Are we effectively approaching a transition zone from 'Oligocene to Eocene' ?

[zankaon]

Pre-industrial era, co_2 has been considered as ~280 ppm. Current value is ~387 ppm.
http://en.wikipedia.org/wiki/Greenhouse_gas.
Some projections are for co_2 to rise to ~540-970 ppm by 2100 (90 yrs away). http://en.wikipedia.org/wiki/Global_warming. Upper range of 970 ppm would represent 2.5 x current value. Would this represent an accelerating curve? Are we increasingly accelerating through a transition zone,effectively in reverse, from 'Oligocene to Eocene' ? The Eocene to Oligocene transition 35 million years ago http://en.wikipedia.org/wiki/Eocene has been estimated to occur at ~750 ppm of co_2. http://en.wikipedia.org/wiki/Eocene. http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature08447.html. Paleocene-Eocene was a greenhouse time of probably essentially no ice on the planet. http://en.wikipedia.org/wiki/Paleocene–Eocene_Thermal_Maximum. For subsequent Oligocene one has cooling and onset of glaciation. If indeed the current upper limit projections of 970 ppm is reasonable, might one have commencemet of melting of East Antarctica in 100's of years, rather than thousands of years? With perhaps a lower limit of 100+ yrs before any significant melting of East Antarctica?

Total surface area of ice in all of Antarctica (east and west) is ~ 13,720,000 km^2, with average thickness of 1.6 km.; giving ice volume of 21,952,000 km^3. http://en.wikipedia.org/wiki/Anarctica.
Ocean surface area is 361,132,000 km^2 (70.8% of planet surface area). http://en.wikipedia.org/wiki/Oceans.
Volume_ice /S.A._ocean = h ; ~ 22 M km^3 /~361 M km^2 = .06 km. Thus for total melting of all of Antarctica, and even distribution over all oceans, one would have increased sea level rise of .06 km. 1 meter is 3.28 ft.1000 m.=3280 ft. So .06 x 3280= 199 ft sea level rise. But if West Antarctica's earlier contribution is ~11 ft (3-4 m.), then sea level rise from later process of East Antarctica complete melting, would be ~ 188 ft or 57 meters. 100 meters equaling 328 ft. Would prudence suggest entertaining and planning for a worse case scenario?

Paul N. Pearson, Gavin L. Foster, & Bridget S. Wade
Nature 13 September 2009
Atmospheric carbon dioxide through the Eocene–Oligocene climate transition

 

[Andre]

From the abstract

Geological and geochemical evidence1, 2, 3 indicates that the Antarctic ice sheet formed during the Eocene–Oligocene transition4, 33.5–34.0 million years ago. Modelling studies5, 6 suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels () fell below a critical threshold of 750 p.p.m.v.,

Hmm close to triple pre-industrial pCO2 and ice sheets building? Who gave permission for that?

But:

Here we use the boron isotope pH proxy

Expect in a couple of decades that the interpretation of "proxies" will all be heavily revised. After all it's per definition an affirming the consequent fallacy. Compare for instance with Royer 2003 finding near present day values for the preceding (warm) period:

Here I present a CO2 reconstruction for the very latest Cretaceous to early Eocene and middle Miocene based on the stomatal distributions in fossil and extant Ginkgo and Metasequoia cuticles. Although both of these intervals are representative of globally warm climates, my CO2 reconstruction indicates near present-day values (300–450 ppmV) for both times.

Notice also (fig 3) that Dana Royer also found a big CO2 spike at the Paleocene Eocene Thermal Maximum (PETM, 55 million years ago), see fig 3, which would suggest some robustness for his method of stomata density - proxies.

Which seems logical since atmospheric CO2 should be in a more or less dynamic equilibrium between sources and sinks after 4.55 billion years.

 

[Xnn]

As far as I know, the Eocene to Oligocene transition took place over between 400,000 to 1,000,000 years. Currently, we have a fairly low level of understanding of how large ice sheets melt. Yes, there are alarmist that may claim it can happen quickly, but the tendency of experts in the area is to talk in terms of 1000's years. So, even if the Antarctic were to completely melt and sea levels were to rise 60 meters, that would be spread out over a very long time.

