To conclude my three-part series on solar energy (Part 1 and Part 2), I will now address the aspect of global warming that is largely being ignored and which may still doom humanity to a long, hot Dark Age if not dealt with: Even with emission-free energy, humanity will still be pouring prodigious amounts of heat into the atmosphere at a time when the loss of ice caps and glaciers has darkened planetary albedo (i.e., made Earth more absorptive of energy that would otherwise be reflected back into space). Fortunately, the solutions are simple and cheap - provided we have the foresight to implement them in tandem with clean energy.
First, a review of basic physics. We've all had the experience of burning our hand on a metal surface in the hot sun, and yet find other surfaces - e.g., wood - are merely warm to the touch in the same light. While there are chemical complexities, we can say more or less correctly that this is not because the metal is hotter than the wood: Even at identical temperatures, the metal can burn your hand without the wood doing so. The reason is that metal can dump its accumulated energy into your hand much faster than wood can, and - more importantly - much faster than your hand can dump it into the rest of your body and the air.
So even though the metal and wood may be the same temperature, the wood gently warms your hand over time while the metal blasts the first layer of skin on your hand with all it's got. The relevant part of this example is your hand: Whenever thermal input into a system exceeds output, the result is an increase in temperature (again, with caveats for chemistry) until equilibrium is restored. The skin of your hand is heated much faster than the internal structure can absorb it, so the skin may be damaged as a result. We see in this example that the problem is not the absolute amount of energy passing through your hand - as long as the rates of input and output are in balance, the total amount of energy is thermally irrelevant (again, caveats).
Planet Earth only has two significant sources of energy - heat from its core, and absorption of radiant energy from the Sun. While there are small ecosystems based around seafloor vents and natural geothermal pools, the vast majority of the biosphere - including humanity - is directly dependent on solar input for survival, and no longer has as much contact with geological processes as it did in earlier eons when the crust was much more fluid. So while there are worthy investigations into such topics as the climate effects of geothermal outgassing, volcanism, and evaporation of greenhouse gases (GGs) dissolved in rocks, what mainly concerns me (as a modestly informed layman) is the overall balance of solar input with planetary re-radiation.
As noted, if these rates are permitted to remain imbalanced, the result will be continued global warming even with zero CO2, CH4, or other GG emissions. Consider the following graphic from Wikipedia, which looks roughly plausible (though I wouldn't rely on these numbers for any kind of mathematical calculation):
The small red block in the above graphic is not the current global consumption of clean energy, but the current global consumption of all energy combined. I'm not sure whether the author of the image generated his figure for solar using the total amount of solar energy that reaches Earth, or if it was a more nuanced calculation finding the amount of solar energy that would be practically obtainable, but the figure would be staggering even if it were a hundredth of what is shown. The upshot is this: The amount of heat being released into the atmosphere is trivial compared to what it will be after we transition to clean energy.
The process works like this:
1. Solar radiation reaches the Earth's atmosphere. At each given layer of the atmosphere, it can be reflected back upward, passed transparently to a lower layer, or absorbed by the gases that are then heated.
2. The radiation that passes the entire atmosphere transparently then reaches the ground, where it can be (similarly) reflected back upward or absorbed, heating the ground.
3. The atmosphere is only transparent or reflective to certain wavelengths of radiant energy, and others are absorbed. Unfortunately, when the ground absorbs solar energy at a wavelength the atmosphere passes, it can re-radiate it at wavelengths the atmosphere is not transparent to, causing the heat to be trapped. GGs are a problem because they make the atmosphere less transparent to long-wavelength radiation re-emitted by the ground, trapping it in the lower atmosphere where the biosphere exists.
So we have two BIG problems, both immediate but only one getting any attention: We are making the atmosphere less able to release energy, like the hand in the analogy above, and at the same time are pouring more energy into it at an increasing rate. Clean energy partially addresses the first problem by seeking to end additional direct GG pollution (though it will not undo that already released, and the consequent natural releases that follow), but as the above graphic illustrates, it will radically exacerbate the second problem. While I doubt we will allow this to happen, it seems that even a fully-renewable, zero-emission energy system could very easily make the planet unlivable without coming anywhere near maximum production.
Here is the problem of heat, boiled down to its essence: When you use energy, the waste heat that is radiated is always at a longer wavelength than the original. There is no way around this - it is inherent in thermodynamics. So without some manipulation of the Earth's reception of solar radiation, or increasing its ability to release heat back into space, more efficient, sustainable energy systems are a double-edged sword: They reduce the amount of energy released by a single application, but radically increase the total pool of available energy worldwide, ultimately guaranteeing an increase in the total power output (and thus, waste heat) of human civilization.
