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Oceans (Regime Shifts) - Summary
Is there a "natural " explanation for the supposedly "unprecedented" warming of the past quarter-century? ... and could the highly-hyped decadal-scale warming soon be coming to an end? We explore these questions via a review of what is known about natural but abrupt regime shifts in ocean temperature and biology, based on a number of studies that have been conducted over the past few years.

Gedalof and Smith (2001) compiled a set of six tree-ring width chronologies from stands of mountain hemlock growing near the treeline along the mountain range that stretches from southern Oregon to the Kenai Peninsula of Alaska, analyzing the data in a way that enabled them to "directly relate changes in radial growth to annual variations in the North Pacific ocean-atmosphere system." Their study spanned a period of nearly 400 years, stretching from 1599 to 1983, and it revealed that "much of the pre-instrumental record in the Pacific Northwest region of North America is characterized by alternating regimes of relatively warmer and cooler sea surface temperature in the North Pacific, punctuated by abrupt shifts in the mean background state," which climatic transitions or regime shifts were found to be "relatively common occurrences." Indeed, the two researchers say their data indicate that "regime shifts in the North Pacific have occurred 11 times since 1650," and that "another regime-scale shift in the North Pacific is almost certainly imminent."

An important implication of these findings is that the abrupt 1976-77 shift in this Pacific Decadal Oscillation, as it is generally called, is what was responsible for the vast majority of the past half-century's warming in Alaska, which climate alarmists wrongly hype as evidence for gradual CO2-induced global warming. Take away what occurred in that single year, for example, and Alaska is no different from the rest of the world, with most of its temperature stations showing little subsequent warming, and some of them actually exhibiting cooling.

Investigating this phenomenon over the past century from a marine biological perspective, Chavez et al. (2003) reviewed both "physical and biological fluctuations with periods of about 50 years that are particularly prominent in the Pacific Ocean," focusing on air and ocean temperatures, landings of anchovies and sardines, and the productivity of coastal and open-ocean ecosystems. In doing so, they determined that "sardine and anchovy fluctuations are associated with large-scale changes in ocean temperatures: for 25 years, the Pacific is warmer than average (the warm, sardine regime) and then switches to cooler than average for the next 25 years (the cool, anchovy regime)." They also report that "instrumental data provide evidence for two full cycles: cool phases from about 1900 to 1925 and 1950 to 1975 and warm phases from about 1925 to 1950 and 1975 to the mid-1990s." These warm and cool regimes, which they respectively call El Viejo (the old man) and La Vieja (the old woman), are manifest in myriad matching biological fluctuations that may be even better indicators of climate change than climate data themselves, according to the four researchers.

The findings of this important study have many ramifications. The one that we highlight here is the challenge the new results present for the detection of CO2-induced global warming. Chavez et al. correctly note, for example, that data used in climate change projections are "strongly influenced by multidecadal variability of the sort described here, creating an interpretive problem." Specifically, they conclude that "these large-scale, naturally occurring variations must be taken into account when considering human-induced climate change," and in this regard, we note that the warming of the late 1970s to late 1990s, which returned much of the world to the level of warmth experienced during the 1930s and 1940s, may well be about to end. In fact, Chavez et al. cite evidence that indicates a change from El Viejo to La Vieja conditions may already be in progress; and if this is true, we could well see global temperatures begin to drop in the not too distant future.

Concentrating on the more recent past, Freeland et al. (2003) analyzed water temperature and salinity measurements that were made at a number of depths over a period of several years along two lines emanating from central Oregon and Vancouver Island westward into the Pacific Ocean. This work revealed that subsurface waters in an approximate 100-meter-thick layer located between 30 and 150 meters depth off central Oregon were, in their words, "unexpectedly cool in July 2002." Specifically, mid-depth temperatures over the outer continental shelf and upper slope were more than 0.5°C colder than the historical summer average calculated by Smith et al. (2001) for the period 1961-2000, which Freeland et al. say "might be cooler than a longer-term mean because the 1961-71 decade coincided with a cool phase of the Pacific Decadal Oscillation (Mantua et al., 1997)." At the most offshore station, in fact, they report that "the upper halocline is >1°C colder than normal and about 0.5°C colder than any prior observation [our italics]." In addition to being substantially cooler, the anomalous water was also considerably fresher; and the combined effects of these two phenomena made the water less spicy, as they describe it, so much so, in fact, that they refer to the intensity of the "spiciness anomaly" as "remarkable."

