Part 3 of 4: U.S. Emissions Target

This is the third installment of a four-part series to be published each Wednesday on Action Needed to Stop Global Warming.

1. How Warm is Too Warm?
2. Worldwide Emissions Target
3. U.S. Emissions Target
4. Technologies to Get Us There

In Part 1 of this series, I defined the global tipping point as the melting of the Greenland ice sheet, which could cause sea levels to rise 20 feet. In Part 2, I showed by how much global emissions of carbon dioxide (CO₂) must drop to avoid this tipping point. They must start to decline around 2020, drop 50 percent by 2050, and drop at least 75 percent by the end of the century.

Meeting these global emissions targets will require a global effort. Even if the U.S. and other developed countries were to cut their emissions to zero, global emissions would likely exceed the targets by mid-century. This is because of the rapid rise in emissions from China and other developing countries.

So both developed and developing countries must participate, but how much of the burden should each bear? We could require all countries to make the same emission cuts at the same time, but many believe that would be neither realistic nor fair.

Although the U.S. can’t solve the problem alone, its participation is crucial because the U.S. is the single largest CO₂ emitter. China is a close second and rapidly catching up – but only if we consider current emissions.

If we look at historical or accumulated emissions, the dominant role of the U.S. is even more apparent. The U.S. is responsible for almost 30 percent of accumulated emissions in the atmosphere today; China is responsible for only 8 percent. If we look at emissions per person, the distribution is even more lopsided: the U.S. emits about six times more than China.

Graph adapted from J. Hansen presentation.

Developed countries have the resources to cut emissions immediately without damaging their economies. It’s therefore reasonable to expect them to take the lead. Some of the bills currently before Congress recognize this, and would have the U.S. cut emissions almost immediately, so that total emissions are capped at 10 to 30 percent below current emissions in 2020, and 60 to 80 percent by 2050.

Note that the cut for the U.S. of 60 to 80 percent by 2050 is higher than the global requirement of 50 percent by 2050, and the U.S. peak in 2008 is earlier than the global requirement of 2020. This allows developing countries like China to take more time to drop their emissions so their vulnerable economies aren’t over-burdened. But it doesn’t give them a free ride. The growth rate of emissions in developing countries would have to slow almost immediately, then around 2025 emissions would begin to decrease at a rate comparable to that of developed countries. The challenge for the global community in the “son of Kyoto” negotiations will be to get both developed and developing countries to commit to this scenario.

Next week, in the last part of this series, I’ll talk about the technologies we can use to meet these emissions targets.