El Nino events are characterized by surface warming of the tropical Pacific Ocean and weakening of equatorial trade winds that occur every few years. Such conditions are accompanied by changes in atmospheric and oceanic circulation, affecting global climate, marine and terrestrial ecosystems, fisheries and human activities. The alternation of warm El Nino and cold La Nina conditions, referred to as the El Nino-Southern Oscillation (ENSO), represents the strongest year-to-year fluctuation of the global climate system. Here we provide a synopsis of our current understanding of the spatio-temporal complexity of this important climate mode and its influence on the Earth system.
The El Niño—Southern Oscillation (ENSO) drives large changes in global climate patterns from year to year, yet its sensitivity to continued anthropogenic greenhouse forcing is uncertain. We analyzed fossil coral reconstructions of ENSO spanning the past 7000 years from the Northern Line Islands, located in the center of action for ENSO. The corals document highly variable ENSO activity, with no evidence for a systematic trend in ENSO variance, which is contrary to some models that exhibit a response to insolation forcing over this same period. Twentieth-century ENSO variance is significantly higher than average fossil coral ENSO variance but is not unprecedented. Our results suggest that forced changes in ENSO, whether natural or anthropogenic, may be difficult to detect against a background of large internal variability.
The effects of natural variability, especially El Nino-Southern Oscillation (ENSO) effects, have been the focus of several recent studies on the change of drought patterns with climate change. The interannual relationship between ENSO and the global climate is not stationary and can be modulated by the Pacific Decadal Oscillation (PDO). However, the global land distribution of the dry-wet changes associated with the combination of ENSO and the PDO remains unclear. In the present study, this is investigated using a revised Palmer Drought Severity Index dataset (sc_PDSI_pm). We find that the effect of ENSO on dry-wet changes varies with the PDO phase. When in phase with the PDO, ENSO-induced dry-wet changes are magnified with respect to the canonical pattern. When out of phase, these dry-wet variations weaken or even disappear. This remarkable contrast in ENSO's influence between the two phases of the PDO highlights exciting new avenues for obtaining improved global climate predictions. In recent decades, the PDO has turned negative with more La Nina events, implying more rain and flooding over land. La Nina-induced wet areas become wetter and the dry areas become drier and smaller due to the effects of the cold PDO phase.
Prediction of monsoon changes in the coming decades is important for infrastructure planning and sustainable economic development. The decadal prediction involves both natural decadal variability and anthropogenic forcing. Hitherto, the causes of the decadal variability of Northern Hemisphere summer monsoon (NHSM) are largely unknown because the monsoons over Asia, West Africa, and North America have been studied primarily on a regional basis, which is unable to identify coherent decadal changes and the overriding controls on planetary scales. Here, we show that, during the recent global warming of about 0.4 °C since the late 1970s, a coherent decadal change of precipitation and circulation emerges in the entirety of the NHSM system. Surprisingly, the NHSM as well as the Hadley and Walker circulations have all shown substantial intensification, with a striking increase of NHSM rainfall by 9.5% per degree of global warming. This is unexpected from recent theoretical prediction and model projections of the 21st century. The intensification is primarily attributed to a mega-El Niño/Southern Oscillation (a leading mode of interannual-to-interdecadal variation of global sea surface temperature) and the Atlantic Multidecadal Oscillation, and further influenced by hemispherical asymmetric global warming. These factors driving the present changes of the NHSM system are instrumental for understanding and predicting future decadal changes and determining the proportions of climate change that are attributable to anthropogenic effects and long-term internal variability in the complex climate system.
The El Niño–Southern Oscillation (ENSO) phenomenon, the most pronounced feature of internally generated climate variability, occurs on interannual timescales and impacts the global climate system through an interaction with the annual cycle. The tight coupling between ENSO and the annual cycle is particularly pronounced over the tropical Western Pacific. Here we show that this nonlinear interaction results in a frequency cascade in the atmospheric circulation, which is characterized by deterministic high-frequency variability on near-annual and subannual timescales. Through climate model experiments and observational analysis, it is documented that a substantial fraction of the anomalous Northwest Pacific anticyclone variability, which is the main atmospheric link between ENSO and the East Asian Monsoon system, can be explained by these interactions and is thus deterministic and potentially predictable.