Most disturbing of all, the technology with the greatest promise also carries the greatest peril: Solar energy transforms surface area that would have been at least somewhat reflective into an efficient energy-capture system. The electricity that is thus generated results in heat that is then captured by the atmosphere, and at rates likely far higher than whatever heat would have been emitted by the original surface. This is especially acute given how solar installations are most financially attractive in desert environments, where the surface is largely light-colored, somewhat reflective sand, rock, and dust. Replacing these surfaces with solar energy systems is thermally equivalent to replacing dull mirrors with black metal - it absorbs light, and then radiates out infrared heat the atmosphere traps. As ice packs disappear and planetary reflectivity is diminished, this becomes increasingly relevant.
What is the solution? Clearly we can, should, and must make the transition to clean energy - there are not only climatological reasons for doing so, but also the simple fact that other forms of energy are unsustainable. Oil, coal, natural gas, and rare fissile materials cannot continue to underpin our economies over the long-term - they are diminishing, non-renewable commodities that incur vast unnecessary expenses to discover, acquire, process, transport, use, and defend (or steal) militarily. But we must also deal with the problems our technology would cause, and this time deal with them with foresight rather than waiting to be bitten in the ass later. That means the world should begin to cooperate on ways to manage the total energy input/output of the planet, to assure that we are not absorbing it more quickly than our atmosphere can release.
Fortunately, the ways to accomplish this are relatively trivial. All that has to be done is to replace and exceed lost reflective surface - enough to compensate for the warming effects of GGs by absorbing less overall energy, as well as compensating for the increased absorption caused by solar energy infrastructure. As Energy Secretary Chu has noted, this can be as simple as painting roofs white rather than darker colors. But the discussion on this subject needs to ramp up soon, because this is not a secondary concern - it is something that must be addressed in tandem with our elimination of GG emissions, or else the whole climatological purpose of clean energy is negated.
I can see any number of steps being feasible to address the problem efficiently, affordably, and in ways that minimize further unintended consequences. First, as noted, people can simply utilize more white and reflective surfaces in developed environments - much as many Mediterranean cities already have white roofs for their passive cooling ability. Second, there can and should eventually be large-scale projects whose purpose is to offset the albedo effect - large fields of mirrors and other reflective environments established to offset new solar plants.
But more importantly, these steps should begin to be taken in a systematic, quantitative way: Companies that provide solar panels could calculate what a system's global albedo impact would be, and give customers options for offsetting it. Companies that build large utility-scale installations could begin to offset them by creating more reflective sand for the surrounding environment. More desperate measures (e.g., blanketing huge tracts of desert and ocean dead zones with mirrored material) are imaginable if it comes to that, but I see no reason it should: This is common sense, and not expensive at all.
The biggest obstacle, I think, is that there is no direct profit in it. We can convince individuals on the forefront to pay extra to offset the thermal effects of clean energy, but businesses would have very marginal (if any) motivation to do so. They sell energy, and compensating for its externalities does not add anything to their profit margins: And that is how we got into this mess in the first place. But I am optimistic given the relatively low marginal cost of addressing the problem - I don't imagine white sand or white paint cost much relative to solar panels and thermal plants - as well as the greater awareness that the rise of clean energy business brings to the fore.
If we do this right, the possibilities of clean energy are more than utopian - the sheer amount of energy that's available, not to mention its sustainability, will permit us to realize previously abandoned science fiction dreams, transform economies into freer and more decentralized configurations, and make possible levels of civil engineering and urban planning that would be absurd today. They will give us technologies and mentalities that would serve us even in space, on other worlds, and allow our species to spread and diversify over the long-term. It would also give us a profound ecological awareness and appreciation for both the perils and the promise of any given environment, and make us more adaptable and far-sighted as a species. But it has to be done right, and soon.
Mon Jul 25, 2011 at 5:08 PM PT: Some of the comments indicate to me that I need to clarify something: Increasing surface reflectivity is important not merely to compensate for increased darkening due to solar panels, loss of ice, and urbanization, but also as a simple way to immediately compensate for heating caused by greenhouse gases. It expels energy at wavelengths better able to leave the atmosphere rather than being absorbed, and saved tons of CO2 emissions by keeping buildings cool. There is no downside.