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One of the key findings of the Intergovernmental Panel on Climate Change (IPCC) report released last week was that we need to emit no more than one trillion tons of carbon in order to stand a good chance of limiting global warming to 2 °C. The problem is this: technology is not progressing fast enough to make this happen.

The trillion-ton figure is really an estimate, as no one knows precisely how many tons of carbon will raise the temperature of the planet by 2 °C. And less warming than that could cause significant damage, while humans will probably survive higher levels. That said, the number provides one of the clearest ways of thinking about what most climate scientists believe needs to be done to avert serious climate change.

Unfortunately, we’re on track to hit one trillion tons just 27 years from now. And if we keep increasing the rate of emissions as we have been, we’ll hit it even sooner. To avoid this, the world needs to reduce carbon dioxide emissions by 2.5 percent a year, according to data from climate scientists at Oxford University. That figure seems like a nice, manageable one until you realize what order of change would be required to achieve it.

One of the most remarkable energy transitions in history happened when, starting in earnest in the 1970s, France went from getting 1 percent of its energy from nuclear power to getting 80 percent over a period of just 30 years. As it replaced fossil-burning plants with nuclear ones, the country reduced emissions by only about 2 percent a year, according to David Victor, co-director of the Laboratory on International Law and Regulation at the University of California, San Diego. To come in under the limit, the whole world would need to undergo a similar transition even faster.

Achieving this in the United States, which is struggling to build any nuclear power plants, is hard to imagine. Its transition toward natural gas power from coal is helping. Increased use of natural gas, plus a recession, led to a reduction in carbon dioxide emissions of 6.7 percent in 2009, well in excess of the rate needed to avoid emitting one trillion tons. Unfortunately, emissions jumped 3.8 percent the following year. Over the last 10 years, on average, emissions decreased by just 1 percent per year.

A continued transition to natural gas could help sustain that decrease in the United States for a while. But natural gas power is ultimately a dead end. It can cut emissions in half compared to coal, but it still emits carbon dioxide.

“Long-term ‘sustainable’ emissions of fossil carbon are essentially zero,” says Myles Allen, professor of geosystem science at Oxford University, whose research has helped establish the trillion-ton number.

Allen doesn’t think we have to shut down all the fossil fuel plants. Instead, he’s for capturing carbon dioxide and storing it. But so far, the technology, which could involve capturing the carbon dioxide from a power plant and injecting it into underground reservoirs, hasn’t been demonstrated at a large scale. “It will take decades to work out which reservoirs leak and which don’t, and we won’t get that information until it is deployed at scale,” he says. Only a few demonstrations of CCS are planned, though, and many of those probably won’t go forward (see “EPA Carbon Regs Won’t Help Advance Technology” and “Cheaper Ways to Capture Carbon Dioxide”). The International Energy Agency has warned that demonstrations are “seriously off pace.”

Renewable power is often held up as the way to reduce carbon emissions over the long term. But even with fast growth in recent years, wind and solar account for only about 4 percent of electricity in the United States, and reaching much higher levels will bring challenges. The more that wind and solar power are added to the grid, the more utilities need to spend to deal with their intermittency (see “Wind Turbines, Battery Included, Can Keep Power Supplies Stable”). In one sense, wind power isn’t really zero emissions, since it typically requires backup from natural gas power plants.

To make matters even more difficult, changes would have to be made not only in the power sector, but also in transportation, where alternatives like nuclear power don’t exist. While nuclear power can offer the same kind of consistent, around-the-clock power as fossil fuels, you can’t yet buy a zero-emissions car with the same performance as a gas-powered one.

The closest you can come is probably the Tesla Model S, but that doesn’t go as far per charge as a gas-powered car (265 miles compared to 350 or so), and the existing network of charging options means that in most places in the U.S. you need hours to recharge (“How Tesla Is Driving Electric Car Innovation”). The car also costs $80,000, which means only a few people can afford it. And at any rate, it isn’t really a zero-emissions vehicle because it runs on power from the grid, which comes largely from fossil fuels.

Even assuming grid energy gets considerably cleaner over the next two decades, by 2030 electric vehicles will still involve about one-third the emissions of gas-powered cars when you factor in the emissions from power plants, according to a recent analysis from John Heywood, a professor of mechanical engineering at MIT.

What’s more, given the performance limitations and costs of electric vehicles, they’re unlikely to go mainstream soon, Heywood says. A more realistic scenario, he thinks, is that existing cars will gradually get more efficient as a result of fuel economy regulations, and emissions will be cut in half. But that won’t happen until 2050, in part because cars with existing technology will stay on the roads for decades.

Reducing emissions faster will require people to drive less, or expect less from their vehicles. “It’s very difficult because you have to change people’s behavior,” Heywood says. The same probably goes for reducing emissions throughout the economy.

But the question isn’t really whether we’ll limit emissions to a trillion tons. It seems inevitable that humankind will blow past that goal. The bigger question is how much more carbon will be emitted, given that several trillion tons remain in the ground, waiting to be extracted and burned.

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Tagged: Energy, energy, renewable energy, climate change, electric vehicles, carbon dioxide, natural gas, global warming, coal, nuclear

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