Before I introduce El Niño and its impact, let’s first have a glimpse of Walker Circulation. (Figure 1).
When an El Niño (the boy in Spanish) event happens, the normal location of Indonesian Low continuously moves eastward, which eventually reverses the high-low pressure relation. The eastward moving Indonesian Low weakens the strength of the southeastern trade wind and the upwelling at southeastern Pacific. Consequently, the ocean circulation closes, producing an anomalously warm temperature at southeastern Peru. The reverse of the high and low pressure over the southern Pacific Ocean is called El Niño Southern Oscillation(ENSO). When Indonesia Low moves westward, it creates La Niña (the girl in spanish) events. Click here to see ENSO’s global climate impact.
This figure below shows the trend of the occurrence of El Niño and La Niña events since 1880. As it shows, the more frequency of El Niño than La Niña is clear since 1970s (Trenberth and Hoar, 1996).
Does global warming increase the frequency of El Niño? The answer is we don’t know yet. As a super complicated equilibrium system, the Walker Circulation is influenced by several different physical process, such as the role of the ocean, the effect of the cloud covers, etc. (NOAA, 2012). Due to the complexity of the mechanism, there is not yet an effective computer model suggesting the direct relationship between El Niño and global warming. Meehl et al. in the 2006 paper believes that the amplitude of El Niño events will decrease as the carbon dioxide increases. Other researchers such as Zhang et al. believe that the amplitude will be strengthened for a short term, and then as the ocean vertical temperature reaches equilibrium status, the frequency of ENSO will decrease (Zhang et al. 2008). On the other hand, Timmerman et al. predict that the El Niño frequency will increase due to the global warming. In these series blogs, I will explain this three major predications on the amplitude of ENSO in my future posts (Timmermann et al., 1999).
Other general questions about El Niño, please visit here.
McPhaden, M., Soreide, N.,2012, El Niño Theme Page, NOAA, retrieve from: http://www.pmel.noaa.gov/tao/elnino/faq.html
Meehl, G. A., H. Teng, G. Branstator, 2006, Future changes of El Niño in two global cou- pled climate models. Climate Dynamic. no. 26, pp. 549-566
Timmermann, A., M. Latif, A. Bacher, J. Oberhuber, E. Roeckner, 1999, Increased El Nin ̃o frequency in a climate model forced by future greenhouse warming. Nature, no. 398, pp. 694–696.
Trenberth, K. E., T. J. Hoar, 1996, The 1990–1995 El Niño-Southern Oscillation event: Longest on record. Geophysics Research Letters., no. 23, pp. 57–60.
Zhang, Q., Guan, Y., Yang, H., 2008, ENSO Amplitude Change in Observation and Coupled Models, Advances in atmospheric sciences, vol. 25, no. 3, 2008, pp. 361–366.