3/21/09, "Climate and the Carboniferous Period," geocraft.com, West Virginia Fossils, Monte Hieb
"West Virginia today is mostly an erosional plateau carved up into steep ridges and narrow valleys, but 300 million years ago, during the Carboniferous Period, it was part of a vast equatorial coastal swamp extending many hundreds of miles and barely rising above sea level. This steamy, tropical quagmire served as the nursery for Earth's first primitive forests, comprised of giant lycopods, ferns, and seed ferns.
North America was located along Earth's equator then, courtesy of the forces of continental drift. The hot and humid climate of the Middle Carboniferous Period was accompanied by an explosion of terrestrial plant life. However by the Late Carboniferous Period Earth's climate had become increasingly cooler and drier. By the beginning of the Permian Period average global temperatures declined by about 10° C.....
Our planet has mostly been much hotter and more humid than we know it to be today, and with far more carbon dioxide (the greenhouse gas) in the atmosphere than exists today. The notable exception is 300,000,000 years ago during the late Carboniferous Period, which resembles our own climate and atmosphere like no other.
With this in mind the road to understanding global warming and our present climate begins with an historical journey through a chapter in Earth's history, some 30 million years before dinosaurs appeared, known as the Carboniferous Period-- a time when terrestrial Earth was ruled by giant plants and insects, and glaciers waxed and waned over a huge southern continent...."Similarities with our present world"
"Average global temperatures in the Early Carboniferous Period were hot- approximately 20° C (68° F). However, cooling during the Middle Carboniferous reduced average global temperatures to about 12° C (54° F). As shown on the chart below, this is comparable to the average global temperature on Earth today!
- Late Carboniferous to Early Permian time (315 mya -- 270 mya) is the only time period in the last 600 million years when both atmospheric CO2 and temperatures were as low as they are today (Quaternary Period ).
- Temperature after C.R. Scotese http://www.scotese.com/climate.htm
- See an estimate of CO2 concentrations over the past 15,000 years, based on plant stomata.
Earth's atmosphere today contains about 380 ppm CO2 (0.038%). Compared to former geologic times, our present atmosphere, like the Late Carboniferous atmosphere, is CO2- impoverished! In the last 600 million years of Earth's history only the Carboniferous Period and our present age, the Quaternary Period,
- have witnessed CO2 levels less than 400 ppm.
The Carboniferous Period and the Ordovician Period were the only geological periods during the Paleozoic Era when global temperatures were as low as they are today. To the consternation of global warming proponents, the Late Ordovician Period was also an Ice Age while at the same time CO2 concentrations then were nearly 12 times higher than today-- 4400 ppm. According to greenhouse theory, Earth should have been exceedingly hot. Instead, global temperatures were no warmer than today. Clearly, other factors besides atmospheric carbon influence earth temperatures and global warming."
"Two special conditions of terrestrial landmass distribution, when they exist concurrently, appear as a sort of common denominator for the occurrence of very long-term simultaneous
- declines in both global temperature
- and atmospheric carbon dioxide (CO2):
1) the existence of a continuous continental landmass stretching from pole to pole, restricting free circulation of polar and tropical waters, and
2) the existence of a large (south) polar landmass capable of supporting thick glacial ice accumulations.
These special conditions existed during the Carboniferous Period,
- as they do today
- in our present Quaternary Period.
Climate change during the Carboniferous Period was dominated by the great Carboniferous Ice Age. As the Earth alternately cooled then warmed, great sheets of glacial ice thousands of feet thick accumulated, then melted, then reaccumulated in synchronous cycles.
Vast glaciers up to 8,000 feet thick existed at the south pole then, moving from higher elevations to lower, driven by gravity and their tremendous weight. These colossal slow-motion tidal waves of ice destroyed and pulverized everything in their path, scraping the landscape to bare bedrock-- altering mountains, valleys, and river courses. Ancient bedrock in Africa, Australia, India and South America show scratches and gouges from this glaciation.
