Okay, let’s get into it.
[quote=“Rhythmdvl, post:14, topic:525197”]
I’m hoping that someone on the spectrum of (whatever you want to call it) through fence sitting can take a step back from politicking and talk about the fundamentals of the science.
To put it as briefly as possible:
[ul]
[li]Greenhouse gases are translucent to ultraviolet radiation. [/li][li]Greenhouse gases are opaque to infrared radiation. [/li][li]The greenhouse effect means that greenhouse gases trap energy in the atmosphere.[/ul][/li][/quote]
No one disputes the above. NO ONE. I find this is somewhat typical of those on the pro-global warming side: They quote the most-established science as being the sum total of the theory of global warming, and then challenge people to refute it. But the debate doesn’t exist here, so this is a straw man.
And this is a very broad statement that gets to the crux of the real scientific question: HOW does it react? If CO2 forcing pushes the temperature up, how does the earth respond? Some global warming advocates believe this is settled science, that we know what the world will do to an accuracy so great that we can predict temperatures a century from now to within a couple of degrees. There is legitimate dispute over this.
No question. However, you do realize that the change we’re talking about is rather small? We’re talking about an increase in CO2 of about 80 parts per million over the past 100 years. This is within the range of normal CO2 variance in the interglacial period.
[quote]
[ul][li]China, India, and the rest of the developing world’s populations are six to seven times that of the developed world (figure very general, feel free to correct)[/ul][/li][/quote]
China and India are also extremely energy inefficient, and as they become wealthier, we can expect their energy efficiency to increase. That means the rate of energy consumption will not be a linear relationship to economic growth times population. No doubt their output of CO2 will increase somewhat - especially in the short term.
[quote]
[ul][li]Over the next fifty years, China, India, et al will likely pursue a carbon-dependant development path.[/ul][/li][/quote]
“Likely” is a fairly broad guess. I agree that it’s likely. I just don’t know how likely. If ‘peak oil’ happens, they’ll shift rapidly to nuclear and other technologies. If the cost of wind and solar keeps declining, they may move away from fossil fuels because they aren’t economical. If an economic collapse happens in China and/or Japan or both, Asia’s economic output and energy consumption will actually decline. Perhaps substantially. There are a whole lot of unknowns here.
We don’t know that. The U.S.'s CO2 emissions are actually declining. The economy is shrinking, and energy efficiency is increasing. It’s entirely possible that energy efficiency and/or the switch to non-CO2 energy sources could increase at a rate faster than GDP growth, meaning that even in a growing economy the rate of CO2 emissions could decline. Note that China and India are undertaking large programs to build nuclear plants. Also note that China’s economic growth is bound to slow down, and probably quite dramatically, as they finish picking the low-hanging economic fruit.
This is the big question, isn’t it? Assume everyone agrees with the basic chemistry of global warming. The big question is what will it do to the earth in the long run?
There are huge unknowns here. Let’s look at them:
CO2 lifespan
We have only the vaguest idea of how long CO2 stays in the atmosphere. It’s complex, because a molecule of CO2 can go through several cycles of moving out of the atmosphere and back before it is permanently sequestered. The ‘short term’ cycle seems to be on the order of a few years. The long term cycle seems to be on the order of 50-200 years.
The difference in atmospheric accumulation over time between a 50 year lifespan and a 200 year lifespan is huge. If new CO2 is completely sequestered within 50 years, then the stuff we’re putting up today will be gone in 2060, and the accumulation by 2100 will be less than half of what it will be if the lifespan is 200 years.
What makes this more complicated is that there are feedback effects - the lifespan of CO2 in an atmosphere of 450 ppm CO2 may be dramatically different than the lifespan of CO2 in an atmosphere of 330ppm. This makes it hard to measure.
Long-Term Feedback
This is a difficult question. How does the earth respond to increases in CO2? We still don’t really know. And yet, this is really the critical question.
The basic chemistry of global warming calls for an increase from CO2 forcing of only a degree or two - not enough to worry about. To get to the scary increases of 4-8 degrees, you have to assume positive feedbacks from CO2 forcing - the one that’s most cited as being the big issue is water vapor. A warmer atmosphere can hold more water vapor. Water vapor is a potent greenhouse gas. So, the theory goes that CO2 forces temp up by a degree, which increases water vapor, which forces temperatures up even more, in a vicious positive feedback cycle.
However, there are many other feedbacks, which we only vaguely understand. A big one is cloud cover. Higher water vapor in the atmosphere will possibly mean more high clouds. This in turn will increase the Earth’s albedo and keep a lot of solar energy out of the lower atmosphere. This effect is potentially large enough to cause the temperature to swing by 2-4 degrees - maybe enough to completely countact the water vapor feedback.
Unfortunately for us, our cloud modeling is terrible. So terrible that the IPCC won’t even venture to issue one of its “Somewhat likely/somewhat unlikely” WAGs to it. The science just isn’t there yet.
Another possibility is that increased atmospheric water vapor will result in more snowfall at the poles, increasing the size of the ice caps over time and again increasing the Earth’s albedo. That was a common theory a few years ago - I don’t know what the latest research shows.
Another possible feedback mechanism is dust. If higher energy translates into more winds, particulate counts could go up in the atmosphere, cooling it.
Then there’s the various biological pumps that affect CO2 levels. A potential positive feedback is that the oceans can absorb less CO2 as they warm up, causing the lifespan to increase. Recent research indicates this effect is smaller than once thought. Negative feedbacks include the increase in plant growth when CO2 increases. This can be quite dramatic. It’s entirely possible that the result of our increased CO2 emissions will be increasingly rapid regrowth of rainforests and new pine forest.
Another feedback is algae. A large algae bloom can absorb as much carbon as the US emits in a year. We don’t have a good handle on how increased CO2 will affect algae blooms, because blooms themselves are affected by many changing variable - ocean acidification, temperature, etc.
Another feedback is ocean currents. We still don’t understand these very well. Ocean currents act as heat transfer mechanisms, moderating temperatures around the world. We’re still trying to figure out exactly what affect a warmer atmosphere will have on ocean currents.
Then there are the feedback mechanisms we don’t understand, or perhaps don’t even know exist. But the earth’s climate gets upended all the time - major volcanoes can change the temperature faster in one year than we’ll manage in several decades. CO2 levels fluctuate. Massive forest fires and other disasters can wipe out huge CO2 sinks and simultaneously release large amounts of CO2. And yet, measured on the order of decades, the temperature seems remarkably stable.
Cont’d.