Archives for August 20, 2008

The extended title of the post is “Sea Surface Temperatures of the Oceans Surrounding Australia and the Magnitude of ENSO Events, ” because the following illustrations of Sea Surface Temperatures (SSTs) of Australian waters present an interesting effect, the impact of the magnitude of El Nino-Southern Oscillation (ENSO) events on SST. While I’ve seen it before in other data sets, I haven’t yet singled it out for discussion.

(Note: To economize words, throughout the rest of the post, I’ll use “Australian waters” in place of “oceans surrounding Australia” or the “combined Southwest South Pacific and Southeast South Indian Ocean data set.”)

First, to determine the area to evaluate, I downloaded data for two geographical areas from the NOAA NOMADS system. They’re identified by the red and blue boxes in Figure 1. The coordinates used are 10-45S, 105-165E for the red area and 0-55S, 95-175E for the blue.

Figure 1

Figure 2 illustrates the SST anomalies from January 1854 to June 2008 for the two ocean areas surrounding Australia. Both data sets have been smoothed with a 37-month filter. Picking the start date in the trough at 1905 and the end date at a peak in 2000 (There must be an alarmist side to me.), both data sets show rises in SST that are on the order of 1.0 to 1.2 deg C. The two signals are similar, with the smaller area having the greater variations. For the remainder of this post, I’ll use the data from the smaller area, the red curve.

Figure 2

Figure 3 shows the raw long-term data for the SST anomalies of Australian waters. Also illustrated is data that’s been smoothed with a 12-month running-average filter. Typical of many other oceanic data sets, there is an overall decline in SSTs from the late 1800s to 1910 and a rebound in SSTs until 1940. Then, though there are underlying oscillations, SSTs rise almost continuously from 1940 to present. El Nino events appear to stand out.

Note: The step change (temperature drop) at 1945 has been identified as an error in a recent Thompson et al letter to “Nature” with the title “A Large Discontinuity in the Mid-Twentieth Century in Observed Global-Mean Surface Temperature”.
http://www.nature.com/nature/journal/v453/n7195/abs/nature06982.html

Figure 3

But there’s something that seems to be missing from the data in later years. Refer to Figure 4, which illustrates short-term (January 1978 to June 2008) SST anomalies for Australian waters. The delayed responses to the 82/83, the 86/87/88, and the 97/98 El Nino events are again easy to find with the sudden rises in SST, but…

Where are the effects of the La Ninas?

The 97/98 El Nino is so much larger than the subsequent multiyear La Nina that it gives the impression that it supplied enough heat to create a step change in the SSTs of Australian waters and that the heat then dissipated over a ten year period. But that impression is only partly correct. The effects of the La Ninas are there, but they are overwhelmed by the magnitudes of those major El Ninos.

Figure 4

In Figure 5, I’ve added NINO3.4 SST anomaly data to the graph of short-term SST anomalies for Australian waters. A scaling factor of 0.3 has been applied to the NINO3.4 data. I’ve also noted the timing of the two major volcanic eruptions in case someone feels they’re relevant.

The time lags between an ENSO event and the response of SST for Australian waters appear to be on the order of a few months to a year. And with the scaling factor used (0.3), the magnitude of the NINO3.4 SSTs during the 82/83, the 86/87/88, and the 97/98 events appear to generate similarly sized reactions in the SSTs of Australian waters.

Then, starting at 1998, it would appear that the entire drop in NINO3.4 SST should result in a similarly sized response in SST, but the response of the Australian waters falls far short. The logic behind the “Would-Should” statement is wrong.

In simple terms, ENSO events supply heat to sea surfaces when the NINO3.4 SST anomalies are greater than zero and remove heat when they’re less than zero. So the reference point for the NINO3.4 data is zero when comparing it to other anomaly data. Looking at the data again and using zero as the reference for the multiyear La Nina episode after the 97/98 El Nino, the reaction by the SSTs of Australian waters is in the proper scale. There are minor differences in the cause and effect and in the time lags in prior ENSO events, but all in all, there are no surprises.

