There is that famous saying for us dummies "keep it simple stupid" commonly known as the KISS Principle. One of the problems people have in following the global warming debate is the very real fact that our climate is a very complex system which few people are inclined to study less alone try to understand.
What is seldom explained however and easily understood is the theory itself. In my re-post below I summarize it thus:
I have no way of knowing for sure but I seriously doubt that the general public realizes that this is the theory. I suspect that people who may have reached the point that they even recognize that carbon dioxide is what they breathe out and is not the same as smog understand that it is not carbon dioxide which is going to cause the "catastrophic" warming, but rather the water vapor.
To summarize, a doubling of CO2 will cause the temperature to increase by 1.2 degC, this increased temperature will then cause more evaporation of water vapor (the primary greenhouse gas) into the atmosphere which will amplify the effect of the CO2 caused warming, got it? This is known as the "enhanced greenhouse effect".
Warren Meyer does a wonderful job of explaining all this in his video Catastrophe Denied: The Science of the Skeptics Position (studio version) but I doubt the general public is aware of it. They hear people like James Hanson going on and on about "tipping points" yet have little idea how central this is to the entire theory and how it is the AGW alarmist greatest weakness and growing weaker all the time. From the BBC interview with Phil Jones
The importance of whether or not the MWP was warmer than today really has little to do with precedented or unprecedented as if it was some sort of sports record, the real importance has to do with the "enhanced" greenhouse theory itself. If a period of time measured in centuries not decades were more than 1.2 degrees warmer on average than is projected to occur due to increased CO2, what happened to the famous tipping point? Yet we are to believe in a few short decades we will reach a tipping point that centuries of warmer temperatures of the past did not tip? This is the true importance of the Hockey Stick. Remember too we have not, to my knowledge, ever been told where the starting point is. What is the pre-industrial temperature which was the starting point on our road to the fabled cataclysmic tipping point ?
There is much debate over whether the Medieval Warm Period was global in extent or not. The MWP is most clearly expressed in parts of North America, the North Atlantic and Europe and parts of Asia. For it to be global in extent the MWP would need to be seen clearly in more records from the tropical regions and the Southern Hemisphere. There are very few palaeoclimatic records for these latter two regions.
Of course, if the MWP was shown to be global in extent and as warm or warmer than today (based on an equivalent coverage over the NH and SH) then obviously the late-20th century warmth would not be unprecedented. On the other hand, if the MWP was global, but was less warm that today, then current warmth would be unprecedented.
We know from the instrumental temperature record that the two hemispheres do not always follow one another. We cannot, therefore, make the assumption that temperatures in the global average will be similar to those in the northern hemisphere.
When James Hanson says " Carbon dioxide amount is already 385 ppm and rising about 2 ppm per year. Shocking corollary: the oft-stated goal to keep global warming less than two degrees Celsius (3.6 degrees Fahrenheit) is a recipe for global disaster, not salvation." It is based on the idea that we have never experienced this degree of warming before and boy when we do we are all going to fry! As I point out below the tipping point which they forecast really has nothing to do with atmospheric carbon dioxide at all, it has to do with temperatures. What the theory clearly states (read below) when global temperatures reach a certain point there will be a tipping point, carbon dioxide is just the catalyst.
I do not believe that the general public, or policy makers or even many scientist understand this. The AGW mythology has taken on so many facets that the theory itself has been neglected. If Phil Jones is saying that there is doubt about the MWP, he is in fact saying there is doubt about the entire theory, plain and simple. This simple truth should be the cornerstone of any argument against this perversion of science.
The alarmist, especially the so called scientist, who promote it have done a masterful job in both equating carbon dioxide to warming and obscuring the true theory which is supposed to be the foundation of their argument. James Hanson at least admits and fights to keep temperatures below the tipping point on which the theory depends. The rest of our erstwhile climate gurus seem not to be concerned with their own theory only that we peons believe that they have one and we should follow their edicts.
Rolling balls and good grades
Imagine a ball rolling down an incline then hitting the bottom which is completely flat, totally level. We all know that eventually the ball will stop. The gravity that caused the ball to roll is no longer influencing it but why does it stop, why doesn't it just roll forever? Friction, the contact of the ball with the surface creates friction which eventually stops the ball.
In this case the friction which stops the ball is called a negative feedback, without the negative feedback of friction the momentum of the ball initially caused by the gravity would just go on rolling until some other force stopped it.
