7: Consequences of the Thermal Maximum

The abrupt 'Big Burp' of CO2 resulting from the methane release produced a dramatic warming of earth that lasted for around 100,000 years before the additional CO2 was gradually re-absorbed into natural sinks and temperatures fell back to their original levels.

Over 10,000 years temperatures rose by as much as 8°C (14°F). The rising temperatures caused precipitation patterns to change. Because there were no sharp warm and cold fronts meeting to trigger rainfall, large amounts of water got transferred from the tropics and sub-tropics to the Arctic, dramatically increasing its humidity and precipitation, but leaving the middle latitudes a lot dryer.

The atmosphere became more humid but the higher latitudes also became wetter. Sediment layers in the Pyrenees show the debris of massive storms and floods whilst evidence from Austria and America suggest the climate regime became warmer, moister and monsoonal. Rainfall in Utah jumped from 40 cm (16 inches) per year to 66 cm (26 inches) per year.

Mangroves and rain forests spread as far north as England and Belgium and as far south as Tasmania and New Zealand; turtles, hippo’s, alligators and palm trees graced Ellesmere Island in the Canadian Arctic.

There is also evidence for seasonal aridity on the eastern margins of the Atlantic.

The Arctic was very warm and moist; sea temperatures rose from 18°C (64°F) to over 23°C (73°F) but the Arctic sea became stagnant.

The northern latitudes appear to have warmed at a greater rate than the equatorial regions. As the seas warmed further still the ocean currents reversed direction. (The formation and subsidence of a great undersea ridge between Greenland and the Faeroes also interfered with currents.)

On land tropical and sub-tropical forests spread further north, evidence has been found of palm trees in Alaska whilst from Ellesmere Island, inside the Arctic Circle, fossils have been found of a Pantodont, a plant-eating hippopotamus-like creature weighing about 400 kilograms. Map from: Laurasia, America And The NE Atlantic In The Early Paleocene. MantlePlumes dot org.

This was a period of rapid extinctions and adaptations as species struggled to adapt to changing environments while facing fierce competition from migrating species (It’s estimated that of speciation and extinction rates quadrupled.).

During the Paleocene the larger landmass, Laurasia, had been able to support a larger diversity of animals, particularly in northern Asia, than North America had been able to.

The fossil record shows that as the temperature rose, changes to the climate zones meant that flora and fauna were able to spread from Laurasia across into North America; this they did with vigour, driving many North American species into extinction in the process.

Wyoming’s Bighorn and Green River Basins are fossil rich areas and been extensively excavated. (Isotope analysis of plant and organic matter e.g. charcoal, wood, leaves and pollen in the clay clearly shows the negative carbon isotopic excursion C-13 / C-12 that marks the PETM.)

Fossilized plant remains show that the Bighorn Basin of 55 mya was a hot, humid subtropical forest containing trees related to those found today in Panama and large Sequoias, related to those now found in California.

Primates (e.g. Teilhardina brandti, Teilhardina belgica) makes its first appearance, having previously been found only in Laurasia as does the Creodont, a now-extinct carnivorous, hoofed animal that appears earlier in the fossil record in Mongolia.

Hyaenodontid creodonts, a group of dog-like predators that were present in Asia before the PTEM were also found; fossils from America were matched with similar specimens from the Paleocene found in the Hengyang Basin in southern China.

Odd-toed ungulates such as horses and rhinoceroses and even-toed ungulates like sheep and antelope also migrated from Laurasia to America. After the onset of the PETM half of all fossils found in N America for this time are of migrant species. It’s estimated these animals’ migrations took between 15 to 25 thousand years to accomplish. Fossil leaves and pollen show that tropical plants also greatly extended their range.

The ancestors of many modern mammals such as hoofed animals (pygmy horses and elk), tapirs, rodents, bats, owls, elephants and early whales also appeared during or shortly after the PETM, heralding a new period of life, the Eocene.

Note: A mass extinction event 12,500 years ago eliminated from the Americas many mammal species including mammoths, sabre tooth tigers, camels, horses, donkeys and oxen. North American Mass Extinction Event 12,500 Years Ago. General Info.

