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."
The use of fossil fuels as the cause of it, however, is not. The Anasazi Indians left the American Southwest due to an onset of severe drought. It is safe to assume this was not caused by their use of fossil fuels, SUVs, factories, or power plants. I distinctly recall from the third grade, which was a very long time ago for me, we were taught that we'd just come out of an ice age. We were taught to expect it to get warmer, then after many years the cycle would reverse. I can only assume that these new scientists didn't listen to the teacher during the third grade.
Momma Nature is in charge here.
Past time. LOL!
It looks like changing your story to fit the fad is the way. A few years ago this same fellow, James Zachos, said that the earth's orbital "wobble" was the cause of past climate change. Since you can't blame that on capitalism, (well I guess some of Greenies could figure a way to do that) I guess it didn't attract any funding by the leftie foundations, so now he says it was really deep sea methane hydrate releases, changing into carbon dioxide that really did it.
BTW. No mention in the article that methane, molecule for molecule, has 21 times the greenhouse effect as CO2.
I keep returning to the same old question...WHO knows what the temperature of the Earth SHOULD be? No one seems to be able to answer this.
Good point. Let the science stand on it's own. But, keep the politicians from using data as a weapon to force unnecessary changes onto our society.
It's arrogant to think that the sliver of time that man has been 'impacting' the globe can overcome the Sun's, and thus the Earth's natural heating and cooling cycles. I see the hysteria of global warming more akin to religion than science. And we all know about mixing religion and politics.
I've taken a quick look at the sites. These comments capture it nicely:
"Our current 'best guess' is that the global mean changes in temperature (including the 1940-1970 cooling) are actually quite closely related to the forcings."
GUESS!??!?! I guess they are wrong.
"However, in no case has anyone managed to show that the recent warming can be matched without the increases in CO2 "
So, instead of proving that CO2 causes GW, opponents have to prove that it doesn't....BRILLIANT!!
And they can track this...how? None of their "models" is accurate worth a damn!
"Records of past climate change show that change starts slowly and then accelerates," he said. "The system crosses some kind of threshold."
Hmm...and these "past climate changes" were due to ancient SUV's? Or whatever the "Technological advancement du Jour" is?
This tells me that the Climate Change is something BEYOND our control...like maybe the Sun?!?!
But these pinheads wnat more gub'Mint GREEN (their FAVORITE color) to keep their false theology going!
These pinheads are the equivalent of the damn Druids, or techno-Pagans! Their "facts" do not resemble our Earth "facts".
Anyway, this release of methane seems speculative and not a good indicator for what could happen with our current release of CO2.
Spang on! Worth repeating!
Surely, you jest?
Exactly. And the danger is to allow one or the other 'political' party to be the one that wants to 'save the planet'; while the other 'evil' party supports 'big oil'...Pleeese.
I'm sure whatever your degree is in taught you that if you begin with a faulty premise, you will likely reach a faulty conclusion.
Your premise that scientists say that global warming is a fact is simply incorrect. Don't believe me? Go to The Oregon Petition and you will see that "scientists" are not only not in agreement over man made global warming, but in fact the vast majority of scientists who specialize in climate sciences consider the idea to be junk science.
Even a step further. Of those those "scientists" who signed on to the UN ICCP report, few had any expertise in climate studies, and a majority represent the biological or social sciences and on the topic of climate change, their opinion is no more valid than yours.
Just little tid bits that you won't hear from the MSM.
Not really. The artcle you posted is about studies of the Oligocene and Miocene, 20-25.5 million years ago. The article I posted that led off the thread is about the unique Paleocene-Eocene Thermal Maximum, which was 55 million years ago. Different times, different climate change mechanisms.
Cool?
Women, children, and minorities hurt worst!
Which sites?
The climate in the Northern Hemisphere has significantly warmed in the last 12,000 years, a mere geological eyeblink. People in Wisconsin would have to say that the warming has been a Very Good Thing.
Let me give it a shot, based again on the Voshtok Ice Core data, which reaches back 420 000 years.
There is not a "normal" temperature, in the sense that there is an average with a lot of small deviations and a few large ones. The temperature distribution is more like a gamma distribution (roughly speaking), for those of you statisticians out there.
The average (mean) temperature over the past 420 000 years is 4.5 degrees C (8.1 degrees F) colder than today. The median temperature (half the time it is warmer, half the time it is colder) is 5.1 degrees C (9.2 degrees F) colder than today. The mode (most likely temperature) is 7.6 degrees C (13.7 degrees F) colder than today. The minimum temperature was 9.4 degrees C (16.9 degrees F) colder than today, and the maximum was 3.2 degrees C (5.8 degrees F) warmer than today.
In other words, almost all of the last 420 000 years have been A LOT colder than it is today.
During that time, there have been five episodes of "Global Warming"; 420 000 years ago, 330 000 years ago, 240 000 years ago, 140 000 years ago, and the current one which began about 10 000 years ago. During each of these periods, the temperature increased (from the low point) somewhere in the neighborhood of 8 - 10 degrees C (14 - 18 degrees F)over a relatively short time (maybe a couple thousand years).
The release of a large amount of methane is the only plausible explanation for the large shift observed in stable carbon and oxygen isotope ratios at the PETM. There are references to publications by Katz (et al.) that might provide an explanation for the cause of the release. It seems clear that the ultimate cause of the methane release is unclear, but it is clear that the methane release followed by oxidation to CO2 is what actually happened.
Anyway, this release of methane seems speculative and not a good indicator for what could happen with our current release of CO2.
Both methane and CO2 are greenhouse gases that change the Earth's radiative balance if their atmospheric concentration changes. Provided that a methane release and oxidation to CO2 is what happened at the PETM (and that's what "fits the facts at hand"), then the PETM shows that greenhouse gas increases in the atmosphere can drive a warming trend.
What would be the mean global temperature during the interglacials only?
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