Detecting cross‐equatorial wind change as a fingerprint of climate response to anthropogenic aerosol forcing

Wang, Hai; Xie, Shang‐Ping; Tokinaga, Hiroki; Liu, Qinyu; Kosaka, Yu

doi:10.1002/2016gl068521

Cited by 38 publications

(34 citation statements)

References 45 publications

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“…Warming of the global tropical oceans “upped the ante” for deep convection (Chou and Neelin 2004 ; Held et al 2005 ), while the absence of warming in the North Atlantic reduced the moisture supply to the monsoon and thus its potential to meet the “upped ante” and to trigger vertical instability (Giannini et al 2008 ). Our argument is distinct from others previously proposed, which attributed late twentieth century Sahel drought solely to aerosols, whether through cooling of the North Atlantic or of the entire northern hemisphere (Rotstayn and Lohmann 2002 ; Kawase et al 2010 ; Ackerley et al 2011 ; Booth et al 2012 ; Hwang et al 2013 ; Park et al 2015 ; Wang et al 2016 ), in three ways. First of all, we argue for an indirect effect of anthropogenic emissions, i.e., mediated by sea surface temperatures.…”

Section: Conclusion: Past Is Not Prologuecontrasting

confidence: 91%

The role of aerosols and greenhouse gases in Sahel drought and recovery

Giannini¹,

Kaplan

2018

Climatic Change

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We exploit the multi-model ensemble produced by phase 5 of the Coupled Model Intercomparison Project (CMIP5) to synthesize current understanding of external forcing of Sahel rainfall change, past and future, through the lens of oceanic influence. The CMIP5 multi-model mean simulates the twentieth century evolution of Sahel rainfall, including the mid-century decline toward the driest years in the early 1980s and the partial recovery since. We exploit a physical argument linking anthropogenic emissions to the change in the temperature of the sub-tropical North Atlantic Ocean relative to the global tropical oceans to demonstrate indirect attribution of late twentieth century Sahel drought to the unique combination of aerosols and greenhouse gases that characterized the post-World War II period. The subsequent reduction in aerosol emissions around the North Atlantic that resulted from environmental legislation to curb acid rain, occurring as global tropical warming continued unabated, is consistent with the current partial recovery and with projections of future wetting. Singular Value Decomposition (SVD) applied to the above-mentioned sea surface temperature (SST) indices provides a succinct description of oceanic influence on Sahel rainfall and reveals the near-orthogonality in the influence of emissions between twentieth and twenty-first centuries: the independent effects of aerosols and greenhouse gases project on the difference of SST indices and explain past variation, while the dominance of greenhouse gases projects on their sum and explains future projection. This result challenges the assumption that because anthropogenic warming had a hand in past Sahel drought, continued warming will result in further drying. In fact, the twenty-first century dominance of greenhouse gases, unchallenged by aerosols, results in projections consistent with warming-induced strengthening of the monsoon, a response that has gained in coherence in CMIP5 compared to prior multi-model exercises. Electronic supplementary material The online version of this article (10.1007/s10584-018-2341-9) contains supplementary material, which is available to authorized users.

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Section: Conclusion: Past Is Not Prologuecontrasting

confidence: 91%

The role of aerosols and greenhouse gases in Sahel drought and recovery

Giannini¹,

Kaplan

2018

Climatic Change

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“…This two‐stage evolution of the ITCZ has important implications for global hydrological cycle. The fast ITCZ response to Arctic sea ice loss during the first stage is consistent with the northward ITCZ shift since the mid‐1980s typically attributed to the reduction in atmospheric aerosols (Allen et al, ; H. Wang et al, ). Our results indicate that the Arctic sea ice retreat may have contributed to the northward displacement of the ITCZ, although the sea ice retreat itself may be partially caused by the aerosol reduction (Gagné et al, ; Navarro et al, ).…”

