My father was in the coal business. One of the happiest memories of my youth is climbing mountains of Pennsylvania anthracite he imported to Green Bay, Wis., on Great Lakes freighters. Trucks delivered the coal to the furnaces of homes and factories to fuel the life of my community and my family.

Still, no one hugs his natural-gas-fired furnace more than I do through a long Minnesota winter. And just as natural gas knocked my father out of the polluting coal business, green energy is rapidly replacing fossil fuels. That's because zero carbon emissions is what the times require, for carbon emissions are dangerously altering the global climate and the chemistry and temperature of oceans and lakes, endangering almost every living thing.

Which is why I, a 70-year-old grandfather, along with thousands of other citizens, have pledged that if the Keystone XL tar-sands pipeline is approved, we will peacefully contest every foot of its construction across the heart of America.

By 20th-century economic measures, Keystone XL was clearly a good investment. But by the standards of the 21st, with the fire alarm of climate change ringing in our ears, it is an $8 billion anachronism. The argument supporting construction of Keystone XL, that the oil will be transported by other means, ignores the urgency of these alarms — and a few salient facts ("For safety's sake, approve Keystone," editorial, Jan. 24).

Keystone XL completion will increase gasoline prices across the United States. Landlocked Alberta can only sell its tar-sands crude to the U.S. market, already glutted with Bakken and other oil. Even before the current crash in oil prices, U.S. gasoline was cheap relative to other countries. That's why tar-sands producers desperately seek access to higher-priced global markets through the Keystone XL and other pipelines inside Canada also thwarted by intense opposition.

Safety of oil trains is a legitimate concern; also, the disruption that massive trains already inflict on Minnesota communities. But it is not clear Keystone XL will eliminate them, as the products from Texas and Louisiana refineries will be shipped to higher-priced overseas markets, meaning other U.S. refineries will receive their share just as they do now.

Finally, by the time the pipeline is completed, it should be obsolete. China and India have just pledged major swerves toward green energy, unimaginable when the pipeline was first proposed. And global agreements already moving forward mean tar-sands production will be fully shuttered by 2050, as the green-energy revolution will have fully taken over. The Obama administration will do our good neighbor Canada a favor by declining to host a pipe dream to the sea.

I can foresee one circumstance in which President Obama should permit Keystone: If Congress passed a $15-per-ton carbon tax, escalating $10 per ton for 10 years. Carbon-tax proceeds could be fully rebated to American families and businesses, spent to repair and improve infrastructure or pay down the national debt, or all three — whatever Congress debated and decided. Such a carbon tax would eliminate the unfair market advantage that fossil fuels have exploited for 150 years — using the atmosphere as a free sewer, the way nations once used rivers and lakes as free sewers.

The ironic effect of such a trade for marketplace efficiency is that the Keystone pipeline's economics, dubious today, would collapse, and it certainly would never be built.

James P. Lenfestey is a former editorial writer for the Star Tribune, and a volunteer for Minnesota Interfaith Power and Light, MN350.org and the Citizen's Climate Lobby.