Image credit: Dept. of Environmental and Geophysical Sciences,
Manchester Metropolitan University, Manchester UK
Earth's continents during the Carboniferous Period were arranged differently than they are today. South America, Africa, India, Australia, Antarctica, and a few minor pieces were joined together near the south pole to comprise the supercontinent known as Gondwanaland.
Gondwanaland was a formidable polar landmass. While ice caps and glaciers can't grow large over open oceans, they can and do attain great thickness over polar continents-- like Gondwanaland.
Although cycles of glaciation are believed to occur in response to solar input variations like the Milankovich Cycle and Precession of the Equinoxes, another important factor is the rearrangement of continental landmasses
- over geologic time by the
- processes of continental drift.
Throughout the Carboniferous Period, continental drift was rearranging most (but not all) of the Earth's landmasses into a single supercontinent stretching from the south polar region to the north polar region. Although the precise mechanisms involved are still a matter of debate this appears to cause regional humidity changes and redistribution of ocean currents which in turn promote ice accumulation and glacier formation over the earth's polar continents. These glacial ice caps grow larger during periods of reduced solar input, and because ice caps are very good solar reflectors this tended to accelerate and perpetuate cyclical relapses to global cooling.
Basically, Earth undergoes alternating periods of ice ages and warming whenever a continuous continental landmass extends from one polar region to the other while at the same time there exists a large polar continent capable of supporting thick ice accumulations. These conditions existed 300 million years ago during the Carboniferous Period as they do for the Earth today. However for most of geologic history the distribution of the continents across the globe did not satisfy this criteria. Continental drift continually rearranges the continents, moving at rates of only a few centimeters per year.
We are actually in an ice age climate today. However for the last 10,000 years or so we have enjoyed a warm but temporary interglacial vacation. We know from geological records like ocean sediments and ice cores from permanent glaciers that for at least the last 750,000 years interglacial periods happen at 100,000 year intervals, lasting about 15,000 to 20,000 years before returning to an icehouse climate. We are currently about 18,000 years into Earth's present interglacial cycle. These cycles have been occurring for at least the last 2-4 million years,
- although the Earth has been cooling gradually
- for the last 30 million years."...
""Stomatal data increasingly substantiate a much more dynamic Holocene CO2 evolution than suggested by ice core data L. Kouwenberg, et.al. 2005 (9), Laboratory of Palaeobotany and Palynology, Utrecht University, Netherlands"
"The Ice Core Record"
"Ice cores obtained by drilling into permanent ice caps in Antarctica and Greenland have been the most important way to determine past levels of carbon dioxide-- however, recent stomata studies show that the ice core record may be
- misleading in several important respects.
For example, when ice cores are crushed to extract the gases from trapped air bubbles to determine CO2 content, there is an assumption made that ice bubbles preserve an accurate record of the Earths CO2 history. However, the chemical composition of ice bubbles undergo changes that may distort this record.
Accumulating ice layers can take a century or more to become buried deep enough to be isolated from the atmosphere, which at the South Pole occurs at a depth of approximately 120 m. The resulting heat and pressure causes gas exchange between ice layers, which modifies the chemistry of ice air bubbles. At burial depths of between 900 and 1200 meters the pressure is so great that air bubbles in ice disappear and the gases recombine with liquids and ice crystals. Such processes tend to smooth away variability in the ice record and may also make CO2 levels appear lower than they really were, obscuring much of the resolution pertaining to CO2 variability (1-4).
ice core photo by: Vin Morgan
Palaeo Environment (Ice Cores) Field Work
"Liquid water is common in polar snow and ice, even at temperatures as low as -72C, (and) in cold water, CO2 is 70 times more soluble than nitrogen and 30 times more soluble than oxygen-- guaranteeing that the proportions of the various gases that remain in the trapped, ancient air will change. Moreover, under the extreme pressure that deep ice is subjected to -- 320 bars, or more than 300 times normal atmospheric pressure -- high levels of CO2 get squeezed out of ancient air."
expert in the atmospheric deposition of radioactive contaminants in glacial ice
Fig, 1, ref. 22
Fig. 2, ref. 22
Although the ice core record represents a very nice overall view of temperature and CO2 trends over many thousands of years, their reliability for resolving details over timescales of decades-- or in some cases several centuries-- is limited. Nonethess, these data are used as the principle evidence to show that CO2 levels in excess of 300 parts per million are unprecedented in all of human history and a cause for concern."...
