Certainty on the Science of Climate Change

CAP's Joseph Romm discussed the physical science behind climate change and the inner workings of the IPCC with two experts at a CAP event.

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“A wait-and-see policy,” on climate change, observed Center for American Progress Senior Fellow Dr. Joseph Romm on Wednesday, “may mean waiting until it’s too late.” Romm was speaking at a CAP event on “The Science of Climate Change,” and was joined by Dr. Chris Field, the director of the department of global ecology at the Carnegie Institution for Science and the Working Group II Co-Chair of the Intergovernmental Panel on Climate Change, and Michael MacCracken, Ph.D., the chief scientist for climate change programs at the Climate Institute.

Human activity generates heat-trapping gases like carbon dioxide that are warming the planet and changing the climate. In framing the conversation, Romm summarized an MIT study concluding that on our current emissions path, the atmospheric concentration of carbon dioxide will more than double from pre-industrial levels and the median temperature increase at the Earth’s surface in the 2090s could be 5.2˚C, or nearly 10˚F. “We’re talking about a completely different planet,” he said.

MacCracken emphasized during his panel presentation that our understanding of the fundamental physical science behind climate change is sound and has been for decades. In fact, the idea that human-caused emissions of carbon dioxide could warm the planet is more than a century old—the Swedish scientist Svante Arrhenius explained the concept in 1896. The first official report submitted to a U.S. president on the impact of atmospheric carbon dioxide arrived on Lyndon B. Johnson’s desk in 1965.

Human-generated emissions enhance the natural greenhouse effect and disrupt the planet’s carbon cycle, MacCracken explained. Observations of carbon dioxide levels since the middle of the 20th century show a clear annual oscillation: concentrations of the gas go up and down with the “seasonal breathing” of the biosphere. Part of that cycle is plants absorbing carbon from the air during spring and summer and releasing it during the fall and winter; part of it is ocean absorption. But increasing human emissions mean that the cycle is no longer balanced, and the concentration of heat-trapping gases in the atmosphere is climbing steadily. “We’ve had a huge subsidy for our carbon,” Field said, because so much of it absorbed by “sinks” on land and in the water.

When sunlight strikes the atmosphere, MacCracken explained, some of its energy is reflected back into space, and some of it passes through, warming the surface of the planet. A small portion of that surface heat radiates back into space again, but greenhouses gases absorb most of it, recirculating the energy back to land and the lower atmosphere. As concentrations of carbon dioxide and other gases increase, more of that heat stays within the atmosphere, leading to a warmer and warmer planet.

Moreover, the warming effects of carbon dioxide in particular are long lasting and the increased concentrations already in the air would continue to warm the Earth for decades to come, even if emissions were immediately reduced to zero. That’s why it is the most important emissions product under consideration by governments around the world.

Surface temperatures and ocean temperatures are rising, MacCracken said, summarizing multiple lines of evidence that confirm the climate is changing now. Sea ice is shrinking, glacier and permafrost are melting, and snow lines are creeping toward mountain peaks. Consequently, sea levels are rising, and increased amounts of evaporated water in the air lead to more intense precipitation where rain falls. And plant and animal species are retreating toward the poles as their original habitats get warmer.

Field reemphasized the importance of focusing on carbon dioxide as the leading cause of these changes because it is intimately linked to human prosperity. “We haven’t figured out how to make people rich without associating that with a high-carbon lifestyle,” he said. Historical data indicates that there is a linear relationship between national wealth and carbon emissions. The question, he said, is how to move from an environment where this relationship is strong to one that breaks that link, creating the “opportunity for more economic activity with lower carbon emissions.”

In 2007, the Intergovernmental Panel on Climate Change stated that the global “warming is unequivocal,” and Field emphasized that analyses cannot look selectively at merely a few years or even a single decade within the climate record to see this trend. It requires a longer view, but multiple independent temperature records confirm the fact that the planet is getting warmer.

In explaining the process that generates these massive reports on climate science, Field said that, “The IPCC is the most ambitious, thorough, and successful assessment of anything that I think has ever been done.” The process is designed to keep errors to a minimum, but he spoke from personal experience in describing the particular frame it creates for presenting information.

Author teams draw scientists from a variety of disciplinary perspectives and from countries all over the world; they then absorb and synthesize a huge amount of information. For the chapter Field worked on for the last IPCC report, two rounds of expert review each produced 250 pages of notes.

Representatives from all of the United Nations countries later approve, line by line, the IPCC summary chapters for policymakers that synthesize the scientific reports. Field described displaying sentences on a board for a room of participants and being unable to proceed before there was total consensus on the characterization of the science. This produces a “very tight boundary” around what appears in the final summaries, and the characterizations of the science are therefore very measured, not extreme.

MacCracken said that some critics of the process have suggested that scientists simply give policymakers the original research and leave the interpretation up to them. He compared the folly of that approach to giving a cancer patient all of the available medical research on his or her condition, expecting them to make a decision independent of a doctor’s advice. The IPCC summaries are the record of a conversation in clear terms, he said, between scientists and government policymakers.

Most recently, the IPCC came under fire for erroneous projections published in a scientific chapter on the rate at which the Himalayan glaciers are melting. The dubious information originated from a piece of “gray literature,” that is, a report that did not come from a peer-reviewed scientific journal. Addressing the use of gray literature in the IPCC process, Field explained the value of this information in understanding the impact and implications of climate change. These sources include insurance company research, unpublished scientific work, observations of impacts in various publications, and industrial and corporate reports. It is hard to imagine how the IPCC could tackle the range of subjects it is tasked with understanding without access to this gray literature, he said.

Video: Interview with Christopher Field, Ph.D. “Climate Change Is a Clear and Present Danger

Video: Interview with Michael MacCracken, Ph.D. “How We Know Humans Are Changing the Climate

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