Predicting India's monsoon future from its past
More than 1 billion people on the Indian subcontinent are directly or indirectly affected by the amount of rainfall brought by annual monsoons. Since warmer air has greater moisture-carrying capacity, it is possible that global warming will increase the volume of India's monsoons. As a result, scientists and policymakers are actively searching for accurate means of predicting how the monsoons may change. Knowing what could be at stake and seeking to provide answers, EU-funded researchers initiated the project 'Role of the Indian monsoon on global climate change' (MONSOON). In particular, they sought indication of the effects of past warming cycles on the region's rainfall. MONSOON analysed soil cores collected from various locations in the Bay of Bengal, which is fed by four different rivers. The samples were evaluated according to concentrations of oxygen and carbon isotopes and Mg/Ca thermometry, as well as salinity levels. Doing so enabled MONSOON researchers to reconstruct the region's rainfall history. Research showed that warm air did indeed influence India's monsoons. During the so-called Roman Warm Period (RWP) and Medieval Warm Period (MWP), the monsoons produced more rain. In contrast, during the Little Ice Age rainfall fluctuated considerably. Similarly, from 1600 to the year 2000, rainfall has varied greatly. Project findings uphold the scientific consensus that there is an inverse relationship between the El Nino southern oscillation (ENSO) and the Indian Ocean monsoon cycles. There were fewer ENSO events during the RWP and MWP. When assessed over differing time scales, the relationship holds true — for the past 2 000 years, ENSO events and monsoon rainfall variability evaluated on decadal time scales correlate strongly. The same is true for rainfall variability analysed on a sub-centennial scale over the past 10 000 years. Notably, however, MONSOON also found that this relationship has broken down over the past 140 years. MONSOON results substantiate scientific consensus that climate shifts can and do have a strong influence on the Indian subcontinent's monsoon cycles. Incorporating these data into climate change models should provide scientists and policymakers with more accurate information about how India will be affected by modern global warming.
