DAVID HARDEN/Arizona Daily Wildcat Professor Malcolm Hughes studies tree rings to determine weather patterns throughout history. Using these techniques, scientists established records of Earth's activities reaching back 1,500 years.

UA researcher finds new info on climate changes

For the last 30 years, many scholars believed that people in medieval times experienced a global warming period like the one being experienced today, but one UA researcher says that might not be true.

Dendrochronolgy professor Malcolm Hughes said that there is not enough evidence to prove that the Earth is as warm today as it was 900 years ago.

By using tree rings, ice cores, corral reefs and other natural elements that can determine fluctuation in the Earth's climate, he concluded that parts of the world experienced a warming trend, but the Earth as a whole might not have.

"Something is definitely unusual about Earth's climate today," Hughes said. "At the moment, the prime suspect is greenhouse gases."

Hubert Lamb, the English scientist who published a book in the 1970s that claimed the medieval ages experienced a warming trend, might have been focusing on one area instead of the world as a whole, Hughes said.

"You have to look globally at the temperatures," Hughes said. "I see no reason for saying that the medieval times were uniformly warmer."

With more sophisticated computers, researchers can date tree rings, ice cores and coral reefs with more precision. This allows for a clearer picture of Earth's climate and precipitation.

Using these techniques, scientists established records of Earth's activities reaching back 1,500 years.

Tree rings have been one of the main methods used to figure out what a climate was like before official records were kept.

In most trees, rings indicate the temperature of the specific year in which they were formed.

The size of the tree ring depends on the climate. If it is a hot, dry year, the tree ring is thinner than if it were a wet, cool year.

By taking tree ring samples from various locations, averages and fluctuations of the climate can be determined.

A global database that allows for worldwide researchers to correlate findings is available online.

Research has shown that out of the last 1,000 years, temperatures have not been as warm as they have been in the last 30 years.

Temperatures across the world today are approximately two degrees Celsius warmer than just decades ago.

This might not sound significant, but the difference in temperature during the ice age and today's temperatures is six degrees Celsius, Hughes said.

This rise in temperature statistically matches the rise in greenhouse gases, which are chemical compounds that trap radiation in Earth's atmosphere.

Some of the gases are caused naturally from water vapor, carbon dioxide and other gases, and this is needed to keep the Earth warm enough for humans to exist.

It is the rise in greenhouse gases caused by population growth, deforestation and burning of oil, coal and natural gas that many feel has caused global warming, according to the U.S. Environmental Protection Agency Web site.

Since the beginning of the Industrial Revolution, greenhouse gases have risen 30 percent and the climate has become warmer, the Web site also stated.

The rise in temperature could raise the sea level and alter forests and water supply.

"Absence of evidence is not evidence," Hughes said, "but the climate today is very unusual."

In order to really understand how today's climate contrasts with climates in the past, more samples and more research is needed, Hughes said.