After Kyoto, Science Still Probes Global Warming Causes

Gerald Westbrook
TSBV Consultants
Houston

The Kyoto meeting has come and gone. And we have a new global warming treaty on the scene.

In the U.S., the treaty still has to be signed by President Bill Clinton and ratified by the Senate, an action that is most unlikely in view of last year's 95-0 vote on the issue. It is believed that ratification will be delayed, possibly up to and beyond the 1998 congressional elections and possibly even into and beyond the presidential election at the turn of the century.

In the short term 36 senators are up for reelection in November and therefore likely to come under intense pressure to change their positions, to support the Kyoto treaty, and to push for Senate action. Such pressure likely would be aimed not at getting the treaty ratified but at achieving a better result in the 1998 elections than would otherwise be expected.

Senators will need support, additional inputs, and overall reinforcement of their positions. Arguments will need to be updated and fine-tuned in several areas such as the global warming science, the alleged climate impacts, and the long-term economic impacts. One area that this writer believes still has much to offer in this context is the quality-more specifically, the lack of quality-of much of the scientific evidence behind this treaty.

Part of that subject is the natural variability in our climate. Natural climate variability is based on cyclical forces, random events, and the Earth's response to these two factors. These forces create the variability in our climate, the background noise above which any signal of anthropogenic warming must rise in order to be detected. A review of key climatic cycles is the subject of this article.

Cyclical forces

The presence of cyclical forces in our climate should not be a surprise to anyone as we see the daily rotation of the Earth, the approximate monthly revolution of the moon, and the yearly revolution of the Earth about the sun. These earth motion basics (EMBs) are responsible for daily temperature ranges that can amount to as much as 50° C. in the deserts and for the seasons of the year. They are responsible for the diurnal tides, whose ranges can reach as high as 50 ft such as those seen in Canada at the Bay of Fundy. They are responsible for eclipses of the sun and the moon.

There are many other cyclical forces. These include long-term cyclical factors, as described in a theory developed by Serbian astronomer-climatologist Milutin Milankovitch during 1920-1941. The Milankovitch theory was not translated into English until 1969. It has been debated extensively and fine-tuned since then.

The basic tenet of this work is that the Earth, in its travels around the sun, exhibits three key attributes:

• An elliptical orbit with a modest, but varying, eccentricity over a 100,000 year cycle (100 KY).
• A tilt of the planet, with variation over a 41 KY cycle. As an example, the tilt of the Earth would vary from 22.0° to 24.5°.
• A wobble of the Earth's axis with variations over 23 and 19 KY cycles.

Most important, changes in these factors cause major variation in the solar energy that reaches the Earth-solar insolation-at any latitude and season.

The Milankovitch Theory is widely accepted as the primary reason behind the many glacial and interglacial events that have occurred over the past 2 million years and the last Ice Age. These forces are what this writer calls earth motion anomalies (EMAs).

As an example of the couple between solar insolation and temperature, one multiple regression model showed that a temperature proxy, when regressed against six insolation time series (for different seasons and latitude) plus a 3 KY lagged temperature proxy, explained 87% of the variation in the data over a 400 KY period. This model was of sufficient quality that the scientists believed it could be used to predict 60 KY into the future.

As shown inFig. 1 [45,734 bytes], it indicates a gradual cooling over the next 25 KY and beyond. This outlook defines part of a very slowly varying, underlying rhythm in our climate. It clearly does not show any of the alleged or potential anthropogenic effects to which the Kyoto treaty attempts to respond. Nor does it show any of the much shorter term cycles that are known to exist.

It is believed that the sun plays a major role in these cycles. Clearly, the sun is dominant over the short term due to the EMBs. It is also clear that solar insolation changes play a major role over the longer term due to the EMAs. It is logical that the sun, the body that provides essentially all of the Earth's energy, should be a factor over intermediate periods, either directly or through the Earth system's response to any solar changes.

Two solar output anomalies (SOAs) will be discussed here.

Sunspot cycles

One SOA includes sunspot cycles and sunspot cycle length.

The period from 1880 to the present suggests the sun played a role in measurable climate change. The average temperature over the past 115 years, as indicated in the NASA/GISS data set, exhibits three distinct trends: a warming of 0.6° C. over 1880-1939, a cooling of 0.2° C. over 1939-65, and an additional warming of 0.4° C. over 1965-95. Other data sets show less warming. Indeed, the last United Nations position on temperature increase over this period was 0.3°-0.6° C.

What are the forces that have shaped this record? More of the warming occurred over the first trend, whereas most CO₂ emissions have occurred over the third trend. Clearly, these emissions could not cause the warming in the first period. All of that warming must be part of the natural rhythm of the climate.

Further, since there is nothing in global warming theory to account for a cooling, then the second trend must also be part of the background rhythm. It follows that at least some of the warming over the third trend would also be due to natural forces.

Another scientist, using a somewhat different data set, concluded that at least half of the 0.55° C. total temperature rise in her data set was due to solar variability.

One area of research aimed at resolving this enigma of the above three trends has focused on the sunspot cycle. The sunspot cycle record now goes back to the 17th century and shows a well-defined cycle with a mean length of 11 years. The sunspot count is an indirect indicator of magnetic activity under way in the sun. This in turn is an indicator of solar activity. The higher the count, the higher the solar output.

