Natural Carbon Sequestration by Forestry

Abstract

Carbon dioxide (CO2) levels have been rapidly rising in the atmosphere following the beginning of industrialisation and reaching new highs in the last recent years. Global carbon cycle studies established that the interannual variability in observed atmospheric CO2 growth rates is attributed mainly to interannual inconsistent changes in carbon sequestration by terrestrial ecosystems, instead to oceans or changes in anthropogenic emissions. This terrestrial ecosystems sink is mainly in the forests of the world, which are enormous repositories of both biomass and soil carbon. In 1997, the United Nations Framework Convention on Climate Change (UNFCC) at Kyoto agreed on a protocol with an aim of reducing anthropogenic CO2 emissions in the atmosphere through terrestrial ecosystems CO2 sequestration. This ignited increased interest and efforts from the science community since the beginning of the twenty-first century, to probe the potential of terrestrial ecosystems CO2 assimilation in offsetting the anthropogenic CO2 impact in the atmosphere and subsequently in the global climate; this also inspired investigations on the role of environment and climate variables on the land ecosystems carbon sequestration. This study reviews the developments in the understanding of the role of the terrestrial biosphere mainly the forests in anthropogenic carbon sequestration. It first examines the influence of the environment and climate variables in the global carbon cycle processes of the terrestrial ecosystems, including the effects of climate extremes. Then it assimilates the knowledge in global carbon budget generated in the past few decades. Studies indicate that the combined effect of nitrogen deposition, high atmospheric CO2, warm climate, increased diffuse radiation support the capability of the terrestrial ecosystems to assimilate atmospheric carbon. Extreme climate change events and disturbances (ECE&D) can transform land ecosystems from sinks into sources. The aggregate of the global terrestrial ecosystems CO2 net sink has been growing in the sequence of 0.1 ± 0.8, 1.1 ± 0.9 and 1.5 ± 0.9 Pg C year −1, in the past few decades of the 1980s, 1990s and 2000s, respectively. Current global tree cover has increased by 7.1% relative to the 1982 level. The global forests are a substantial and persistence carbon sink.