Temperature in Earths history

KTevolved

I was just wondering when the last time the global average temperature was 90 degrees F? Also wondering what a temperature of this extream would do to todays environment and life it self?

Andre

What exactly is your intention with that question? Has there ever been a period when the global temperature was 90F? Reconstructing paleologic temperatures is something like solving N variables with maybe N-10 equations. or another comparison would be, trying to overview the complete ocean while looking through a porthole.

There are reasons to believe that Earth was somewhat warmer in the late Miocene a few million years ago, (LaRiviere et al 2012), but certainly not 90F. It was probably a good bit warmer during the Paleocene especially the Paleocene Eocene Thermal Maximum but 90F as an average appears unlikely. Maybe at the at the time the Earth was formed.

KTevolved

Just wondering beause of global warming. I didnt realize it wouldnt have occured since the beginning of earth formation, i thought it would hae occured when the dinosaurs were alive and there were no ice caps.

Andre

This is not the place to discuss that. See why

KTevolved

Alright so do you know of any forums that deal with this? Im getting into the topic.

Evo

Average temperature since records have been kept average ~57F. The sun is slowly getting hotter, eventually, it will be too hot for life as we know it.

http://en.wikipedia.org/wiki/Sun#Earth.27s_fate

You can easily search for information online.

SW VandeCarr

http://www.cgd.ucar.edu/ccr/aboutus/...hl-Shields.pdf

This paper suggests the temperatures at the end of the Permian period were higher than previously thought, possibly higher than at any time in the past 600 million years. The Permian mass extinction, which was the largest ever, occurred at this time (251 mya). The authors believe that low oxygen levels in the ocean contributed to the loss of 90-95% of all marine species. The dinosaurs came later (215-65 mya).

Temperature simulations indicate summer mean temperatures in parts of subtropical Pangaea (the single super-continent that existed at that time) to be in excess of 40C (104F). The overall simulated mean annual temperature for the planet at that time was about 8C higher than today.

EDIT: The paper seems to be unavailable right now, 0300 Aug 29 2012. Here's another study on late Permian climate: They are only estimating a mean global temperature 6C higher than the present level, at least with one of two models they're looking at. This paper is looking at the late Permian, but not necessarily at the end of the Permian (Permian-Triassic boundary) which is the subject of the first paper. In any case, there seems to be no evidence that the mean global temperature was ever much higher than 8C above the present level over the past 600 million years based on available estimates.

http://www.ipgp.fr/~fluteau/UIA/arti...ea-climate.pdf

Evo

Can you point out for me where it says the average GLOBAL temperature was estimated to be that high, not just in some areas. I'm sure it's there, but I don't have time to look.

The map seems to show temperature variations in different locations.

SW VandeCarr

The last sentence before the RESULTS section says the simulated mean annual global surface temperature was 7.98 C higher than it is today. BTW, I edited the second paragraph.

Evo

Thanks!

Then that would only bring the average temp then to 22.5C or 72.5F. And 7.98 C is very high, other estimates range from 5 to 6.5 C. I wonder if they goofed on their data for current world temperature?

http://www.currentresults.com/Enviro...emperature.php

I am only providing this to show what the current Global Mean Annual Temperature is.

Andre

It appears that this Kiehl & Shields 2005 study is the result of a simulation model, which I guess would not have any higher status than a hypothesis.

Remarkable is the mentioning of the Siberian traps, the main suspect for the P-T extinction, remarkable because the last three known eruptions with high aerosol emissions, Agung 1963, El Chinon 1982 and Pinotubo 1991 were followed by a few years of cooler temperatures. Also following the largest eruption of modern times, the Tambora was followed by the year without summer (1816). All in all, and also giving the uncertainty of temperatures only several thousand years, due to conflicting evidence, it would suggest that their outcome may not be the most robust.

SW VandeCarr

I'm not an earth scientist although I've had a lifelong interest in meteorology. Wouldn't the value of simulations depend on the quality of data? How much could one say about the climate of Pangaea in the late Permian without computer simulation? I guess we could say it would have an extreme continental climate with monsoons and a lot of deserts. Beyond that, it would depend on specific evidence from various parts of the supercontinent that are accessible today. Can we categorically say that computer simulations based on such evidence are not very useful in investigating paleoclimates?

BTW: Did you see the Fluteau, Besse et al paper I posted later?

Andre

Maybe the quality of suppositions is even more important. You're looking at the end of the line of a lot of them, for instance the temperature supposition are based on stable oxygen isotopes (18O), for instance Tabora & Montanez 2005, if you have worked your way through the isotopes in the water cycle textbook and the GNIP database for isotopes in precipitation, you'll find a plethora of variables that has to be accounted for. You just have to make a lot of suppositions, that might be wrong.

