Aerosols, Change Points, and the Evolving Land Carbon Sink

Abstract

Multiple lines of evidence indicate that the terrestrial biosphere has been a growing sink for anthropogenic CO2 since the 1950s [Ciais et al., 2013], but the nature and origin of this growth are not well understood. I investigate if the growth in the net land carbon sink (NLS) – estimated as the difference between fossil fuel emissions, the observed atmospheric growth rate, and the ocean uptake – has been abrupt or gradual by applying change point analysis. Similar to two recent studies, I identify an abrupt increase in mean NLS of 0.92-1.30 PgC year–1 in 1988. I add to these studies by showing that although identification of an abrupt increase in 1988 is insensitive to the choice of ocean estimate used to calculate NLS, this result is highly sensitive to the choice of statistical framework (parametric versus nonparametric). Attempts to explain the growth in NLS have so far proven inconclusive, but much attention has focused on the carbon sink potential of Northern Eurasia, in particular, of Northern Europe. Using simulations with the Geophysical Fluid Dynamics Laboratory (GFDL) AM3/LM3V model, I find a link between declining aerosol pollution, due to the collapse of the Soviet Union and environmental regulations in Europe, and increasing regional net primary production. While this link does not explain the global NLS increase, an improved set of simulations with AM3/LM3V can be used to determine the historical influence of anthropogenic aerosols on the evolution of NLS.