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Current Climate Models May Underestimate Future Warming

18 February 2006

Whoispot
A team of scientists analyzed three long sediment columns cored from the seafloor off Suriname to determine ancient ocean temperatures. The black box marks their research location.

Scientists from Woods Hole Oceanographic Institution (WHOI) have found evidence that tropical Atlantic Ocean temperatures may have once reached 107°F (42°C)—about 25°F (14°C) higher than ocean temperatures today and warmer than a hot tub.

The surprisingly high ocean temperatures, the warmest estimates to date for any place on Earth, occurred millions of year ago when carbon dioxide levels in Earth’s atmosphere were also high, but researchers say they may be an indication that greenhouse gases could heat the oceans in the future much more than currently anticipated. The study suggests that climate models underestimate future warming.

These temperatures are off the charts from what we’ve seen before.

—Karen Bice, paleoclimatologist at WHOI

Bice reported the findings at the annual meeting of the American Association for the Advancement of Science (AAAS) in St. Louis and is also lead author of a study to be published in an upcoming issue of the journal Paleoceanography, published by the American Geophysical Union.

Bice and a multi-institutional team of scientists studied three long columns of sediment cored from the seafloor in 2003 off Suriname, on the northeast coast of South America, by the drillship JOIDES Resolution, operated by the international Ocean Drilling Program.

The sediments contained an unusually rich and well-preserved accumulation of both carbon-rich organic matter and the fossilized shells of microscopic marine organisms that had settled and piled up on the seafloor over tens of millions of years.

The team analyzed the shells’ isotopic and trace element chemistry, which changes along with temperature changes in the surface waters where they lived. They determined that ocean temperatures in the region ranged between 91° and 107°F (33° and 42°C) between 84 million and 100 million years ago in an era when dinosaurs roamed the Earth. Temperatures range between 75° and 82°F (24° and 28°C) in the same region now. The approximate uncertainty in the paleotemperature estimates is +/-2°C.

Using organic matter from the sediments, the group also estimated atmospheric carbon dioxide concentrations during the same time span. They were 1,300 to 2,300 parts per million (ppm), compared with 380 ppm today.

The findings, if confirmed, create a dilemma for scientists seeking to forecast how Earth’s climate and environment will change in response to the rising amounts of heat-trapping carbon dioxide in the atmosphere, caused by deforestation and the burning of oil, coal, and other fossil fuels. When 1,300 to 2,300 ppm of carbon dioxide is factored into current computer models that simulate global climate, it does not produce such high ocean temperatures.

The climate models underestimate temperatures and the amount of warming that would accompany an increase in CO2 of more than 1,000 ppm above today’s level.

—Karen Bice

If the scientists’ interpretations of past ocean temperatures and carbon dioxide levels prove accurate, actual future warming from elevated atmospheric carbon dioxide concentrations may be much greater than predicted by the models.

One of the most important impacts this evidence suggests is the change to the Earth’s hydrologic cycle. Higher tropical temperatures will increase the intensity of hurricanes and winter storms. In addition, precipitation patterns will change, moving even more rain that now falls on the central US—an area known as the breadbasket of the US for its food production—to higher latitudes where the quality of the soil may not be as conducive to agriculture.

Policymakers use these models to predict likely climate change with increasing CO2 levels, and if the models are not right, society is not well informed or well served.

—Karen Bice

Alternatively, the models used to predict future climate may be missing a critical factor that amplifies heating, Bice said. During past warm periods, oceans and wetlands may have released much more methane gas to the atmosphere. Methane traps heat 10 times more effectively than carbon dioxide.

However, extraordinarily high concentrations of methane in the model still fail to produce the tropical Atlantic and Arctic Ocean temperatures inferred for 91 million years ago. This supports the idea that the model’s response to increased greenhouse gas concentrations underestimates the actual climate system’s response.

The research team included Bice and Kristina Dahl of WHOI, Philip A. Meyers of the University of Michigan, Daniel Birgel and Kai-Uwe Hinrichs of the University of Bremen, and Richard D. Norris of Scripps Institution of Oceanography. Bice’s work was supported by private funding from the Woods Hole Oceanographic Institution through the Ocean and Climate Change Institute and The Andrew W. Mellon Foundation Endowed Fund for Innovative Research. Funding for this research was also provided by the Joint Oceanographic Institutions U.S. Science Support Program and Deutsche Forschungsgemeinschaft through the DFG-Research Center Ocean Margins.

February 18, 2006 in Climate Change | Permalink | Comments (6) | TrackBack (0)

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Comments

Perhaps the warm ocean at that time and place was due to the fact that the "Atlantic" was just beginning to grow (Tectonics) and was quite narrow (also perhaps shallow).

You have to consider the complete environment at that time before jumping to statements about the current situation.

DoctorD

The climate warnings Fascists are obsessed with single factors, not for them a multiple variable equation. If we don't understand a variable in determining say, temperature now, or at some time in the past or future.... cloud formation, dust, albido effect, etc., etc., just ignore it.

There could have been other factors affecting ocean temperature, such as underwater volcanic activity at that time. Also, I heard a scientist saying the increase in CO2 has effects on plants that essentially keep them from extracting and evaporating as much water into the atmosphere, so there's a lot of factors yet to be fully integrated into these models.

It ain't the heat, it's the humidity.

You are 100% right if you say that the models may have underestimated the warming---or the models may have overestimated the warming. There is virtually 0% probability the models have estimated the warming exactly right. So you are 50% sure of being right.

Jeffrey, you can read the paper here

The researchers used a standard climate model (used commonly for estimating future temperatures under global warming) and found it did not predict the ocean heat they found. They initialized the model to the ocean characteristics of the Cretaceous period they were examining (I had to look at earlier papers they referenced to find more details).

They certainly did not ignore that the ocean was different in the Cretaceous period! Their point is that the model appears to be lacking in explaining the ocean temperatures they found given the initial conditions as best understood today. The implication that global warming may cause bigger increases in sea temperature than now expected is, however, a pretty indirect one, which Bice et al. certainly make clear in their paper. Of course this cautiousness doesn't necessarily come across well in the press release.

As a side note, while publications in peer-reviewed journals can be wrong, sometimes even spectacularly so, if an objection seems so obvious that we non-specialists can think of it immediately (like mentioning the ocean was shaped differently in the Cretaceous), then you can darn well believe they didn't get published without at least trying to address that objection.

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