OC concentrations in the Zuoqiupu ice core for the monsoon (June–September) and nonmonsoon (October–May) seasons, and for the annual mean. Baiqing Xua, 2009

Organic carbon (OC) concentrations in the Zuoqiupu ice core for the monsoon (June–September) and nonmonsoon (October–May) seasons, and for the annual mean. Fig. 3 shows the Zuoqiupu data broken down by monsoonal and nonmonsoonal periods. The monsoonal period has lower BC and OC concentrations because of the high precipitation rate, but the source is unambiguously Asian, primarily the Indian subcontinent. The Zuoqiupu data indicate an increasing Asian source since the 1990s, especially during the present decade of rapid industrial growth. An increase of BC and OC emissions by about 30% between 1990 and 2003 has been estimated (20). Our Zuoqiupu data suggest that Asian emissions continued to increase after 2003. In addition to contributions from the monsoon, the brown haze found during winter and spring to lie against the Himalayas (12) contains black soot blown onto the southeastern Tibetan Plateau by the southern branch of the westerlies that sweep over the south side of the Himalaya–Hindu Kush range (Fig. 1). This makes the Zuoqiupu site the most representative of Asian sources among the five glaciers. We show that the black soot content is sufficient to affect the surface reflectivity of the glaciers and that the black soot amount has increased rapidly since the 1990s, coincidentally with the accelerating glacier retreat and increasing industrial activity in South and East Asia. We suggest that a successful strategy for humanity to retain the fresh water benefits of Himalayan glaciers will need to reduce black soot emissions so as to restore more pristine high-reflectivity snow and ice surfaces, as well as stabilize and possibly reduce greenhouse gas amount. …

Baiqing Xua, et al., Black soot and the survival of Tibetan glaciers [pdf], Proceedings of the National Academy of Sciences, December 8, 2009, doi: 10.1073/pnas.0910444106