Andre

Maybe I should elaborate on those suppositions. Tabora & Montanez 2005 state:

There is already one 'if'. Obviously during chemical processes there will be some isotopic fractination because of physical differences between heavy and light isotopes, these processes are temperature dependent, hence it's use as paleo thermometer. Unfortunately there are also many other (often unknown) factors to take into account. Let's just confine ourselfs to one of them "meteoric water", if I read that correctly it would suggest that they assume the original isotope ratio of the rain water in contact with the rocks would be consistent with water of those temperature.

However have a look at the isotope in precipitation chart of GNIP:



Although there is a clear temperature dependence for isotope in precipitation, there are also abberations. You can't see the cold winters in Argentine or the hot summers in China, based on the isotopes.

Also:



These isotopes would suggest that the temps of Greece and Belgium are about equal. The locals will tell you that this is not really the case, also when yellow here is the same yellow in the upper chart, then Shri Lanka would be as cold as The Netherlands. That would be hard to sell too.

The main reason for this abbaration is the Rayleigh process or Rayleigh fractionation. As condensation in clouds prefers heavy isotopes (deuterium and 18O) the cloud gets gradually depleted from heavy isotopes. The further the clouds move away from the source, the lighter the remaining isotopes are. This spoils the effectiviness of many isotope thermometers, if the rayleigh factor is unknown, which is obviously the case for the Permian past. So the isotope values of that meteoric water is not a very reliable isotope thermometer.

SW VandeCarr

The value of simulations can be tested against current climates. One takes a set variables that are believed to be correlated with various climate parameters and sees how well the simulation based on these variables predicts known climates. The problem arises in how well this set of variables can be measured or assessed in paleo-environments. One big set of assumptions regards solar output and axial tilt. For late Permian Pangaea, the assumption in the Kiehl paper was that these variables were essentially the same as today. Again, I'm saying it's the quality and relevance of the data or lack of data that determines the value of a simulation. A simulation that works well in the current environment does so because the variables and correlations are well known. But but a good simulation model will nevertheless pass or fail based on the quality and relevance of the data available for paleo-environments.

Andre

Exactly, so let us see how the modelers are doing in a setting that is well known. This is a copy paste from what I wrote in a discussion elsewhere.

It's now common knowledge now that there was no ice sheet on Siberia during the last glacial maximum, a phenomonon that appears to contradict the current understanding of ice ages and interglacials. Hence such an anomaly begs for an explanation. Krinner et al 2006 assume that it had been very cold in Siberia, in accordance with the assumed glacial regime and they propose that the impact of wind blown dust deposition on snow has decreased the reflectivity of the ice and caused it to melt again, thus preventing the accumulation of an ice sheet, especially in the arid conditions. They model this event and sure enough, manage to simulate that. To validate their work they refer to Hubberten et al 2004 which abstract indeed suggest that this might be correct.

Evidently they did not study their whole reference, otherwise they would have noticed (page 1340) :

Reason enough for the ice to melt during the summer, no need for aeolian dust. On the contrary, the reconstructed biotope of North Siberia during the Last Glacial Maximum was a combination of an arid grassy steppe and tundra vegetations, supporting a mega fauna (Hubberten et al 2004, Kienast et al 2005, Mol et al 2004, 2006).

Refs:

Hubberten et (21) al 2004 The periglacial climate and environment in northern Eurasia during the Last Glaciation, Quaternary Science Reviews 23 (2004) 1333–1357

Kienast, F., Schirrmeister, L., Siegert, C., Tarasov, P., 2005. Palaeobotanical evidence
for warm summers in the East Siberian Arctic during the last cold stage.
Quaternary Research 63, 283e300.

Krinner G. et al 2006; Ice-free glacial northern Asia due to dust deposition on snow, Climate Dynamics (2006) 27:613–625 DOI 10.1007/s00382-006-0159-z 123

Mol, D., L et al, 2004 Brief history , 14C dates, individual age, gender and size of the Yukagir mammoth. Symposium: The Yukagir mammoth: outcome of the first stageof research work. Academy of Sciences of the Republicof Sahka .(Yakutsk) p. 51-55

Mol, D., et al, 2006. Results of theCERPOLEX/Mammuthus Expeditions on the Taimyr Peninsula, Arctic Siberia. Russian Federation Quaternary International,January volumes 142-143 pp. 186-202.