Climate mitigation potential of natural climate solutions and clean energy on The Nature Conservancy properties in California, USA

management lease or agreement. Utility data was collected for all properties from 2021 billing records. CO2e was calculated based on the carbon emitting activity data (i.e., gallons of pro- pane) times a carbon emission factor per activity and the global warming potential (S2 Table) [26]. Replacing the use of grid-sourced electricity and burning of fossil fuels with solar panels and heat pumps is presumed to reduce the CO2e emissions completely. Results Based on the literature review, the NCS activity with the highest sequestration rate was tidal wetland restoration, with a mean value of 14.2 MTCO2e ha –1 year –1 (Fig 1, S4 Table). The activity with the lowest sequestration rate was cover cropping with a mean value of 2.75 MTCO2e ha –1 year –1. All NCS activities stored on average 9.5 MTCO2e ha –1 year –1. Potential NCS activities were identified across 37 fee properties covering 7,842 ha, or 11% of all fee-owned land (Fig 2). This total area is close to the goal of NCS activities being imple- mented on 10% of fee lands in California by 2030. NCS activities on conservations easements were identified across 65 properties covering a smaller total area, 3,149 ha. Clean energy transi- tions were identified for 14 properties (Table 3). The total climate mitigation potential of all the NCS activities and clean energy solutions was 63,663 MTCO2e year –1 on fee lands and 27,091 MTCO2e year –1 on conservation ease- ments (Fig 3). Clean energy accounted for 516 MTCO2e year –1 across fee lands and other

properties with 85% of the total reduction potential from water pumps at the Staten Island property. The CO2e reduction potential on fee properties is equivalent to 15,152 gasoline-pow- ered cars driven for one year or 8,302 homes’ energy use for one year [27]. The annual reduc- tion potential of all properties combined was less than the ongoing annual sequestration at the Fig 1. Sequestration rates for all NCS activities. Mean and ranges based on past studies (S1 Table). https://doi.org/10.1371/journal.pone.0311195.g001 PLOS ONE Climate mitigation potential of natural climate solutions and clean energy: The nature conservancy, California PLOS ONE | https://doi.org/10.1371/journal.pone.0311195 October 21, 2024 6 / 14