Climate Change is thought by many scientists to be at the forefront of issues facing the global community. With the increase in greenhouse gases, there is expected to be a significant shift in natural variability, with climate being a primary concern (Collins et al., 2010). One of the most important climate patterns is the El Niño-Southern Oscillation (ENSO), a large shift of Pacific trade winds from westerly to easterly directions. It is possible to examine these changes through the use of complex coupled global circulation models (CGCM), which suggest that there will be a significant change in the mean climate of the Pacific, played out partly in El Niño variability. However, it is still too early to determine whether there will be an increase or decrease in ENSO activity, or if it’s intensity will be heightened, since one or more of its causative characteristics will be modified by global warming’s effect on climate.—Brian Nadler
Collins, M., An, S., Cai, W., Ganachaud, A. Guilyardi, E., Jin, F., Jochum, M., Lengaigne, M., Power, S., Timmermann, A., Vecchi, G. and Wittenberg, A. The impact of global warming on the tropical Pacific Ocean and El Nino. Nature Geoscience 3, 391—397.
There are many outside variables that factor into the variability of the ENSO, and how much each factor plays a role has been the subject of a great deal of debate. Changes in mean climate, sensitivity to climate change, mean upwelling and advection, thermocline feedback, sea surface temperature/wind stress feedback, atmospheric damping or variability, or surface sonal advective feedback all effects on ENSO formation. However, Collins et al. decided to determine what had the most significant effects on ENSO characteristics to more accurately determine future changes due to global warming.
The study utilized information from all of the previously stated characteristics. It was observed that all of the ENSO characteristics were increased to the point where they would have a significant amplification on ENSO activity, save for atmospheric damping, which seemed to reduce variability. The projected changes were modeled using an inter-annual standard deviation of a mean sea-level-pressure index, in which a positive or negative change indicated a strength or weakness of the ENSO, respectively. The sensitivity of ENSO to climate change was also observed using climate reconstructions over the past millennium. In order to compensate for variation in externally forced changes in ENSO characteristics, multiple runs using the same model were performed. It is noted that this is not possible in a real-world scenario, and that variability may be obscuring changes that are caused due to global warming.
The authors found a significant relationship between climate change on the process and feedbacks that determine the characteristics of ENSO. The only negative linear relationship is between atmospheric damping feedback and ENSO strength. The overall tendency for larger ENSO events is expected to increase greatly, and the decrease in atmospheric damping will lead to a likely decrease in ENSO variability. For any other feedbacks, there is expected to be little change, there is very little evidence to suggest there is any significant effect otherwise.
The increase in El Niño strength due to global warming will have an important effect on tropical storm activity. More tropical cyclones tend to form during El Niño years in the Eastern Pacific, whereas conversely, more cyclone activity is present in the Atlantic during La Niña years. Being able to determine how the correlation between the strength of ENSO events and frequency and intensity of tropical storms is essential for preparing against future storm activity.