Question ii): Causes of early 20th century warming

ii) What caused the early 20th century warming?

An analysis of the connection between temperature and circulation based on the newly available 20 century reanalysis data disentangles the contribution to early 20th century warming from circulation and from greenhouse gas, volcanic, and solar forcing. This estimate is based on integrating information from multiple data sources, and will resolve presently conflicting results based on limited period analysis or large-scale mean temperatures only (Stott et al., 2003; Hegerl et al., 2007b; Hegerl et al., 2007a; Wood and Overland, 2010). The analysis makes full use of the spatial and temporal pattern of warming. The role of atmospheric and ocean circulation, and individual forcings such as black carbon are analyzed through modelling.