Pacific Decadal Oscillation (PDO) is a long-lived El Niño-like pattern of Pacific climate variability. Primarily found in the North Pacific, PDO moves through warm phases and cool phases that last from ten years to forty years at a time.

George Taylor’s talk, The Pacific Decadal Oscillation: A Dominant Mode of Climate Variability, stresses that the PDO appears to be a permanent feature of the earth’s climate system, and PDO changes correlate well with the variation in temperature over the last century.

There are two radiative ways to cause global warming: An increase in solar radiation being absorbed and decreasing infrared radiation (IR) being lost to space. The IPCC is focused on the latter. Dr. Willie Soon, who presented earlier today, focuses on the former. Roy Spencer, a professor at the University of Alabama, focuses on the effects of the feedback and PDO.

Spencer mentions that feedback in the climate system will determine whether man-made global warming is an environmental blip or something that cold lead to catastrophic consequences. That’s the uncertainty in the science today. As Ron Bailey of Reason paraphrases from Dr. Lindzen’s earlier talk,

The idea behind greenhouse warming is that greenhouse gases like carbon dioxide emitted from burning fossil fuels tend to trap heat from the sun. As the atmosphere warms up it holds more water vapor and produces more high thin clouds which in turn inhibit the emission of heat radiation increasing the temperature even more. It is this positive feedback loop that produces ever higher global temperatures in the computer climate models.”

It’s the magnitude of the feedback climate alarmists warn will lead to doomsday scenarios, but even with all the scientific research, there is little conclusion as to what this magnitude is. (In speaking one-on-one with a professor from the Netherlands, he said it then boils down to a matter of risk assessment.) Dr. Spencer analyzes satellite data in space and found that there is strong evidence that there is negative feedback, which could cause a cooling effect or negate effects of a positive feedback.

Spencer then relates the negative feedback he’s observed from the satellite data to the PDO. He concludes this negative feedback is the reason for the PDO changes, and agrees with Taylor that PDO has a large effect on the global temperature.

William Gray focuses more broadly on the oceans and says deep ocean circulation changes are the primary cause of climate change. After discounting solar activity and sunspot changes, volcanic activities, cosmic rays, aerosols and other factors (which he acknowledges all play a role), he concludes it’s the deep ocean circulations that ultimately lead to global cooling during some periods and global warming during others.

It’s interesting to see that even climatologists who are skeptics about man-made global warming being the dominant cause have differing opinions.