Posted on 02/17/2006 8:54:21 AM PST by cogitator
Human activities are releasing greenhouse gases more than 30 times faster than the rate of emissions that triggered a period of extreme global warming in the Earth's past, according to an expert on ancient climates.
"The emissions that caused this past episode of global warming probably lasted 10,000 years. By burning fossil fuels, we are likely to emit the same amount over the next three centuries," said James Zachos, professor of Earth sciences at the University of California, Santa Cruz.
Zachos will present his findings this week at the annual meeting of the American Association for the Advancement of Science (AAAS) in St. Louis. He is a leading expert on the episode of global warming known as the Paleocene-Eocene Thermal Maximum (PETM), when global temperatures shot up by 5 degrees Celsius (9 degrees Fahrenheit). This abrupt shift in the Earth's climate took place 55 million years ago at the end of the Paleocene epoch as the result of a massive release of carbon into the atmosphere in the form of two greenhouse gases: methane and carbon dioxide.
Previous estimates put the amount of released carbon at 2 trillion tons, but Zachos showed that more than twice that amount--about 4.5 trillion tons--entered the atmosphere over a period of 10,000 years (Science, June 10, 2005). If present trends continue, this is the same amount of carbon that industries and automobiles will emit during the next 300 years, Zachos said.
Once the carbon is released into the atmosphere, it takes a long time for natural mechanisms, such as ocean absorption and rock weathering, to remove excess carbon from the air and store it in the soil and marine sediments. Weathering of land rocks removes carbon dioxide permanently from the air, but is a slow process requiring tens of thousands of years. The ocean absorbs carbon dioxide much more rapidly, but only to a point. The gas first dissolves in the thin surface layer of the ocean, but this surface layer quickly becomes saturated and its ability to absorb more carbon dioxide declines.
Only mixing with the deeper layers can help restore the ability of the surface water to absorb additional carbon dioxide from the atmosphere. But the natural processes that mix and circulate water between the ocean surface and deeper ocean layers work very slowly. A complete "mixing cycle" takes about 500 to 1,000 years, Zachos said.
The greenhouse emissions that triggered the PETM initially exceeded the ocean's absorption capacity, allowing carbon to accumulate in the atmosphere. Unfortunately, humans appear to be adding carbon dioxide to the air at a much faster rate: about the same amount of carbon (4.5 trillion tons), but within a few centuries instead of 10,000 years. What was emitted 55 million years ago over a period of about 20 ocean mixing cycles is now being emitted over a fraction of a cycle.
"The rate at which the ocean is absorbing carbon will soon decrease," Zachos said.
Compounding this concern is the possibility that higher temperatures could retard ocean mixing, further reducing the ocean's capacity to absorb carbon dioxide. This could have the kind of "positive feedback" effect that climate researchers worry about: reduced absorption, leaving more carbon dioxide in the air, causing more warming.
Higher ocean temperatures could also slowly release massive quantities of methane that now lie frozen in marine deposits. A greenhouse gas 20 times more potent than carbon dioxide, methane in the atmosphere would accelerate global warming even further.
Such positive feedback or "threshold" effects probably drove global warming during the PETM and a few other ancient climate extremes, Zachos said, and they could happen again. It is possible that we already are in the early stages of a similar climate shift, he said.
"Records of past climate change show that change starts slowly and then accelerates," he said. "The system crosses some kind of threshold."
Clues to what happened during the PETM lie buried deep inside the sediment at the bottom of the sea, which Zachos and his colleagues have probed during several cruises of the Ocean Drilling Program (ODP). Composed mainly of clay and the carbonate shells of microplankton, this sediment accumulates slowly, but steadily--up to 2 centimeters every millennium--and faithfully records changes in ocean chemistry. The layer of sediment deposited during the PETM, now buried hundreds of meters below the seafloor, tells a clear and compelling story of sudden change and slow recovery, he said.
During the PETM, unknown factors released vast quantities of methane that had been lying frozen in sediment deposits on the ocean floor. After release, most of the methane reacted with dissolved oxygen to form carbon dioxide, which made the seawater more acidic. Acidic seawater corrodes the carbonate shells of microplankton, dissolving them before they can reach the ocean floor and reducing the carbonate content of marine sediment.
