SW-NCA-color-FINALweb

Present Weather and Climate: Evolving Conditions 89Figure 5.7 Proxy and modeled data for the past 2000 years. (A) Solar variability (solar irradiance)shown in watts per square meter (Bard et al. 2000), (B) Multi-proxy reconstructions of NorthernHemisphere temperatures, two estimates (Mann et al. 2008), (C) ECHO-G GCM simulations oftemperatures for the U.S. Southwest-Intermountain region (Stevens, Gonzalez-Ruico and Beltrani2008), (D) Temperature reconstruction for the Colorado Plateau from tree rings (Salzer and Kipfmueller2005). The lighter shading indicates the period of the Medieval Climate Anomaly and the darker shadingindicates the mid-12th century megadrought in the Colorado River Basin. Adapted from Woodhouse etal. (2010).Regardless of how warm the MCA was, it is clear that the reconstructed warmestperiods during the MCA were associated with widespread severe drought in the Southwest(MacDonald et al. 2008; Woodhouse et al. 2010; Woodhouse, Pederson, and Gray2011), as indicated by the paleodrought records described below. More generally, thepaleorecord indicates that warmer periods of the past 2,000 years have often been associatedwith increased aridity (Woodhouse, Pederson, and Gray 2011).PaleodroughtThe Southwest contains one of the greatest concentrations in the world of yearly paleodroughtrecords, in the form of hundreds of highly moisture-sensitive tree-ring records.These site-level tree-ring data have been calibrated with observed records at regional tosub-regional scales to reconstruct summer and winter PDSI (see Figure 5.8; Woodhouse