Friday, March 21, 2008

Earth's Oceans Aren't Warming

An article on NPR discusses research showing that there has been no warming in the world's oceans over the last four years. The article states in part:
Some 3,000 scientific robots that are plying the ocean have sent home a puzzling message. These diving instruments suggest that the oceans have not warmed up at all over the past four or five years. That could mean global warming has taken a breather. Or it could mean scientists aren't quite understanding what their robots are telling them.

This is puzzling in part because here on the surface of the Earth, the years since 2003 have been some of the hottest on record. But Josh Willis at NASA's Jet Propulsion Laboratory says the oceans are what really matter when it comes to global warming.

In fact, 80 percent to 90 percent of global warming involves heating up ocean waters. They hold much more heat than the atmosphere can. So Willis has been studying the ocean with a fleet of robotic instruments called the Argo system. The buoys can dive 3,000 feet down and measure ocean temperature. Since the system was fully deployed in 2003, it has recorded no warming of the global oceans.

I suppose it's possible that scientists are misinterpreting the data, a possibility that the article raises. But there are other possibilities as well for what NPR has dubbed a "mystery." The first, of course, being that the oceans aren't warming. It is also quite possible that they haven't been warming for some time and we are just learning of it. It is also possible that the warming suddenly abated in 2003.

As bad as the land-based surface temperature record is, the ocean temperature record is worse. Coverage is spotty at best, with a good portion of the record restricted to shipping lanes, leaving vast areas of the ocean wholly unsampled. Moreover, numerous methods have been employed over the years to measure the ocean's temperature, including dipping uninsulated wooden buckets into the ocean, bringing them on deck and inserting a thermometer (prior to WWII). Using the same method but with insulated buckets (after WWII) and measuring the temperature at the engine intake (also after WWII).

Temperature readings from uninsulated buckets have a cold bias due to evaporation. Engine intake temperatures contained a warm bias due to the engine room. Taken together, a warming trend is introduced over and above whatever is actually occurring in the oceans.

There have also been buoy measurements and infrared sea surface data taken by satellites. The buoy data is good, but again somewhat spotty. The satellite data give much better coverage but is affected by cloud cover and volcanic aerosol contamination, introducing a cooling bias. So all of the methods used to measure ocean temperature have had problems and biases that make it difficult to know exactly what has been going on with ocean temperatures over the last 100 years.

The ARGO array has only been deployed since 2003 and offers far better coverage and accuracy than previous measurements. It will be interesting to watch the data coming out of the ARGO array over the next couple of decades. Here's a flash demonstration of the ARGO system.

The article also states:
In recent years, heat has actually been flowing out of the ocean and into the air. This is a feature of the weather phenomenon known as El Nino. So it is indeed possible the air has warmed but the ocean has not. But it's also possible that something more mysterious is going on.
However, the air hasn't warmed either. Indeed, according to Richard Lindzen at MIT, there has been no warming since 1997 and no statistically significant warming since 1995.

This graphic from a post by Basil Copeland at Watts Up With That? further emphasizes the lack of warming over the last few years.

Here are some comments on the NPR story from Roger Pielke, Sr. at Climate Science.

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