By John Pastor, for the Duluth News-Tribune October 24, 2009

We have known about the greenhouse effect for more than 100 years . In the 1890s, the Swedish chemist and later Nobel Prize winner, Svante Arrhenius, first calculated that the Earth’s temperature would rise approximately 3.6 degrees Fahrenheit if the concentration of carbon dioxide doubled. Arrhenius also realized that with this much warming, much of the Earth’s snow and ice cover would melt. This would increase the warming further by an additional 5 degrees Fahrenheit because snow and ice reflect much of the sun’s heat back into space while the darker rocks and tree canopies uncovered by snowmelt would absorb more heat. Therefore, the response of the biosphere might actually amplify the warming effects of carbon dioxide from fossil fuels.

If we do not pass legislation soon to reduce carbon-dioxide emissions, the northwoods of Minnesota and everything that depends on them will be gone by the end of my son’s life.

Although we have refined these calculations further, Arrhenius was correct with one exception: He thought it would take thousands of years for carbon dioxide to double and for the Earth to warm. Arrhenius did not foresee the exponential increase of a fossil fuel-driven economy since his time.

We are well on the way to a doubling of carbon dioxide by the end of this century, if not in the next few decades. The atmosphere already has warmed by slightly more than 1 degree Fahrenheit since Arrhenius’s time. We know for a fact that natural causes cannot have been responsible for this rapid rise in temperature. Only when we add Arrhenius’s equations to our computer models of the Earth’s climate can we come close to matching the temperature rise that our weather stations already have recorded.

Since Arrhenius’ time, we have learned that most of the warming will take place in mid-continent areas such as from Minnesota northward. It is in these regions that we have begun to see some of the first and most rapid effects of warming: the melting of the Arctic sea ice and Greenland’s glaciers as well as the migration of plant and animal species northward and the retreat of their southern borders.

Twenty years ago, Mac Post and I published a scientific paper in which we used a computer model of forest growth to predict that with the amount of warming calculated by Arrhenius, the spruce, fir, pine, aspen and birch forests of northern Minnesota would be replaced largely by brush and prairie grasses where soils are thin or sandy and don’t hold much water or by maples on clay soils that can hold enough water to mitigate against increased drought. We already have begun to see these changes on the ground: Balsam firs are dying here in northern Minnesota, especially west toward Hackensack, and red maple is replacing fir and spruce in some places. The moose, loons, trout, and walleye we also associate with northern Minnesota similarly will decline because they depend on these northwoods tree species for their habitat.

Our tourism and timber industries depend on this mix of conifers, birches and aspen for a sound economy. The chance to see moose and hear loons and wolves, smell pine needles and breath cool, fresh summer air is what draws people to northern Minnesota in summer. Pine and aspen have been the foundation of our timber industry. All this will be gone with even the most conservative predictions of global warming.

But what is even more threatened is our sense of what it means to be a Minnesotan. We are the people of the land of loon calls and moose, walleye and trout, towering pines and firs. What will we be when northern Minnesota looks like Nebraska? Is this the landscape in which any of us would wish to live?

I do not, and I suspect you do not, either. It is for this reason, if for no other, that we need to reduce the amount of carbon dioxide in the atmosphere. This is being debated in Congress, but this is not a partisan issue. Hot days do not care if you are Democrat or Republican. If we do not pass legislation soon to reduce carbon-dioxide emissions, the northwoods of Minnesota and everything that depends on them will be gone by the end of my son’s life.

John Pastor is a professor in the department of biology at the University of Minnesota Duluth.