Figure 5

The effects of ENSO events on SST trends are obvious once we’re reminded of them. Keep in mind that it is not only the frequency of El Nino and La Nina events but also the magnitude of those events that must be considered during discussions of their impacts on global or local climate.

In “The Evolution of ENSO and Global Atmospheric Temperatures”, Trenberth et al identify the linear trend in global temperatures that result from ENSO events: “For 1950-98, ENSO linearly accounts for 0.06 deg C of global warming.” http://www.cgd.ucar.edu/cas/papers/jgr2001b/jgr2.html

The effects of ENSO events appear much greater on regional levels.

Closing Note: The additional problems with measuring and calculating global mean sea surface temperature are discussed at length in numerous posts at ClimateAudit and in the papers that are the subjects of or the references used for those posts. For further information, refer to the following ClimateAudit posts:
http://www.climateaudit.org/?p=3114
http://www.climateaudit.org/?p=1272

SOURCE

Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).
http://nomads.ncdc.noaa.gov/#climatencdc

Bob Tisdale

A stalagmite in a West Virginia cave has yielded the most detailed geological record to date on climate cycles in eastern North America over the past 7,000 years. The new study confirms that during periods when Earth received less solar radiation, the Atlantic Ocean cooled, icebergs increased and precipitation fell, creating a series of century-long droughts.

A research team led by Ohio University geologist Gregory Springer examined the trace metal strontium and carbon and oxygen isotopes in the stalagmite, which preserved climate conditions averaged over periods as brief as a few years. The scientists found evidence of at least seven major drought periods during the Holocene era, according to an article published online in the journal Geophysical Research Letters.

“This really nails down the idea of solar influence on continental drought,” said Springer, an assistant professor of geological sciences.

Geologist Gerald Bond suggested that every 1,500 years, weak solar activity caused by fluctuations in the sun’s magnetic fields cools the North Atlantic Ocean and creates more icebergs and ice rafting, or the movement of sediment to ocean floors. Other scientists have sought more evidence of these so-called “Bond events” and have studied their possible impact on droughts and precipitation. But studies to date have been hampered by incomplete, less detailed records, Springer said.

The stalagmites from the Buckeye Creek Cave provide an excellent record of climate cycles, he said, because West Virginia is affected by the jet streams and moisture from the Gulf of Mexico and the Pacific Ocean.

Other studies have gleaned climate cycle data from lakes, but fish and other critters tend to churn the sediment, muddying the geological record there, said study co-author Harold Rowe, an assistant professor of geological sciences at the University of Texas at Arlington.

“(The caves) haven’t been disturbed by anything. We can see what happened on the scale of a few decades. In lakes of the Appalachian region, you’re looking more at the scale of a millennium,” Rowe said.

Strontium occurs naturally in the soil, and rain washes the element through the limestone. During dry periods, it is concentrated in stalagmites, making them good markers of drought, Rowe explained. Carbon isotopes also record drought, Springer added, because drier soils slow biological activity. This causes the soil to “breathe less, changing the mix of light and heavy carbon atoms in it,” he said.

In the recent study, the scientists cut and polished the stalagmite, examined the growth layers and then used a drill to take 200 samples along the growth axis. They weighed and analyzed the metals and isotopes to determine their concentrations over time.

The data are consistent with the Bond events, which showed the connection between weak solar activity and ice rafting, the researchers said. But the study also confirmed that this climate cycle triggers droughts, including some that were particularly pronounced during the mid-Holocene period, about 6,300 to 4,200 years ago. These droughts lasted for decades or even entire centuries.

Though modern records show that a cooling North Atlantic Ocean actually increases moisture and precipitation, the historic climate events were different, Springer said. In the past, the tropical regions of the Atlantic Ocean also grew colder, creating a drier climate and prompting the series of droughts, he explained.

Unfortunately, at this point the media release replaces data with computer modelled global warming alarmism:

The climate record suggests that North America could face a major drought event again in 500 to 1,000 years, though Springer said that manmade global warming could offset the cycle.

