How does rising atmospheric CO2 affect marine organisms?

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Ocean Temperatures (The Past Century) -- Summary
Are the world's oceans -- and the air above them -- warming in response to the ongoing rise in the atmosphere's CO2 concentration? In this summary we attempt to answer this question on the basis of seawater temperature measurements made over the past century.

As an intermediate step in an attempt to determine the reliability of predictions of cod populations in the Barents Sea based on climate data, Dippner and Ottersen (2001) produced a 20th-century (1900-1995) history of mean sea water temperature from the surface to a depth of 200 meters for the Kola Section of the Barents Sea, which stretches from 7030'N to 7230'N along the 3330' E meridian. This record indicated that the mean temperature of the upper 200 meters of water rose by approximately 1C from 1900 to 1940, after which it declined until about 1980 and then rose to the end of the record. The latter increase, however, was not great enough to bring water temperatures back to the highs they experienced in the 1940s and early 1950s; and a linear regression from 1940 onward (or even 1930 onward) would clearly produce a negative slope indicative of an overall cooling trend over the final 55 (or 65) years of the record.

In the report of another century-long study published the following year, Bratcher and Giese (2002) began by noting that the general trend of global surface air temperature was one of warming, but cautioned that there was "considerable variation in the upward trend," and that "how much of this variability is attributable to natural variations and how much is due to anthropogenic contributions to atmospheric greenhouse gases has not yet been resolved," adding that "the possibility exists that some portion of the recent increase in global surface air temperature is part of a naturally oscillating system." Hence, they decided to explore "the recent record of Southern Hemisphere subsurface [ocean water] temperature anomalies and whether they may be an indicator of future global surface air temperature trends."

In doing so, the two researchers found that "low frequency changes of tropical Pacific temperature lead global surface air temperature changes by about four years," and that "anomalies of tropical Pacific surface temperature are in turn preceded by subsurface temperature anomalies in the southern tropical Pacific by approximately seven years." In addition, they documented a distinct cooling of the southern tropical Pacific over the prior eight years, leading them to conclude that "the warming trend in global surface air temperature observed since the late 1970s may soon weaken." Interestingly, their premonition proved to be more than correct, as the previous upward trend in the globe's mean surface air temperature -- from the time of their writing -- not only weakened but actually reversed course and began to trend downward.

The following year, Chavez et al. (2003) analyzed "physical and biological fluctuations with periods of about 50 years that are particularly prominent in the Pacific Ocean," including air and ocean temperatures, atmospheric CO2 concentration, landings of anchovies and sardines, and the productivity of coastal and open ocean ecosystems. This work revealed 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 found 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." And these warm and cool regimes, which they respectively called El Viejo (the old man) and La Vieja (the old woman), were manifest in myriad similar-scale biological fluctuations that may be even better indicators of climate change than climate data themselves, in their estimation.

The findings of this unique study have many ramifications. The one that we highlight is the challenge they 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." Hence, 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, has in fact ended and actually reversed course. In fact, Chavez et al. cited much evidence that indicated a change from El Viejo to La Vieja conditions was already in progress at the time of their writing.

Two years later, 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 (USA), located at the southern end of Monterey Bay, for the period 1920-2001, the intent of which 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. Based on monthly averages, this work revealed that approximately 44% of the variability in the Pacific Grove data came from the annual cycle, 18% from El Nio warming episodes, 6% from the Pacific Decadal Oscillation (PDO), 4% from the long-term trend, and 3% from the semiannual cycle, while linear analysis of the 82-year record revealed a statistically significant SST increase of 0.01C per year, which trend is similar to the findings of other researchers who have attributed the trend to CO2-induced global warming. However, further analyses conducted by Breaker suggested that this attribution may have been a bit premature.

First of all, Breaker discovered that there were two major regime shifts associated with the PDO over the course of the record, one at about 1930 and one in 1976, which could 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." Furthermore, if one computes the linear SST trend subsequent to this regime shift, which Breaker did, the resulting 72-year trend is a non-statistically significant +0.0042C. As a result, Breaker concluded 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."

The results of Breaker's study clearly demonstrate that decadal-scale regime shifts have the potential to totally dwarf any potential "fingerprint" of CO2-induced global warming that might possibly be present in 20th-century SST data sets. Also, it is clear that the regime shift in the vicinity of 1930 was not the product of anthropogenic-induced global warming, because so little of the current burden of anthropogenic greenhouse gases had been released to the atmosphere prior to that time compared to what was subsequently released.

Last of all, and most recently, Hobson et al. (2008) used SST data from the International Comprehensive Ocean-Atmosphere Data Set to calculate, in annual time steps, the mean August-September positions of the 12, 15 and 18C isotherms in the North Atlantic Ocean from 1854 to 2005 at 2-degree longitudinal intervals. This effort revealed, in their words, that (1) the three isotherms "have tended to move northwards during two distinct periods: in the 1930s-1940s and then again at the end of the 20th century," that (2) "the chances of this occurring randomly are negligible," that (3) the 15C isotherm "reached a maximum latitude of 52.0N in 1932, and a latitude of 51.7N in 2005, a difference of approximately 33 km," and that (4) "of the 10 most extreme years, 4 have occurred in the 1992-2005 warm era and 3 have occurred in the 1926-1939 era."

Considering the totality of their findings, the UK and Australian researchers concluded, in the broadest of terms, that "current 'warm era conditions' do not eclipse prior 'warm' conditions during the instrumental record," which indicates that during the period of most significant greenhouse gas buildup over the past century (1930 and onward) there was little to no net increase in SSTs throughout this large sector of the North Atlantic Ocean.

In concluding this summary, it thus appears that whenever an approximate century's worth of SST data have been properly analyzed, it has typically been found that the results provide no backing for the theory of CO2-induced global warming. In fact, the data tend to argue against that hypothesis.

Bratcher, A.J. and Giese, B.S. 2002. Tropical Pacific decadal variability and global warming. Geophysical Research Letters 29: 10.1029/2002GL015191.

Breaker, L.C. 2005. What's happening in Monterey Bay on seasonal to interdecadal time scales? Continental Shelf Research 25: 1159-1193.

Chavez, F.P., Ryan, J., Lluch-Cota, S.E. and Niquen C., M. 2003. From anchovies to sardines and back: multidecadal change in the Pacific Ocean. Science 299: 217-221.

Dippner, J.W. and Ottersen, G. 2001. Cod and climate variability in the Barents Sea. Climate Research 17: 73-82.

Hobson, V.J., McMahon, C.R., Richardson, A. and Hays, G.C. 2008. Ocean surface warming: The North Atlantic remains within the envelope of previous recorded conditions. Deep-Sea Research I 55: 155-162.

Last updated 15 July 2009