Response to Comment on “No consistent ENSO response to volcanic forcing over the last millennium”

Robock claims that our analysis fails to acknowledge that pan-tropical surface cooling caused by large volcanic eruptions may mask El Niño warming at our central Pacific site, potentially obscuring a volcano–El Niño connection suggested in previous studies. Although observational support for a dynamical response linking volcanic cooling to El Niño remains ambiguous, Robock raises some important questions about our study that we address here.

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Comment on “No consistent ENSO response to volcanic forcing over the last millennium”

Science ◽

10.1126/science.abc0502 ◽

2020 ◽

Vol 369 (6509) ◽

pp. eabc0502 ◽

Cited By ~ 1

Author(s):

Alan Robock

Keyword(s):

El Niño ◽

El Nino ◽

Volcanic Eruptions ◽

Last Millennium ◽

Climate Response ◽

Volcanic Forcing ◽

Large Volcanic Eruptions

Dee et al. (Reports, 27 March 2020, p. 1477) claimed that large volcanic eruptions do not produce a detectable El Niño response. However, they come to the wrong conclusion because they have ignored the fundamental climate response to large volcanic eruptions: Volcanic eruptions cool the surface, thus masking the relative El Niño warming.

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No consistent ENSO response to volcanic forcing over the last millennium

Science ◽

10.1126/science.aax2000 ◽

2020 ◽

Vol 367 (6485) ◽

pp. 1477-1481 ◽

Cited By ~ 10

Author(s):

Sylvia G. Dee ◽

Kim M. Cobb ◽

Julien Emile-Geay ◽

Toby R. Ault ◽

R. Lawrence Edwards ◽

...

Keyword(s):

El Niño ◽

El Nino ◽

Southern Oscillation ◽

Global Climate ◽

Volcanic Eruptions ◽

Explosive Volcanism ◽

Forced Response ◽

Last Millennium ◽

Superposed Epoch Analysis ◽

Volcanic Forcing

The El Niño–Southern Oscillation (ENSO) shapes global climate patterns yet its sensitivity to external climate forcing remains uncertain. Modeling studies suggest that ENSO is sensitive to sulfate aerosol forcing associated with explosive volcanism but observational support for this effect remains ambiguous. Here, we used absolutely dated fossil corals from the central tropical Pacific to gauge ENSO’s response to large volcanic eruptions of the last millennium. Superposed epoch analysis reveals a weak tendency for an El Niño–like response in the year after an eruption, but this response is not statistically significant, nor does it appear after the outsized 1257 Samalas eruption. Our results suggest that those models showing a strong ENSO response to volcanic forcing may overestimate the size of the forced response relative to natural ENSO variability.

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“El Niño Like” Hydroclimate Responses to Last Millennium Volcanic Eruptions

Journal of Climate ◽

10.1175/jcli-d-15-0239.1 ◽

2016 ◽

Vol 29 (8) ◽

pp. 2907-2921 ◽

Cited By ~ 76

Author(s):

Samantha Stevenson ◽

Bette Otto-Bliesner ◽

John Fasullo ◽

Esther Brady

Keyword(s):

El Niño ◽

El Nino ◽

Southern Oscillation ◽

Temporal Structure ◽

Volcanic Eruptions ◽

Teleconnection Pattern ◽

Last Millennium ◽

Surface Cooling ◽

Proxy Reconstructions ◽

Neutral Conditions

Abstract The hydroclimate response to volcanic eruptions depends both on volcanically induced changes to the hydrologic cycle and on teleconnections with the El Niño–Southern Oscillation (ENSO), complicating the interpretation of offsets between proxy reconstructions and model output. Here, these effects are separated, using the Community Earth System Model Last Millennium Ensemble (CESM-LME), by examination of ensemble realizations with distinct posteruption ENSO responses. Hydroclimate anomalies in monsoon Asia and the western United States resemble the El Niño teleconnection pattern after “Tropical” and “Northern” eruptions, even when ENSO-neutral conditions are present. This pattern results from Northern Hemisphere (NH) surface cooling, which shifts the intertropical convergence zone equatorward, intensifies the NH subtropical jet, and suppresses the Southeast Asian monsoon. El Niño events following an eruption can then intensify the ENSO-neutral hydroclimate signature, and El Niño probability is enhanced two boreal winters following all eruption types. Additionally, the eruption-year ENSO response to eruptions is hemispherically dependent: the winter following a Northern eruption tends toward El Niño, while Southern volcanoes enhance the probability of La Niña events and Tropical eruptions have a very slight cooling effect. Overall, eruption-year hydroclimate anomalies in CESM disagree with the proxy record in both Southeast Asia and North America, suggesting that model monsoon representation cannot be solely responsible. Possible explanations include issues with the model ENSO response, the spatial or temporal structure of volcanic aerosol distribution, or data uncertainties.

