Ancient 'hyperthermals' a guide to anticipated climate changes

Mar 16, 2011
Sediment samples in the lab of Richard Norris obtained by the Ocean Drilling Program reveal the mark of "hyperthermals," warming events lasting thousands of years that changed the composition of the sediment and its color. The packaged sediment sample on the left contains sediment formed in the wake of a 55-million-year-old warming event and the sample on the right is sediment from a later era after global temperatures stabilized. Credit: Scripps Institution of Oceanography, UC San Diego

Bursts of intense global warming that have lasted tens of thousands of years have taken place more frequently throughout history than previously believe, according to evidence gathered by a team led by Scripps Institution of Oceanography, UC San Diego researchers.

Richard Norris, a professor of geology at Scripps who co-authored the report, said that releases of sequestered in the deep oceans were the most likely trigger of these ancient "hyperthermal" events. Most of the events raised average between 2° and 3° Celsius (3.6 and 5.4° F), an amount comparable to current conservative estimates of how much temperatures are expected to rise in coming decades as a consequence of anthropogenic global warming. Most hyperthermals lasted about 40,000 years before temperatures returned to normal.

The study appears in the March 17 issue of the journal Nature.

"These hyperthermals seem not to have been rare events," Norris said, "hence there are lots of ancient examples of on a scale broadly like the expected future warming. We can use these events to examine the impact of global change on marine ecosystems, climate and ocean circulation."

The hyperthermals took place roughly every 400,000 years during a warm period of Earth history that prevailed some 50 million years ago. The strongest of them coincided with an event known as the Paleocene-Eocene Thermal Maximum, the transition between two geologic epochs in which global temperatures rose between 4° and 7° C (7.2° and 12.6° F) and needed 200,000 years to return to historical norms. The events stopped taking place around 40 million years ago, when the planet entered a cooling phase. No warming events of the magnitude of these hyperthermals have been detected in the geological record since then.

Phil Sexton, a former student of Norris' now at the Open University in the United Kingdom, led the analysis of sediment cores collected off the South American coast. In the cores, evidence of the warm periods presented itself in bands of gray sediment layered within otherwise pale greenish mud. The gray sediment contained increased amounts of clay left after the calcareous shells of microscopic organisms were dissolved on the sea floor. These clay-rich intervals are consistent with ocean acidification episodes that would have been triggered by large-scale releases of carbon dioxide. Large influxes of carbon dioxide change the chemistry of seawater by producing greater amounts of carbonic acid in the oceans.

The authors concluded that a release of carbon dioxide from the deep oceans was a more likely cause of the hyperthermals than other triggering events that have been hypothesized. The regularity of the hyperthermals and relatively warm ocean temperatures of the period makes them less likely to have been caused by events such as large melt-offs of methane hydrates, terrestrial burning of peat or even proposed cometary impacts. The hyperthermals could have been set in motion by a build-up of carbon dioxide in the deep oceans caused by slowing or stopping of circulation in ocean basins that prevented carbon dioxide release.

Norris noted that the hyperthermals provide historical perspective on what Earth will experience as it continues to warm from widespread use of fossil fuels, which has increased carbon dioxide concentrations in the atmosphere nearly 50 percent since the beginning of the Industrial Revolution. Hyperthermals can help scientists produce a range of estimates for how long it will take for temperatures to fully revert to historical norms depending on how much warming human activities cause.

"In 100 to 300 years, we could produce a signal on Earth that takes tens of thousands of years to equilibrate, judging from the geologic record," he said.

The scientists hope to better understand how fast the conditions that set off hyperthermals developed. Norris said that 50 million year old sediments in the North Sea are finely layered enough for scientists to distinguish decade-to-decade or even year-to-year changes.

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eachus
1 / 5 (1) Mar 16, 2011
Sigh! More good research spoiled by the ingrown branches of research. I would never, ever, consider publishing a paper, independent of the formal review process, without review by a physicist and a regular mathematician. (My degrees are in economics, statistics, and operations research.) Lost a few papers that way, but saved myself blushes.