A hint of a relationship was first suggested by a plot of sea surface temperature and the sunspot count. Another study was based on a correlation versus sunspot cycle length. A longer cycle length means lower solar activity and a shorter one, higher activity. The resultant temperature correlation from 1862 to 1983, over 120 years, explained 91% of the variation in the data and caught each of the above defined trends. More recent work now suggests that this type of relationship extends back at least 240 years and boosts the number of major trends tracked from four to eight.

Sunspot activity lulls

Another SOA is the long-term lull in sunspot activity. Studies by astronomers and other scientists have established that a variety of cycles exists over the century to millennium time scale. Some examples:

• A study of climate records in England found protracted periods of cold occurred roughly every 200 years-in the 13th, 15th, 17th, and 19th centuries. The coldest decade was perhaps the 1690s, marked by failed harvests, famine, and social upheaval. The tragic story of Queen Anne gives one reason to reflect. She was pregnant 18 times from 1683 to 1700, but only five children were born alive. And only one of these children survived infancy but died at the age of 11. Is this a testimony to her overall poor health? Is it simply testimony to the general state of medical practice at that time? Or could it be testimony to the fact that the large stone castles she lived in were impossible to keep warm and dry?
• The history of Alpine glacier advance and retreat has been studied with records dating back to 8,000 B.C. There were at least 14 century-scale cool periods over this chronology. For the last 1,500 years there have been six cycles that average about 250 years between peaks.
• Climate reconstruction initiatives have been undertaken. One scientist, in reconstructing a solar irradiance history since A.D. 1610, based her reconstruction on the 11 year sunspot cycle and a slowly varying background cycle.
• Scientists have reconstructed sunspot cycles. Dark spots on the sun were first noted as far back as the 4th century. With the advent of the telescope in 1610, interest increased. However, it was not until 1848 that Rudolf Wolf, director of the Bern and later the Zurich Observatory in Switzerland, started to record spots on a regular and standardized basis. Wolf also noted recent discussions of the cyclical behavior of this phenomena and undertook the effort to recover past data on sunspots.

Others have followed his lead. The resulting record can be viewed as reliable from 1848 on, but spotty to weak back to 1700. Wolf tried to go back to 1610, but this research was undoubtedly confounded by moving into a period now known as the Maunder Minimum. In any event, an inspection of a modern interpretation of this history shows a dramatic change from 1645 to 1715.

• The study of stars similar to our sun indicates that periodic stellar anomalies exist. One of these is called a long-term lull in starspot or sunspot activity. In such an event the magnetic activity is lower than the low recorded in the normal sunspot cycle.

The Maunder Minimum, a period named after British astronomer Walter Maunder, occurred from 1645 to 1715 and was a part of the Little Ice Age. It was a time when sunspots virtually disappeared.

It is believed the Maunder Minimum was a long-term lull with major Earth impacts. While total solar irradiance was down only 0.2%, the overall ultraviolet (UV) portion of this radiation was down by 1%. Part of the UV spectrum was down by as much as 64%, and ozone concentration was down by 4%. It is believed this reduction in UV input, which would lead to a major reduction in stratospheric ozone production and reduced stratospheric temperature, was the ultimate cause of the period called the Maunder Minimum.

• Cycles also appear in study of a 9,600 year production chronology for the carbon-14 (14C) isotope. The 14C isotope is produced by the reaction of cosmic rays on nitrogen. The cosmic ray flux in turn is modulated by solar magnetic activity and the solar wind. Two parts of this study are of interest:

1. A detrended plot of the 14C production rate indicated many cycles. Two different cycle types were defined-an M (Maunder) type with a period of about 180 years and an S (Sporer) type with a period of about 220 years. The latter cycle was named after the German astronomer Gustov Sporer. Nine of the M and eight of the S cycles were flagged over this period.
2. A spectral analysis of the 14C production record identified many harmonics, with the strongest periods at 420 and 218 years and nearly as strong at 143 years.

Changes and cycles

Table 1 [33,319 bytes] shows climate changes with cycles varying from 1 day's duration to hundreds of thousands of years. Research in these areas can help us understand phenomena such as long-term lulls in sunspot activity and their effects on our climate.

Questions marks in the table indicate uncertainty about the duration and number of cycles involved.

One obvious conclusion is that understanding the natural variability in our climate is far from a simple task. And Table 1's listing of cycles is far from complete. In the past 2 years, this author, an interested observer of the climate-change debate, has identified more than 25 cycles involved in our climate.

There is little question that the science of climate change is making great strides. But surely there is much more that needs to be done to remove some of the above question marks and to reduce the overall level of uncertainty. Study of other areas of climate change science and computer models shows that uncertainty isn't confined to the number and duration of cycles.

Given such a high level of uncertainty over just the cyclical portion of natural climate variability, it is hard to believe that we have adequate evidence that an anthropogenic global warming signal has emerged from the background noise. Those who claim that the science is done and that 2,500 scientists are in absolute accord about climate change and what ought to be done about it are being specious at best. While roughly this number of scientists participated in the Intergovernmental Panel on Climate Change report-Climate Change 1995-very few of these participated in the controversial Summary for Policymakers that claims the balance of evidence suggests a discerible human influence on global climate.

It would be most interesting to see a detailed breakdown of these 2,500 scientists by discipline. It would also be most interesting to see what a confidential vote of these 2,500 scientists would show.

The Author