One of the world's richest forests stretches across northern Alberta, making the Canadian province home to a vast array of migrating birds, diverse wildlife, and the First Nations people who once thrived on the region’s natural bounty. 

But in recent decades, mining companies have torn up the land and polluted its waters in a quest to extract tar sands, which yield a heavy crude oil trapped in a mixture of sand and clay.

The fuel is dirty; the extraction and refining process is even dirtier. 

It's so energy-intensive, in fact, that tar sands oil is barely economical to bring to market.

That's why the industry is so desperate to build Keystone XL. 

The proposed $7 billion tar sands oil pipeline would run 2,000 miles across the American heartland, crossing the country's largest freshwater aquifer to reach the Texas Gulf Coast. 

There, refineries would process a projected 830,000 barrels of dirty crude daily, most of them bound for overseas markets, with negligible impact on U.S. energy independence or gas prices.

The new pipeline would be harmful for people, water, wildlife, and climate. 

Here are five reasons why Keystone XL is a bad idea and tar sands oil should stay in the ground.

1. It's not safe.

Studies show that tar sands pipelines are more vulnerable to leaks than those carrying traditional crude because of the oil's corrosive nature and the chemicals necessary to make it run through the pipes.

Despite the industry's grand safety claims, we also know from recent spills and subsequent government investigations that its leak-detection systems are subpar and its spill containment and clean-up methods inadequate.

Just look at the 2010 tar sands disaster in western Michigan--the site of what has become the most expensive onshore oil spill in U.S. history. 

Four years and a billion dollars later, tar sands contamination still plagues the Kalamazoo River and nearby communities.

A pipeline spill would threaten the land and water supply of some 110,000 ranches and farms in Montana, South Dakota, and Nebraska that produced more than $40 billion worth of food in 2012. 

In those three states alone, the pipeline would cross 1,073 rivers, lakes, and streams, including the Yellowstone River in Montana and the Platte River in Nebraska, along with tens of thousands of acres of wetlands. 

It would also run within a mile of more than 3,000 wells that provide drinking and irrigation water in those states.

2. It's bad for climate.

Because of its silty composition, mining and refining tar sands oil demands an enormous amount of energy--much more than conventional crude. 

Keystone XL would ramp up tar sands production, requiring even more energy and creating greater carbon pollution: the equivalent of Americans driving an unthinkable 60 billion extra miles every year.

NASA scientist James Hansen estimates that the remaining tar sands reserves contain twice the amount of carbon pollution emitted by the entire global oil industry--in all of human history. 

"If Canada proceeds and we do nothing," Hansen wrote in a New York Times editorial, "it will be game over for the climate."

3. It's bad for health and the environment.

Once mined, tar sands leave behind a filthy legacy in the form of toxic sludge stored in giant, largely unregulated "ponds," which are leaking a combined three million gallons of toxic sludge into the once-pristine Athabasca River--every day.

Health-care providers fear they are causing cancer and other illnesses in the native communities.

The mining operations are also tearing up Alberta's boreal forest, home to millions of migratory birds, caribou, bears, wolves, and endangered species like the whooping crane.

4. It's bad for the economy.

Advocates tout the project as a national jobs creator.

The reality is Keystone XL would likely kill more jobs than it would add. 

According the State Department, it would create 1,950 construction jobs for two years. 

Once complete? 

Thirty-five new permanent American jobs, according to pipeline builder TransCanada.

But won't refined tar sands oil help fuel the United States and reduce gas prices? 

Think again. 

Tar sands miners want Keystone XL because it will help them ship oil overseas to an international market, where their product will fetch more money and add billions of dollars in annual profits.

That's a losing deal for everyone--except Big Oil.

5. It's a step backward.

At a moment when climate action is more urgent than ever, building this pipeline would be a step into a past instead of a shift into a clean energy future. 

Keystone XL would represent a long-term commitment to the expansion of dangerous tar sands oil when we need to be investing in safe, renewable sources of energy instead.

But Keystone XL is the linchpin for further tar sands investment.

Without it, tar sands mining doesn't stand much of a future. 

The pipeline must be rejected, before it's too late!