Table 1 Summary of scenarios

Reference

On-the-books federal and state electric sector policies and incentives

Net-zero

Net carbon emissions equal zero nationally

Carbon-free

Electricity generation does not use fossil fuels or does not emit carbon

2035

Zero emissions target by 2035

2050

Zero emissions target by 2050

Low

U.S. EIA Annual Energy Outlook High Oil and Gas Supply

Reference

U.S. EIA Annual Energy Outlook Reference

High

U.S. EIA Annual Energy Outlook Low Oil and Gas Supply

Reference (NZ ref)

N/A

Lower renewables and battery costs (LoRE)

Capital costs for wind, solar, and batteries exhibit faster declines (Supplementary Fig. 5)

Zero emission fossil CCS (HiCapture)

Availability of a CCS-equipped gas technology where the flue gas has CO₂ concentration similar to the atmosphere and costs similar to 90% capture

No new NGCC capacity (NoGas)

No new NGCC capacity investment allowed in any region after 2020

No new NGCC or CCS capacity (NoGasCCS)

No new NGCC or CCS-equipped capacity allowed in any region after 2020

Upstream methane with 3% leakage (3% Leak)

Adjust upstream gas system CH₄ releases with 3% leakage rate (instead of the reference assumption of 1.5%)

CCS tax credits (45Q)

Section 45Q tax credits of $32/t-CO₂ for sequestered CO₂ in 2020 increasing to $50/t-CO₂ by 2026

Low-cost long-duration energy storage (LDES)

Stylized long-duration storage availability with energy capacity costs of $10/kWh, consistent with the U.S. DOE’s Long Duration Storage Shot

Pessimistic natural gas assumptions (Pess)

Combining pessimistic assumptions about gas (high CH₄ leakage, high prices, high BECCS cost, no DAC, and high CO₂ storage costs) and optimistic renewables, storage, and electrolyzer costs