Doubts on Whether 20th Century the Hottest Ever
By Cristina Hernández-Espinoza*
Some U.S. scientists question the theories that have served as the basis of the global fight against climate change, saying periods of unusually warm or cool temperatures are explained by natural fluctuations in the Earth's climate processes.
SAN FRANCISCO - Assertions that the 20th century was the warmest of the millennium and that within a hundred years the Earth's average temperatures could rise 3.5 degrees centigrade are two of the most publicized hypotheses in the international community's battle to curb climate change.
But is there sufficient evidence to sustain those theories? Not according to astrophysicist Willie Soon.
After analyzing fossils, ice accumulation rates, sediments on the ocean floor and the rings in tree trunk cross-sections, among other indicators that scientists refer to as "paleoclimate proxies", Soon suggests that the measurements that have given rise to global climate policies are flawed.
As a researcher at the Harvard-Smithsonian Center for Astrophysics at Harvard University in the United States, Soon heads a team that collected and analyzed more than 200 scientific studies produced over the past 10 years.
"The goal of our work is to derive understanding of climate change on local and regional spatial scales, instead of global, because those are the most relevant measures of change, in a practical sense," Soon told Tierramérica.
"This is especially important since societies and economies -- or our human spheres -- are not 'living' under a global temperature," he explained.
The team, which includes experts from the U.S.-based universities of Harvard and Delaware, analyzed studies of the remains of Viking settlements in Greenland (986 a.c.), of variations in Argentine glaciers and isotopic records from stalagmites taken from China's Buddha Cave.
The team's findings, published in the "Journal of Energy and Environment" in April suggest that the latest warm and cold periods correspond to natural climate changes and not to the emissions of greenhouse gases as has been argued in recent decades, and that the 20th century was not the warmest of the millennium.
Soon is one among the ranks of scientists who have expressed reservations about the statements made by the Inter-Governmental Panel on Climate Change (IPCC), considered the world's leading authority on the subject.
According to the IPCC, which is attempting to decipher the global climate puzzle using mathematical models that simulate the interactions of land, sea and atmosphere, the 20th century is thought to be the warmest in the past thousand years, presumably the result of human activities (mostly the burning of fossil fuels) that produce greenhouse gases, the accumulation of which contributes to global warming.
The IPCC forecasts that between 1990 and 2100, the average global temperature could rise 1.0 to 3.5 degrees centigrade. If this bears out, there should be increased frequency of heatwaves, flooding and drought.
From that basis, the IPCC (created in 1988) seeks to establish international rules -- such as the Kyoto Protocol-- for controlling greenhouse gas emissions.
The Kyoto Protocol, signed in 1997, has not yet entered into force due mostly to the fact that the United States, at the behest of President George W. Bush, withdrew from the agreement, arguing that the questionable scientific evidence behind climate change was not worth sacrificing the U.S. economy for.
The stance of the United States, which produces 23 percent of all carbon dioxide emissions worldwide, met with international condemnation.
But the IPCC's mathematical models confront questioning from several sides as well.
"It is increasingly clear that the primary record adopted by the IPCC, developed by Mann et al. (1999), may have been biased by their underestimation of natural climate variabilities on timescales of several decades to a century," says Soon.
According to the astrophysicist's study titled "Reconstructing Climatic and Environmental Changes of the Past 1000 Years: A Reappraisal", the paleoclimate proxies in several locations confirm the global existence of a climate anomaly known as the Medieval Warm Period (800 to 1300 a.c.) during which it is estimated that the temperatures were higher than those of the 20th century.
For example, a study of the marine proxy indicators in the region known as the Pacific Warm Pool (Indonesia) shows that during the Medieval Warm Period the surface water temperatures reached a maximum of 30 degrees centigrade, while in the last two decades it has been 28 to 29 degrees.
Furthermore, the indicators confirm the occurrence of the Little Ice Age (1300 to 1900 a.c.), which saw extremely low temperatures.
And there are other prominent scientists agree with Soon's theories.
"To the best of my knowledge, Dr. Soon is correct (to state that the 20th century is not the warmest period of the last millennium). The bulk of the literature accepts a Medieval Warm Period, though there is some argument as to whether it was truly global," Richard S. Lindzen, professor of meteorology and atmospheric sciences at the Massachusetts Institute of Technology (MIT), said in a conversation with Tierramérica.
In its Third Assessment Review (2001), drafted by dozens of the world's leading climate scientists, the IPCC plants doubts that the Little Ice Age and Medieval Warm Period were global in scope, and underscored the rate of global warming in the 20th century.
Despite the discrepancies, members of the IPCC and the experts at Harvard agree that there are a great number of uncertainties when trying to determine to what extent global warming is the result of natural causes or to greenhouse gas emissions from human activities.
Can we expect to see further inclusion of natural variables in future IPCC reports?
Lindzen is skeptical: "I have my doubts. I participated fully in the Third Assessment, and it was clear that there were political pressures. Participation was very time consuming and scientifically of no value," commented the MIT expert.
As the IPCC prepares its Fourth Assessment Review, experts like Soon, whose scientific arguments are used in decision-making in Washington, aim for more solid theories on climate change.
* Cristina Hernández- Espinoza is a Tierramérica contributor.