"The presumption of CO2 stability"
"The youngest CO2 data, is not based on ice cores but on South Pole Air Flask samples-- which consistently show CO2 higher than 300 ppm. The point in time useful for considering what CO2 concentrations really were before humans started to burn fossil fuels is at the start of the Industrial Revolution-- about 1750 AD. A key assumption is that pre-Industrial CO2 concentrations were less than 280 ppm and that everything above that is caused by humans. This assumption, however, is not without problems,
"Basis for the Estimate of Pre-Industrial CO2"
"The Industrial Revolution started in Europe in the mid 1700's. The time before is referred to as "Pre-Industrial" time.
Because reliable CO2 air tests were not being performed until the 1800's, the presumed CO2 concentration in 1750 is 280 ppm, based largely on ice core data and early work by G.S. Callendar.
In the 1800's direct air CO2 measurements were performed by various researchers. Interestingly, the CO2 levels reported by them were mostly in excess of 300 ppm. For reasons that are unclear, only a few of these tests were considered valid by G.S. Calendar (1898-1964)-- the grandfather of the theory of man-made global warming. Today, the remaining data are largely ignored, although a few commentators like E. Beck and Z. Jaworoski suggest the data--some compiled by Nobel Prize laureates-- are generally valid and were inappropriately dismissed (4, 21) .
Callendar claimed humans had increased CO2 concentrations in the atmosphere by burning fossil fuels, and had thereby changed the atmosphere from 274 ppmv to 325 ppmv by 1935-- resulting in a 18.3 percent increase which had caused the global surface temperature to rise 0.33 deg. C (5). However, CO2 data available at the time showed concentrations ranged between 250 ppm and 550 ppm (Figure 4). Callendar has been accused of cherry-picking data from a sampling of 19th century averages, using 26 that supported his ideas, but rejecting 16 that were higher than his assumed low global average, and 2 that were lower (6).
Despite numerous 19th century air measurements showing +300 ppm CO2 levels, and despite the fact that many of the youngest ice cores showed higher than expected CO2 values and so were shifted forward 90-100 years from previously-established dates so that they would match the more elevated CO2 levels of 20th century air samples, the ice core record is today generally used to represent pre-1957 CO2 concentrations. The Intergovernmental Panel on Climate Change (IPCC) places the pre-industrial concentration of CO2 in the atmosphere at 280 ppm, based largely on the ice core record,
- although this has never been otherwise substantiated (7).
When systematic air readings began in 1957 AD, CO2 air values were about 315 ppm. Today, CO2 concentrations are about 384 ppm. Current estimates of the anthropogenic (man-made) component of atmospheric CO2 range between 4% (9) and 25% (the latter assumes Pre-Industrial levels were 280 ppm, and assumes everything over that today is man-made). The problem with the 280 ppm baseline figure is that increasing evidence suggests this figure may be too low.
CO2 levels exceeding 300 ppm, we are told, are unnatural and unprecedented, but available 19th century CO2 air data and studies of plant stomata suggest another side to the story.
"The recent rate of change is dramatic and unprecedented; increases in CO2 never exceeded 30 ppm in 1 kyr – yet now CO2 has risen by 30 ppm in just the last 17 years. "
Working Group I: The Physical Science Basis of Climate Change
4th Assessment Report, 2007
"At no point in the last 650,000 years before the pre-industrial era did the CO2 concentrations go above 300 part per million..."
by, former Vice President Al Gore
(now, chairman and co-founder of Generation Investment Management--
a London-based business that sells carbon credits)
"The majority of the stomatal frequency-based estimates of CO2 for the Holocene do not support the widely accepted concept of comparably stable CO2 concentrations throughout the past 11,500 years."
F. Wagner, et.al., 2004