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Different Impacts of Northern, Tropical, and Southern Volcanic Eruptions on the Tropical Pacific SST in the Last Millennium

Journal of Climate ◽

10.1175/jcli-d-17-0571.1 ◽

2018 ◽

Vol 31 (17) ◽

pp. 6729-6744 ◽

Cited By ~ 10

Author(s):

Meng Zuo ◽

Wenmin Man ◽

Tianjun Zhou ◽

Zhun Guo

Keyword(s):

El Niño ◽

El Nino ◽

Volcanic Eruptions ◽

Enso Cycle ◽

Last Millennium ◽

Westerly Wind ◽

Central Pacific ◽

The Pacific ◽

Sst Anomaly ◽

The Impact

The impact of northern, tropical, and southern volcanic eruptions on the Pacific sea surface temperature (SST) and the different response mechanisms arising due to differences in the volcanic forcing structure are investigated using the Community Earth System Model Last Millennium Ensemble (CESM-LME). Analysis of the simulations indicates that the Pacific features a significant El Niño–like SST anomaly 5–10 months after northern and tropical eruptions, and with a weaker such tendency after southern eruptions, possibly reflective of the weaker magnitude of these eruptions. The Niño-3 index peaks with a lag of one and a half years after northern and tropical eruptions. Two years after all three types of volcanic eruptions, a La Niña–like SST anomaly pattern over the equatorial Pacific is observed, which seems to form an El Niño–Southern Oscillation (ENSO) cycle. The westerly wind anomaly over the western to central Pacific plays an essential role in favoring the development of an El Niño following all three types of eruptions. Thus, the key point of the question is to find the causes of the westerly wind enhancement. The shift of the intertropical convergence zone (ITCZ) can explain the El Niño–like response to northern eruptions, which is not applicable for tropical or southern eruptions. The ocean dynamical thermostat mechanism is the fundamental cause of the anomalous westerly wind for all three types of eruptions.

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Uncertainty and detectability of climate surface response to large volcanic eruptions

10.5194/acp-2016-173 ◽

2016 ◽

Author(s):

Fabian Wunderlich ◽

Daniel M. Mitchell

Keyword(s):

El Niño ◽

El Nino ◽

Temperature Response ◽

Coupled Model ◽

Volcanic Eruptions ◽

Shortwave Radiation ◽

Cmip5 Models ◽

Surface Cooling ◽

Positive Tendency ◽

Large Volcanic Eruptions

Abstract. In light of the range in presently available observational, reanalysis and model data, we revisit the surface climate response to large tropical volcanic eruptions from the end of the 19th century until present. We focus on the dynamical driven response of the North Atlantic Oscillation (NAO) and the radiative driven tropical temperature response. Using ten different reanalysis products and the Hadley Centre Sea Level Pressure observational dataset (HadSLP2) we confirm a positive tendency in the phase of the NAO during boreal winters following large volcanic eruptions, although conclude that it is not as clear cut as the current literature suggests. Especially during poorly observed periods where higher uncertainties produce a less robust signal. The phase of the NAO leads to a dynamically driven warm anomaly over Northern Europe. At the same time, there is a general cooling of the tropical surface temperatures due to the reduced incoming shortwave radiation. The magnitude of this cooling is uncertain and is hard to isolate using observational data alone (mainly due to the presence of El Niño). Therefore we use regression-based detection and attribution techniques to investigate the volcanic temperature signal with eight Coupled Model Inter-comparison Project phase 5 (CMIP5) models. In all models the volcanic signal can be detected but a general overestimation of the surface cooling is found. The enhanced surface cooling in models is likely driven, in part, by an over absorption of SW radiation in the lower stratosphere, but aliasing with El Niño events is also an issue and further process based studies are necessary to confirm these.

