Introduction to the early-Anthropocene Special Issue

The first records of Holocene CO2 and CH4 concentrations in the were published two decades ago (Barnola et al., 1987; Chappellaz et al., 1990), and the observation that both gas had increased during the last several thousand has drawn considerable attention from scientists. Compet- hypotheses attribute these increases either to natural forcing anthropogenic intervention in the climate system. This ongoing is the focus of this volume. in Part 1 of this issue explore the history of Holocene growth and land clearance. Part 2 examines possible of the CH4 increase during the last 5000 years, and Part 3 possible sources of the CO2 increase over the last 7000 . Part 4 investigates whether or not the drops in CO2 and CH4 proposed in the early anthropogenic hypothesis have been sufficient to cause glacial inception in the Northern . Part 5 explores possible causes of the decreases in 2 concentrations during the last 1000 years. A final paper one assessment of whether the natural or anthropogenic for the late-Holocene greenhouse-gas increases can be based on currently available evidence. this issue was first planned, the editors sent out invita- to all scientists who had first-authored papers relevant to the or had otherwise played a prominent role in the discussion. list was closely balanced among those favoring natural, those favoring the anthropogenic explanation, and who had not taken a strong position on either side of the. Roughly half of the scientists invited chose to participate, papers that support the natural and anthropogenic explana- can be found in each of the five major parts of the issue. of the most prominent proponents of natural forcing did not to participate, but their views are frequently discussed in 14 papers that form this issue.