Sea levels are currently rising about 3mm/yr (0.003 m/yr). 60/0.003=20,000 years.
20,000 years is of course greatly accelerated compared to 400,000 years as its about 20times faster. However, consider this in the context of a persons lifetime. 100 years can be considered as bounding for the duration of over 99% of people's lifetimes.

0.003mm/yr * 100 years = 0.3 m = 12 inches.

12 inches is of course about the size of a typical wave on the ocean.
So, at current rates of sea level rise, there isn't really much for anybody to currently worry about or plan for within the context of impact on most peoples lifetimes.

Longer term is another matter, as many large cities are <60 m above sea level. So, in the distant future, there will be a gradual abandoning of lower elevations, but it will resemble more of a migration as opposed to an exodus.

 

[Skyhunter]

That paper doesn't cover the time period being discussed Andre.

This thread is about the climate transition 33.5 - 34 million years ago, not a debate about the validity of the various reconstructions.

Let's stick to the proxy evidence presented by Pearson et al, which is from the period being discussed.

 

[Xnn]

Good point Skyhunter; red herrings are not welcome!

Here's something that is relevant:

The Eocene–Oligocene transition towards a cool climate (33.5 million years ago) was one of the most pronounced climate events during the Cenozoic era. The marine record of this transition has been extensively studied. However, significantly less research has focused on continental climate change at the time, yielding partly inconsistent results on the magnitude and timing of the changes. Here we use a combination of in vivo stable isotope compositions of fossil tooth enamel with diagenetic stable isotope compositions of fossil bone to derive a high-resolution (about 40,000 years) continental temperature record for the Eocene–Oligocene transition. We find a large drop in mean annual temperature of 8.2 +-3.1 °C over about 400,000 years, the possibility of a small increase in temperature seasonality, and no resolvable change in aridity across the transition. The large change in mean annual temperature, exceeding changes in sea surface temperatures at comparable latitudes and possibly delayed in time with respect to marine changes by up to 400,000 years, explains the faunal turnover for gastropods, amphibians and reptiles, whereas most mammals in the region were unaffected. Our results are in agreement with modelling studies that attribute the climate cooling at the Eocene–Oligocene transition to a significant drop in atmospheric carbon dioxide concentrations.

http://www.nature.com/nature/journal/v445/n7128/abs/nature05551.html

Notice the last sentence!

 

[Xnn]

And this...

As massive ice sheets grew on Antarctica during the first major glaciation of the
Cenozoic era, the northern continents cooled and dried. The coincidence in timing implies that the cause was global rather than regional.

http://www.nature.com/nature/journal/v445/n7128/full/445607a.html


...cause was global rather than regional!

 

[zankaon]

Total surface area of ice in all of Antarctica (east and west) is ~ 13,720,000 km^2, with average thickness of 1.6 km.; giving ice volume of 21,952,000 km^3. http://en.wikipedia.org/wiki/Anarctica.
Ocean surface area is 361,132,000 km^2 (70.8% of planet surface area). http://en.wikipedia.org/wiki/Oceans.
Volume_ice /S.A._ocean = h ; ~ 22 M km^3 /~361 M km^2 = .06 km. Thus for total melting of all of Antarctica, and even distribution over all oceans, one would have increased sea level rise of .06 km. 1 meter is 3.28 ft.1000 m.=3280 ft. So .06 x 3280= 199 ft sea level rise. But if West Antarctica's earlier contribution is ~11 ft (3-4 m.), then sea level rise from later process of East Antarctica complete melting, would be ~ 188 ft or 57 meters. 100 meters equaling 328 ft. Would prudence suggest entertaining and planning for a worse case scenario?

For a worse case scenario, maintenance of transportation of containers and of people would be of importance. All sea ports would be gone, together with docking for any ship. Shallow inland water intrusions would prevent access from sea, and also isolation of 'island' communities on mainland. One solution and option might be Truck amphibious vehicles (TAV) which go on highways and water, carrying 50 people, or 1 container. Waterways, seaways, onloading and off loading of somewhat larger ships would allow access to coastal land areas. Such TAV would have usage in hurricane areas and river floods, and would be pre-positioned inland for all coasts, and also for Great Lakes region, and for major river systems; analogous to RV trailer shelter pre-positioning.