This is the third chapter of an ongoing series. Other parts of the series are here:
- Greenhouse Gas Theory
- Feedbacks (this article)
- A) Actual Temperature Data; B) Problems with the Surface Temperature Record
- Attribution of Past Warming: A) Arguments for it being Man-Made; B) Natural Attribution
- Climate Models vs. Actual Temperatures
- Are We Already Seeing Climate Change
- The Lukewarmer Middle Ground
- A Low-Cost Insurance Policy
We ended the last chapter on the greenhouse gas theory with this:
So whence comes the catastrophe? As mentioned in the introduction, the catastrophe comes from a second, independent theory that the Earth's climate system is dominated by strong positive feedbacks that multiply greenhouse warming many times into a catastrophe.
In this chapter, we will discuss this second, independent theory: that the Earth's climate system is dominated by positive feedbacks. I suppose the first question is, "What do we mean by feedback?"
In a strict sense, feedback is the connection of the output of a system to its input, creating a process that is circular: A system creates an output based on some initial input, that output changes the system's input, which then changes its output, which then in turn changes its input, etc.
Typically, there are two types of feedback: negative and positive. Negative feedback is a bit like the ball in the trough in the illustration above. If we tap the ball, it moves, but that movement creates new forces (e.g. gravity and the walls of the trough) that tend to send the ball back where it started. Negative feedback tends to attenuate any input to a system -- meaning that for any given push on the system, the output will end up being less than one might have expected from the push.
Positive feedback is more like the ball sitting on top of the hill. Even a small tap will send it rolling very far away, because the shape of the hill and gravity tend to push the ball even further in the direction of the tap. Positive feedback amplifies or multiplies any input to a system, meaning that even small pushes can lead to very large results.
The climate temperature system has a mix of positive and negative feedbacks.
For example, consider cumulus clouds. If the Earth warms, more water tends to evaporate from the oceans, and some of that water will form big fluffy white clouds. These clouds act as an umbrella for the Earth, reflecting heat back into space. So as more clouds form due to warming, there is a net new cooling effect that offsets some of the original warming. The amount of warming we might have expected is smaller due to the negative feedback of cloud formation.
On the other side, consider ice and snow. Ice and snow reflect sunlight back into space and keep the Earth cooler than it would be without the ice and snow cover. As the world warms, ice and snow will melt and thus reflect less sunlight back into space, having the effect of warming the Earth even more. So an initial warming leads to more warming, amplifying the effect of the initial warming.
Since we know both types of feedback exist, what we care about is the net effect -- does negative or positive feedback dominate? In every catastrophic forecast you have seen for global warming, in nearly every climate model the IPCC uses, the authors have assumed that the climate is dominated by strong positive feedbacks that multiply incremental warming from greenhouse gasses many times.
This is the result:
As a reminder, the green line is the warming from increases in atmospheric CO2 concentration solely from the greenhouse gas effect, without any feedbacks taken into account. It is generally agreed to be a warming rate of about 1.2C per doubling of CO2 concentrations, with which I and many (or most) science-based skeptics agree. The other lines, then, are a variety of forecasts for warming after feedbacks are taken into account. You can see that all these forecasts assume positive feedback, as the effect is multiplicative of the initial greenhouse gas warming (the pink, purple, and orange lines are approximately 3x, 5x, and 10x the green line, implying very high levels of positive feedback).
The pink line is the mean forecast from the 4th IPCC, implying a temperature sensitivity to CO2 of about 3C. The purple line is the high end of the IPCC forecast band, implying a temperature sensitivity of 5C. And the highest is not from a mathematical model per se, but from the mouth of Bill McKibben (sorry for the misspelling in the chart) who has on several occasions threatened that we could see as much as 10C of warming from CO2 by the end of the century.
Skeptics have pointed out a myriad of issues with the climate computer models that develop these forecasts, but I will leave those aside for now. Suffice it to say that the models exclude many important aspects of the climate and are subject to hand tuning that allows modellers to produce pretty much any output they like.
But I do want to say a few words about computer models and scientific proof. Despite what you will hear from the media, and even from the mouths of prominent alarmist scientists, computer models do not and cannot constitute "proof" of any sort. Computer models are merely tools we use to derive the predicted values of physical parameters from complex hypotheses. They are no different than the pen and paper computations an 18th century researcher might have made for the position of Saturn from Newton's celestial mechanics equations. The "proof" comes when we take these predicted values and compare them against actual measurements over time and find that they are or are not accurate predictions. Newton's laws were proved as his equations' outputs for Saturn's position were compared to Saturn's actual measured position (and in fact they were disproved, to a small extent, when Mercury's position did not accurately match and Einstein has to fix things a bit). Similarly, hypotheses about global warming will be proved or disproved when the predictions of various models are compared to actual temperatures.
So we can't really get much further until we get to actual observations of the climate, which we will address in the next several chapters. But I want to make sure that the two-part theory that leads to catastrophic global warming is clear.
This is the portion of the warming due to greenhouse gas theory:
As you can see, the portion due to greenhouse gas theory is relatively small and likely not catastrophic. The catastrophe comes from the second independent theory that the Earth's climate system is dominated by strong (very strong!) positive feedbacks.
It is the positive feedback that causes the catastrophe, not greenhouse gas theory. So in debating catastrophic man-made global warming theory, we should be spending most of our time debating the theory that the climate is dominated by strong positive feedbacks, rather than debating the greenhouse gas theory.
But in fact, this does not happen in the mainstream media. If you are an average consumer of climate news, I will be you have never heard a discussion in the media about this second theory.
And this second theory is far from settled. If on the "settled" scale from 1-10, greenhouse gas theory is an 8 or 9, this theory of strong positive feedbacks dominating the climate is about a 2. In fact, there is plenty of evidence that not only are scientists estimating feedbacks incorrectly, but that they don't even have the sign right and that net feedbacks may be negative.
This is a bit hard to communicate to a layman, but the positive feedbacks assumed by the most alarmist and catastrophic climate forecasts are very, very high. Way higher than one might expect in advance upon encountering a new system. This assumption of strong positive feedbacks is one that might even offend the sensibilities of the natural scientist. Natural systems that are long-term stable (and certainly for all its variation the climate system has remained in a pretty narrow range for millions and millions of years) are typically not dominated by positive feedbacks, they are dominated by negative feedbacks.
If in fact our climate temperature system is dominated by negative feedbacks, the future warming forecast would actually be below the green line:
OK, without getting in and criticizing the details of these models (which would by the way be a pointless wack-a-mole game because there are dozens of them) the best way to assess the validity of these various forecasts is to now consult actual observations. Which we will begin to do in our next chapter, part 4a on actual temperature measurements.