ANCHORAGE, Alaska – A group of U.S. Senators are planning a trip to Alaska in two weeks to view melting permafrost, retreating glaciers and other consequences of global climate change in cold latitudes.

Sen. John McCain, R-Ariz., who co-authored a bill to reduce emissions of greenhouse gases blamed for global warming, and Sen. Hillary Clinton, D-N.Y., are scheduled to tour Alaska and northwestern Canada.

Sens. Susan Collins, R-Maine, and Lindsey Graham, R-S.C., are also expected to make the trip, tentatively planned for Aug. 16 to 19. McCain’s office is coordinating the trip.

Sens. Lisa Murkowski and Ted Stevens on Monday said they do not plan to join the tour. The Alaska senators oppose mandatory emission reductions included in the bipartisan Climate Stewardship and Innovation Act, written by McCain and Sen. Joseph Lieberman, D-Conn.

The legislation would require a reduction in carbon dioxide emissions to 2000 levels by the year 2010.

Stevens said he is skeptical that human activity is responsible for climate changes observed worldwide. He said cyclical geophysical forces could also be responsible for rising temperatures.

Murkowski has said she does not believe scientists have conclusively demonstrated that human activity is the main cause for global warming and mandatory emission standards could unnecessarily harm some sectors of the economy. She also pointed to her support of a provision in the recently passed energy bill that included incentives to develop technologies that would reduce greenhouse gas production.

Carbon dioxide and other gases reduce the Earth’s ability to reflect solar heat into space, much like the glass of a greenhouse. The growing number of scientists who support the global warming theory say more than a century of heavy industrial activity, and the world’s heavy dependence on oil, is causing inevitable climate change. Many researchers say the degree of change can still lessened with strict controls.