Abstract
AbstractThe Northern Hemisphere monsoons are an integral component of Earth's hydrological cycle and affect the lives of billions of people. Observed precipitation in the monsoon regions underwent substantial changes during the second half of the twentieth century, with drying from the 1950s to mid‐1980s and increasing precipitation in recent decades. Modeling studies suggest that anthropogenic aerosols have been a key factor driving changes in tropical and monsoon precipitation. Here we apply detection and attribution methods to determine whether observed changes are driven by human influences using fingerprints of individual forcings (i.e., greenhouse gas, anthropogenic aerosol, and natural) derived from climate models. The results show that the observed changes can only be explained when including the influence of anthropogenic aerosols, even after accounting for internal climate variability. Anthropogenic aerosol, not greenhouse gas or natural forcing, has been the dominant influence on Northern Hemisphere monsoon precipitation over the second half of the twentieth century.
Highlights
Human-induced changes to the hydrological cycle are among the most serious impacts of climate change, with potential consequences for water resources, health, agriculture, and ecosystems worldwide
All observational data sets show a decrease in precipitation from 1951 to 2005; fitting linear trends gives an overall decrease of 5%–11% of the mean precipitation, depending on the data set
Spatial linear trend patterns show more similarity between observed, all external forcings (ALL), anthropogenic forcings (ANT), and anthropogenic aerosol forcing (AA), which show drying in many areas, than greenhouse gas forcing (GHG) which results in increasing precipitation over most of the Northern Hemisphere summer monsoon (NHSM) region (Figure S2 in the supporting information)
Summary
Human-induced changes to the hydrological cycle are among the most serious impacts of climate change, with potential consequences for water resources, health, agriculture, and ecosystems worldwide. Detection and attribution studies have shown that greenhouse gas forcing has influenced changes in global precipitation [Polson et al, 2013a, 2013b; Wu et al, 2013]. These studies attribute observed changes to individual forcings using statistical analysis techniques that account for the internal variability of the climate. Climate models that include anthropogenic aerosol forcing better reproduce the observed decrease in South Asian monsoon precipitation [Bollasina et al, 2011]. Detection and attribution methods are applied to determine which forcing, if any, can explain the observed changes
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