CO2-equivalence metrics for surface albedo change based on the radiative forcing concept: a critical review

Abstract

Abstract. Management of Earth s surface albedo is increasingly viewed as an important climate change mitigation strategy both on (Seneviratne et\xa0al., 2018)\nand off (Field et\xa0al., 2018; Kravitz et\xa0al., 2018) the land. Assessing the impact of a surface albedo change involves employing a measure like\nradiative forcing (RF) which can be challenging to digest for decision-makers who deal in the currency of CO2-equivalent\nemissions. As a result, many researchers express albedo change (Δα) RFs in terms of their CO2-equivalent effects,\ndespite the lack of a standard method for doing so, such as there is for emissions of well-mixed greenhouse gases (WMGHGs; e.g., IPCC AR5, Myhre\net\xa0al., 2013). A major challenge for converting Δα RFs into their CO2-equivalent effects in a manner consistent\nwith current IPCC emission metric approaches stems from the lack of a universal time dependency following the perturbation (perturbation\n“lifetime”). Here, we review existing methodologies based on the RF concept with the goal of highlighting the context(s) in which the\nresulting CO2-equivalent metrics may or may not have merit. To our knowledge this is the first review dedicated entirely to the topic\nsince the first CO2-eq. metric for Δα surfaced 20\xa0years ago. We find that, although there are some methods that sufficiently\naddress the time-dependency issue, none address or sufficiently account for the spatial disparity between the climate response to CO2\nemissions and Δα\xa0– a major critique of Δα metrics based on the RF concept (Jones et\xa0al., 2013). We conclude that\nconsiderable research efforts are needed to build consensus surrounding the RF “efficacy” of various surface forcing types associated\nwith Δα (e.g., crop change, forest harvest), and the degree to which these are sensitive to the spatial pattern, extent, and\nmagnitude of the underlying surface forcings.\n