Several animal species took drastic adaptive measures by becoming increasingly diminutive; fossil evidence for horses the size of a Siamese cat, Hyracotherium sandrae, have been found for example. Natural selection favoured smallness in size for survival in warm, densely forested habitats.

Another possible reason why many species may have shrunk in size is that though increased levels of CO2 fertilises plant growth, this does not affect all plants equally. Trees benefit the most, shrubs and grass the least.

Plants grown experimentally today in CO2 enriched environments [Ainsworth et al. 2005.] show that many plants have reduced nutritional value (they produce less protein in their leaves, so their nutritional value to animals drops), have tougher leaves and higher levels of defensive chemicals (e.g. tannins & phenolics) making them a poorer food source.

In the seas live immense numbers of microscopic creatures – e.g. foraminifera – with shells largely made from calcimate (CaCO3) secreted by the organism. When these organisms die their calcareous shells fall to the bottom of the ocean.

Examination of the fossilised remains of these and other creatures from the sediment layers below, in and above the acidic layer of 55 mya shows that the acidic layer marked a period of mass extinction for Phytoplankton, with dire consequences throughout the food chain and many deep sea creatures. Much marine life became extinct in the anoxic, acidic seas, particularly in the deep ocean.

The most disruptive periods in the history of life on earth have been those where the changes were very abrupt, with too short a time-scale for species to adapt. e.g. the extinction event at the end of the Cretaceous that led to the extinction of the dinosaurs.

The Paleocene was also an unusually abrupt disruption, this time lasting 140,000 years. This is considered a very short period in terms of geological and evolutionary time-scales.

Although earth’s climate has changed many times in the past, the key factor for life on earth has been the speed or rate of change. When we talk of species migration, to get an idea of the time-scales involved think how long it takes an oak forest to extend its range (migrate).

If climate change means acorns dropped at the edge of the forest can grow more easily, then they survive to grow into trees; in turn they drop an acorn a little further out from the forest, that grows into a tree and drops another acorn still further out. Animals and birds can transport acorns further away, but measured in terms of human lifetimes it is a very, very slow process.

As an example, during the PETM, Rhus Nigricans, a fossil relative of the sumac tree spread north from the Gulf of Mexico into Wyoming, a distance some 1,000 miles, in 10,000 years or less. At the end of the PETM they disappeared from Wyoming. (Source: Smithsonian Institute.)

The PETM was an aberration in earth’s history, but an instructive one in demonstrating the role that CO2 plays in determining earth’s global temperature, as the rise in CO2 was accompanied by a sychronous rise in temperature.

The earth’s global temperature only fell back to its previous levels, over a period of tens of thousands of years, as the CO2 was re-absorbed into earth’s natural sinks and atmospheric CO2 concentrations subsided.

The PETM is CO2’s smoking gun, evidence that rising atmospheric CO2 concentrations directly influence earth’s temperature.

Note: Other hypotheses have been put forward to account for the PTEM: emission of CO2 from peat fires, a large comet strike on an area of carbonate rock, a large shallow sea drying and seabed material decaying etc. but all have relied on rising CO2 concentrations to explain the steep rise in temperature. Past comet strikes have been associated with periods of climatic cooling, as have past surface volcanic activity. Estimates of hydrocarbons contained in organic materials (peat or bacteria) seem too small to account for the amounts of CO2 in the record.

Any alternative hypothesis that didn’t rely on rising amounts of CO2 to account for the rise in temperature would also have to account for the rise and fall of the temperature matching so closely the rise and fall of the CO2 concentrations. Then there is the no small matter of providing evidence and building a case.



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CO2: Then & Now


Where possible I have tried to connect links to either full copies or abstracts of the papers below. If links are broken try copying and pasting the title into Google or Google Scholar; that should help you locate an abstract at least. Also please let me know at: climatehistory@googlemail.com

The Oldest North American Primate And Mammalian Biogeography During The Paleocene–Eocene Thermal Maximum.
K. Beard. PNAS. 2008.

Rapid Warming Caused Vegetation Changes. Terradaily  2008.

Ancient Global Warming Gave Bugs the Munchies. National Geographic. 2008.