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The role of tropical volcanic eruptions in exacerbating Indian droughts

Scientific Reports ◽

10.1038/s41598-021-81566-0 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Suvarna Fadnavis ◽

Rolf Müller ◽

Tanusri Chakraborty ◽

T. P. Sabin ◽

Anton Laakso ◽

...

Keyword(s):

El Niño ◽

Climate Model ◽

El Nino ◽

Volcanic Eruptions ◽

Summer Monsoon Rainfall ◽

Indian Region ◽

Volcanic Plume ◽

Kelvin Wave ◽

Central Pacific ◽

Climate Model Simulations

AbstractThe Indian summer monsoon rainfall (ISMR) is vital for the livelihood of millions of people in the Indian region; droughts caused by monsoon failures often resulted in famines. Large volcanic eruptions have been linked with reductions in ISMR, but the responsible mechanisms remain unclear. Here, using 145-year (1871–2016) records of volcanic eruptions and ISMR, we show that ISMR deficits prevail for two years after moderate and large (VEI > 3) tropical volcanic eruptions; this is not the case for extra-tropical eruptions. Moreover, tropical volcanic eruptions strengthen El Niño and weaken La Niña conditions, further enhancing Indian droughts. Using climate-model simulations of the 2011 Nabro volcanic eruption, we show that eruption induced an El Niño like warming in the central Pacific for two consecutive years due to Kelvin wave dissipation triggered by the eruption. This El Niño like warming in the central Pacific led to a precipitation reduction in the Indian region. In addition, solar dimming caused by the volcanic plume in 2011 reduced Indian rainfall.

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Summer Cooling Driven by Large Volcanic Eruptions over the Tibetan Plateau

Journal of Climate ◽

10.1175/jcli-d-17-0664.1 ◽

2018 ◽

Vol 31 (24) ◽

pp. 9869-9879 ◽

Cited By ~ 7

Author(s):

Jianping Duan ◽

Lun Li ◽

Zhuguo Ma ◽

Jan Esper ◽

Ulf Büntgen ◽

...

Keyword(s):

Tibetan Plateau ◽

El Niño ◽

El Nino ◽

Volcanic Eruptions ◽

The Tibetan Plateau ◽

Temperature Deviation ◽

El Niño Event ◽

El Niño Events ◽

Large Volcanic Eruptions ◽

El Nino Events

Large volcanic eruptions may cause abrupt summer cooling over large parts of the globe. However, no comparable imprint has been found on the Tibetan Plateau (TP). Here, we introduce a 400-yr-long temperature-sensitive network of 17 tree-ring maximum latewood density sites from the TP that demonstrates that the effects of tropical eruptions on the TP are generally greater than those of extratropical eruptions. Moreover, we found that large tropical eruptions accompanied by subsequent El Niño events caused less summer cooling than those that occurred without El Niño association. Superposed epoch analysis (SEA) based on 27 events, including 14 tropical eruptions and 13 extratropical eruptions, shows that the summer cooling driven by extratropical eruptions is insignificant on the TP, while significant summer temperature decreases occur subsequent to tropical eruptions. Further analysis of the TP August–September temperature responses reveals a significant postvolcanic cooling only when no El Niño event occurred. However, there is no such cooling for all other situations, that is, tropical eruptions together with a subsequent El Niño event, as well as extratropical eruptions regardless of the occurrence of an El Niño event. The averaged August–September temperature deviation ( Tdev) following 10 large tropical eruptions without a subsequent El Niño event is up to −0.48° ± 0.19°C (with respect to the preceding 5-yr mean), whereas the temperature deviation following 4 large tropical eruptions with an El Niño association is approximately 0.23° ± 0.16°C. These results indicate a mitigation effect of El Niño events on the TP temperature response to large tropical eruptions. The possible mechanism is that El Niño events can weaken the Indian summer monsoon with a subsequent decrease in rainfall and cooling effect, which may lead to a relatively high temperature on the TP, one of the regions affected by the Indian summer monsoon.

