February 22, 2005
Ocean Warming

Toiling away at the day job this afternoon, I had a spare moment to pen this whine about the ruckus over the past several days about Tim Barnett's new work on ocean temperatures and climate change.

There's been a lot of arguing in the comments over on David Appell's blog (come to think of it, there's always a lot of arguing in the comments on David's blog) about the Barnett stuff, and it occurs to me that in this case no one knows what they're talking about because Barnett's stuff hasn't been published yet. It's not so much that, as David notes, it hasn't been peer-reviewed yet. It's that there simply is no paper to look at yet, only a news release and a bunch of news stories.

I'm not saying it was bad for Barnett to do a talk and news briefing at the AAAS meeting. That's what happens at meetings. And I'm not saying it was bad for the press to cover this (though the usual excess from The Independent is a tad predictable). But for any sort of public discussion of work's implications to move forward, any understanding of where this fits in, we need a little more than we've got right now.

But in the meantime, if you're looking for a little red meat on the subject, there's a new paper in Geophysical Research Letters on ocean temperatures:

In terms of the causes of the increase in ocean heat content we believe that the long-term trend as seen in these records is due to the increase of greenhouse gases in the Earth’s atmosphere. In fact, estimates of the net radiative forcing of the Earth system suggest the possibility that we may be underestimating ocean warming. This is possible since we do not have complete data coverage for the world ocean. However, the large decrease in ocean heat content starting around 1980 suggests that internal variability of the Earth system significantly affects Earth’s heat balance on decadal time-scales.

Actually the real heavy lifting here in the "blame the greenhouse" argument is an earlier paper by Levitus et al. in Science in 2001. Barnett's also got a related paper from the same issue. Here's how Richard Kerr explained what they'd found:

Are humans indeed warming the world? If so, will future warming be big enough to matter· Confident answers depend in large part on the credibility of climate models. Greenhouse critics claim modelers can get any answer they like about warming simply by adjusting any of the numerous inputs whose values in the real world remain uncertain. Climate model running on the warm side· Crank in a bit more pollutant haze to shade the planet and cool it down, they say, and everything will look fine. Modelers have long argued that constraints such as the need to simulate current climate and the history of atmospheric warming keep their models more honest than that. Now a new, independent reality check from the ocean has strengthened their case.

On pages 267 and 270 of this issue, two groups of climate researchers report that two climate models have passed a new test: simulating the warming of the deep oceans during the past half- century. Their success "provides stronger evidence climate is changing," says climate modeler Simon Tett of the Hadley Centre for Climate Prediction and Research in Bracknell, United Kingdom, "and it's likely due to human influence." However, a conflict between the two studies underscores the difficulties in gauging how bad greenhouse warming could be.

Posted by John Fleck at February 22, 2005 07:56 PM