Along the line that runs from the mouth of Juan de Fuca Strait to Station Papa at 50°N, 145°W in the Gulf of Alaska - which was sampled regularly between 1959 and 1981, but irregularly thereafter - similar low spiciness was observed, and Freeland et al. say there is little doubt it is the same feature as that detected off the coast of central Oregon. In this case, they report that "conditions in June 2002 [were] well outside the bounds of all previous experience [our italics]," and that "in summer 2001 the spiciness of this layer was already at the lower bound of previous experience."

The four researchers say their data imply that "the waters off Vancouver Island and Oregon in July 2002 were displaced about 500 km south of their normal summer position." Is this observation an indication the Pacific Ocean is beginning to experience a shift from what Chavez et al. call a "warm, sardine regime" to a "cool, anchovy regime"? It is tempting to suggest that it is. However, Freeland et al. caution against jumping to such a conclusion too quickly, saying there are no obvious signals of such a regime shift in several standard climate indices and that without evidence of a large-scale climate perturbation, the spiciness anomaly may simply be, well, anomalous. Hence, although the pattern of Pacific Ocean regime shifts documented by Chavez et al. suggests that a change from warmer to cooler conditions is imminent, there is not yet sufficient climatic evidence to claim that it is indeed in process of occurring.

On the other hand, in reference to the 1976-77 regime shift in the Pacific, Chavez et al. note that "it took well over a decade to determine that a regime shift had occurred in the mid-1970s" and, hence, that "a regime or climate shift may even be best determined by monitoring marine organisms rather than climate," as suggested by Hare and Mantua (2000). Enlarging on this concept, they cite several recent studies that appear to provide such evidence, including "a dramatic increase in ocean chlorophyll off California," which would appear to be a logical response to what Freeland et al. describe as "an invasion of nutrient-rich Subarctic waters."

Other pertinent evidence cited by Chavez et al. includes "dramatic increases in baitfish (including northern anchovy) and salmon abundance off Oregon and Washington," as well as "increases in zooplankton abundance and changes in community structure from California to Oregon and British Columbia, with dramatic increases in northern or cooler species."

Further observations in this same general region were made by Barth (2003), who during April, July and September of each year from 1998 to 2002 released five ocean drifters in a cross-shelf line at about the latitude of Newport, Oregon, at distances of 18.5, 27.8, 46.3, 83.3 and 120.4 km offshore. All drifters were tracked via satellite, and their locations were measured roughly 9-12 times per day, after which the data were used to compute east-west and north-south drifter displacements and speeds over 15, 30 and 45 days. This protocol revealed, in Barth's words, that "equatorward velocities in the core of the upwelling jet of the northern California Current were found to be on average 0.05-0.06 m s-1 faster in spring and summer 2002 than the average computed over 1998-2002," noting further that "at this speed, anomalous water displacements of over a degree of latitude can occur in 20-25 days."

Barth says that the southward displacement of subarctic water identified in his study is "a plausible explanation for the relatively cool halocline water observed off Oregon during the summer of 2002 (Freeland et al., 2003)," and that it is "consistent with the large-scale forcing events described by Murphree et al. (2003) and provides a quantitative estimate of their combined effect, an increase of near-surface equatorward flow of 0.05-0.06 m s-1." He also notes that his results are consistent with anomalous southward and onshore flow into the northern California Current as measured by cross-track altimeter surface velocities (Strub et al., 2003), and that the drifter velocity near the center of the jet at 27.8 km offshore ranged up to 0.13 m s-1, which he says is consistent with "the 0.12 m s-1 anomalous equatorward velocity measured at a mid-shelf mooring located 18.5 km offshore of Newport, Oregon (Kosro, 2003)." Last of all, Barth reports that "the observed cold halocline water is accompanied by high nutrients (Wheeler et al., 2003) which, when upwelled over the shelf, fuel an increase in the amount of primary productivity off the Pacific Northwest (Wheeler et al., 2003; Thomas et al., 2003).

