vansig wrote:

The sea ice and acidification and methane scares are all hooey.
[…]
–The slight predicted reduction in the alkaline balance of the oceans (not “acidification”!) is a small fraction of the range experienced by ocean organisms throughout paleohistory, while they were evolving – including many types of coral.
[…]
–Finally, MUCH warmer periods in history have been boom times for humanity, with expansion of population, culture, wealth, and nutrition. Vice versa for cooling periods. So — pray for warming!

Well, recent trends in both northern and southern sea ice can be found at
http://nsidc.org/data/seaice_index/images/n_plot_hires.png
http://nsidc.org/data/seaice_index/images/s_plot_hires.png

These are consistent with the ~21,600-year Milankovitch cycle, which alternates longer-or-shorter winters versus summers for northern and southern hemispheres…
http://en.wikipedia.org/wiki/File:Precession_and_seasons.jpg

Re ocean acidification: calcium carbonate is the main buffer of pH in the ocean. I found a chart of
calcium carbonate solubility as a function of CO2 partial pressure, at
http://en.wikipedia.org/wiki/Calcium_carbonate#Solubility

P(CO2) atm pH solubility [Ca2+] (mol/L)
3.5 × 10^-4 8.27 4.70×10^-4
10^-3 7.96 6.62×10^-4

If i’m reading that right, then at 1000ppm CO2 in atmosphere, ~40% more CaCO3 will dissolve, which (some insist), drives shellfish and corals into crisis and degrades the ocean’s CO2 absorption capability. Decreasing the pH from 8 to 7 increases the maximum Ca2+ concentration by a factor 100.

There is a tipping point in there, somewhere, that could be good for some plants, but may be associated with past mass extinctions. The scenario is: CO2 spike triggers massive algae bloom, which carpets the sea floor, destroying ecosystems; then absorbs huge amounts of CO2, and drives Earth into an ice-age. I’m not trying to scare anyone, i would just like to understand these complex, nonlinear feedback mechanisms better.

http://www.physorg.com/news189066777.html
http://www.thekrib.com/Plants/CO2/caco3.html
http://findarticles.com/p/articles/mi_m1200/is_7_162/ai_91040540/

The “tipping point” rhetoric is pretty much nonsense. There have been wide excursions (many times anything we could possibly cause, even with maximum effort to do so) of temp and CO2 in the last few hundred million years without any positive feedback runaways. This is because the postulated mechanisms are actually “unphysical” (meaning contrary to scientific law) in part, and in part because if such mechanisms existed we wouldn’t be here to worry about them (the ‘anthropic principle’).

The one actual climate danger is the implementation (at ruinous cost, naturally) of some hare-brained geo-forming project which actually works and we discover that you must be VERY careful what you ask for, lest you get it!