Yesterday I attended a talk at Cornell by Dan Miller titled "A Really Inconvenient Truth." He was one of the people trained by Al Gore to give the "Inconvenient Truth" lecture to businesses, schools, etc. He also gives another, slightly darker, talk. That's the one I mentioned above. You can read the outline of the talk here.
According to Miller...
The IPCC (Intergovernmental Panel on Climate Change) produces a consensus report of climate and other scientists actively working on climate change that summarizes the known research and the certainty levels of the scientists on various effects. Policy-makers use this document to better understand the science and what policies should be enacted to prevent or mitigate for future damage.
The IPCC report shows what could happen in the future based on their linear models of climate change and predictions based on societal behavior (i.e. we stop emissions immediately, we don't do anything, we emit less, etc). Bad things for the climate are predicted if we don't change our behavior soon based on IPCC models of the climate.
However, IPCC is a consensus opinion, meaning that they have to use the best understood models and find an agreement between many different scientists. Therefore, the consensus opinion is more conservative than many IPCC scientists would prefer. It also uses linear models, which are easier to calculate, but don't always reflect the way the natural world works. Things like feedback cycles are not incorporated into the IPCC's predictions.
Feedback cycles to worry about that weren't addressed by IPCC models:
2) Glacial melt feedback loops
3) Methane traps
Permafrost - In Siberia, Canada, and Alaska, portions of the ground are permanently frozen year-round. The ground in many of these places is made of peat, which has a high organic content. The peat was never allowed to decompose because it was frozen, thereby trapping carbon dioxide in the frozen ground.
As it gets warmer, the ground melts and the peat begins to decompose. This process releases carbon dioxide into the atmosphere, which raises the temperature a little. This causes more permafrost to melt, which releases more carbon dioxide, which raises the temperature a little more...this is a positive feedback cycle.
Glacial melt - Arctic sea ice is ice that floats on the water near the poles. It is connected to land in some way, and prevents the glaciers from traveling into the water. As the sea ice melts, the glaciers are not held back from the oceans. This will expose the glaciers to warmer temperatures and cause the ice to melt. This will cause sea level to rise and will encourage more glacial movement.
Methane Traps - This one isn't likely to occur in the near future, but may happen someday. Methane is stored frozen at the bottom of the ocean, and the gas is 20x as effective as an atmospheric blanket as carbon dioxide. The ocean warms first at the surface, and eventually (over, say 1000 years) the heat could cycle through to the bottom. If parts of the ocean warm enough to release methane gas, this will raise the temperature of the Earth. When that happens, the oceans will warm more, more methane gas will be released, and the temperature of Earth will rise further...
That's Dan Miller's "REALLY" Inconvenient Truth.