AGU journal highlights -- Aug. 1, 2007

1. Surface warming and the solar cycle

To accurately assess the effects of human-induced climate change, scientists must be able to quantify the contribution of natural variation in solar irradiance to temperature changes. The existence of a long-term trend in solar output is controversial, but its periodic change within an 11-year cycle has been measured by satellites. To assess how this less-controversial oscillatory forcing affects climate on Earth, Camp and Tung compare surface temperature measurements across the globe between years of solar maximum (with higher heat output) and years of solar minimum. They find that times of high solar activity are on average 0.2º C warmer than times of low solar activity, and that there is a polar amplification of the warming. This result is the first to document a statistically significant globally coherent temperature response to the solar cycle, the authors note.

Title: Surface warming by the solar cycle as revealed by the composite mean difference projection

Authors: Charles D. Camp and Ka Kit Tung: Department of Applied Mathematics, University of Washington, Seattle, Washington, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030207, 2007

2. Early humans in China 1 million years ago

Chronology and adaptability of early humans in different paleoclimatic and paleoenvironmental settings are important topics in the study of human evolution. China houses several early-human (Paleolithic) archaeological sites along the Nihewan Basin near Mongolia, some with artifacts that date back about 1 million years ago. Deng et al. analyze one specific locality in the Nihewan Basin, called the Feiliang Paleolithic Site, where several stone artifacts and mammalian bone fragments have been found buried in basin silts. By analyzing remnant magnetizations of basin silt layers and comparing these data with charts of known magnetic reversals, the authors identify that the artifact layer was deposited about 1.2 million years ago, just prior to a major climate transition that occurred during the mid-Pleistocene. The transition brought increased climate variability to the region. This finding, coupled with other studies, indicates a prominent early human presence in the high northern latitudes of East Asia. The authors indicate that further studies on the artifacts themselves could reveal the manner in which humans weathered these climate shifts.

Title: Magnetochronology of the Feiliang Paleolithic site in the Nihewan Basin and implications for early human adaptability to high northern latitudes in East Asia

Authors: Chenglong Deng, Caicai Liu, Hong Ao, Yongxin Pan and Rixiang Zhu: Paleomagnetism and Geochronology Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China;

Fei Xie: Hebei Province Institute of Cultural Relics, Shijiazhuang, China.