The United States is the richest, most powerful nation in history -- this you have heard many times before. What you have not heard so often is that America has also been, for nearly 200 years, the safest, most secure nation ever. Far from being aware of that fact and enjoying it, we have become a nation filled with fear and anxiety. But we fear the wrong invader.
Not since the British burned our capital in 1814 has a foreign army succeeded in invading our continental domain. Pearl Harbor lay thousands of miles from our mainland homes. And the World Trade Center bombing was no real invasion or victory of a foreign power, but one act by a handful of fanatics, all killed. Their brothers are hiding in caves along the Pakistan-Afghanistan border, no more able to invade America, if we keep our eyes open, than camels could take over our national parks.
Yet a far more serious threat has appeared that our leaders are ignoring. It is global climate change. And it has the potential to bring the United States down economically, socially and agriculturally, making us a much poorer and weaker nation.
In February the Intergovernmental Panel on Climate Change released its latest major report of scientific data. Based on the greenhouse gases already affecting the atmosphere, and on expected increases in those gases under various economic scenarios, the IPCC projects -- too cautiously, many say -- that the Earth's overall surface temperature will rise 3 to 7 degrees by the end of this century, and the sea may rise almost 2 feet.
In an April IPCC report, world policy-makers were told to expect long-term flooding of coastal areas, more intense tropical storms, increased drought in drought-prone areas, and a decline in crop productivity with increased risk of hunger.
Here is where the danger comes to the United States: Not only may we be forced to protect people on the coasts, or move them inland, we will also be in great danger of losing our agricultural heartland -- the Corn Belt and the Wheat Belt. Today, half of our wheat crop goes overseas. In a few decades we may not have enough food to support our own population, let alone share with others.
And our Western cities may be paying a lot more for water, if they can find any, than for the last drops of oil.
We are most threatened today, not by terrorists, but by impersonal physical forces. And as the century goes on, that invasion will gather speed and effect with biological threats like invasive plants and malaria.
Such talk, we are told, is scare mongering. We also are told that defensive measures would cost too much.
Yet which place is worse off today? New York, which lost two major buildings and thousands of lives to terrorists? Or New Orleans, which lost many lives as well and may never recover much of its displaced population or destroyed territory after being hit by a hurricane that drew its energy from warming gulf waters?
And how can we not afford to invest in conservation and alternative energy sources to defend our own land against the ravages of global climate change, but afford to fight wars in Iraq and Afghanistan, which cost $120 billion a year? And pay four to five times that, depending on the calculation, for the military as a whole? And spend more than $40 billion more on the Homeland Security Department?
All that money to defend a country that is the most secure and safe in the world from outside human invasion!
Our homeland is facing a change of unprecedented danger, one that we have helped create by wasteful consumption. This is likely to be the greatest threat to security and prosperity in our history.
When will our leaders stop beating the drums about "a war on terrorism" and start facing the real dangers we face? When will they wake up and take action -- today, this year? Will they wait until Washington is under water and the Great Plains are a burning desert?
Donald Worster, author of books including "Nature's Economy: A History of Ecological Ideas," is an environmental historian at the University of Kansas. He wrote this comment for the Land Institute's Prairie Writers Circle, Salina, Kan.