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El Niño–Like Physical and Biogeochemical Ocean Response to Tropical Eruptions

Journal of Climate ◽

10.1175/jcli-d-18-0458.1 ◽

2019 ◽

Vol 32 (9) ◽

pp. 2627-2649 ◽

Cited By ~ 9

Author(s):

Yassir A. Eddebbar ◽

Keith B. Rodgers ◽

Matthew C. Long ◽

Aneesh C. Subramanian ◽

Shang-Ping Xie ◽

...

Keyword(s):

El Niño ◽

El Nino ◽

Tropical Pacific ◽

Earth System Model ◽

Global Climate Models ◽

System Model ◽

Geophysical Fluid Dynamics Laboratory ◽

Earth System ◽

Surface Cooling ◽

Volcanic Forcing

AbstractThe oceanic response to recent tropical eruptions is examined in Large Ensemble (LE) experiments from two fully coupled global climate models, the Community Earth System Model (CESM) and the Geophysical Fluid Dynamics Laboratory Earth System Model (ESM2M), each forced by a distinct volcanic forcing dataset. Following the simulated eruptions of Agung, El Chichón, and Pinatubo, the ocean loses heat and gains oxygen and carbon, in general agreement with available observations. In both models, substantial global surface cooling is accompanied by El Niño–like equatorial Pacific surface warming a year after the volcanic forcing peaks. A mechanistic analysis of the CESM and ESM2M responses to Pinatubo identifies remote wind forcing from the western Pacific as a major driver of this El Niño–like response. Following eruption, faster cooling over the Maritime Continent than adjacent oceans suppresses convection and leads to persistent westerly wind anomalies over the western tropical Pacific. These wind anomalies excite equatorial downwelling Kelvin waves and the upwelling of warm subsurface anomalies in the eastern Pacific, promoting the development of El Niño conditions through Bjerknes feedbacks a year after eruption. This El Niño–like response drives further ocean heat loss through enhanced equatorial cloud albedo, and dominates global carbon uptake as upwelling of carbon-rich waters is suppressed in the tropical Pacific. Oxygen uptake occurs primarily at high latitudes, where surface cooling intensifies the ventilation of subtropical thermocline waters. These volcanically forced ocean responses are large enough to contribute to the observed decadal variability in oceanic heat, carbon, and oxygen.

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Volcanoes and ENSO over the Past Millennium

Journal of Climate ◽

10.1175/2007jcli1884.1 ◽

2008 ◽

Vol 21 (13) ◽

pp. 3134-3148 ◽

Cited By ~ 146

Author(s):

Julien Emile-Geay ◽

Richard Seager ◽

Mark A. Cane ◽

Edward R. Cook ◽

Gerald H. Haug

Keyword(s):

El Niño ◽

El Nino ◽

Volcanic Eruptions ◽

Explosive Volcanism ◽

The Past ◽

El Niño Event ◽

Volcanic Forcing ◽

El Niño Events ◽

Past Millennium ◽

El Nino Events

Abstract The controversial claim that El Niño events might be partially caused by radiative forcing due to volcanic aerosols is reassessed. Building on the work of Mann et al., estimates of volcanic forcing over the past millennium and a climate model of intermediate complexity are used to draw a diagram of El Niño likelihood as a function of the intensity of volcanic forcing. It is shown that in the context of this model, only eruptions larger than that of Mt. Pinatubo (1991, peak dimming of about 3.7 W m−2) can shift the likelihood and amplitude of an El Niño event above the level of the model’s internal variability. Explosive volcanism cannot be said to trigger El Niño events per se, but it is found to raise their likelihood by 50% on average, also favoring higher amplitudes. This reconciles, on one hand, the demonstration by Adams et al. of a statistical relationship between explosive volcanism and El Niño and, on the other hand, the ability to predict El Niño events of the last 148 yr without knowledge of volcanic forcing. The authors then focus on the strongest eruption of the millennium (A.D. 1258), and show that it is likely to have favored the occurrence of a moderate-to-strong El Niño event in the midst of prevailing La Niña–like conditions induced by increased solar activity during the well-documented Medieval Climate Anomaly. Compiling paleoclimate data from a wide array of sources, a number of important hydroclimatic consequences for neighboring areas is documented. The authors propose, in particular, that the event briefly interrupted a solar-induced megadrought in the southwestern United States. Most of the time, however, volcanic eruptions are found to be too small to significantly affect ENSO statistics.

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