I think I may have found some clarification for the PETM. The PETM is one of the strongholds of the AGW ideas. It is pretty well accepted that the PETM, 55 million years ago has been caused by destabilisating clathrate, about 1120 Giga tonnes of Carbon has been released as methane in the atmosphere. A simple eXcel model simulating the carbon flow in the carbon cycle, disturbed by the methane release, suggests that this would slowly lead to concentrations of about 300 ppm CH4 and 1000 ppm of CO2 in several thousands of years. This would lead to a reduce of reradiation of about 20 watt per square meter, which would give several degrees of greenhouse gas warming. BTW Thats' without any positive feedback. And it's that positive feedback, which is so necesary to preach the global warming, Weather of Mass Destruction. I'm perfectly happy with the Clathrate idea and the consequent basic greenhouse gas forcing without positive feedback. Consequently: no positive feedback then, so why now? Without positive feed back the alleged warming warming due to greenhouse gas increase could not have been more than about 0,2 degrees celsius and would not exceed one degree celsius in 2100. However, I had some problems with the simple reasoning: warming => warm ocean water => clathrate destabilisation => greenhouse gassses => runaway greenhouse gas effect. So what caused the PETM? And what is the real story about the temperatures during the PETM?
One of the positive feedbacks facing us today is the release of methane from the Siberian/Alaskan permafrost - which wouldn't have existed during the greenhouse climate of the Cretaceous/Paleocene. The starting point for the PETM was a greenhouse, whereas today we start from an ice age - so other feedbacks may be different too Please Register or Log in to view the hidden image!
Perhaps not. Compare the recent palea climate, We can discriminate huge differences within few hundred years. The Last Glacial Maximum, the Dansgaard Oeschger Events or interstadials, the Heinrich events, the Bolling Allerod event, the Younger Dryas, the Medievan Warming Period, the Little Ice Age etc. All major impacts on climate, all within 50,000 years with fast and violent transients to be measured in decades. Now, how many 50,000 years era's fit in the Paleocene from 65 milions years to 55 million years ago and how many decades? So how stable would the climate have been in that era? We can only peek through some very very small windows, an odd fossile'every oncle and a while, some visible sediments, some magnetic measurements of sediment cores on a few spots. That's all there is available. Then we see Mosasaurus and moderate warm forests in Antarctica and Palm trees in Alaska as well as a few more finds. We use it to create a picture of the Paleocene and the conclusion is simple: the whole paleocene was about subtropical conditions all over the world. But we may miss a gigantic polar ice sheet on -say- Japan, whatever, from 59,255,950 to 59,241,908 years ago. But there are neither fossils nor magnetic imprints, nor sediments that would reveal that ice sheet. I know, the benthic foraminifera isotopes of the ocean cores are supposed to register variation in 18O. More 18O means ice sheets. The problem is that more 18O also means more acidity, lower local temperatures. The spikes may be concealed. Furthermore we may have measured 59,300,000 and 59,200,000 years ago and never found the isotope excursion associated with that ice sheet. Our visual resolution may be way to small to see the real Paleocene. It may have been totally different.
Well the same really applies throughout Earth's history: if the climate is chaotic now, has it always been so? Personally I think chaos is a sympton of what we call 'ice age' and that the usual, greenhouse, position is marked by long term stability. But I can't prove that Please Register or Log in to view the hidden image! The PETM occurred before the creation of the Transantarctic mountains and before Antarctica became centrally placed across the S Pole as it is today. With a different configuration of mountain ranges, continents and oceans it's not easy to determine - in comparison with today - how and why the global climate would have been different. But it's not unreasonable to suppose that it was different. So anyway, are you suggesting that the PETM was in fact a very short-term event? Or didn't occur at all? Please Register or Log in to view the hidden image!
Interesting thought indeed about greenhouse = stability. It seems to hold grounds. There is no need to prove hypotheses, just do a couple of correct predictions. Like: "in 2050, with CO2 at say 500 pppm, the general difference between average Arctic and average equatorial temperatures will be 0,5 - 1 degrees less than today" Less lateral temperature difference is more stability. However vertical temperature difference will increase, causing instability again. The PETM was at 55 Million years, lasted problably several thousand years (estimates range from 1000 - 20,000 years). But Antarctica seemed to have reached it's current destination or was very close some 80-60 million years ago according to this animation. The PETM was very real. We just wonder about the cause and we wonder about the impossible climate, sub tropical worldwide, contempting the general idea that temperature is depending mostly on solar energy, which is many orders of magnitude less at the poles compared to the equator. If we assume that temperature variations really differ with lattitude, then we have to come up with another explanation. One that also could trigger the PETM. Can't be hard anymore.
I would second Essan's point on how difficult it is to predict the nature of weather when the configurations of the world's oceans/continents was drastically different. If we assume that it is indeed similar to today's climate, there should've been a single or closely packed string of events that caused the initial release of greenhouse gases. I am going to make a hypothesis. Suppose that right after the dino wipe-out, all that's left is a bunch of small rodents and plants, but in a unstable ratio, i.e. less than the 10:1 energy trophic level that naturally develops with evolution, given that there is not a huge catastrophic disturbance. This unbalanced ratio, however, would persist for several hundred thousand generations, because the rodents that survived the KT blast would have to be an extremely promiscuous species of animal, and without the predators that have in large part died out, they would roam the planet and eat all they can manage before a significant fraction of angiosperm plants evolved to become as tall as their predecessor gymnosperms. This would probably dump a crapload of CO2 into the atmosphere, enough to initiate the positive feedback mechanism. However, I have no evidence. There hasn't been evidence in the fossil record of large numbers of rodents or small animals living right after the KT impact. Or could it, since smaller non-arthropods are hell as hard to fossilize?
I agree, however things that should not change are natural physical laws. Even if it is much warmer on the planet, you still need the sun to produce it and the amount of sunshine on the poles is minimal. Hence there cannot be palm trees over there. Back soon.
It would be interesting to think that there were actually plants at the poles sometime in earth's past - given that they have to adapt to a 365-day circadian rhythm. Or should I say, circanum rhythm?
Well trees can - and do - grow within the arctic circle..... But I'm no biologist to know whether it's just climate or also the length of darkness that puts a constraint on which species can survive there Please Register or Log in to view the hidden image!
