News•March 28, 2013

Two Key Climate Change Concepts Are 'Misunderstood'

There is widespread confusion about the near-term benefits of reducing greenhouse gas emissions, and that misunderstanding may be complicating the formidable task of reducing manmade global warming, argue two climate researchers in Science in a story published Thursday.

The scientists, Damon Matthews of Concordia University in Montreal and Susan Solomon of MIT, make the case that policymakers, the media, and to some extent the public have misunderstood the implications of two key concepts — the “irreversibility” of climate change, and the amount of global warming already in the pipeline due to historical greenhouse gas emissions.

The duo challenge what they say have become pervasive misinterpretations of recent scientific results, including findings from a 2010 National Research Council report they helped write that said that the amount of global warming to date is essentially irreversible on the timescale of about 1,000 years. That study has been repeatedly cited by policymakers to justify delays in tackling carbon emissions by making global warming appear to be inexorable, regardless of what actions are taken.

But Matthews and Solomon rebut that justification, writing instead that, “the irreversibility of past changes does not mean that future warming is unavoidable.”

In addition, they said the notion that global warming would continue to take place even if the amount of greenhouse gases in the atmosphere were to be frozen at current levels — rather than increasing year-after-year as they are now — has also helped justify inaction.

These findings have “been misinterpreted to mean that the rate of increase in Earth’s global temperature is inevitable, regardless of how much or how quickly emissions decrease,” the Science article said.

In an interview, Matthews said that confusion over the irreversibility and the amount of future warming that is already baked into the climate system has been widespread, and is serving to overcomplicate the global-warming issue, which is already challenging. “Anything that makes the problem seem more complicated than it is, is disempowering I think,” Matthews said.

“Over the years, I keep hearing both scientists and certainly policymakers talk about future warming, particularly near-term future warming, as if it is inevitable or predetermined by emissions that we’ve already put into the atmosphere,” Matthews said. “That’s actually a misinterpretation” of the published research, he said, since future warming depends mainly on future emissions, leaving the ball squarely in the court of policymakers.

“There will be future warming, but it’s because of human actions. It’s not because of the climate system itself,” Matthews said. “Future emissions are what’s driving future warming.”

Trend in observed atmospheric carbon dioxide concentrations as measured at the Mauna Loa Observatory in Hawaii.
Click on the image to enlarge. Credit: NOAA.

If emissions are cut, that means that future warming will be reduced. If not, then future warming will be higher. It’s as simple as that, Matthews said.

For example, “freezing” the amount of greenhouse gases in the air at current levels — about 397 parts per million — would require massive emissions cuts from present emissions trajectories, but the emissions that would continue would still contribute to global warming, Matthews said.

In other words, freezing carbon dioxide concentrations in the atmosphere at a particular level, such as 350 parts per million, — the target of the environmental advocacy group 350.org — is not the same thing as eliminating all emissions.

In reality, neither scenario is likely anytime soon. Given recent global emissions trends, with rapidly increasing emissions from developing countries like China and India and a lack of sharp emissions cuts from the industrialized world, a freeze in atmospheric carbon concentrations is nowhere in sight, let alone a shutdown of all emissions, and a massive global effort would be needed to reverse course.

Matthews said that if emissions were reduced significantly in the near term, global warming would also be reduced over that time period, although it might not be detectable given the presence of natural climate variability.

Gavin Schmidt, a climate scientist at NASA’s Goddard Institute for Space Studies in New York, said that near-term actions to reduce emissions wouldn’t have a noticeable impact on the climate system for many years. “The fact remains that plausible near-term actions to reduce emissions are not going to have a detectable impact on trends for a couple of decades,” he said in an interview.

The Science article said the critical factor determining future warming is “societal inertia,” rather than the inertia of the climate system, since actions taken now will determine the amount of emissions in the next few decades, and thereby determine how much additional global warming is likely to take place. “The future is within our hands. The amount of climate warming will be whatever we make it. We have not yet committed ourselves to anything particular other than by lack of action,” Matthews said.

Energy infrastructure such as coal-burning power plants, oil refineries, and pipelines are built to last several decades, so decisions made today regarding the building of such plants will affect emissions for many years to come.

Katharine Hayhoe, a climate scientist at Texas Tech University who was not involved in the Science article, said the misconceptions that Matthews and Solomon set out to correct are more common, and more problematic, among policymakers than in the general public. She said she thinks the main message that emerges from the article is a hopeful one.

“It is often said — and I have said it myself — that a certain amount of change is inevitable. As the authors point out, that is largely because of the inertia in our energy systems that do not allow us to rapidly transition from carbon-emitting to carbon-free sources,” she said in an email. “This sad fact can make us feel like any action is futile. Reality, however, is very different: action is necessary, possible, and important. To me, that's the main point of this paper.”