Ancient Leaves Point To Climate Change Effect On Insects. Science Centric. 2008.

Oldest Primate Fossil in North America Discovered. National Geographic. 2008.

Abrupt Increase In Seasonal Extreme Precipitation At The Paleocene-Eocene Boundary. B. Schmitz et al. Geology. 2007.

Subtropical Arctic Ocean Temperatures During The Palaeocene/Eocene Thermal Maximum. A. Sluijs et al. Letter to Nature: 2006. PDF.

Arctic Hydrology During Global Warming At The Palaeocene/Eocene Thermal Maximum. M. Pagani et al. Nature. 2006. PDF.

Related: Ancient Arctic Water Cycles. Science Daily. 2006.

Extremely High Late Paleocene - Early Eocene Sea Surface Temperatures On The North Pole. A. Slujis et al. American Geophysical Union, Fall Meeting 2005. Abstract.

Related article: Yale University News Release. 2007.

Related article: E-Biology News. Article. 2006.

Related article: North Poles Ancient Past Holds Clues About Future Global Warming. Physorg dot com. 2006.

Related article: Historic Polar Cruise Yields New Clues About Global Warming. Rice University. 2006.

Related article: Arctic's Tropical Past Uncovered. BBC. 2006.

Related article: From Hot To Cold In The Arctic. Geotimes. 2006.

Related: Study Breaks Ice On Ancient Arctic Thaw. Science Daily. 2006.

The Palaeocene-Eocene Thermal Maximum Super Greenhouse. A. Sluijs et al. 2006. Paper.

Abrupt Reversal In Ocean Overturning During The Palaeocene/Eocene Warm Period. F. Nunes et al. Nature. 2006. Abstract.

Related article: Global Warming Can Trigger Extreme Ocean Changes. Scripps Institute of Oceanography

Related article: Global Warming Can Trigger Extreme Ocean, Climate Changes. Science Daily.

Rapid Asia–Europe–North America Geographic Dispersal Of Earliest Eocene Primate During The Paleocene–Eocene Thermal Maximum. T. Smith et al. Proceedings of the National Academy of Sciences. 2006. PDF.

The First Primates Web page

Related: Summary of above: "Rapid Asia–Europe–North America Dispersal Of Earliest Eocene Primate Teilhardina... T. Smith et al. Proceeding of the National Acadademy of Science. 2006.

Related: Mammalian Dispersal At The Paleocene/Eocene Boundary. G. Bowen et al. Science. 2002. Paper. PDF.

Related article: Global Warming 55 Million Years Ago Caused Migration To North America. Article. 2003. Post Gazette.

Related article: Global Warming 55 Million Years Ago Caused Migration To North America. Article. 2003. UCSC.

Related article: Ancient Global Warming Spurred Primates Into North America. National Geographic. 2006.

Bighorn Basin, Wyoming. Paleocene-Eocene Mammals And The Paleocene-Eocene Thermal Maximum. University of Michigan web site on research at the Bighorn Basin, Wyoming.

Catastrophe and Opportunity in an Ancient Hot-House Climate. Geotimes dot org. 2006.

Mammalian Community Response To The Latest Paleocene Thermal Maximum: An Isotaphonomic Study In The Northern Bighorn Basin, Wyoming. (Animals became smaller.) W. Clyde. Geology. 1998. Paper. PDF.

Mammalian Responses To Climate Change At The Paleocene-Eocene Boundary: Polecat Bench Record In The Northern Bighorn Basin, Wyoming. P. Gingerich. Geological Society of America Special Paper 369. 2003.

Related article: Wyoming’s Wildlife Changes At Time Of PETM. New Hampshire University magazine.

Related article: Methane And Mini-horses: Fossils Reveal Effects Of Global Warming 55m Yr ago. 2003. Science Daily.

Related article: Wyoming's Garden of Eden. Natural History. 2001. Overview on Bighorn Basin PETM paleontology by K. Rose.

Transient Floral Change and Rapid Global Warming at the Paleocene-Eocene Boundary. S. Wing et al. Science. 2005. Abstract.

Related article: Rapid Warming Caused Vegetation Changes. Science Daily. 2005.

