Quantifying the Effects of Historical Land Cover Conversion Uncertainty on Global Carbon and Climate Estimates
Land cover conversion uncertainty constitutes a 5 ppmv range in estimated 2004 atmospheric CO2 concentration, a range of 2004 terrestrial carbon stock uncertainty that is 80% of net historical CO2 and climate effects on this stock, and over 1 °C range in local surface temperature estimates (1984-2004 average).
Global socioeconomic and Earth system modeling efforts, such as phase 5 of the Coupled Model Intercomparison Project (CMIP5) for the Fifth Assessment Report (AR5) of the Inter-Governmental Panel on Climate Change (IPCC), aim to provide an understanding of potential climate change given scenarios of human economic and agricultural activity. However, only land use scenarios were harmonized across models, with each Earth System Model (ESM) using a unique implementation for Land Use and Land Cover Change (LULCC). As LULCC has both biophysical and biogeochemical effects on the Earth system, different implementations of the same land use scenario can constitute vastly different ESM LULCC scenarios, with corresponding differences in regional and global and climate projections. Thus it is imperative that scenario-based global modeling efforts aim to standardize land use and land cover data to reduce uncertainties.
In order to help people adjust to and lessen the local impacts of global change, international modeling efforts aim to understand global change and its impacts on humans and the environment. Most human activities are on land, such as living, agriculture, and wood harvest, and these activities both contribute to and are affected by global change. Modeling how these activities change vegetation cover, and subsequently the greater environment, is difficult and highly uncertain, yet crucial to understanding impacts of global change. Here, we estimate an uncertainty in year-2004 global forest cover of 5.1 km2 using one historical agriculture pattern, and corresponding uncertainties of 5ppmv in atmospheric carbon dioxide concentration and greater than 1 °C in local surface temperature. The associated uncertainty in land carbon storage is 80% of the estimated additional carbon stored due to historical changes in carbon dioxide concentration and climate, and 124% of the additional carbon attributed to nitrogen deposition. We conclude that future studies of global change and its impacts on humans and the environment need to constrain and reduce land cover uncertainties.