Climate change in northwest China over the past millennium - a podcast by UCL

Around half of the world’s population lives under the influence of the Asian monsoons. The sustainability of water resources, which is intimately tied up with future monsoon variability, is a critically-important issue in northwest China where development is taking place at the margins of agricultural productivity and towards the fringe of the landward penetration of summer monsoon rainfall. Understanding the likely future behaviour of the Asian monsoons is therefore critical for the people of northwest China. Knowledge of past variations in the monsoons is important for our understanding of the monsoon system as a whole and for how it might respond to changing global conditions in the future. However, climatological records only extend back around 50 years or so in northwest China, much too short a time span to allow the full range of natural variability in the monsoons to be assessed. An alternative approach is to use so-called natural archives of climate variability, which include tree rings, ice cores and various sediment records such as those deposited in lakes and the oceans. In this paper, we describe ongoing collaborative work on lake sediments in northwest China being undertaken in University College London and Lanzhou University. Despite its relative dryness, northwest China contains a surprising number of lakes. Many of these are hydrologically closed (i.e. they receive water only from rainfall and lose water only by evaporation) and therefore respond sensitively to changes in effective precipitation, defined as the balance of precipitation to evaporation. Lake sediments are one of the most important sources of evidence for environmental change in dryland areas. Changes in lake level and water chemistry, which are responses to variations in precipitation, runoff and evaporation, are recorded in the stratigraphy, sedimentology, geochemistry and palaeontology of the sediments. Variations in local and regional vegetation may also be reflected in pollen records. Our research has focused on lakes along the northern edge of the Tibetan Plateau and between sand dunes in the deserts of Inner Mongolia, which record climate variability over the past millennium. This period is a particularly important, since there appear to have been large changes in the intensity of monsoon circulation during this time, possibly associated with the major climatic intervals know as the Medieval Warm Period (~AD 1000 – 1300) and Little Ice Age (~AD 1350 – 1900), during which times the monsoon may have strengthened and weakened, respectively. However, evidence from natural archives indicates that the observed changes in climate have been highly variable across the vast region of Northwest China, making the accumulation of more data from additional sites a priority task for the future.

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