Carbon capture and sequestration (CCS) technology offers more hope than generally is believed as a way to allow use of fossil energy while meeting aggressive targets for mitigation of climate change, says a new report.
A study by the Sustainable Gas Institute (SGI) at Imperial College London observes that pessimistic assessments of CCS tend not to look beyond 2050, when advantages of the technology begin to rise in relation to those of other mitigation strategies.
The study suggests CCS could unlock fossil energy reserves now targeted for nondevelopment as “unburnable carbon.”
That concept arises from estimates of the amount of carbon dioxide that can be emitted without compromising a two-thirds chance that global average temperature will rise no more than 2°C. above preindustrial levels. That was a central goal of the Paris climate summit last year.
At current emission rates, the so-called carbon budget of about 1,000 gigatonnes will be depleted within 30 years, according to the study. These trends give rise to estimates of unburnable carbon and political appeals to forswear development of oil, gas, and coal resources.
Capture rate crucial
Past studies of the role of CCS in climate-change mitigation reviewed by SGI tended to assume technical limits on CO2 capture rates of 85-90%. If that rate were increased to “well over 90%,” SGI says, “more of the world’s fossil fuel reserves could be used while still remaining within the limits of a 2°C. climate-change scenario.”
In the second half of this century, it says, “a higher capture rate becomes pivotal if fossil fuel reserves are to be used without unwarranted climate impact.”
The potential effects on fossil-energy development and use are large.
Models used in the Intergovernmental Panel on Climate Change Fifth Assessment Report find that average fossil energy use is almost 33 billion boe/year higher by 2015 when CCS use is assumed than when it is not. The difference in cumulative fossil-fuel consumption between CCS and no-CCS assumptions is 570-816 billion boe in 2050 and rises to 2.3-2.6 trillion boe by 2100.
Consumption rates of coal and natural gas are more sensitive than that of oil to CCS adoption.
While near-term costs of CCS represent a barrier, the costs of alternative strategies will rise above those of CCS over time, the study says.
“Beyond 2050, the costs of capturing and storing CO2 are likely to be significantly less than the marginal cost of alternative ways to mitigate CO2,” it says.
Average marginal costs for emissions abatement in models used to support the IPCC’s Fifth Assessment Report are $473-1,100/tonne of CO2-equivalent by 2050, rising further by 2100.
The estimated cost for CCS, including transportation, is $155-160/tonne.
Storage capacity is “substantial,” the SGI study says. Capacity in oil and gas reservoirs is estimated at 400-1,000 gigatonnes. Other geological sites, such as saline aquifers, can increase capacity to 10,500-33,000 gigatonnes, the study says. The current emission rate is 34 gigatonnes/year of CO2-equivalent.
With economics favorable in comparison with other low-carbon energy technologies and storage capacity adequate, the study says, a central goal of CCS development should be raising capture rates to lower the 10-15% of “residual emissions” assumed for current technologies.