“Global warming will leave things like this in the dust. The natural oscillations here are nothing like what we would expect to see with global warming,” he said.

Though some climate and drought records exist for the Western and Midwest areas of North America, the eastern Appalachian region hasn’t been studied much to date, Rowe said. The research team plans to examine additional stalagmite records from West Virginia and Tennessee to paint a better picture of North American climate cycles.

Collaborators on the study also included Lawrence Edwards, Ben Hardt and Hai Cheng of the University of Minnesota.

Ohio University Research News – ATHENS, Ohio (Aug. 19, 2008): New climate record shows century-long droughts in eastern North America

Weak sun created cool oceans, lowered rainfall seven times in 7,000 years

Geophysical Research Letters

Solar Forcing of Holocene Droughts in a Stalagmite Record from West Virginia in East- Central North America

Abstract:

Elevated Sr/Ca ratios and δ13C values in Holocene-age stalagmite BCC-002 from eastcentral North America record six centennial-scale droughts during the last five North Atlantic Ocean ice-rafted debris (IRD) episodes, previously ascribed to solar irradiance minima. Spectral and cross-spectral analyses of the multi-decadal resolution Sr/Ca and δ13C time series yield coherent ~200 and ~500 years periodicities. The former is consistent with the de Vries solar irradiance cycle. Cross-spectral analysis of the Sr/Ca and IRD time series yields coherent periodicities of 715- and 455-years, which are harmonics of the 1,450±500 year IRD periodicity. These coherencies corroborate strong visual correlations and provide convincing evidence for solar forcing of east-central North American droughts and strengthen the case for solar modulation of mid-continent climates. Moisture transport across North America may have lessened during droughts because of weakened north-south temperature and pressure gradients caused by cooling of the tropical Pacific and Atlantic Oceans. across the region throughout much of the year. As such, hydroclimates of eastern NA are dually sensitive to the climate state of the North AO and mid-latitude transcontinental teleconnections linking the Pacific and North Atlantic oceans [McCabe et al., 2004; Seager, 2007]. Herein, we demonstrate that this dual dependency allowed an east-central NA paleoclimate archive (speleothem) to directly record solar-forcing of Mid- to Late Holocene droughts that were caused by weakening of moisture transport over east-central NA in response to cooling of the Pacific and Atlantic Oceans.

Conclusions:

Seven significant Mid- to Late Holocene droughts are recorded in West Virginia stalagmite BCC-002 as elevated Sr/Ca ratios and δ13C values. Six droughts correlate with cooling of the Atlantic and Pacific Oceans as part of the North Atlantic Ocean ice-rafted debris cycle, which has been linked to the solar irradiance cycle. The Sr/Ca and δ13C time series display periodicities of ~200 and ~500 years and are coherent in those frequency bands. The ~200-year periodicity is consistent with the de Vries (Suess) solar irradiance cycle. We interpret the ~500- year periodicity to be a harmonic of the IRD oscillations. Visually, the Sr/Ca and IRD time series show strong correlations and cross-spectral analysis of the Sr/Ca and IRD time series yields statistically significant coherencies at periodicities of 455 and 715 years. These latter values are very similar to the second (725-years) and third (480-years) harmonics of the 1450±500-years IRD periodicity [Bond et al., 2001]. Collectively, these findings and a 1,200-year periodicity in the Sr/Ca time series, demonstrates solar forcing of droughts in east-central North America on multiple time scales. Droughts typically occur during solar minima when SST in the Atlantic and Pacific Oceans are comparatively cool. These SST anomalies cause migration of the jet stream away from east-central NA, yielding decreased meridional moisture transport and reduced convergence over east-central NA. Our findings appear to corroborate works indicating that millennial-scale solar-forcing is responsible for droughts and ecosystem changes in central and eastern North America [Viau et al., 2002; Willard et al., 2005; Dennison et al., 2007], but our high-resolution time series provide much stronger evidence in favor of solar-forcing of North American drought by yielding unambiguous spectral analysis results.