In this case, their theory for why the excursions took place would be shot down by an astronomer--or maybe a physicist. They might even get a better paper out of it. One of the things statisticians like to do is a BoE (back of envelope, for where many of them are done) sanity check. Back when Nemesis (a hypothetical star in a very long orbit around the sun) was in the news, I started to do a BoE computation of how often the sun comes close to other stars. It turned out to need much more than an envelope, some guesses have been published but the necessary research is still going on.
eachus
1 / 5 (1) Mar 16, 2011
In fact, current research seems to indicate that the sun is in a void in the local star population--or there are nearby stars that haven't been detected yet. The answer is probably a mix of the two. It seems logical that the brightest star in the night sky is also the closest. (Alpha Centuri A, Proxima Centuri a member of the same multiple star system is sometimes as much as a tenth of a lightyear closer.) Part of the reason for the Nemesis search was that if Earth orbited A Cen A, Proxima Centuri would be just another 5th magnitude star.

Back to this paper. In thirty thousand years or so, Ross 248 now 10.3 light years from Earth will be closer than Proxima Centauri, which will have also moved a light year closer. A star probably passes close enough to the sun to rip the proposed Nemesis free in less than a million years. How close to the sun do stars have to come to cause a few degrees of temperature rise? Don't know but it probably fits this data better.
eachus
1 / 5 (1) Mar 16, 2011
The hard part there is how close does a star have to get before it affects climate? The data on which stars were close to the sun when should start showing up in a year or four. In fact, I was just thinking about how to do that using the same interferometry methods used to detect the wobbles induced by exoplanets. (Any astronomers who have read this far, contact me if you want to work up a proposal. My role in life is usually to do the number crunching part in the middle.)
Lino235
1 / 5 (1) Mar 16, 2011
I think the authors are wrong. They talk about "relatively warm ocean temperatures". Naturally, as oceans increase in temperature, they can't hold as much CO2 as usual. The released CO2 doesn't explain the rise in ocean temperatures. I'm sure that if the atmosphere rises 2-3 degrees that this would affect surface water. Anyone who's ever been in a cave will attest, it could be 200 degrees above, but the cave's average temperature is that of the surrounding rocks. Hence, the overall temps of the ocean should not change with a relatively small change in air temperatures.

However, if the ocean temperature were to rise, added water vapor would be found in the air. Water vapor is 10 to 20 times more a greenhouse gas than CO2. Thus, the most likely cause of these "hyperthermals" is magmatic heating of the ocean basins--much like we're experiencing now. If you want to know why we're warming up, look to the ocean below: what do we find? Volcanoes, new ones under the Arctic& Antarctic!
toyo
1 / 5 (1) Mar 16, 2011
"The hyperthermals could have been set in motion by a build-up of carbon dioxide in the deep oceans caused by slowing or stopping of circulation in ocean basins that prevented carbon dioxide release."

Er...yes,...and?
Where's the evidence?
What we've got here is another 'doomsday' scenario set in front of us just so we don't forget the alarmists are still there...
RealScience
5 / 5 (2) Mar 16, 2011
eachus - A star of the same luminosity as the sun even a close as Neptune would only add 0.1% additional energy to the earth, so to directly affect the climate a star would have to pass closer than Neptune.
While passing even a light year from another star should not be rare (astronomically speaking), Neptune is 10,000 time closer and hence a pass that close would happen 1/100,000,000 times less often.
Lino235
not rated yet Mar 16, 2011
toyo:

Guess what? If earthquakes happen, undersea currents can be changed, just as a tsunami can be caused by parts of outer continental shelves falling down into the lower bowels of the ocean. If this happens often enough, and in just the right location, currents will be affected.

The CO2 is the result of changed ocean currents. Well, what causes that? Why don't the authors comment? Isn't this, then, even per their scenario, the cause of global warming?
Birger
not rated yet Mar 17, 2011
"...the mark of "hyperthermals," warming events lasting thousands of years that changed the composition of the sediment and its color"

-So can we at least agree that warming happened, and that it had sufficient effect on the ocean to drastically alter the deposition of sediments??

"hence there are lots of ancient examples of global warming on a scale broadly like the expected future warming. We can use these events to examine the impact of global change on marine ecosystems, climate and ocean circulation."

-Which is the point of the article!! The exact cause of this particular 55 million year old warming is *another* matter, which will of course be debated by geologists for years.