A few years ago, the president of the American Association of State Climatologists confided to me that 75% of U.S. state climatologists, who work intimately with the real data, believe local factors (including urbanization) and natural cycles are more likely responsible for observed climate change than greenhouse gases.

The cycles are apparent in the data. Climate records for the earth show warmer annual temperatures from the late 1800s to the 1930s. The earth cooled then through the 70s, but that was followed by another warming trend over the next two decades. Even greenhouse proponents concede that some natural phenomenon, most likely solar irradiance, is the likely catalyst for warming during the beginning of the twentieth century. They assert, however, that humankind is responsible for the downward then upward trends of temperature that followed, due to our careless emission of particulates and then the increasing greenhouse gases.

In this series we will show that urbanization/land-use changes, cyclical solar energy output, volcanic activity, and the ocean temperature patterns may play a more profound role in these observed fluctuations.

Decadal Changes in the Oceans

With two-thirds of the earth’s surface consisting of water, our oceans are huge storehouses of heat. The world’s serpentine ocean currents can carry that heat great distances. Even small changes in these currents can cause ocean temperature anomalies on a large scale, and through that, affect the favored positions of the jet stream and the resultant land temperatures and storm tracks. A record 27 tropical storms occurred in the Atlantic last season, continuing an active period that began a decade ago. This enhanced hurricane activity is related to large-scale changes in surface temperatures in the Atlantic. During the mid 90s, the Atlantic Ocean reverted to an ocean temperature pattern last observed from the 30s to the 60s. During these modes, summers are hotter and hurricanes more frequent and stronger, with more making landfall in the United States.

Similarly, in the Pacific, there is a flip-flop of the relative positions of warm and cold ocean pools, the Pacific Decadal Oscillation (PDO), that affects global weather patterns and climate and can last for decades.

In 1978, the Pacific Ocean underwent the last such major reversal, the “Great Pacific Climate Shift,” which changed the established worldwide temperature and precipitation patterns. The most evident impact was in Alaska. Rather than greenhouse gases gradually accelerating warming over recent decades, as implied in the press, actual data reveals a steep warming concentrated in one year, 1978. This was concurrent with the sudden PDO phase shift. It was followed by a virtually steady state over the past quarter century.

The PDO also affects the frequency and relative strength of the El Niño and La Niña phenomena. El Niño events create net global warming by supplying more heat to the atmosphere. Conversely, La Niña episodes cause global cooling. The current PDO mode favors more frequent and stronger El Niño occurrences. This relationship is evident in the chart below. The big spike in warming was associated with the Super El Niño of 1997/98.

At issue is the warming that has occurred over the past six years. Some of the warming is due to the El Niño of 2002/03 that was slow to fade. A portion remaining may be due to unusually low levels of volcanic dust at high altitudes in the atmosphere.

Volcanic Activity

In the 1950s, there was speculation that a cold spell during the late 1800s was triggered by high volcanic activity (most notably, Krakatoa) and that the global warming that followed was the result of reduced vulcanism. Large volcanoes cause sulfate aerosols to accumulate at high altitudes where they reside for several years, blocking solar radiation. Several significant eruptions occurred during the 60s, including Agung in 1963 with widespread global cooling. Cooler global temperatures followed the eruptions of Mt. St. Helens (1981), El Chichon (1982), and Pinatubo and Cerro Hudson (1991), clearly evident in the graphic below, which relates the volcanic aerosol levels to the same satellite-derived annual global temperature fluctuations.

During the last six years, aerosols have been at an historic low level (NASA GISS). A cleaner atmosphere, with aerosol levels similar in magnitude to those of the warm decades during the 30s and 50s, may have allowed more solar radiation to reach the earth’s surface, contributing to recent warmer temperatures and the high-latitude summer snowmelt.

Next: Man’s chief impact: urbanization and the catalyst for climate change; the sun.

Joe D’Aleo was a college professor for eight years and a co-founder of the Weather Channel. He was also Chief Meteorologist at WSI and Senior Editor and “Dr. Dewpoint” for WSI’s popular Intellicast.com Web site. In the past year, Joe has been working with a commodity fund.