How we calculated the costs of climate inaction

This Costs of Inaction research series is based on data from multiple sources, including a first-of-its kind study by Hsiang et al. 2017 through the Climate Impact Lab. This study calculated the costs of climate change using climate science, econometric analyses, process models and more than 100 climate projections.

Although many key findings from this study focused on climate costs in the mid-to-late century time frame, this series focuses on median estimates of the near-term costs within the next 20 years.

Arizona

Extreme heat: The number of additional deaths per 100,000 people expected by 2040 from heat-related causes was approximated using median mortality rate estimates from Hsiang et al. 2017 for the 20 year time period 2020-2039. Percent increases were estimated using 2019 data on heat-related deaths from Maricopa County public health and Arizona Department of Health Services.

Electricity costs: Percentage changes in electricity expenditure were taken directly from the Hsiang et al. 2017 study, which used a version of the National Energy Modeling System (NEMS) to model future energy costs. Changes in costs were estimated using state-level average monthly electricity bills for commercial and residential customers and Hsiang et al. 2017 fractional cost increases for the 20-year time period 2020-2039. To learn more about NEMS or the Hsiang et al. 2017 assumptions and methodology, see their article and supplementary materials.

Crop yields: Declines in agricultural yields were taken directly from Hsiang et al. 2017. Determining net revenue changes was beyond the scope of this analysis since we were unable to factor in future commodity prices and trade projections.

Note: All damage estimates assume a Representative Concentration Pathway (RCP) of 8.5, or a “high emissions” scenario, and depict average annual changes from a 2012 baseline over the period 2020-2040. Additionally, significant figures throughout are revised to reflect the degree of uncertainty inherent in the analysis.

Florida

Property taxes: We found the total property tax values expected to be lost by 2030 and 2045 respectively by taking the sum of property taxes lost by each coastal Florida zip code outlined by the Union of Concerned Scientists: Underwater report for each respective time period. For county specific losses, we aggregated zip code property tax data to the county level. Additionally, we included data on the total number of properties at substantial risk of all types of flooding by 2035, including chronic flooding. This was taken directly from a new First Street Foundation flood model dataset, which defines substantial risk as a 1% annual chance of inundation of 1cm or more.

Extreme heat: We found the number of additional deaths per 100,000 people expected by 2040 from heat-related causes by using median mortality rate estimates from Hsiang et al. 2017. These mortality rates are based on the 20 year time period 2020-2039. Estimates for total economic value lost as a result of climate-change-related mortality were derived from the U.S. Environmental Protection Agency's estimate for the value of a statistical life. Factors like lost childcare and education of the next generation, as well as impact on the labor force are incorporated into this value.

Electricity costs: To find the percentage changes in electricity expenditure, we used data from the Hsiang et al. 2017 study, which used a version of the National Energy Modeling System (NEMS) to model future energy costs. We estimated these changes in costs by using state-level average monthly electricity bills for commercial and residential customers, and Hsiang et al. 2017 fractional cost increases for the 20-year time period 2020-2039. To learn more about NEMS or the Hsiang et al. 2017 assumptions and methodology, see their article and supplementary materials.

Note: All mortality and electricity expenditure estimates assume a Representative Concentration Pathway (RCP) of 8.5, or a "high emissions" scenario, and depict average annual changes from a 2012 baseline over the period 2020-2040 (unless otherwise noted). Property Tax flood data assumes a high sea level rise scenario: a scenario that results in 6.6 feet of global sea level rise by 2100. Additionally, significant figures throughout are revised to reflect the degree of uncertainty inherent in the analysis.