What is little understood by the general public in regards to global warming is that carbon dioxide (CO2) by itself can only heat the Earth so much, it is not like adding fuel to the fire, as a matter of fact the more CO2 that is put into the atmosphere, the less that the CO2 is capable of heating. In a sense it saturates it's ability to warm. This is why you hear the discussion on CO2 discussed in terms of "doubling of CO2 from pre-industrial levels" when you reach that point you have pretty much reached the limit of what CO2 can do as far as heating the atmosphere on it's own.
This is not in dispute, from IPCC Fourth Assessment Report: Climate Change 2007 (AR4)
If the amount of carbon dioxide were doubled instantaneously, with everything else remaining the same, the outgoing infrared radiation would be reduced by about 4 Wm-2. In other words, the radiative forcing corresponding to a doubling of the CO2 concentration would be 4 Wm-2. To counteract this imbalance, the temperature of the surface-troposphere system would have to increase by 1.2°C (with an accuracy of ±10%), in the absence of other changes
So as you can see a doubling of CO2 would only account for a 1.2 C of warming-period. This is not in dispute. So why do you hear all these claims that increased CO2 is going to warm the Earth by anywhere from 2-6 degC? The IPCC explains:
In reality, due to feedback, the response of the climate system is much more complex. It is believed that the overall effect of the feedback amplifies the temperature increase to 1.5 to 4.5°C. A significant part of this uncertainty range arises from our limited knowledge of clouds and their interactions with radiation.
So in order to keep the ball rolling they postulate feedback, in this case positive feedback which amplifies the heating caused by the initial heating of increased CO2. Note the caution they put on this based on clouds, perhaps a future topic, but what is it that amplifies that 1.2 degrees into dangerous temperatures which will destroy life as we know it? From the IPCC:
The so-called water vapour feedback, caused by an increase in atmospheric water vapour due to a temperature increase, is the most important feedback responsible for the amplification of the temperature increase.
To summarize, a doubling of CO2 will cause the temperature to increase by 1.2 degC, this increased temperature will then cause more evaporation of water vapor (the primary greenhouse gas) into the atmosphere which will amplify the effect of the CO2 caused warming, got it? This is known as the "enhanced greenhouse effect".
It is as if having reached the bottom of the hill our ball creates its own jet propulsion which overcomes the negative feedback of friction and keeps on going.
I mention all this in order that you may understand why the historical temperature records are so important. You see, in order for the enhanced greenhouse effect to work as a theory, it must work regardless of the agent of temperature increase. In other words according to the theory, to put it simply, at some point the Earth's atmosphere will reach a certain tipping point temperature which will cause this chain reaction (the enhanced greenhouse effect) and it really does not matter how the Earth's atmosphere reaches that tipping point, only that it does-then we are cooked. It is not the CO2 that will increase temperatures, it is the increased water vapor.
The entire enhanced greenhouse effect theory is a sham, but let's assume that it is not. In order for the alarmist to justify drastic action they must convince policy makers and the public that the current temperatures are unprecedented. Why ? Simply put that if in the past had the Earth's temperatures been as high or higher than today for extended periods, then the enhanced greenhouse effect should have kicked in regardless of how the temperatures reached that tipping point.
This is one important reason why the e-mails and data released are so important to the science question. These scientist were manipulating the historical record of past climate changes. It is not just that temperatures in the past were warmer without you driving your SUV, it goes to the very heart of the entire theory. If for example as was proven before the AGW nonsense took hold of science, the Medieval Warming Period was warmer than today, as was accepted until these guys got their hands and agenda on the data and the process, why did we not have runaway warming? Where was the enhanced greenhouse effect while they were making wine in England?
This is also why having proponents and advocates for an unproven theory also being the keepers of the records and the gatekeepers of the process by which the science is examined is so dangerous. It is as if my wife (a teacher) allowed her students to grade their own papers and worse they were paid based on the grades they received.
Update: One not quite insignificant point I wanted to make but forgot is about this one assertion in the IPCC literature quoted above:
It is believed that the overall effect of the feedback amplifies the temperature increase
Does this sound convincing, believed? Obviously it is not proven, it is not, or they would have stated that. Upon that belief the entire theory rests. It is also that "belief" or assumption which is fed into the computer models which forecast global warning. without this "belief" the entire theory falls apart.
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