Here is a summary of what the geologic record tells us about abrupt climate change. This has nothing to do with global warming, but much of this information gets haphazardly and incorrectly tossed about in the global warming debate by both critics and proponents.

The existence of these rapid changes in not controversial
http://www.ncdc.noaa.gov/paleo/abrupt/index.html

Of course some of you will find this one controversial because of the ice core link to temperature and greenhouse gasses over the past several hundred thousand years.
http://www.ncdc.noaa.gov/paleo/globalwarming/index.html

<img src="/forums/images/graemlins/kewl.gif" alt="" />

Now can I go back to driving my SUV?

Al Gore invented paleontology.

The question is what, if anything, is different between today's conditions and those of these particular intervals of the geologic past. Can we determine what caused previous changes and are those same forces at work today? Or, is something different?

Interesting question, but I would also add that we need to ask: does it matter?

Here's why... if we determine that the dinosaurs were killed off due to heat (always taught that in school) and we determine what caused that warming trend, our politicians are going to tax the crap out of us in an effort to change the global climate to prevent it from happening again (which we all know is a false hope).

Look at sun activity; direct correlation to warming and cooling here and other planets/moons. Yet we can't fix that, so we're not willing to accept it as a cause.

I understand people's concerns with politicians. War on drugs? Go after the end users - treat the symptoms not the cause. In our NC drought, we get all these tips from the government on things we can buy to save water but no financial incentives. What's wrong with a rebate for buying that new low-volume toilet or whatnot. Instead, they just intend to raise rates for high users - those poor souls like my friend with a wife and two teenage daughters. <img src="/forums/images/graemlins/lol.gif" alt="" />

Variations in the sun is a good example of the need to determine if conditions differ. We've documented changes in the solar constant at 11, 88 and 210 years. But AFAIK, we don't see evidence of large amplitude temperature change that is coherent with solar output at these frequencies. Extending the record of solar output change beyond when people started staring at the sun with telescopes (~ 1600 I think) relies on geologic records of the radiogenic isotopes C-14, Be-10, and Cl-36. These are formed due to cosmic rays hitting the earth. Problem is the production of these isotopes is modulated in the same fashion by both the solar magnetic field and the earth's magnetic field; teasing apart the effects of each to determine just the solar contribution is very difficult.

Remember the asteroid disaster movies? It appears that a large one hit the Yucatan area 65 million years ago and killed off many things. Was like a nuclear winter. Iridium is rare on the earth but common in many of the meteorites we've collected. Sedimentary deposits world wide from that time have a relative spike in iridium. This is a really cool sediment core through that layer.

http://www.usssp-iodp.org/PDFs/Greatest_Hits/Brochure/Norris.pdf