photo courtesy of Nature

The European Space Agency's Venus Express mission, the first to Venus in nearly a decade, has helped scientists explain the feedback cycles that led to the planet's current inhospitable conditions, the journal Nature reports this week.

Venus is our closest neighbor planet, and her beautifully colored clouds inspired the ancients to call her the Goddess of Love, while fiery Mars became the God of War. But underneath those clouds lies a burning truth – the surface of Venus is nearly 800 degrees Fahrenheit, and her atmosphere - which is 95% carbon dioxide – is essentially a noxious cloud of sulphuric acid. 

Author Eric Hand writes that this latest mission adds, "one more piece in an enduring puzzle: how could two planets in the habitable zone, with roughly the same size, mass and composition, end up so differently?"

The answer is that even though Venus and Earth have roughly the same amount of carbon dioxide, on earth it is stored in the ground, while on Venus it is nearly all in the atmosphere. As the report's scientists note, "The extreme climate at the surface of Venus, driven by this excess of CO2 in the atmosphere, reminds us of pressing problems caused by similar physics on Earth."

According to the NY Times, "Scientists imagine that Venus formed with much liquid water, just like Earth, but that because it is closer to the Sun, with sunlight twice as intense as on Earth, the water began to evaporate. Water vapor, also a greenhouse gas, trapped heat."

All that trapped heat led to more evaporation, which led to more heat, and on and on. This strong feedback loop evaporated the planet's oceans. Once the oceans had been turned to water vapor, solar winds eroded the atmosphere by separating the oxygen and hydrogen.

The hydrogen leaked off into space, and the oxygen sank to the surface where it oxidized, essentially baking the planet's crust – and thus further helping drive up temperatures. The probe measured the rates of hydrogen and oxygen in the atmosphere and confirmed that "Venus is still losing water to space via this runaway greenhouse effect — an extreme version of the Earth's."

So are we going to experience summer days that reach 300 degrees?

Not anytime soon, says Andrew Ingersoll, a Caltech astronomer, who wrote one of the reports in Nature. Speaking to the LA Times this week, he estimates a 1% increase in global warming, saying: "In the next hundred years we will have some problems, but they won't be as drastic as turning the Earth into Venus."

But the latest report from the Nobel Prize-winning U.N. Intergovernmental Panel on Climate Change concludes that we must brace ourselves for "abrupt and irreversible" changes in our lives as a result of global warming.

Berkeley researchers Margaret Torn and John Harte have studied the Vostok ice core and concluded that climate change is capable of producing positive feedback loops, and that current models which don't account for this may underestimate global warming. “A rigorous investigation of the uncertainties in climate change prediction reveals that there is a higher risk that we will experience more severe, not less severe, climate change than is currently forecast,” they write.

What's stunning is how incredibly delicate the system is. We don't need the planet to heat up hundreds of degrees before life becomes unbearable on earth – in fact, just a few would do the trick.

The U.N. Report concludes that with a 2 degree rise in temperature, 25% of the species on earth will likely be at an increased risk of extinction, while if it goes up by even a single degree more, "model projections suggest significant extinctions (40-70% of species assessed) around the globe."

That same 3 degree rise in temperature could raise sea levels at least a meter, which would flood New Orleans all over again, permanently; as well as parts of the San Francisco Bay Area, Honolulu, and dozens of cities from East Boston all the way down to Florida.

The kicker is that there is a lag between carbon emissions, and increased temperatures, so even if we stopped our emissions today, the temperature would still rise. The last time it was this warm, 125,000 years ago, the seas were 4-6 meters higher – which would flood virtually every coastal city on earth.

Meanwhile, we are dangerously close to experiencing the same kind of positive feedback loop that drove the skyrocketing temperatures on Venus.

The scariest part of Paul Hawken's new book, "Blessed Unrest" is this:

"The greatest warming today is occurring at the poles, not the equator, and rising temperatures there are releasing another gas, methane, from permafrost, where it has been locked up for millions of years. Methane is twenty-four times more powerful than carbon dioxide as a greenhouse gas. A rapid rise in its release into the atmosphere would create a dramatic increase in warming, a positive feedback loop that would accelerate additional methane release.  If such a runaway event were to take place, it could occcur within forty years or less, and would transform the planet into a biological desert."

As Rajendra Pachauri, the U.N IPCC's lead scientist has stated, "What we do in the next two or three years will define our future." And while the report provides many possible solutions, we are still a long way from doing all that needs to be done to cool the planet down.

If there is good news, it is that the same feedback loops could work to cool the planet as well. “If we reduce emissions so much that the atmospheric concentration of carbon dioxide actually starts to come down and the global temperature also starts to decrease, then the feedback would work for us and speed the recovery,” says professor Harte . But that is a daunting challenge in a world where emissions are increasing, despite our attempts to control them.

From deep space, the Earth and Venus might appear as a pair of floating blue sisters. But if there is anything to be learned from our twin, it is that a runaway greenhouse gas effect is a future a planet can happily survive. But humankind may not.