As to what these dramatic changes represent, Barth opines they are manifestations of interannual variability at the opposite extreme of "the increased poleward velocity and warmer temperatures observed in this same region during the fall and winter of El Niņo years." Only time will tell if this interpretation is correct, or if the recent anomalous invasion of subarctic water is a harbinger of a more comprehensive and prolonged regime shift of the type described by Chavez et al. (2003).

More evidence for the latter alternative was provided by the study and analysis of Mullin et al. (2003), who reviewed what was known near the turn of the past century about the history of macrozooplankton found within the California Current in relation to the regime-shift hypothesis, after which they presented some new data on the subject based on biovolume measurements made with the optical plankton counter on preserved samples of macrozooplankton taken in the non-El Niņo years of 1955, 1956, 1966, 1981, 1984, 1991, 1995, 1996 and 1999.

With respect to the work of others, Mullin et al. report that Roemmich and McGowan (1995a,b) demonstrated "a decline of approximately 70% in the biomass of zooplankton, and a warming of the surface layer of up to 1.5°C, in the southern California sector of the California Current System (CCS) over the 42 years ending in 1993." They also note that "the decrease in macrozooplankton has continued at least to 1998, exacerbated by the 1997-1998 El Niņo (Hayward et al., 1999; Hayward, 2000)," but that macrozooplankton biomass has subsequently "increased dramatically."

Although Roemmich and McGowan (1995a) originally presented their data as showing a smooth trend, Mullin et al. remark that they and others have subsequently emphasized "the idea of a 'regime shift' - a relatively rapid change in the mid-1970s, from one quasi-steady state of relatively high biomass in the CCS to another of relatively low biomass." This interpretation, in their words, "is supported by North Pacific climatology (e.g. Miller et al., 1994), concurrent (but oppositely directed) ecological changes in the Alaska Gyre, and atmosphere/ocean models linking the two (e.g. Francis and Hare, 1994; Brodeur et al., 1996; Mantua et al., 1997)." In addition, they note that "recent climate and ocean data suggest the 1999 El Viejo may also be the start of a new decadal-scale regime (Stephens et al., 2001; Mackas et al., 2001; Greene, 2002)."

As for their own work, Mullin et al. report that their results from 1955 to 1996 "could be interpreted either as a linearly decreasing trend (total biovolume decreased by 45%) or as a regime shift (decrease of 38% from pre- to post-1975 regimes)." Thereafter, however, in a single year, they say that "total biovolume increased in 1999 to the pre-1975 level, consistent with a possible shift to a new regime." Mullin et al. thus conclude that their 1999 data "are consistent with a shift from the low biovolume regime of 1976-1996 to one more like the high biovolume regime of 1955-1975." However, they say it is still too early to decide "whether the increased biovolume in 1999 is brief (e.g. ENSO-related) or lasting (e.g. a regime)." More time and more data will be required to resolve the issue.

Also weighing in on the subject about the same time were Peterson and Schwing (2003), who describe a number of persistent changes in atmospheric and upper ocean fields and ecosystem structure that suggest that a major climate regime shift occurred in the northeast Pacific Ocean and adjacent coastal areas in the latter part of 1998, which shift is similar (opposite) to shifts observed there in 1947 (1925 and 1976). They report, for example, that "upwelling-favorable winds strengthened over the California Current (CC), and winds weakened in the Gulf of Alaska (GOA)," while "coastal waters of the CC and GOA cooled by several degrees, and the Pacific Decadal Oscillation reversed sign and remained negative through summer 2002." As a result, they say that "zooplankton biomass in the northern CC doubled and switched from warm to cold water species dominance, coho and Chinook salmon stocks rebounded, and anchovy and osmeriids increased." In addition, they report that recent surveys of the GOA reveal that the ecosystem there has been transformed as well.

With respect to the northeast Pacific, the two researchers suggest that the observed changes "imply a shift to stronger coastal upwelling and greater than normal southward transport in the CC." With respect to the planet as a whole, we additionally note that the changes could well presage a return of cooler temperatures, in light of the dramatic shifts in global temperature trends that commenced at approximately the same times as the documented climate regime shifts of 1925 (warming), 1947 (cooling), and 1976 (warming), which can be readily reproduced from the Global Historical Climatology Network and Jones et al. databases of the World Temperatures section of our website.