To predict future coastal hazards, it is important to quantify any links between climate drivers and spatial patterns of coastal change. However, most studies of future coastal vulnerability do not account for the dynamic components of coastal water levels during storms, notably wave-driven processes, storm surges and seasonal water level anomalies, although these components can add metres to water levels during extreme events. Here we synthesize multi-decadal, co-located data assimilated between 1979 and 2012 that describe wave climate, local water levels and coastal change for 48 beaches throughout the Pacific Ocean basin. We find that observed coastal erosion across the Pacific varies most closely with El Nino/Southern Oscillation, with a smaller influence from the Southern Annular Mode and the Pacific North American pattern. In the northern and southern Pacific Ocean, regional wave and water level anomalies are significantly correlated to a suite of climate indices, particularly during boreal winter; conditions in the northeast Pacific Ocean are often opposite to those in the western and southern Pacific. We conclude that, if projections for an increasing frequency of extreme El Nino and La Nina events over the twenty-first century are confirmed, then populated regions on opposite sides of the Pacific Ocean basin could be alternately exposed to extreme coastal erosion and flooding, independent of sea-level rise.
The El Nino/Southern Oscillation (ENSO) is characterized by two main states: El Nino events defined by positive sea surface temperature anomalies in the eastern tropical Pacific Ocean and La Nina events marked by cooler surface temperatures in the same region. ENSO is broadly considered to be an oscillatory instability of the coupled ocean-atmosphere system in the tropical Pacific(1-6) that shows a tight interaction with the seasonal cycle. El Nino events typically peak in the boreal winter, but the mechanism governing this phase synchronization(7) is unclear. Here we show, using observational data and climate model experiments, that the nonlinear atmospheric response to combined seasonal and inter-annual sea surface temperature changes gives rise to a near-annual combination climate mode with periods of 10 and 15 months. Specifically, we find that the associated southward shift of westerly wind anomalies during boreal winter and spring triggers the termination(8) of large El Nino events. We conclude that combination mode dynamics and related shifts in western tropical Pacific rainfall patterns occur most prominently during strong El Nino events.
The significant wave height ( H s ) variability caused by wind anomalies associated with the co‐occurrence of the Madden‐Julian Oscillation (MJO) and El Niño–Southern Oscillation (ENSO) was investigated in the New Zealand region. For this purpose, H s and wind anomalies composites were created using 23 years (1979–2002) of modelled data during November–March periods, when simultaneous ENSO‐MJO phase pairs are potentially most active. The results show striking features: El Niño‐related wave conditions (which consist of increased H s along the west and south coasts of New Zealand) are reinforced during MJO phase 8, whereas the wave conditions associated with La Niña (which consist of larger H s along the north coast) are enhanced during MJO phase 6; Similar wave anomalies are generated during opposing ENSO phases (La Niña and El Niño) when these are combined with MJO phases 3 and 5, respectively; The majority of statistically significant H s anomalies disappear from the study area during El Niño‐MJO phase 6, El Niño‐MJO phase 2, and La Niña‐MJO phase 4, showing the neutralizing nature of some phase combinations; Finally, negative H s anomalies are experienced off the country's west coast during El Niño‐MJO phase 4, in contrast to the positive anomalies expected during El Niño events. These results clearly show the importance of remote forcing to wave anomalies in the New Zealand region, and highlight the need to assess atmospheric and oceanic conditions considering multiple climate oscillations. Significant wave height ( H s ) anomalies are substantially modified during simultaneous ENSO‐MJO phase pairs (as shown by the statistically significant H s daily anomaly composites in the image) relative to those anomalies expected during periods in which only the ENSO is active (e.g., increased H s occurs along the west and south coasts of New Zealand during El Niño). Changes in H s anomalies comprise reinforcement, nullification, and even sign reversal. Some phase combinations are associated with hazardous conditions along the New Zealand coastline.
The monitoring and prediction of climate-induced variations in crop yields, production and export prices in major food-producing regions have become important to enable national governments in import-dependent countries to ensure supplies of affordable food for consumers. Although the El Nino/Southern Oscillation (ENSO) often affects seasonal temperature and precipitation, and thus crop yields in many regions, the overall impacts of ENSO on global yields are uncertain. Here we present a global map of the impacts of ENSO on the yields of major crops and quantify its impacts on their global-mean yield anomalies. Results show that El Nino likely improves the global-mean soybean yield by 2.1-5.4% but appears to change the yields of maize, rice and wheat by - 4.3 to +0.8%. The global-mean yields of all four crops during La Nina years tend to be below normal (- 4.5 to 0.0%). Our findings highlight the importance of ENSO to global crop production.