Abrupt tropical climate change: Past and present

Abstract

Three lines of evidence for abrupt tropical climate change, both past and present, are presented. First, annually and decadally averaged ␦ 18 O and net mass-balance histories for the last 400 and 2,000 yr, respectively, demonstrate that the current warming at high elevations in the mid-to low latitudes is unprecedented for at least the last 2 millennia. Second, the continuing retreat of most mid-to low-latitude glaciers, many having persisted for thousands of years, signals a recent and abrupt change in the Earth's climate system. Finally, rooted, soft-bodied wetland plants, now exposed along the margins as the Quelccaya ice cap (Peru) retreats, have been radiocarbon dated and, when coupled with other widespread proxy evidence, provide strong evidence for an abrupt mid-Holocene climate event that marked the transition from early Holocene (pre-5,000-yr-B.P.) conditions to cooler, late Holocene (post-5,000-yr-B.P.) conditions. This abrupt event, Ϸ5,200 yr ago, was widespread and spatially coherent through much of the tropics and was coincident with structural changes in several civilizations. These three lines of evidence argue that the present warming and associated glacier retreat are unprecedented in some areas for at least 5,200 yr. The ongoing global-scale, rapid retreat of mountain glaciers is not only contributing to global sea-level rise but also threatening freshwater supplies in many of the world's most populous regions.icecore ͉ isotopes ͉ paleoclimate ͉ precipitation ͉ Holocene

Glacier loss on Kilimanjaro continues unabated

“…The remaining glaciers throughout Africa (14-16) will soon disappear, most glaciers in tropical South America are in rapid retreat (12,(17)(18)(19), the few remaining glaciers in Indonesia are rapidly disappearing (20), and on balance most Tibetan glaciers, including many in the Himalayas, are also retreating (21). Moreover, some of the highest glaciers in the Himalayas are now wasting from the surface downward (22) just like the ice fields on Kilimanjaro.…”

“…Regardless of the relative importance of the multiple drivers responsible for the loss of Kilimanjaro's summit ice fields, these shrinking ice fields are not unique (12,13). The remaining glaciers throughout Africa (14-16) will soon disappear, most glaciers in tropical South America are in rapid retreat (12,(17)(18)(19), the few remaining glaciers in Indonesia are rapidly disappearing (20), and on balance most Tibetan glaciers, including many in the Himalayas, are also retreating (21).…”

Rates of temperature change in China during the past 2000 years

“…Although these series were derived from different proxies, such as tree rings, historical documents, stalagmites, ice cores, and lake sediments, they provide quantitative estimates of past temperatures. As seen in Table 1, nine of the series represent annual temperatures [8,19,20,22,23], while the others represent seasonal temperatures [9-18, 21, 24]. In addition, our previous study [25] demonstrated that the proxies of seasonal temperatures can explain 44%-90% of the variability of annual temperature within the instrumental calibration period ( Table 2).…”

“…In China, much effort has been spent in the last few decades to reconstruct regional proxy temperature series with lengths of 500-2000 years from historical documents [8][9][10][11][12][13][14][15], tree rings [16,17], stalagmites [18], ice cores [19], and lake sediments [20][21][22][23][24]. Uncertainty analysis of these regional reconstructions indicates that warming during the 10-14th centuries in some regions might be comparable in magnitude to the warming of the last few decades of the 20th century that was unprecedented in the past 500 years [25].…”

The last deglaciation of Peru and Bolivia

“…Other sites recognizing this included Wright's mapped Taptapa moraine at 10.1 ka (Wright, 1984), followed by rapid deglaciation. The Quelccaya Ice Cap was recognized to be at the limit by 10 ka, given peat exposed at the margin (Thompson et al, 2006;Buffen et al, 2009). …”