Darwin sea level pressure, 1876–1996: Evidence for climate change?

Harrison, D. E.; Larkin, N. K.

doi:10.1029/97gl01789

Cited by 51 publications

(41 citation statements)

References 10 publications

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“…For example, Trenberth and Hoar (1996) pointed out there has been a tendency toward more frequent El Niñ o events and fewer La Niñ a events since the late 1970s and that the prolonged 1990-95 El Niñ o event was highly unusual, which may serve as evidence of the effect of anthropogenically forced global warming and related climate change. However, this conclusion was challenged by two subsequent studies (Harrison and Larkin 1997;Rajagopalan et al 1997), which suggested that the 1990-95 El Niñ o event might have been part of the natural variability. However, using the definition of El Niñ o proposed by Trenberth (1997), Trenberth and Hoar (1997) argued that the (then) newly underway El Niñ o event of 1997 further confirmed that the tendency for more El Niñ o and fewer La Niñ a events since the late 1970s is very unlikely to be accounted for solely by natural variability.…”

Section: Introductionmentioning

confidence: 81%

On Changing El Niño: A View from Time-Varying Annual Cycle, Interannual Variability, and Mean State

Qian

et al. 2011

Journal of Climate

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This study investigates changes in the frequency of ENSO, especially the prolonged 1990-95 El Niñ o event, in the context of secular changes in the annual cycle, ENSO interannual variability, and background mean state of the tropical eastern Pacific sea surface temperature (SST). The ensemble empirical mode decomposition (EEMD) method is applied to isolate those components from the Niñ o-3 SST index for the period 1880-2008. It is shown that the annual cycle [referred to as a refined modulated annual cycle (MAC)] has strong interannual modulation and secular change in both amplitude and phase: a clear transition from increasing to decreasing amplitude around 1947/48, with both linear trends before and after this turning point statistically significant and the amplitude decreasing by 14% since then, and a significant phase delay trend for the period 1881-1938, but hardly any thereafter. A clear transition from significant deceasing to increasing by about 30% in the amplitude of the ENSO interannual variability around 1937 is also found. When El Niñ o events are represented as the collective interannual variability, their frequency is found to be almost equivalent to that of La Niñ a events after 1976. A method for conducting synthetic experiments based on time series analysis further reveals that the apparent prolonged 1990-95 El Niñ o event was not caused solely by ENSO interannual variability. Rather, the 1991/92 warm period is attributable to an interannual variation superimposed by change in the background mean state; the 1993 warm period is attributable to change in the mean state; and the 1994/95 warm period is attributable to a residual annual cycle, which cannot be fully excluded by a 30-yr mean annual cycle approach. The impact that changing base periods has on the classification of ENSO events and possible solutions is also discussed.

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Section: Introductionmentioning

confidence: 81%

On Changing El Niño: A View from Time-Varying Annual Cycle, Interannual Variability, and Mean State

Qian

et al. 2011

Journal of Climate

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“…In comparison, the numbers of strong La Nin Äa and El Nin Äo events were equal during the period 1876±1976. The recent shift toward the predominance of El Nin Äo-type conditions is re¯ected in a decrease in the mean value of the Southern Oscillation Index (Trenberth, 1990;Trenberth & Hurrell, 1994;Trenberth & Hoar, 1996Solow, 1995;Harrison & Larkin, 1997;Rajagopalan, Hall & Cane, 1997). The downward shift in the mean may not simply be a re¯ection of an increase in the frequency and/or magnitude of low-phase (El Nin Äo) events, but may re¯ect a change in the background climate state (Graham, 1994;Kleeman, Colman, Smith & Power, 1996).…”

