responsible for global warming, it does give us yet another tool to study the history of climate change, so we may better understand the Earth's changing climate on a larger scale.

Source:  sciencedaily.com


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