There’s Already Enough Greenhouse Gas in the Air to Heat the Planet by 1.5°C

(Bloomberg) -- The major new report from the Intergovernmental Panel on Climate Change made headlines around the world on Monday with a dire message: climate change is here, and human choices will determine how bad it gets.

That won’t come as any to surprise to those who’ve been paying even a little bit of attention to conversations around the climate. The IPCC report’s main contribution isn’t its message, but rather the precision with which it’s delivered. The United Nations-backed scientists now know that humans have, in fact, pumped enough greenhouse gases into the air to warm the planet about 1.5°C. The majority of that warming is tied to two gases—carbon dioxide and methane—that are largely released by fossil-fuel production and use.

And yet observed warming, according to the IPCC, is so far only about 1.1°C. Why is that?

Ironically, the fine-particulate pollution released by those very fossil fuels is masking some of the warming. While greenhouse gases trap sun’s heat in the form of infrared radiation, the particles that cause air pollution—known as aerosols—reflect sunlight back out into space before it reaches the surface of the planet.

If the world gets serious about air pollution or reducing emissions from fossil-fuel use, it will also wind up reducing the amount of aerosols dumped into the atmosphere. The result would be an improvement in air quality and a reduction in the 9 million or so deaths  that can be attributed to air pollution each year. But at least in the short term, the planet would start to warm up as the cooling effect from aerosol pollution disappears.

Fortunately, there’s a way out of this bind. “That is why it’s particularly important to reduce methane emissions in the next 10 years,” says Piers Forster, professor of physical climate change at the University of Leeds and a lead author of the IPCC report.

Methane is a super-warming gas, with 80 times the short-term climate impact of carbon dioxide, and its rise has been tied to the growth of natural gas and cattle agriculture. That means warming due to the decline of aerosols could be counterbalanced with the rapid, large-scale and sustained reduction in methane emissions.

Climate conundra like this one are more common than you might think. Take trees—planting them would seem to be a pretty straightforward solution to reducing the level of carbon dioxide in the atmosphere. Except it matters where on the planet you put the trees. At higher latitudes, such as in Russian Siberia or the Canadian Tundra, trees don’t just have a cooling impact by reducing CO₂, they also have a warming impact by absorbing sunlight.

The ideal place to grow forests is around the tropics—exactly where they’re being rapidly destroyed.

Reducing methane emissions might be as close as we come to a near-term climate jailbreak, even if it’s not quite a “Get Out of Jail Free” card. Bloomberg Green has spent the past several months reporting on large methane leaks around the world. While most of these leaks come from fossil-fuel infrastructure, a large number of them are found in countries like Russia or Turkmenistan where governments aren’t as inclined to help fight climate change as many others.

Similarly, tackling methane emissions from cows is not a trivial problem. Scientists, startups and large meat producers are trying methods from changing their feed to making them wear masks. The solutions aren’t cheap, and they don’t eliminate all the methane cows produce, either.

One bright spot in all this: 1.5°C is a political goal, informed by the work of scientists but ultimately establish by governments. Ed Hawkins, a professor of climate science at the University of Reading and a IPCC author, cautioned against projecting the urgency of the science onto a rigid numerical goal. There’s much greater flexibility than that.

“Every bit of warming matters,” Hawkins said.

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