Advocates and opponents of capturing CO2 emissions from power plants and storing them underground agree on at least one thing: doing it will not be cheap. Current cost estimates for sending the gas deep underground are in the range of tens of dollars per metric ton of CO2, so sequestering one gigaton (Gt) a year—roughly one sixth of U.S. emissions—would cost tens of billions of dollars annually. Most of that cost arises from the thermodynamics of separating CO2 from flue gas emitted by burning hydrocarbons. There’s no getting around thermodynamics, which has motivated my colleagues and me to propose a radical storage system that could pay for itself (see “Hot Brines Deep Underground Could Store CO2 and Generate Energy,” Scientific American, November 2013).

Our design is a closed-loop system that injects CO2 into hot, methane-saturated brine brought to the surface from deep underground. The CO2-laden brine would be sent back underground for permanent storage. The injection forces out methane and heat, which would be sold for commercial power and heating—paying for the storage. The methane could also power the system and provide energy for carbon capture at the power plant.

Although the methane and geothermal energy produced more than offsets the energy consumed for operating the process, the number of storage and extraction wells and hence the capital required to store one Gt of CO2 per year with this process is large. But so is the cost of any method of reducing greenhouse gas emissions enough to make a similar difference—whether it’s doubling the fuel efficiency of every single car and truck on the road (which would cost a few trillion dollars and take at least 15 years) or building scores of new wind turbines for each turbine already turning today or erecting hundreds of new solar cell arrays for every array in use today. At the one-Gt scale, multiple technologies will be needed, and ultimately energy consumers will bear the costs of construction and operation. For example, conventional geologic storage of CO2 is expected to increase electricity prices 30 to 50 percent.

It is disingenuous to present such increases as reasons not to mitigate emissions. Consider that during the 1990s the price of oil was fairly stable, averaging $28 a barrel (in 2011 dollars). Between 2000 and 2005 the oil price in real dollars doubled, and it doubled again by 2011 (even after plunging during the recession) and has remained high ever since. Yet global oil consumption and the global economy grew steadily throughout this period. (Growth was interrupted in 2008 to 2010 by the recession, the causes of which were unrelated to oil prices.) This suggests that although the supply of energy is crucial to economic activity, the cost of energy is relatively modest in much of the world. And unlike the vagaries of oil prices, the process of implementing and paying for CO2 storage can be planned and structured. Even though debate continues, many experts believe the costs of adapting to the consequences of a changing climate would be even larger than the costs of taking action to reduce CO2 emissions.

The bottom line: We need to expect to pay more than we have been for energy. That’s how large the scale of CO2 emissions has grown.