Landscape change and climate attribution, with a case study of estuarine marshes

Determining effects of climate change on landscapes involves numerous uncertainties. This paper presents and illustrates a protocol for climate attribution of landscape responses. The major steps are ascertaining potential climate-related responses, establishing plausibility for a climatic influence, identifying alternative or additional causes, testing possible climate and non-climate causes, and interpreting the role of climate and climate change in the landscape response. The protocol is based on existing practice in the historical and interpretive branches of Earth and ecological sciences, and explicitly considers negative (non-confirmatory) results for climate and other factors. The protocol is applied to the conversion of brackish marsh to open water in the upper Neuse River estuary, North Carolina. Conversion since at least the mid twentieth century can be attributed to relative sealevel rise, driven primarily by general climate warming, with no supporting evidence for any additional or alternative drivers. The only other factor with supporting evidence is human modification in the form of ditches, around which conversion was concentrated, though marsh loss also occurred in unditched portions. Rapid recent marsh loss is attributable to Hurricane Florence (2018), particularly the storm surge. Weak positive inferential support exists for a role of climate change in the storm, but aspects of the storm's impact not linked to climate are more important for the marsh conversions. Overall, the landscape response can be linked to climate, exacerbated by direct human impacts of marsh ditching, and strongly influenced by local place factors and the specific storm track. Recent and ongoing climate change is a significant factor, but not paramount, in determining the landscape response. The Neuse River case study is not unusual-and is probably typical-in identifying a combination of climate and other factors strongly influencing landscape response.