Accounting for the return on invested energy is the key to understanding the prerequisites of climate change solutions.
Removing carbon from the atmosphere and safely storing it away for millions of years is fundamentally a chemistry problem and chemistry requires energy. It takes energy to capture carbon dioxide and still more to change it from a gas to something more stable for storage. Importantly, it takes more energy to recapture the carbon from burned fossil fuels than the fuels yielded in the first place. As we’ll see in this installment, machine mediated approaches to carbon capture and storage or sequestration can certainly work in prototype but they would consume so much energy that they are fundamentally impractical on a global scale.
The laws of thermodynamics make it clear that energy runs downhill meaning that whenever we convert from one form of energy to another some of the energy is lost due to inefficiencies that are just part of nature. Take a car for example. When they run, cars give off heat which is waste energy caused by friction between parts, between tires and the road, even air resistance produces a form of friction called drag. Some friction is good, for instance brakes take momentum from a car and convert it to heat so that a car can stop safely. Also, if there was no friction between the tires and the road the car couldn’t move. Even green plants are only about 50 percent efficient, for instance light reflecting from them to our eyes is energy not captured for photosynthesis.
Fossil fuel fired electric power plants burn coal to boil water to make steam to drive generators. Only about one third of the energy originally present in the fuel is actually transmitted into electricity, most of the rest goes up the smokestack or is lost to various forms of process friction. But that’s not all; resistance in transmission lines turns some of the electricity into heat meaning it never reaches the consumer.
This is where we are with mechanical carbon capture and sequestration schemes. They consume large amounts of electrical energy generated by fossil fuels so that getting ahead of the problem is impossible. You can actually run a demonstration project that captures and sequesters carbon dioxide but because the process uses so much energy you’ll always be running behind and creating more pollution than you capture.
Some have advocated using renewable power from wind and solar to drive the process but renewable power is already being aimed at retiring fossil fuel power plants and bringing renewable power to the broader electricity market. Renewables are necessary too because fossil fuels are beginning to run out. This means building a great deal of renewable power generation capacity but there’s a better approach.
A carbon capture solution based on solar energy works perfectly if green plants are doing all of the work because plants use an energy source that’s both clean and outside of the earth-bound energy system, i.e. the sun. Green plants use chlorophyll to capture solar energy to split water into hydrogen and oxygen. They attach the hydrogen to carbon dioxide on the way to turning it into sugars while letting the oxygen flow into the atmosphere. The fossil fuels we use today are derived from the work green plants did capturing sunlight millions of years ago and nature has never stopped driving that process. What’s needed now are ways to speed up these processes so that we can reverse some of the most drastic effects of carbon pollution.
Today green plants, including food crops, grasses, trees, mosses, and tiny sea creatures like algae and phytoplankton, capture solar energy at an annual rate estimated at 130 terawatts, which equals more than 6 times the power consumed by human civilization. Green plants turn this solar energy into biomass equal to between 100 and 115 billion tons — importantly, not all of it is food. But there are large swaths of the earth including oceans and deserts where very little photosynthesis happens because one or more factors essential to plant life are absent such as fresh water.
If we could find ways to double the photosynthetic output of all green plants (while greatly limiting the amount of new pollution we generate) we’d have a solution that could remove one trillion tons of CO2 from the air in about ten years.
One trillion tons is a lot and to be clear, some of that biomass would decompose quickly re-releasing carbon back to the environment, but that’s not a bad thing. Using photosynthesis to remove carbon from the environment provides a reversible mechanism to help ensure that the removal effort doesn’t go too far and spawn another ice age. Using this approach the climate problem becomes a chronic problem rather than an emergency and with that change solutions come into view.
The concluding post in this series looks at solutions.