Holocene carbon emissions as a result of anthropogenic land cover change

Abstract

Humans have altered the Earth’s land surface since the Paleolithic mainly by clearing woody vegetation first to improve hunting and gathering opportunities, and later to provide agricultural cropland. In the Holocene, agriculture was established on nearly all continents and led to widespread modification of terrestrial ecosystems. To quantify the role that humans played in the global carbon cycle over the Holocene, we developed a new, annually resolved inventory of anthropogenic land cover change from 8000 years ago to the beginning of large-scale industrialization (ad 1850). This inventory is based on a simple relationship between population and land use observed in several European countries over preindustrial time. Using this data set, and an alternative scenario based on the HYDE 3.1 land use data base, we forced the LPJ dynamic global vegetation model in a series of continuous simulations to evaluate the impacts of humans on terrestrial carbon storage during the preindustrial Holocene. Our model setup allowed us to quantify the importance of land degradation caused by repeated episodes of land use followed by abandonment. By 3 ka BP, cumulative carbon emissions caused by anthropogenic land cover change in our new scenario ranged between 84 and 102 Pg, translating to c. 7 ppm of atmospheric CO2. By ad 1850, emissions were 325–357 Pg in the new scenario, in contrast to 137–189 Pg when driven by HYDE. Regional events that resulted in local emissions or uptake of carbon were often balanced by contrasting patterns in other parts of the world. While we cannot close the carbon budget in the current study, simulated cumulative anthropogenic emissions over the preindustrial Holocene are consistent with the ice core record of atmospheric δ13CO2 and support the hypothesis that anthropogenic activities led to the stabilization of atmospheric CO2 concentrations at a level that made the world substantially warmer than it otherwise would be.

Survival and divergence in a small group: The extraordinary genomic history of the endangered Apennine brown bear stragglers

“…In the last few thousand years, extreme contractions in habitat and population size occurred in Spain and in the Apennine bear, and fragmentation increased among bear populations across Europe. The estimated timing of this fragmentation is compatible with the trend of forest clearance and land cover change related to the introduction and diffusion of agricultural technologies (38)(39)(40).…”

Early land use and centennial scale changes in lake-water organic carbon prior to contemporary monitoring

“…Even though the type of early land use described here may be specific for forested upland and mountainous areas in Europe, our findings exemplify the potential magnitude of past human land-use activities on OC dynamics in surface waters. Globally, humans have extensively altered the natural vegetation cover over centuries (North America, following European settlement) to millennia (Europe, Asia) and with it the long-term terrestrial carbon storage (52). In other regions with observed changes in OC levels, other drivers such as the recovery from acidification in southern Scandinavia and the United Kingdom (4) may dominate current OC dynamics.…”

When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal

“…(1) There is increasing awareness of early human impacts on the landscape, in terms of habitat modification (Kaplan et al 2011;Ellis et al 2013), terrestrial biotic change (e.g. Barnosky, 2008;Ellis et al, 2012), marine microbiotic change as a consequence of land use changes as early as 3700 BP (Wilkinson et al, 2014) and, partly related to this, a hypothesis that early agriculture altered carbon dioxide levels sufficiently (raising them from 260 to 280 ppm over several thousand years : Ruddiman, 2003: Ruddiman, , 2013 to maintain stable Holocene warmth and prevent or delay the transition into the next glacial phase.…”