Section: Discussionsupporting

confidence: 77%

“…This two-stage evolution of the ITCZ has important implications for global hydrological cycle. The fast ITCZ response to Arctic sea ice loss during the first stage is consistent with the northward ITCZ shift since the mid-1980s typically attributed to the reduction in atmospheric aerosols (Allen et al, 2015;H. Wang et al, 2016).…”

Section: Discussionsupporting

confidence: 75%

Global Impacts of Arctic Sea Ice Loss Mediated by the Atlantic Meridional Overturning Circulation

Liu

Fedorov

2019

Geophysical Research Letters

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We explore the global impacts of Arctic sea ice decline in climate model perturbation experiments focusing on the temporal evolution of induced changes. We find that climate response to a realistic reduction in sea ice cover varies dramatically between shorter decadal and longer multidecadal to centennial timescales. During the first two decades, when atmospheric processes dominate, sea ice decline induces a “bipolar seesaw” pattern in surface temperature with warming in the Northern and cooling in the Southern Hemisphere, leading to a northward displacement of the Intertropical Convergence Zone and an expansion of Antarctic sea ice. In contrast, on multidecadal and longer timescales, the weakening of the Atlantic meridional overturning circulation, caused by upper‐ocean buoyancy anomalies spreading from the Arctic, mediates direct sea ice impacts and nearly reverses the original response pattern outside the Arctic. The Southern Hemisphere warms, a Warming Hole emerges in the North Atlantic, the Intertropical Convergence Zone shifts southward, and Antarctic sea ice contracts.

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“…Contrasting trends in emissions and scattering aerosol concentrations in these regions likely affected the ITCZ location in contrasting ways, and could help to explain why we do not observe a clear ITCZ shift over oceans in the last 39 years. Greenhouse gas concentrations were also changing over 1979-2017, and it is well known that the tropical circulation responds differently to aerosol versus greenhouse gas forcings [68,69]. The relative influences of these forcings on historical trends not only in ITCZ location but also in ITCZ width and strength could be disentangled using single-forcing simulations following Xie et al (2013) [70], and would be an interesting topic for future work.…”

Section: Observed Changes In the Itczmentioning

confidence: 99%

Response of the Intertropical Convergence Zone to Climate Change: Location, Width, and Strength

Byrne¹,

Pendergrass²,

Rapp³

et al. 2018

Curr Clim Change Rep

209

193

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Purpose of Review The intertropical convergence zone (ITCZ) is a planetary-scale band of heavy precipitation close to the equator. Here, we consider the response of the ITCZ structure to climate change using observations, simulations, and theory. We focus on the substantial yet underappreciated projected changes in ITCZ width and strength, and highlight an emerging conceptual framework for understanding these changes. Recent FindingsSatellite observations and reanalysis data show a narrowing and strengthening of precipitation in the ITCZ over recent decades in both the Atlantic and Pacific basins, but little change in ITCZ location. Consistent with observations, coupled climate models predict no robust change in the zonal-mean ITCZ location over the twenty-first century. However, the majority of models project a narrowing of the ITCZ and weakening mean ascent. Interestingly, changes in ITCZ width and strength are strongly anti-correlated across models.Summary The ITCZ has narrowed over recent decades yet its location has remained approximately constant. Climate models project further narrowing and a weakening of the average ascent within the ITCZ as the climate continues to warm. Following intense work over the last ten years, the physical mechanisms controlling the ITCZ location are now well understood. The development of complementary theories for ITCZ width and strength is a current research priority. Outstanding challenges include understanding the ITCZ response to past climate changes and over land versus ocean regions, and better constraining all aspects of the ITCZ structure in model projections.

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Detecting cross‐equatorial wind change as a fingerprint of climate response to anthropogenic aerosol forcing

Cited by 38 publications

References 45 publications

The role of aerosols and greenhouse gases in Sahel drought and recovery

The role of aerosols and greenhouse gases in Sahel drought and recovery

Global Impacts of Arctic Sea Ice Loss Mediated by the Atlantic Meridional Overturning Circulation

Response of the Intertropical Convergence Zone to Climate Change: Location, Width, and Strength

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