Related article: Rapid Warming Caused Vegetation Changes. US National Science Foundation. 2005.

Related article: Rapid Warming Caused Vegetation Changes. Penn State University. 2005.

Related article: Changes at time of PTEM. Science Notes Article. 2007.

Related: Hot Times In The Bighorn Basin. Natural History. 2001. Overview on how palaeontologists recover evidence by S. Wing.

Pedogenic Carbonate Proxies For Amount And Seasonality Of Precipitation In Paleosols. G. Retallack Geology. 2005.

Early Eocene Climatic, Volcanic, And Biotic Events In The Northwestern Tethyan Untersberg Section, Austria. H. Egger et al. Palaeogeography, Palaeoclimatology, Palaeoecology. 2004.

The Water Cycle Of The PETM. G. Bowen. Geological Society of America. 2005. Abstract.

What Have We Learnt From Fifteen Years Of Free Air CO2 Enrichment (FACE)? A Meta-Analytic Review Of The Responses Of Photosynthesis, Canopy Properties And Plant Production Of To Rising CO2. A. Ainsworth & S. Long. New Phytologist. 2005. No online abstract available.

Related: Global Warming May Lower Grassland Quality. Science Daily. 2006.

Quantifying Limits On Extinction And Diversification Rates During Rapid Climate Change Events: Calcareous Nannoplankton At The Paleocene-Eocene Thermal Maximum. S. Gibbs. Geological Society of America. 2005. Abstract.

Enhanced Terrestrial Weathering/Runoff And Surface Ocean Carbonate Production During The Recovery Stages Of The Paleocene-Eocene Thermal Maximum. J. Zachos et al. Paleoceanography. 2005. Abstract.

Enhanced Continental Weathering And Pedogenesis Across The Paleocene/Eocene Boundary In The U.S. Western Interior (North Dakota). E. Clechenko. Geological Society of America. 2005. Abstract.

A Humid Climate State During the Palocene/Eocene Thermal Maximum. G. Bowen et al. Letter to Nature. 2004. PDF.

Air Humidity And Temperature During The Latest Paleocene–Earliest Eocene In France From Recent And Fossil Fresh-Water And Marine Gastropod Isotopes. B. Schmitz et al. Geology. 2002. Abstract.

Sea-Level, Humidity, And Land-Erosion Records Across The Initial Eocene Thermal Maximum From A Continental-Marine Transect In Northern Spain. B. Schmitz et al. Geology. 2003. Abstract.

Impact of Paleocene/Eocene Greenhouse Warming on North American Paratropical Forests. G. Harrington. Palios: Society for Sedimentary Geology. 2001. Abstract.

Floral Response To Rapid Warming At The Paleocene/Eocene Boundary And Implications For Concurrent Faunal Change. S. Wing. Paleobiology. 2001. Abstract.

Refined Isotope Stratigraphy Across The Continental Paleocene-Eocene Boundary On Polecat Bench In The Northern Bighorn Basin. G. Bowen et al. Papers on Paleontology. No. 33. 2001.

Mammalian Community Response To The Latest Paleocene Thermal Maximum; An Isotaphonomic Study In The Northern Bighorn Basin, Wyoming. W. Clyde et al. Geology. 1998. Abstract.

Paleocene-Eocene Thermal Maximum. Absolute Astronomy. Feature article.

Books including the Paleocene Eocene Thermal Maximum:

The Weather Makers T. Flannery. [Chpt. 5.] Alan Lane. 2005.

Causes and Consequences of Globally Warm Climates in the Early Paleogene. S. Wing. The Geological Society of America. 2003.

Catastrophic Events and Mass Extinctions: Impacts and Beyond. K. MacLeod et al. The Geological Society of America. Special Paper 356. 2002.

Biodiversity II: Understanding and Protecting Our Biological Resources. M. Reaka-Kudla et al. [Chpt. 11.] Henry (Joseph) Press. 1997.

Warm Climates in Earth History. ed: B. Huber. [Chpt’s. 4, 5, 6 & 7.] Cambridge University Press. 1997.

Subpages (1): 8. CO2: Then & Now