Carbon Dioxide

Time for early action

Carbon dioxide is not the only warming agent

worth tackling now in the bid to cool the planet.

The US House of Representatives must be commended for passing

a comprehensive climate bill last week that would finally set the

United States on a path to lower its greenhouse-gas emissions.

The pending legislation is far from perfect and will face a tough test

in the Senate. But it is a necessary first step for the country that has so

far added the most carbon dioxide to the atmosphere.

However, it will take several decades, if not longer, for the United

States and other nations to significantly reduce carbon dioxide emissions.

This fact has spurred many scientists to intensify research

into techniques that might provide a more immediate way to turn

down the planetary thermostat. Some solutions seek to fine-tune

Earth’s climate through large-scale geoengineering projects, such as

pumping sulphates into the atmosphere to reflect more sunlight back

into space. But another approach — an ‘early action’ climate agenda

increasingly being pushed by environmentalists and some scientists

— might prove safer and much easier to sell to governments and

populations around the world.

A good place to start is with black carbon, the sooty, dark component

of smoke that emanates from diesel engines, inefficient cooking stoves,

forest fires and the like. Black carbon is a danger to human health, having

been implicated in a variety of cardiovascular and respiratory diseases,

and may also be a major player when it comes to global warming,

particularly in regions that spend at least part of the year covered with

ice and snow (see page 29). But unlike carbon dioxide, which stays in

the atmosphere for centuries, black-carbon particles remain in the air

for just a matter of weeks. So, in principle, efforts to eliminate emissions

could quickly reduce the warming power of this pollutant.

Unfortunately, it is not that simple. First, not all black carbon is

anthropogenic in origin. Second, black carbon is accompanied to

varying degrees by its lighter-coloured cousin, organic carbon, which

cools the planet along with most other reflective aerosols. Third,

despite more than a decade of research, the chain of reactions by

which black carbon warms the atmosphere and melts snow remains

surprisingly hazy. All of these factors make black carbon’s effect on

climate difficult to quantify.

However, none of the caveats is a reason for nations not to try their

utmost to control it. Even if the climate benefits turn out to be less

than hoped, cleaner air would save hundreds of thousands of lives

a year. Governments should already be working to clean up diesel

emissions and to improve cooking stoves in southeast Asia, where

the health problems are most acute. But it may be that the threat of

global warming is more effective than health advocacy.

Accompanying black carbon on the early-action agenda are methane

and hydrofluorocarbons (HFCs). The latter are used predominantly

as refrigerants, and can be more than a thousand times more powerful

than CO2 as greenhouse gases (see Nature 459, 1040–1041; 2009).

The international ‘Methane to Markets’ programme provides

money and expertise to help countries to capture methane from

sources such as landfills, farms and coal mines. Once up and running,

these projects produce energy at a profit by making use of a

clean-burning compound that would otherwise have wreaked havoc

in the atmosphere for years. The programme has been a resounding

success, and other nations should find the money and will to

replicate it.

The case for HFCs is a bit more complicated, but no less strong.

HFCs were developed to replace ozone-depleting chlorofluorocarbons

that were phased out in response to the 1989 Montreal

Protocol. Because they don’t affect atmospheric ozone levels, they

were pulled under the United Nations’ Kyoto climate treaty. But

there are now calls to take the chemicals out of the climate treaty

and put them into the Montreal Protocol. This is the right thing to

do. Montreal regulators have already proved their ability to implement

worldwide curbs on emissions, and there is little doubt that they

could handle this problem faster and more cost-effectively than could

a cumbersome treaty aimed at targeting CO2.

Notably, each of these solutions could be pursued immediately,

precisely because they make sense on multiple levels; global warming

might be a driving factor, but it is not the only one. There is no

need to wait for international negotiators to strike a deal on a climate

treaty that would lay the groundwork for a global carbon market. And

they do not pose the ethical or legal challenges that geoengineering

schemes so often face.

Some fear that even talking about such subjects could distract from

the main problem, which is CO2. The opposite is true. Providing workable

solutions in other areas will build momentum and simultaneously

ease the burden that remains. What is there to lose?