A very interesting writeup about the 2009 American Geophysical (AGU) meeting in San Francisco, featuring Dr. Richard Alley as keynote, summarizes the climate history studied to date. His presentation is comprehensive - it is part of a series of presentations at the AGU. The conclusion? Carbon dioxide - CO2 - is the key controller for Earth's climate, and once it's out of the ground, it's very hard to take back out of the atmosphere or the ocean.
In talking about the sensitivity of earth's climate to increasing CO2, the indicators are that the resulting temperature change is significant:
The IPCC report talks extensively about computer climate models' calculations of "climate sensitivity"--how much Earth's climate would warm if CO2 doubled from pre-industrial levels of 280 ppm, to 560 ppm (we're currently at 390 ppm). A mid-range number from the 2007 IPCC report often used by climatologists is that the climate sensitivity is 3°C for a doubling of CO2. Dr. Alley takes a look at what paleoclimate has to say about the climate sensitivity to CO2. "The models actually do pretty well when you compare them to the past. The best fit is 2.8°C.
This roughly correlates with the temperature increases that we've been seeing over the last 200 years, and a peak shows up in prehistoric fossil records indicating a planetary die-off at the end of the Paleocene due to extreme global warming. The full video of Dr. Alley's presentation is fascinating and it can be accessed here.
The analogy used by Dr. Alley to show how the CO2 correlation follows the temperature changes is that of interest on debt. CO2 feeds more warming in much the way that interest on debt feeds more debt. Considering the economic devastation that these heated-up fiscal bubbles have created in our global society is a direct analogy to that which is occurring with the debt created by CO2 being dumped into the atmosphere. Thomas Friedman has also drawn the analogy between global fiscal mismanagement and the ecological issues created by carbon, and hence the need for a carbon tax.
Friedman's take on the lack of consensus at Copenhagen in December 2009 is that it is vital to use the markets in human society to rapidly cut down on carbon, and to use these market mechanisms basically from the ground up - ironically, "grassroots". Waiting for government to respond to this global problem while under the direct influence of corporate lobbyists will be an exercise in futility. The corporate influence in climate change denial is a prime example of this strategy.
Meantime, the deterioration of the food chain in the oceans and on land will be difficult, if not impossible, to stop.