El Nino, hurricanes, other atmospheric-oceanic circulations are part of global warming debate

PART III: This is the final segment in a three-part series on global climate science and its relationship to global warming.

The first two papers in this series covered an incredible panorama of climate change:

• 100 kilo-year (KY) glaciation cycles
• Sea level rise over the past 20 KYs
• Possible 10 KY lag associated with changes in Antarctica
• Multiplicity of glacier advance/retreat periods over the past 9.6 KYs (leading to the concept of a 250-year cycle coupled to the sun, and to such renowned climate periods as the Little Ice Age)
• An 11-year sunspot cycle with potential couple to major temperature trends over the past 240 years (and even to interaction with cosmic rays and cloud formation).

This paper will focus on cycles with a seasonal to decadal time scale. These tend to be tied to the earth's atmospheric-oceanic circulations. Understanding atmospheric and oceanic circulation is the pathway to predicting weather and climate.

Indeed, a major portion of the case for action on global warming is based on results from computer simulation of atmospheric and oceanic circulation. Such models are referred to as general circulation models (GCMs). Over 30 models have been developed around the world. Some of this effort has included coupled models that include both atmospheric and oceanic simulations. By and large, the scientific research and the analysis conducted has been striking and represents the outstanding creativity in the scientific community.

These models have been most useful in research planning and to some degree in education and communications. But the models are far from perfect. There are many serious concerns on both the models' logic and performance. Dr. William Gray, a pre-eminent US hurricane forecaster from Colorado State University, said during a 1997 meeting that "Global models can neither predict seasonal temperatures nor hindcast. The reason is the atmosphere is so very complicated. The models have been superb when used for the next 5-10 days, but when modelers move into the climate area, the complexity becomes too great."

A review of the concerns over GCMs is beyond the scope of this article. The objective here is to ask, and answer, the question: Is the science of global warming, including the science of climate modeling, done sufficiently to support the kind of economic and social changes contemplated by the proponents of this issue?

El Niño history

Earlier papers by this writer noted that recordings of El Niño went back to 1525, but the phenomenon was undoubtedly older than that. Recent reports now hypothesize that the origin of this phenomenon dates back not just 500 years, but 10 times that (5.8 KYs). The El Niño occurs every 2-7 years, with a strong one about every 5-10 years.

For some unknown reason, the trade winds reverse their normal direction causing warm Western Pacific surface waters to move east. Dr. James Baker, head of NOAA, recently noted that, "El Niño is a natural phenomenon. We know it is linked, to both short term and long term time scales. El Niño is superimposed on some long term fluctuations whose origin we do not know."

There is little question that the recent El Niño was very strong. However, the proponents of global warming have exploited its strength, rushing to claim a direct couple to their cause. "Undoubtedly, some will want to interpret this warmest on record El Niño as a partial response to the atmospheric greenhouse gas buildup," Dr Gray explained. "We do not subscribe to this view. Rather, it is likely due to a peculiar juxtaposition of favorable El Niño enhancing mechanisms. Its strength is believed to be due to a buildup of the western Pacific warm water pool of deep water to a very high level over the past three years."

The fact that the El Niño involves sea surface temperatures (SST) is well known. The many vivid color-enhanced temperature maps of the Pacific - with the tongue of red, manifesting warmer sea water, projecting into the ocean off of Peru - has been seen by millions.

Ocean-atmosphere event

The El Niño/Southern Oscillation (ENSO) is a combined oceanic-atmospheric event where the Southern Oscillation (SO) part is the atmospheric pressure difference between Tahiti and Darwin. The ENSO is the strongest source of natural climate variability, with global impacts on seasonal to decadal time scales.

The Southern Oscillation Index (SOI) is this pressure difference normalized by its standard deviation. The SOI was first discovered and defined in 1923. There is a very strong inverse correlation between SST and the SOI. Here, the SST is the average over the east central Pacific at the equator. When the SOI is strongly negative, trade winds are reversed and the SST becomes strongly positive.

The SST is one of six variables used in the MEI, the multi-variate ENSO index (see table). The recent El Niño started earlier and peaked earlier than the previous strongest event. Yet, on balance, over the complete cycle, this phenomenon may not have been stronger than the 82/83 event.

Observations on SST are not limited to the Pacific. Various scientists have noted changes in the Atlantic SST. A recent news item reported that SSTs in the northern, tropical Atlantic have been very high this year, perhaps a switch in temperature, around the mid-1990s, from several decades of relatively lower temperatures. Dr. Gray has reported on a major change in the Atlantic Ocean SSTs temperatures that began late in 1994 and continues to the present.

Also, several authors have noted an apparent link between SST and solar activity. For example, a recent study compared North Pacific SSTs versus a record of the 11-year solar irradiance cycle. They matched each other.

Dr. Gray noted that the strength of the 1997 El Niño was not anticipated by any prediction models. However, one result of the 1997/1998 El Niño is an indication of significant progress in forecasting. It was the timing of this El Niño which was captured by several modeling efforts. This success on timing has won the ENSO models a larger role in forecasting out to a six-month horizon.

SST anomalies can now be forecast at lead times of six months and possibly longer. Forecasting includes the averages over a month or a season, but not specific events. We still have a very long way to go, but progress is being made and the forecast of the early arrival of this El Niño is testimony to that.

More hurricanes

Hurricane occurrence for North America clearly follows a seasonal cycle, peaking in late August and September. It has been known for some time that strong El Niños will reduce the number of Atlantic hurricanes. A reversal of the trade winds will lead to stronger wind shear in the upper atmosphere that inhibits strong updrafts, thereby ripping apart most embryonic storms.

Dr. Gray reported that 1997 was a year of below normal hurricane activity and a busted forecast due to the unexpectedly strong

El Niño. It just overwhelmed a host of other positive hurricane enhancing factors. The 1998 season saw a return to a very active hurricane season.

Is global warming triggering more hurricanes? Prior to 1997, the Atlantic Hurricane activity had been on the increase for 2-3 years. Dr. Gray recently wrote on this subject as follows: "Some individuals will interpret that recent upswing in hurricane activity... as evidence of climate changes.... This may be a logical interpretation, given all the media hype on this topic. But this speculation cannot be accepted.

"Anthropogenic greenhouse gas warming, if a physical valid hypothesis, is a very slow and gradual process that, at best, could only be expected to bring about small changes in global circulation over periods of 50-100 years. This would not result in the abrupt and dramatic one year upturn in hurricane activity, as occurred in 1994-95."

A major change in the Atlantic Ocean SSTs began late in 1994 and has continued to the present. Dr. Gray and his colleagues noted, "We hypothesize that the strong broad-scale SST changes are due to a major increase in the strength of Atlantic thermo-haline circulation (THC). This interpretation is consistent with changes in a number of our global circulation features that have occurred during the last three years. We appear to be experiencing a shift towards a stronger Atlantic Ocean THC and likely will experience greater amounts of hurricane activity in the coming decades than occurred in the 1970s, 1980s, and early 1990s."