1. Uncertainty in Climate Effects of Power from Coal and Natural Gas with CCS Greg Schivley, Constantine Samaras, and Paulina Jaramillo gs1@cmu.edu

2. Fossil fuels are difficult to shake Provide baseload power ~70% of current install capacity Primarily coal and natural gas Limiting CO 2 emissions will require CCS Uncertain when CCS will start Does timing affect fuels choice? 2

3. Background on coal vs gas Without CCS: Natural gas power has lower GHG emissions than coal unless CH 4 emissions are very high With CCS: ~2% CH 4 emissions needed for climate benefit (90% capture) Current emission rate is uncertain, likely 1-5% –Potential for reductions in methane emitted is not covered in current literature 3

4. Research questions How does CCS start time change climate impacts? Will reducing methane emissions from NG change results? What if coal plants use CCS at less than 90% capture? –EPA 111b limits new coal CO 2 emissions to 1,400 lbs/MWh (16% capture) 4

5. Scenarios Compare radiative forcing from 1 GW of new SCPC or NGCC power plants over 60 years to determine the effect of uncertainty from: 1.CCS deployment: Now, or retrofit in 20 years 2.CCS capture amount: 90% of CO 2 from SCPC and NGCC, or 16% capture from SCPC (111b) 3.Natural gas CH 4 emission rate: 1-5% 4.Reduce CH 4 emissions: Constant emission rate or halve over 10 years 5

6. Calculation of radiative forcing Emissions take place over 60 years of operation Every emission decays according to a response function (right) Mass of a species in the atmosphere is calculated using a convolution of the emission and response functions (above) Code available at github.com/gschivley/co-firegithub.com/gschivley/co-fire 6

7. Results SCPC starting with CCS similar to NGCC with constant 2-3% emission rate (subplot a) Delaying CCS for both increase RF from coal more than natural gas (subplots b, d) If CH 4 from natural gas is reduced within 10 years, initial emissions have almost no effect on the peak RF (subplots a, c) 7

8. Results If only coal has CCS, the coal plant will have lower RF over nearly all time frames (subplot e) Delaying CCS for coal and not using it for natural gas leads to a cross-over in forcing (subplot f) 8

9. Results SCPC power plants meeting 111b regulations have RF close to that of uncaptured NGCC with constant 4+% emissions, but peak higher (subplot a) Unless it leads to higher capture rates, SCPC 111b capture will have higher RF than uncaptured NGCC in cases where methane emissions are reduced over time (subplot b) 9

10. Discussion Natural gas methane emission rates are important –Under several scenarios they need to be under 3% to achieve lower radiative forcing than coal –If it is possible to reduce methane emissions in the near future, current emission rates are less important than the new emissions It is possible for coal with CCS to have lower RF than natural gas, but only if methane emissions stay high or CCS is not available for NGCC –Constant emissions of 3% or more can lead to higher RF for NGCC in several scenarios –Immediate implementation of CCS for SCPC (but not NGCC) favors coal as a fuel 10

11. Discussion Partial implementation of CCS for SCPC (111b) is useful if it enables higher capture rates in the future –SCPC stack emissions of 1,400 lbs/MWh lead to RF higher than uncaptured NGCC CCS is likely to start as capture and use –Use of CO 2 for enhanced oil recovery (EOR) may help to offset cost of capital equipment and operations –EOR is not primarily designed for sequestration, and it may lead to higher total oil production –Future research should investigate the effects of using CO 2 in EOR on RF, and how quickly operations would need to transition to full storage to provide a climate benefit 11

12. Acknowledgments This research was supported in part by the Climate and Energy Decision Making (CEDM) center through a cooperative agreement between the National Science Foundation (SES-0949710) and Carnegie Mellon University. Valuable data and feedback have been provided by the NETL LCA Team. 12