Zachos led an international team of scientists that analyzed sediment cores recovered from several locations during an ODP cruise in the southeastern Atlantic. Collected at depths ranging from 2.5 to 4.8 kilometers (1.6 to 3.0 miles), each sediment core bore a telltale PETM imprint: a 10- to 30-centimeter layer of dark red carbonate-free clay sandwiched between bright white carbonate-rich layers.
by relating the thickness of the clay layer to the rate of accumulation of marine sediment, Zachos estimated that it took 100,000 years after the PETM for carbon dioxide levels in the air and water to return to normal. This finding is consistent with what geochemists have predicted using models of how the global carbon cycle will respond to carbon dioxide emissions from the burning of fossil fuels.
"We set out to test the hypotheses put forward by a small group of geochemists who model the global carbon cycle, and our findings support their predictions," Zachos said. "It will take tens of thousands of years before atmospheric carbon dioxide comes down to preindustrial levels. Even after humans stop burning fossil fuels, the effects will be long lasting."
I get to be first?
WE ARE DOOMED!/sarcasm alert
In other news, studies of climate studies suggest climate studies on fast track to nowhere.
I wish it would hurry up. I am old and cold.
"Human activities are releasing greenhouse gases more than 30 times faster than the rate of emissions that triggered a period of extreme global warming in the Earth's past, according to an expert on ancient climates."
Let's just kill all the humans and solve the problem....ooops, sorry the Iranian president already is pushing that idea.
It is a wonderful scam. I highly suggest reading "State of Fear" by Crichton...awesome book.
My kids need a new frontier to explore. Lets get the temp up about 10 degrees so we can move this popsicle stand to Alaska.
Dear Congress: Do not sell Alaska back to the Ruskies. We are going to need it!
...James Zachos, professor of Earth sciences at the University of California, Santa Cruz...
The Santa Cruz part should tell you all you need to know about the scientific objectivity of this latest 'report'.
I suggest reading these two articles to get a sense of Crichton's accuracy -- even if the book was enjoyable.
Michael Crichton's State of Confusion
Michael Crichton’s State of Confusion II: Return of the Science
I think comparing human activity today against human activity 55 million years ago may not be scientifically accurate.
"Previous estimates put the amount of released carbon at 2 trillion tons, but Zachos showed that more than twice that amount--about 4.5 trillion tons.."
So they were off by more than a factor of 2. But I'm sure that ~now~ they got everything right... /sarc
"James Zachos, professor of Earth sciences at the University of California, Santa Cruz."
Enough said.... by professor at socialist university of Santa Cruz. He undoubtedly came to these scholarly conclusions in between tokes on his bong.
Buncha crap.
"Once the carbon is released into the atmosphere, it takes a long time for natural mechanisms, such as ocean absorption and rock weathering, to remove excess carbon from the air and store it in the soil and marine sediments."
Nonsense. Absolute, complete, utter, incalculably incorrect nonsense.
Carbon dioxide is continuously removed from the atmosphere by plants, which use it to form sugars to store energy from sunlight. More carbon dioxide in the atmosphere means more plant biomass, which consumes more carbon dioxide, which makes less carbon dioxide in the atmosphere.
Be careful what you read. Most journalists never made it past their fourth grade science classes.
Sea level rising is the most catastrophic thing, particularly if it occurs quickly, like in a year or two.
Which makes it even more senseless to rebuild New Orleans now, along with the billions of dollars Louisiana is costing the taxpayers otherwise.
Relocate if you're on a coastline, to at least five feet higher than where you are now...not like anyone has not been warned.
I think a barge is a far better investment on any coastal area, if not a boat altogether, for those of us who love the ocean and coastal living. Things are going to change and soon, as to sea level and New Orleans is hardly an isolated catastrophe, I am thinking.
The main analogous factor is that the PETM is the only period in the Cenozoic where there was clearly a rapid rise in atmospheric greenhouse gases absent any other climate forcing agents. The resulting effect on global temperatures is pretty obvious.
But this fails to answer the critical question - was the release the cause of the warming? Or an effect of the warming?
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