Originally published November 29, 2009 at 12:04 a.m., updated November 30, 2009 at 7:20 a.m.
Carbon dioxide, or CO2, is the best-known of the compounds that warms the earth’s atmosphere, but some scientists want more attention paid to minimizing other greenhouse gases.
— Black carbon, or soot, may be the second leading cause of global warming. Unlike CO2, it remains in the atmosphere for only a few days or weeks.
— Hydrofluorocarbons have replaced ozone-depleting chlorofluorocarbons as common refrigerants but some are potent climate-warming compounds.
— Methane is more than 20 times as effective in trapping heat in the atmosphere than carbon dioxide. Man-made sources include landfills, farming and coal mining.
— Low-level ozone is formed by the interaction of sunlight with hydrocarbons and nitrogen oxides, which are emitted by automobiles, gasoline vapors, fossil fuel power plants and other sources.
Source: Institute for Governance & Sustainable Development; U.S. Environmental Protection Agency; University Corporation for Atmospheric Research.
When it comes to climate change, carbon dioxide is seen by many as the biggest villain and the main target of a much-anticipated meeting next month in Copenhagen to fashion an international strategy on global warming.
But two high-powered scientists at the University of California San Diego and their colleagues are trying to focus attention on a handful of other climate enemies that lurk in the shadows. By quickly arresting soot, methane, low-level ozone and hydrofluorocarbons, the researchers said the world can delay climate change by roughly 40 years — enough time to significantly trim emissions of carbon dioxide.
So-called fast-action strategies generally rely on available technologies so that they can be launched in two or three years with relatively little cost, according to advocates for that approach.
They said trimming potent lesser-known pollutants will produce results in a matter of decades while carbon-dioxide remain in the atmosphere for centuries even after emissions stop. Many scientists say it’s important to avoid raising the world temperature by 3.6 degrees Fahrenheit above preindustrial levels, a “tipping point” at which they predict major irreversible problems such as disappearing ice sheets.
“As important as the CO2 side is, it’s not enough to save us from irreversible and catastrophic changes,” said Durwood Zaelke, a sustainable development expert at UC Santa Barbara. “We need these fast-action strategies to put the brakes on.”
Such thinking is starting to spread and it may gain more traction because of a report issued last week by an international group of climate scientists. It said carbon dioxide emissions from fossil fuels have skyrocketed since 1990 and the effects of global warming appear to be worse than predicted just a few years ago.
“There remains some scientific uncertainty about some of these (non-CO2) pollutants’ precise contribution to global warming. But a growing body of science points to a potentially significant role,” Achim Steiner, executive director of the United Nations Environment Programme, said recently.
He called for urgent efforts to determine their impacts and options for reducing them.
Regardless, non-CO2 compounds aren’t likely to be a major agenda item in Copenhagen, said Stephen Seidel, vice president for policy analysis at the Pew Center on Global Climate Change, a nonpartisan analysis group in Arlington, Va.
“In part, it’s because the science has just been developing,” he said. “Without that, it’s hard to build up a scientific consensus.”
Seidel said the fast-action strategy is potentially attractive but may get complicated by efforts to address several elements at once.
The Copenhagen meeting is expected to generate lots of talk about climate change — including a recent controversy over the accuracy of climate models — though a legally binding treaty to replace the Kyoto Protocol is likely at least a year away. That’s partly because carbon dioxide emissions are tightly linked to economic growth.“After (Copenhagen), when people start churning out the numbers, they will realize it’s not enough” to address carbon dioxide, said Veerabhadran Ramanathan, a professor of atmospheric sciences at the Scripps Institution of Oceanography, part of UCSD.
Ramanathan, Zaelke and others published an article last month in the Proceedings of the National Academy of Sciences that called for a new emphasis on non-CO2 climate pollutants.
Zaelke called the paper “an effort to bring a little hope to the world that there are things we can do now.”
Non-CO2 pollutants individually are less significant than carbon dioxide and they come from multiple sources. That makes attacking them less straightforward than reducing emissions from power plants and autos, the main sources of carbon dioxide.
“It’s complex in terms of the science but it is incredibly simple in terms of mitigation because the technology is there,” Ramanathan said.
Besides, Zaelke said, cutting lesser-known climate compounds means not having to fight big oil and car companies that have resisted slashing carbon dioxide.
Ramanathan’s focus is black carbon soot, an aerosol produced by the incomplete combustion of diesel fuels and biofuels such as wood. It is now considered to be the second or third largest contributor to climate change and linked to melting of Himalayan-Tibetan glaciers that provide fresh water to billions of people in Asia and India.
Researchers consider black carbon an ideal target for achieving quick mitigation because it remains in the atmosphere just a few weeks. It can be reduced by expanding the use of diesel particulate filters on vehicles and clean-burning cookstoves to replace those burning dung and wood.
The U.S. Senate recently directed the Environmental Protection Agency to study the most cost-effective ways to cut black carbon emissions.
“We can lessen the threat of global warming and improve global public health,” said Sen. Tom Carper, D-Del., who pushed for the assessment.
Like black carbon, low-level ozone doubles as a major climate change agent and health hazard. It is formed by “ozone precursor” gases such as carbon monoxide, nitrogen oxides, methane and other hydrocarbons, many of which can be reduced by improving the efficiency of industrial combustion processes.
Ramanathan and others are optimistic about the world’s ability to focus on non-CO2 compounds because they have a precedent. The Montreal Protocol, considered one of the most successful international environmental treaties, has led to the near elimination of dozens of ozone-depleting chemicals, some of which double as greenhouse gases.
“The Montreal Protocol has already delayed climate change by seven to 12 years and put the ozone layer on the path to recovery later this century,” said Nobel laureate Mario Molina, a co-author of the paper and a chemistry professor at UCSD. “We have to take advantage of the proven ability of this legally binding treaty to quickly phase down hydrofluorocarbons.”