Changes in Land Cover and Terrestrial Biogeochemistry in the US: Key Findings from the Climate Science Special Report (CSSR)

Friday, December 15, 2017 - 09:45
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The continual increase in annual average temperatures (1.0°C for the period 1901–2016 for the contiguous US), growing number of high temperature records, increasing intensity and frequency of heavy precipitation events in most parts of the US, and rising global mean sea level are among the key findings from the forthcoming Climate Science Special Report (CSSR) produced by the US Global Change Research Program (USGCRP). A chapter new to the climate science assessments directly addresses the feedbacks between climate change, land use and land cover change, and the carbon cycle. While the terrestrial biosphere is presently a net carbon sink, which has steadily increased since 1980, the future sign and magnitude of biosphere uptake cannot be determined because of uncertainties in the future trajectory of land cover and land use. Citing recent research, the chapter highlights that the combined effects of land use and land cover changes due to human activities account for 40% ± 16% of the human-caused global radiative forcing from 1850 to present. Moverover, plant community structure has already been altered by climate change and changes in the frequency and intensity of extreme events. Changes in temperature also have direct effects on the land surface as well as feedbacks to the atmosphere. For example, the number of consecutive frost-free days and the length of the growing season have increased across all regions in the contiguous US; however, overall plant productivity has been limited by biotic factors and seasonal limitations in water and nutrient availability. Within cities, the urban heat island (UHI) effect results in daytime temperatures 0.5°C–4.0°C higher and nighttime temperatures 1.0°C–2.5°C higher in urban areas than surrounding rural areas. We discuss terrestrial and biogeochemical forcings and feedbacks that can serve as critical evaluation and paramaterization datasets for Earth system modeling approaches with implications for management of agriculture, forestry, and urban environments.

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