Hi everyone,

My thanks to Larry Schwitters and Caren Park for (off-list) correcting my incorrect assumptions about plate tectonics/continental drift.? My interest in the topic was peaked enough to contact the Royal Tyrrell Museum in Alberta, Canada (the amazing dinosaur/fossil museum mentioned in my original post on the topic) to get some additional info about the topic directly from the source.? I asked the following question of their staff:

What caused Alberta to have a tropical climate at the time of fossil deposition - cyclical climate changes, plate tectonics/continental drift, a combination of the two, or something different entirely??

Quite quickly, I received the attached very thorough and very well-written response from a museum senior research scientist.? Rather than paraphrase the response, it is shown below for those interested in reading it.? The original question was directed only at the history of previous climate change, not the current debate on global warming, but Dr. Eberth touched a bit on the current situation as part of his response.

I think the history should be of interest as a long-term backdrop for the current situation.

John Tubbs
Snoqualmie, WA
johntubbs at comcast.net

----- Original Message -----
From: "David Eberth" <David.Eberth at gov.ab.ca>
To: johntubbs at comcast.net
Cc: "Winda Peevey" <Winda.Peevey at gov.ab.ca>
Sent: Friday, January 7, 2011 11:44:41 AM
Subject: RE: Question Regarding Climate Change and its Causes (in a historical sense - not the current debate)






Hi John,



The answer is not an easy one because geological time on Earth encompasses 4.6 billion years. ?During that time atmospheric compositions and geologic conditions have varied through many extremes. ?But if we restrict ourselves to the Phanerozoic ? the last 600 million years when complex life dominated our planet -- the important thing to note is that our modern Ice Age climate (the past 2 million years including the present) is strongly unusual relative to most of this Earth history when climates and temperatures were generally much warmer. ?Given that ?warmer was the norm? through the past 600 million years, the question really becomes: why have there been numerous Ice Ages during the past 2 million years? ?The answer to that question is very complex but involves interactions between solar activity/cycles, and a wide variety of factors influencing the Earth?s heat budget over the past 50 million years, including the emergence of new mountain belts like the Himalayas, the balances of atmospheric gases, the distribution of continental land masses and oceans, and heat flow via currents in the oceans.



In the context of the foregoing, it shouldn?t be surprising that 80-65 million years ago, during the last 15 million years of the age of dinosaurs ? the time interval that is so well represented in the fossils and badlands here in southern Alberta ? the North American Plate was actually ~5 degrees farther north than its current position (and rotated slightly counter-clockwise), but that global climates were warmer with no polar ice caps (again, polar ice caps are quite unusual in Earth History).? This ?normally? warmer climate coincides with much higher greenhouse gas content in the paleoatmosphere (relatively easily measured by using stable isotope geochemistry). ?In fact, we often refer to the Earth during the Cretaceous Period as a greenhouse world.



There is much more to this story of course, but the short answer to your question is that the Earth was considerably warmer during the age of dinosaurs (215-65 million years ago) and that warmer conditions have been the norm for our planet for more than 600 million years.? The Ice Ages have been active only for the past 2 million years.? FYI Today we are either (1) in an interglacial (with more cold to come 100,000s of years from now) or (2) at the end of the Ice Ages with only warming ahead (this is the more likely scenario ? but it is not yet proven).



Just a sidenote: the overall rate of warming that we are seeing now in human lifetimes is faster than any rates that have been documented any time in the past using geological and paleontological data sets. ?So, although it can?t be said with absolute certainty that we are heading into a long term greenhouse future, there is no doubt that high rates of global temp change will continue to result in greater climatic volatility than we have experienced previously.



Hope this helps.



Cheers,






David A. Eberth, Ph.D.

Senior Research Scientist

Royal Tyrrell Museum

Box 7500

Drumheller, AB T0J 0Y0

403-820-6216 office

403-820-6536 cell

403-823-7131 fax

www.tyrrellmuseum.com