I often learn more from answering my 6-year-old son's endless questions than he does. Usually we make it a game, searching out answers together to queries like, "How many stars are there?" Or, "What is in our air?"

But he stumped me recently when – after quizzing me about what I was reading – he asked why some people want to build the Keystone XL TransCanada pipeline to pump tar sands oil from Alberta to the Texas coast.

Like most, I thought this pipeline was just another fight between an oil company and environmentalists (yawn) until my son insisted I learn something.

It turns out that tar sands oil isn't really oil at all.

Polluted lakes

The thick goo of tar sands only becomes oil when treated with toxic chemicals, heat and pressure. This process is so dirty that even the Canadian government — which backs the project — says that this high-sulfur crude is polluting lakes 50 miles from the tar sands with cancer-causing contaminants.

My kid is into maps, so we studied the pipeline route. It crosses over the Ogallala Aquifer, part of the High Plains Aquifer System, a vast shallow underground water table. That aquifer waters about 27 percent of the irrigated farmland in the United States and provides drinking water to 82 percent of the people living inside the aquifer's boundaries.

How do I answer my kid when he asks: "What happens to people when the pipeline leaks?" I can't. Groundwater, once polluted, stays polluted.

"Why build this?" he asks again. I grasped for facts about investment and jobs. However, TransCanada hasn't been forthright about this. They say the project means $7 billion in U.S. investments. But most of that has either already been spent on design or would be invested on the Canadian portion of the pipeline, according to a Cornell University study. And the steel used to construct it will come from Canada or India.

Gas price rise

At least the price of gasoline will go down, right?

Sorry. No. TransCanada, the builder, admits gas prices will go up 10 cents to 20 cents a gallon in the Midwest. That's because refineries there already get some tar sands oil. If the pipeline gets built, all that oil will go straight to the Gulf, where it will be refined for shipment to China.

That's right. Keystone XL will actually reduce the amount of oil available to the United States. And the leading project investors, it turns out, are Saudi and Chinese oil interests.

One question leads to another: "Whose backyard will the pipeline go through?" my son asks. The answer: Anyone's TransCanada wants it to.

The project has been granted eminent domain rights in Midwestern states, allowing TransCanada — a foreign company — to take the private property of American citizens so it can transport Canadian oil to China.

Backyard poop

For my son, who protects our backyard from neighborhood dogs intent on pooping there, this was the greatest injustice of all.

"So emm-nant doh-mane means someone can poop in somebody else's backyard even if they don't want them to?" he asked.

Yes. That's exactly what thousands of farmers and ranchers in Texas, Oklahoma, Nebraska and elsewhere are learning.

That's when my own inner 6-year-old woke up and asked, "So, why are we doing this?"

Certainly not for my son. James Hansen, NASA's most respected climate scientist, calls the Keystone XL pipeline "a fuse to the largest carbon bomb on the planet." Hansen was arrested Feb. 13, in front of the White House, along with four dozen others. If all the carbon stored in the Canadian tar sands is released into the Earth's atmosphere, says Hansen, it will mean "game over" for the planet — for my kids and for yours.

I can't bear to tell my son this.

"Why do some people want to build the TransCanda pipeline?" I ask myself again. The only credible answer: Because some people stand to make a lot of money, and their political allies want to help them.

Millions of Americans have asked President Obama to kill Keystone XL. His authority can stop the pipeline at the Canadian border. I hope he will.

If he does, I'll have no trouble explaining the reasons to my son.

Blue Ridge Press editor David Lillard is editor of The Observer newspaper in Jefferson County, W.Va. This story was originally written for The Daily Climate and was republished with permission here. The Daily Climate is a foundation-funded, independent newsletter covering climate change.

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