With oil prices hovering near historic highs and coal, natural gas and uranium prices yo-yoing during the last several years, concerns about the future of fossil fuel and uranium supplies often elicit the response: "They'll think of something. They always do."
This kind of thinking is usually premised on the idea that the future will look like the past, only bigger and better. It does not even admit the possibility that we may need to reduce our energy use. We'll come back this issue later.
The pronoun "they" in the generic quote above is vague, and the speaker does not know that he or she is actually referring to two distinct technological approaches to our energy future. Each technology progresses amid a different and highly consequential backdrop.
Let me cut to the chase. Advancements in technology designed to extract more oil, natural gas, coal and uranium from the ground are in a race with geological constraints. The more of each type of fuel we extract, the more difficult it is to wrest each subsequent barrel, cubic foot, or ton from the Earth's crust. The deposits become leaner, that is, there are fewer units of what we want per ton of earth--and more refractory, that is, more challenging to process in order to separate the stuff want from the stuff that isn't oil, natural gas, coal and uranium. The empirically established principle is that we go after the easy deposits first and save the difficult ones for later.
So now, we are arriving at the difficult ones: shale gas, tight oil, tar sands and low-grade uranium deposits. Rather than debate the future supplies of each which cannot be known with any certainty, let me turn to the the backdrop for what we call renewable energy.
The technological progress we make in solar and wind occur against a dramatically different backdrop. The light from the sun is not becoming less and less intense over the long run forcing researchers to think of ways to capture more and more of the diminishing intensity of sunlight. Instead, even though there are cycles to the sun and cloudy days, the light from the Sun that hits the Earth is remarkably steady. In fact, over the next 5 billion years, the Sun will actually increase in brightness before starting its transformation into a red giant.
Unlike researchers who experiment with methods for extracting ever more lean and refractory deposits of fossil fuels and uranium, solar energy researchers are not fighting a depleting Sun in any time frame meaningful to humans. Their task is to find ever more efficient ways to capture sunlight and turn it into heat and electricity, sunlight that is so ubiquitous and so plentiful that the equivalent of 7,000 times the current human usage of all forms of energy is absorbed by the Earth's land, oceans and atmosphere each year. With solar we are not and will never be in a race against depletion (unless the human species lasts for 5 billion years--which is unlikely since the lifespan of mammalian species averages about 1 million years, though some may persist for up to 10 million years).
Wind, of course, is a derivative of solar power since it merely represents air currents which form in response to the uneven heating of the atmosphere. Given existing technology, there are, naturally, only certain places that are suitable for wind generators. But, as the technology improves, more places will be practical for the placement of wind towers and small household wind devices.
I suppose it is theoretically possible to place enough wind generators on the surface of the Earth to dissipate all the winds. But we are so very far from that, that I think it will likely never become anything but a sporadic local issue far into the future.
Geothermal energy has vast potential, but low efficiency given the costs of extracting it from deep in the Earth. I still see a role for geothermal, but I can't make the claim that it is as a practical matter ubiquitous or, on a local scale, inexhaustible.
I ultimately see a limited role for biofuels to provide liquid fuels for emergency vehicles, rural transport and farm machinery. But, they will not actually be renewable until we stop engaging in agriculture which erodes and degrades rather than builds the soil. For now we must accept that biofuels are actually part of a mining operation--only in this case what is being mined is the fertility of the soils and the fossil fuels used to plant, fertilize, weed and protect biofuel crops from pests.
Ocean thermal, tidal power and wave energy will certainly be niche players. Hydroelectric power has some new potential in developing countries where all the major rivers have yet to be dammed. Small hydroelectric still has possibilities in developed countries. But, most major rivers there have already been dammed. Keep in mind that dams eventually silt up (unless they are dredged) and cease to be sources of energy for society.
So, here's the score so far. Researchers seeking to extract fossil fuels and uranium from the Earth's crust are in a race with ever more stringent geological constraints, a race they will ultimately lose. If that were not the case, we would not already be seeing declines in oil production in country after country in the last 40 years. And, we can expect that this will happen for the world at some point, not only for oil, but for natural gas, coal and uranium as well.
But, as a practical matter, the physical limits of sunlight will NEVER, EVER be reached. What's more, sunlight is not becoming more difficult to access. We have the same access to it today, tomorrow and for the next 5 billion years.
There are some limits to solar and wind power, however, that have nothing to do with their fuel source, sunlight. To scale solar and wind energy production large enough to produce the amount of energy we use today as a global society would take so long--even at vastly increased rates of deployment--that we will almost certainly fail to do so before fossil fuels begin their inevitable and perhaps swift decline.
The other task is to transform an infrastructure dependent on liquid fuels for transportation into one which uses primarily electricity. We are slowly beginning the transition to electric vehicles. But it is at a very slow rate compared to the rate we need. And, private automobiles are almost certainly not the answer for the future. Electric trains, trolleys and buses are a better alternative.
Then, there is the problem of electricity storage. We know how to store electricity, but it is very costly. We need new low-cost solutions, and many researchers are trying to find them.
All these limits on renewable energy explain in part why we have not embraced it as fully as we need to, and why we still prefer fossil fuels and uranium for the lion's share of our energy needs.
But it won't matter what we prefer when the rate of production of nonrenewable energy sources starts to decline. If we are not ready, we will be in a world of hurt.
The only sensible response to this looming possibility is to begin reducing our energy use now in earnest. If we do that, we have a much better chance of making a successful transition to a renewable energy economy--a transition which will happen whether we like it or not.
We actually know right now how to make dramatic reductions in energy use while only affecting our daily activities minimally. But, it will cost money up front (which we'll get back in the form of energy savings). And, it will require enormous political will because some of the changes will have to take place in our transportation and utility infrastructures, both of which are now largely committed to fossil fuels and nuclear power.
Reductions in energy use and the rapid transformation of our infrastructure are not typically what people think about when they say, "They'll think of something. They always do."
We have indeed thought of something. But that something is going to require the active participation of everyone. It isn't going to be done TO us. It will have to be done BY us.