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Natural climate swings contribute more to increased monsoon rainfall than global warming

Date:
March 20, 2013
Source:
University of Hawaii ‑ SOEST
Summary:
Natural swings in the climate have significantly intensified Northern Hemisphere monsoon rainfall, showing that these swings must be taken into account for climate predictions in the coming decades.

This is a three-layered cloud structure in a developing Madden-Julian Oscillation during the Indian Ocean DYNAMO field experiments (November 2011). The photo won first place in the DYNAMO photo contest.
Credit: Owen Shieh, University of Hawaii

Natural swings in the climate have significantly intensified Northern Hemisphere monsoon rainfall, showing that these swings must be taken into account for climate predictions in the coming decades, a new study finds.

The findings are published in the March 18 online publication of the Proceedings of the National Academy of Sciences.

Monsoon rainfall in the Northern Hemisphere impacts about 60% of the World population in Southeast Asia, West Africa and North America. Given the possible impacts of global warming, solid predictions of monsoon rainfall for the next decades are important for infrastructure planning and sustainable economic development. Such predictions, however, are very complex because they require not only pinning down how humanmade greenhouse gas emissions will impact the monsoons and monsoon rainfall, but also a knowledge of natural long-term climate swings, about which little is known so far.

To tackle this problem an international team of scientists around Meteorology Professor Bin Wang at the International Pacific Research Center, University of Hawaii at Manoa, examined climate data to see what happened in the Northern Hemisphere during the last three decades, a time during which the global-mean surface-air temperature rose by about 0.4°C. Current theory predicts that the Northern Hemisphere summer monsoon circulation should weaken under anthropogenic global warming.

Wang and his colleagues, however, found that over the past 30 years, the summer monsoon circulation, as well as the Hadley and Walker circulations, have all substantially intensified. This intensification has resulted in significantly greater global summer monsoon rainfall in the Northern Hemisphere than predicted from greenhouse-gas-induced warming alone: namely a 9.5% increase, compared to the anthropogenic predicted contribution of 2.6% per degree of global warming.

Most of the recent intensification is attributable to a cooling of the eastern Pacific that began in 1998. This cooling is the result of natural long-term swings in ocean surface temperatures, particularly swings in the Interdecadal Pacific Oscillation or mega-El Niño-Southern Oscillation, which has lately been in a mega-La Niña or cool phase. Another natural climate swing, called the Atlantic Multidecadal Oscillation, also contributes to the intensification of monsoon rainfall.

"These natural swings in the climate system must be understood in order to make realistic predictions of monsoon rainfall and of other climate features in the coming decades," says Wang. "We must be able to determine the relative contributions of greenhouse-gas emissions and of long-term natural swings to future climate change."


Story Source:

The above story is based on materials provided by University of Hawaii ‑ SOEST. Note: Materials may be edited for content and length.


Journal Reference:

  1. B. Wang, J. Liu, H.-J. Kim, P. J. Webster, S.-Y. Yim, B. Xiang. Northern Hemisphere summer monsoon intensified by mega-El Nino/southern oscillation and Atlantic multidecadal oscillation. Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1219405110

Cite This Page:

University of Hawaii ‑ SOEST. "Natural climate swings contribute more to increased monsoon rainfall than global warming." ScienceDaily. ScienceDaily, 20 March 2013. <www.sciencedaily.com/releases/2013/03/130320155251.htm>.
University of Hawaii ‑ SOEST. (2013, March 20). Natural climate swings contribute more to increased monsoon rainfall than global warming. ScienceDaily. Retrieved July 25, 2014 from www.sciencedaily.com/releases/2013/03/130320155251.htm
University of Hawaii ‑ SOEST. "Natural climate swings contribute more to increased monsoon rainfall than global warming." ScienceDaily. www.sciencedaily.com/releases/2013/03/130320155251.htm (accessed July 25, 2014).

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