Section: Change In the Background Climate Statementioning

confidence: 91%

El Niño, climate change, and Southern African climate

Mason

2001

Environmetrics

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SUMMARYThe El Nin Äo phenomenon involves a large-scale warming of the equatorial eastern and central Paci®c Ocean. Recent developments in the El Nin Äo±Southern Oscillation (ENSO) phenomenon have raised concerns about climate change. In this review paper, these recent developments are critically assessed and forecasts of possible future changes are reviewed. Since the late-1970s, El Nin Äo episodes have been unusually recurrent, while the frequency of strong La Nin Äa events has been low. Prolonged/recurrent warm event conditions of the ®rst half of the 1990s were the result of the persistence of an anomalously warm pool near the date line, which, in turn, may be part of an abrupt warming trend in tropical sea-surface temperatures that occurred in the late-1970s. The abrupt warming of tropical sea-surface temperatures has been attributed to the enhanced-greenhouse effect, but may be indicative of inter-decadal variability: earlier changes in the frequency of ENSO events and earlier persistent El Nin Äo and La Nin Äa sequences have occurred. Most forecasts of ENSO variability in a doubled-CO 2 climate suggest that the recent changes in the tropical Paci®c are anomalous. Of potential concern, however, is a possible reduction in the predictability of ENSO events given a warmer background climate.El Nin Äo events usually are associated with below-normal rainfall over much of southern Africa. Mechanisms for this in¯uence on southern African climate are discussed, and the implications of possible changes in ENSO variability on the climate of the region are assessed. Recent observed changes in southern African climate and their possible relationships with trends in ENSO variability are investigated. The El Nin Äo in¯uence on rainfall over southern Africa occurs largely because of a weakening of tropical convection over the subcontinent. A warming of the Indian Ocean during El Nin Äo events appears to be important in providing a teleconnection from the equatorial Paci®c Ocean. The abrupt warming of the tropical Paci®c and Indian oceans in the late-1970s is probably partly responsible for increasing air temperatures over southern Africa, and may have contributed to a prolongation of predominantly dry conditions. A return to a wet phase appears to have occurred, despite the persistence of anomalously high sea-surface temperatures associated with the late-1970s warming, and a recordbreaking El Nin Äo in 1997/98.

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“…For example, this simple analysis does not place any additional weight on high wind events and on wind duration. In addition, the length of our record does not permit rigorous determination of effective degrees of freedom (e.g., Leith et al, 1973;Harrison and Larkin, 1997) to filter out other cyclic and auto-correlated variations, such as diurnal influences on wind speeds and seasonal changes in radiation. Despite these limitations, we think that our interpretation of the association of watercolumn data and lagged wind vectors may be instructive for future research efforts in the Bering Strait.…”

Section: Resultsmentioning

confidence: 99%

The Potential for Using Little Diomede Island as a Platform for Observing Environmental Conditions in Bering Strait

Cooper¹,

Codispoti²,

Kelly³

et al. 2009

ARCTIC

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ABSTRACT. The Pacific waters that enter the Arctic via the Bering Strait exert a major influence on the Arctic Ocean's stratification, ice cover, and ecosystem. We demonstrate the potential of a shore-based laboratory to monitor the water masses that flow predominantly northward past Little Diomede Island in the center of the Bering Strait into the Arctic Ocean. We determined near-surface water column salinity, inorganic nutrient concentrations, natural fluorescence associated with chlorophyll, and the oxygen isotope composition of seawater, both in summer during the open-water period and in late winter under ice-covered conditions, by pumping ashore water from shallow depths near the island. Additional surveys were undertaken within 5 km of the island to assess the influence of local sources of nutrients. Water mass variability was much greater during the open-water period than under ice-covered conditions, presumably because the relatively immobile ice cover attenuates wind forcing and the decrease in run-off reduces cross-shelf gradients. The mean oxygen isotope composition of the summer (δ 18 O = -1.11‰) and late winter (δ 18 O = -0.98) collections, however, was close to that which has been established for Bering Sea waters in the Pacific-dominated upper halocline of the Arctic Ocean (-1.1‰) particularly considering the higher seasonal flow of runoff in the summer. A comparison with data from shipboard sampling at various locations across the Bering Strait indicates that the oxygen isotope composition of near-surface water sampled at Diomede varies in response to wind-forcing. If the least saline (< 30.5) water near the Alaska coast is excluded, the δ 18O values of Diomede and shipboard samples cannot be distinguished statistically. This similarity suggests that the water sampled from the island also reasonably represents the δ 18O value of Bering Sea waters that contribute to the upper halocline of the Arctic Ocean. Effects of benthic recycling, human activity, and seabird nesting on nutrient concentrations appeared to be concentrated within ~200 m of the island. Our results are discussed in the practical context of availability of electricity, interested local residents, and a geotechnical study indicating that it is feasible to construct and operate a more permanent undersea water intake system to improve environmental observation capabilities in the Bering Strait region.

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Darwin sea level pressure, 1876–1996: Evidence for climate change?

Abstract: Abstract. It has been argued that there was a period of prolonged ENSO conditions between 1990-95 so anomalous that it is "highly unlikely" to be due to "natural decadal-timescale

Cited by 51 publications

References 10 publications

On Changing El Niño: A View from Time-Varying Annual Cycle, Interannual Variability, and Mean State

On Changing El Niño: A View from Time-Varying Annual Cycle, Interannual Variability, and Mean State

El Niño, climate change, and Southern African climate

The Potential for Using Little Diomede Island as a Platform for Observing Environmental Conditions in Bering Strait

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