Not all scientists agree on human impact on climate.

Byline: The Register-Guard

Ocean currents, volcanic eruptions, changes in solar radiation and wobbles in the Earth's tilt as it rotates around the sun all play a role in the planet's climate.

And so do people. Most scientists agree that carbon dioxide is increasing in the atmosphere and contributing to global warming. Where agreement breaks down is the degree to which human activities such as burning fossil fuels and cutting down forests impact the climate system.

Most scientists think the human impact is significant. They can be found on the International Panel on Climate Change, at the National Academy of Sciences, at the U.S. Geophysical Survey and in the Environmental Protection Agency, as well as at universities and research facilities throughout the world.

However, a vocal cadre of scientists begs to differ with this consensus view.

Among them is Oregon State Climatologist George Taylor.

Among the factors he raises is the relatively short period of the instrumental records, which at best go back just 150 years, a mere blink in geological time.

Even within that short time, the climate picture shifts, depending on which data you select.

For example, the governor's Advisory Group on Global Warming notes that the Pacific Northwest has warmed significantly since 1975.

But the warmest decade in Oregon was the 1930s, Taylor notes, a decade that he says saw little increase in carbon dioxide emissions.

And snowpack in Oregon may well have declined between 1950 and 2000, but the 1950s were one of the snowiest decades of the past 100 years, he said. The decrease in snowpack of the past few years is a lot less significant compared to the 1930s, he said.

The variations in climate that we see are part of natural cycles driven by Pacific Ocean temperatures and currents, he said.

Climate change skeptics have raised questions about the validity of widely used computer models that simulate continued warming. They also point to discrepancies between ground observations and satellite data, and have called into question the validity of geologic markers such as ice core and tree ring records that serve as indicators of past climates.

But recent advances have made it more difficult for skeptics, said Pat Bartlein, a paleoclimatologist at the University of Oregon.

Looking at ice core, tree ring and coral data - known as proxy records - that go back hundreds and even thousands of years, the temperature trend is relatively flat until the mid- to end of the 1800s. Then there's a rapid rise. It's become known as the hockey stick curve because of the way the changes look on a graph.

More and more proxy climate records show similar patterns, Bartlein said.

"It would be really strange if all those patterns were coincidentally wrong in the same way," he said.

Satellite records that have been at odds with surface temperature records have been reconciled because of recent work that identified and corrected errors in the calculations, Bartlein said.

Computer models have been improving as well, he said. While they still don't work perfectly, they do a better job of simulating past climates, which makes them more reliable as predictors of the future.

- Susan Palmer

INFORMATION

While skeptics have the minority viewpoint regarding climate change, it's important to remember that unpopular scientific conclusions sometimes turn out to be correct. Here are Web sites with information from several different sources.

General climate information: www.ncdc.noaa.gov/oa/ncdc.html and www.ocs.oregonstate.edu

Climate change: www.realclimate.org, www .climateaudit.org, www .pewclimate.org and www .marshall.org/

Oregon plan to reduce greenhouse gases: egov.oregon.gov/ENERGY /GBLWRM/Strategy.shtml

What you can do: www .climatesolutions.org

SAY, WHAT?

Climate change comes with its own jargon. Here's a list of common terms and what they mean:

Climate: The long-term average weather of a region including typical weather patterns, the frequency and intensity of storms, cold spells and heat waves.

Global warming: The progressive gradual rise of the Earth's average surface temperature.

Greenhouse effect: The reason the Earth is habitable. Water vapor and other gases envelop the planet like a blanket. The sun radiates heat to the surface and it's trapped here by the gases, making the planet about 60 degrees warmer than it would otherwise be.

Greenhouse gases: Water vapor, carbon dioxide, methane, nitrous oxide and others. Natural processes produce these gases. Animals release carbon dioxide while breathing and plants take it up. Methane is a by-product of decomposition, and soils and oceans release nitrous oxide. Human activities add more gases to the atmosphere.

Anthropogenic emissions: Greenhouse gas emissions caused by human activities such as burning fossil fuels, which releases carbon dioxide. Landfills, livestock, natural gas and petroleum systems, coal mines, rice fields and wastewater treatment plants release methane; and nitrous oxide is released by nitrogen fertilizers and fossil fuel combustion.

Albedo: The ratio of light from the sun that is reflected by the Earth's surface to the light received by it. Surfaces with a high albedo, such as snow and ice, generally contribute to cooling, whereas surfaces with a low albedo, such as forests, generally contribute to warming. Changes in land use that alter the characteristics of land surfaces can influence the climate.

Carbon sinks: Things that remove more carbon dioxide from the atmosphere than they release, such as forests and oceans.

- Source: Pew Center on Global

Climate Change