What Drives the Climate: Man or Nature?

Traditionally, human-environment interactions are discussed in terms of the influence of climatic changes and catastrophes on civilizations (Battarbee et al., 2004; Yasuda and Shinde, 2004). Recently, a hypothesis suggesting the onset of the “anthropogenic greenhouse era” about 8 ka ago as a result of forest clearance and agriculture was proposed to explain the pre-industrial rise in CO2 and CH4 concentrations (Ruddiman, 2003; see also PAGES News 2004/1). Consequently, man was deemed the “rescuer” of the Earth from a new Ice Age, otherwise predicted at about 4 ka ago. Opponents of this hypothesis argued that natural forces were responsible for the pre-industrial increase in greenhouse gases (Broecker and Clark, 2003, Joos et al., 2004). These contradictory views and the current discussion they have provoked (Claussen et al. 2005; Crucifix et al. 2005; Ruddiman, 2005; Broecker and Stocker, 2005) are far more than a scholastic debate with only theoretical value. We regard integrative palynological and archeological studies in combination with modeling as a promising path towards a better understanding of the mechanisms and forces driving the Holocene climate. This understanding is crucial for reliable projections of climate in the future.