The world can be a dirty place. Carbon dioxide emissions are headed higher everywhere, and some countries are contributing more to the problem than others. Here are the world's three most polluted countries.

3. India

Source: Wikimedia Commons, Biswarup Ganguly. Underground coal miner in Bachra, India.

The odds are not with India. Although the country's carbon emissions per capita are the exact same as clean and green Costa Rica, its 1.2 billion  citizens push reasonable numbers to a scary scale. At just over 2 billion metric tons of carbon dioxide emitted, India is the third most polluted country in the world.

The South Asian nation is in a dirty economic transition stage. Along with Brazil, Russia, and China, business in the four "BRIC" countries is booming. But infrastructure and regulation haven't kept up, and a rapidly expanding economy has often sacrificed pollution control for profit. In 2010, India's annual GDP growth rate clocked in at a whopping 10.5%, more than four times the United States' 2.4%. 

While India's 45 cites with more than a million people (Mumbai tops the list at 12.5 million) offer their own challenges of local pollution, a major contributor to this country's pollution is its coal addiction. The International Energy Agency predicts India will rival China for the title of top coal importer in the next five years.

2. United States

Times Square traffic jam, New York City. Source: joiseyshowaa.

You might be shocked to find the U.S. on this list – or you might be wondering why we're not No. 1. But by carbon dioxide emissions alone, the United States snags silver for most polluted countries.

Its 5.4 billion metric tons clock in at more than twice that of India and it's easy to understand why. India's GDP growth is soaring compared to America's, but our stalwart economy still accounts for nearly 20% of the entire world's economic output, more than any other country. And if you drive a car, you're part of the problem, too. Transportation accounts for an estimated 31% of carbon dioxide pollution in the U.S.

But even with such a large economy and so many vehicles on the roads, the U.S. has kept its pollution down by reorienting its economy to services (the sector accounts for nearly 80% of output), increasing industrial efficiency, upping vehicle fuel efficiency, and enforcing environmental standards.

In a not-so-sneaky move, the United States has also outsourced much of its messier manufacturing to other countries. Which is why the top spot for most polluted countries goes to...

1. China

Source: Wikimedia Commons, Brian Jeffery Beggerly; smog over Beijing's Forbidden City, 2005. 

"Made in China" may be the three most common words ever printed on anything ever. Not only does this East Asian nation produce and pollute for its own 1.4 billion citizens  – it also sells its wares around the world. While the U.S. exported $109 billion of goods to China in 2013, China shipped back an astounding $403 billion worth.

International trade has helped push China's total carbon dioxide emissions to 8.3 billion metric tons, 50% higher than the U.S.' own emissions.

China's pollution problem is further augmented by the fact that most of its industries are clustered around a few key economic zones and megacities on its east coast. Hazardous particulate matter often blots out Beijing's sky, and thick Shanghai smog periodically shades the city's impressive skyline.

In January 2013, Beijing's Air Quality Index hit a record high of 755 -- 30 times the World Health Organization's safety level standard. And a shocking study released this July estimates that air pollution in northern China shortens 500 million Chinese lives by an average 5.5 years, according to a report in The Guardian.

But recently appointed President Xi Jinping has called pollution and corruption China's two most pressing problems, and he's working hard to address both. In October, China adopted the same vehicle emission standards as the European Union, and recently the Beijing government announced it would be phasing out 500 polluting facilities around its city center.

Pollution without borders
Pollution is a global problem. No matter where you live, carbon dioxide emissions from the most polluted countries are crossing borders. These three countries are the worst offenders, and addressing worldwide carbon dioxide emissions is the only way we'll all eventually breathe easier.