Just 15 More Years?

In mid-December 2013 a draft report by Working Group III of the UN’s Intergovernmental Panel on Climate Change was leaked to the press. Here’s how the New York Times began its article on the report (emphasis added):

Nations have so dragged their feet in battling climate change that the situation has grown critical and the risk of severe economic disruption is rising, according to a draft United Nations report. Another 15 years of failure to limit carbon emissions could make the problem virtually impossible to solve with current technologies, experts found.

Climate change is a difficult concept to get people aroused about. Its dire consequences lie in the future, so it’s easy to think about it as something our children or grandchildren can take care of. But climate scientists worry that if we wait too long, we may reach a point of no return where no one will be able to take care of it.

What’s generally not understood is that the climate is changing more than we perceive. Burning fossil fuels and clearing forests emit carbon dioxide (CO₂) that increases the thickness of the greenhouse gases (GHGs) blanketing the Earth and upset its energy balance by preventing it from radiating away all of the energy it absorbs as heat from the Sun. In accordance with the law of physics, the resulting imbalance increases Earth’s surface temperature and thereby the amount of heat it radiates away until radiated heat again matches absorbed heat.

But energy rebalancing is slow, principally because warming the ocean that contains 90 percent of Earth’s living space takes a long time. In the last century Earth’s temperature has increased about 1.3 degrees Fahrenheit. 
That’s an insignificant change when we relate it to our local temperature, but not when it represents the change in temperature of Earth’s entire surface — almost 200 million square miles, 70 percent of which is ocean — averaged across opposite seasons and day/night variations. And because of the thermal inertia of the ocean described above, the temperature will keep rising even if we immediately stop all new GHG emissions until the ocean catches up and the energy imbalance created by current GHG emissions has been eliminated.

Another inertial factor is the longevity of atmospheric CO₂, which is more potent than all other GHGs combined in warming the planet. Unlike the other major long-term GHGs, which have chemical (and global warming) lifetimes from a decade or so (methane) to a century (nitrous oxide), CO₂’s longevity is controlled by the Earth’s carbon cycle. Under current conditions, about half of an emission of CO₂ is redistributed to the ocean, terrestrial biosphere and soil within a quarter century, but almost a fifth remains in the atmosphere to keep the planet warm for more than 500 years.

To forestall global overheating and “preserve a planet similar to that on which civilization developed and to which life on earth is adapted,” NASA climatologist James Hansen and other scientists concluded in 2008 that we need to reduce atmospheric CO₂ concentration (trim the blanket) from what was then 385 ppm (parts per million molecules of air) and is now almost 400 ppm to a maximum of 350 ppm. How?

According to Hansen’s latest calculations, if we reduce fossil fuel emissions of GHGs by 6 percent a year beginning now, phase out deforestation and other land-use emissions in 2020-2030 and then reverse them — store atmospheric CO₂ in the biosphere and soil  through reforestation and advanced land-use techniques — at twice the annual rate of current emissions, we can achieve 350 ppm by the end of the century (2100).

The timing is critical. What concerns climatologists are so-called “slow” feedbacks that gradually reinforce and aggravate global warming. Unlike “fast” feedbacks like the melting of the Arctic sea ice in summer that climatologists can observe and take into account, slow feedbacks are difficult to measure. Some that occurred during the ice ages of the last several thousand centuries like CO₂ that the ocean emits when it’s warming are well known. Others like the breakup of the glacial ice sheets in Greenland and Antarctica and the release of vast methane deposits frozen beneath the permafrost, are more speculative since they haven’t occurred in millions of years. But given enough time to develop, slow feedbacks like these could run away with the climate and offset the benefit of eliminating GHG emissions.

Continuing business as usual and not starting the Hansen 6 percent annual cuts in fossil fuel emissions until 2020 would delay reaching the 350 ppm target until 2300 and give slow feedbacks two centuries (beyond 2100) to gather steam. Waiting until 2030 — just 15 more years — would give slow feedbacks four centuries.

If we want to avoid the risk that slow feedbacks will make climate stabilization impossible, our years of foot-dragging seem to be over. That is, we don't have 15 more years. Yet all Congress has to do is enact a gradually rising carbon tax or (better) a refundable revenue-neutral carbon fee to facilitate the replacement of fossil fuels with non-carbon fuels.

That’s as easy as convening the day after Pearl Harbor and declaring that a state of war existed, thereby allowing the U.S. to commit all the resources it needed to fight it. Call the state we’re in today whatever you want, it still represents an existential threat to the livelihood of everyone who comes after us that must be fought now.