“Once there was a world,” booms Neil deGrasse Tyson to begin the 12th episode of Cosmos. We see white, foamy waves lapping against a rocky coastline. The CGI landscape – an unspoiled, primordial paradise – is not unlike certain parts of the Pacific coast.

This planet is Venus, intones Tyson, and things are about to go terribly wrong. On cue, lava spews from the ground and the sky darkens with volcanic dust. The ocean – steaming and boiling – soon evaporates, leaving nothing to absorb excess carbon dioxide (CO 2 ) from the air. Without a disposal system, a deep voice reminds us, atmospheric CO 2 will accumulate en masse. Now heat from the sun, trapped by the greenhouse effect, can’t escape. Venus – the scorching sulfurous orb we all know – is born.

Of course, it doesn’t take Venus-levels of CO 2 to warm a planet. Earth’s atmosphere only contains a tiny fraction of this gas. Take it away and our world freezes into a sterile snowball. Double the amount of CO 2 , however, and the temperature rises uncomfortably. Ice caps melt. Sea levels rise. Once fertile areas begin to look like Death Valley. Not Venus, but not exactly Club Med.

Using ice core samples, scientists have been able to look deep into Earth’s atmospheric past. For hundreds of thousands of years, the concentration of CO 2 did not exceed 0.03%. Then humans began burning coal. And oil. And forests. Now the level sits around 0.04%. This recent spike in CO 2 is the prime culprit in the planet’s warming trend.

Are we to blame for this increase in atmospheric carbon? Scientists have measured the excess CO 2 , and – surprise surprise – it matches up with human emissions. To seal the case, the surplus CO 2 bears the mark of industry: a heavier isotope than normal atmospheric carbon. This souped-up greenhouse – today’s planet Earth – is not a natural phenomenon. We built it.

But now it’s not just smokestacks and refineries warming the planet. We’ve awakened a sleeping giant. As temperatures rise, permafrost – the frozen soil in Northern latitudes – is melting at increasing rates. This melt releases bundles of CO 2 and methane (another potent greenhouse gas) into the atmosphere. Big bundles.

We’re stuck in a feedback loop: the planet warms, frost melts, greenhouse gases are released, the atmosphere traps more heat, the planet warms…and so on. The amount of gas released from melting permafrost is “on par with current U.S. rates of emission,” says Susan Natali of the Woods Hole Research Center. And try getting arctic frost to show up to a climate convention.

The consequences of climate change, although the worst may be in store, are already serious. In Bangladesh, rising sea levels have forced millions to migrate to Dhaka, the country’s congested capital. With over 115,000 people per square mile, there’s hardly room for these folks to breathe. They cram into huts, eking out an existence amongst hordes of fellow refugees. This is a real humanitarian crisis.

Closer to home, in the Western US, higher temperatures and extended dry spells have created conditions ripe for forest fires. These blazes have grown to hellish proportions. Last summer, vast swaths of the country were bathed in smoke as millions of trees burned to ash. In the past 10 years, in fact, we’ve seen the 6 worst wildfires in recorded history. “There is no more wildfire season,” said former California governor Arnold Schwarzenegger. “We now have wildfires all year round.”

And wildfires aren’t the only threat to North American trees tied to global warming. Longer summers have allowed the bark beetle – a pestilence to forests – to reproduce twice in a single season. Over the last 10 years, these critters have killed more trees than all fires combined. Strange things happen when you play with the planet’s thermostat.

Hope remains. The sun and the wind – abundant sources of energy – are begging to be tapped to the full. But it’s still far too easy for energy companies to combust their way to record profits. It isn’t legal to toss litter on the ground. It shouldn’t be free or legal to dump waste into the atmosphere either.

Life requires a delicate balance of conditions. The Earth may never become Venus, but our nasty habit of shooting CO 2 into the sky is starting to bite us. If we want to preserve our one home, we need to stop burning things sooner rather than later.

“It all depends on what we truly value,” rumbles deGrasse Tyson as he views Earth from the comfort of his spaceship. “And if we can summon the will to act.”