"As someone who worked on the IPCC...I can assure you that there are many disagreements, that the final words do not represent the iron-clad truth about something, it's an evolving document that often makes compromises, and consensus is a political notion, it is not something based on things that are hard and fast."
Carbon dioxide has increased 35% in the previous 150 years due to human activity, and is increasing about 0.5% per year. "We know that it's radiative force will increase. There is no question about that."
Mean Global Surface Temperature rose 0.7°C in the past 100 years.
Mean Surface Temperature is NOT an appropriate index for the greenhouse effect because urbanization and irrigation dramatically impacts the circulation of surface and atmospheric year at night, distorting the surface temperature measurements upwards.
Surface temperature measurements of California central valley disclose that the temperature at the valley floor has increased dramatically (4-5° Celsius!) over the last 100 years, while the surrounding foothills have cooled slightly. He comments, "That tells you right there that this is not a greenhouse gas effect. It's going in the opposite way of what greenhouse theory indicates... it is a false signal. It is not greenhouse warming that is occurring there, it is the development of surface warming that is occurring there...Humans up are causing that rise, but it's not greenhouse gas effects."
Greenhouse gas models predict that the greatest change (the biggest signal in the data) in the atmosphere caused by greenhouse gases will be in the tropics and the troposphere. However, when we examine the data sets of changes in temperature in the tropics, they show far less warming (median of actual measurements = 0.05°C/decade) then greenhouse theory would predict (0.16°C/decade). He comments that the UAH Satellite Data through 9/2007 shows that the 20 years of data before the 1997-1998 El Nino shows no pattern, but that "there is an upward trend in [this data], I suspect it's due in part to the extra greenhouse gases, but the magnitude of the trend is much less than what models suggest."
If we double the carbon dioxide in the atmosphere, without any other feedbacks or interactions, the surface temperature will increase approximately 1°C.
The uncertainties, he suggests, are in the associated feedback loops that an increase in temperature or carbon dioxide will trigger. "Water vapor and clouds, by far, dominate the greenhouse effect. And they are variable. I mean, they vary. The greenhouse effect of clouds and water vapor vary more than the whole carbon dioxide effect. Climate models suggest this, well, they don't suggest it they show it. That when you add carbon dioxide, that the clouds and water vapor effect multiplies...It's a positive feedback effect…" He also says, "all of those feedbacks are where the enormous types of warming scenarios you are, that are foisted upon you by the media come from. A climate model will have a trigger in it, that if you add a little bit of heat due to carbon dioxide, then this trigger occurs and the heating goes off the charts. So that's where the uncertainties really are."
However, he points out that the latest research of satellite data
Spencer, et al 2007 into the cloud variations in the tropics demonstrate, not a positive, but a negative feedback effect. "It turns out that there is a negative feedback. In other words, as temperature rises, the way the clouds respond is to cool the climate. It's like a thermostat. It turns out that the clouds that cause warming, cirrus clouds, shrink whenever the temperature goes up, and that allows radiation to escape to space. And so it cools. It's an automatic kind if cooling mechanism. This is in the opposite direction of climate models, and missing a feedback like that will lead you astray very quickly...The models overestimate [poorly charaterize] this feedback and that's why they show this warming about which everyone gets so excited."
If we enacted legislation that mandated that the average MPG per fleet of cars from every automobile manufacturer in the USA be above 43 MPG and people complied, then using the IPCC estimate for temperature over the next century, it would lower the temperature 0.01° (1/100th of a degree) by 2100. If every car manufacturer in the world met this standard, it would lower the predicted temperature 0.03° (3/100th of a degree) by 2100.
Sir David's concerns