More recently, Breaker (2005) performed a number of statistical analyses on a daily sea-surface temperature (SST) record from the Hopkins Marine Station in Pacific Grove, California, located at the southern end of Monterey Bay, for the period 1920-2001. The intent of the study was to identify and estimate the relative importance of atmospheric and oceanic processes that contribute to the variability in the SST record from seasonal to interdecadal time scales. This work revealed that variability in the Pacific Grove data was accounted for as follows: approximately 44% came from the annual cycle, 18% from El Niņo warming episodes, 6% from the Pacific Decadal Oscillation, 4% from the long-term trend, and 3% from the semiannual cycle. In addition, linear analysis of the 82-year record revealed a statistically significant SST increase of 0.01°C per year, which trend is similar to the findings of other researchers who have attributed the trend to global warming (Barry et al., 1995; Sagarin et al., 1999). However, additional analyses conducted by Breaker suggest that this attribution may have been premature.

In further examining the Pacific Grove SST data, Breaker found there were two major regime shifts associated with the PDO over the course of the record, one that occurred about 1930 and one that occurred in 1976. Furthermore, these regime shifts could readily explain most of the 82-year warming. Prior to the regime shift in the vicinity of 1930, for example, the waters of Monterey Bay were, in Breaker's words, "much colder than at any time since then." Also, if one computes the linear SST trend subsequent to this regime shift, which Beaker did, the result is not statistically significant. Consequently, Beaker concludes that "although the long-term increase in SST at Pacific Grove appears to be consistent with global warming, the integrated anomaly suggests that temperature increases in Monterey Bay have occurred rather abruptly and thus it becomes more difficult to invoke the global warming scenario."

Shifting our attention to the North Atlantic, we find a return to more frigid conditions there as well, as recent observations on the other side of North America point to a similar invasion of abnormally cold water. In a news item in the 24 April 2003 issue of Nature, for example, Hoag (2003) reports that "more than 700 tonnes of Atlantic cod [froze] to death in chilly waters off eastern Newfoundland" in early April, when "the temperature of the water column in Smith Sound fell to -1.7°C." Hoag further notes that "historical temperature profiles from the region indicate that such temperatures are very unusual for the sound." In fact, to find a comparable "fish freeze," Hoag had to hearken all the way back to 1882, when millions of warm-water tilefish died off the northeastern coast of the United States.

These remarkable marine water cooling events on both sides of North America could not help but draw our attention to what happened about the same time to the continent's great inland fresh waters in March of 2003. As reported in our Editorial of 16 April 2003, three of the five Great Lakes - Superior, Huron and Erie - all froze over completely; and the last time this 100% triple-freeze occurred was, well, never ... at least over the period for which reliable data are available, i.e., 1963 to the present.

In concluding this summary, we shift our attention to the far-away Cook Islands in the South Pacific, where previous studies of a Rarotonga coral-based SST reconstruction focused on documenting and interpreting decadal and interdecadal variability without separating distinct modes of variability within this frequency band (Linsley et al. 2000, 2004; Evans et al. 2001), but where Dima et al. (2005) reanalyze the original coral record using Singular Spectrum Analysis in an effort to determine the dominant periods of multi-decadal variability over the period 1727-1996.

Results of the new analysis revealed two dominant multi-decadal cycles, with periods of approximately 25 and 80 years. These modes of variability were determined to be similar to multi-decadal modes found in the global SST field of Kaplan et al. (1998) for the period 1856-1996. The ~25-year cycle was found to be associated with the well-known Pacific Decadal Oscillation that figures prominently in the regime shifts described above, whereas the ~80-year cycle was determined to be "almost identical" to a pattern of solar forcing found by Lohmann et al. (2004), which, according to Dima et al., "points to a possible solar origin" of this mode of SST variability.

All in all, these several observations point to the strong possibility that abrupt regime shifts figure prominently in the normal course of earth's natural climatic progression, and that the warming trend of the past quarter-century may not be so unusual after all.

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Last updated 8 March 2006