- American Physical Society Sites
- Meetings & Events
- Policy & Advocacy
- Careers In Physics
- About APS
- Become a Member
by James Hansen (Bloombury USA, New York, 2009), ISBN 978-1-60819-200-7, 304 pages, hardcover $25
Reviewed by Art Hobson
James Hansen is concerned about the world that his grandchildren, Sophie age nine and Conner age four, will inherit. He's written a blockbuster that will be widely discussed. During the past two decades there has been a deluge of books, most of them good, about global warming. This is the most important of the lot.
Hansen is an accomplished scientist. He came to national attention in the 1980s when he testified before Congress and made a series of accurate predictions regarding the severity of global warming. He directs NASA's Goddard Institute for Space Studies, and is adjunct professor at Columbia University's Department of Earth and Environmental Sciences. Congress frequently calls him to testify on climate issues. He has authored and co-authored an impressive number and variety of scholarly papers centering around climate change, papers that are unusual for their depth of analysis and breadth of focus.
The book is primarily about the science of global warming. It argues that present policies will lead to a climate catastrophe; in particular, the present atmospheric carbon dioxide (CO2 - the primary cause of global warming) concentration is already too high and needs to be reduced from its present 390 parts per million (ppm) to around 350 ppm. More briefly, toward the end of the book, Hansen offers his remedies: a moratorium on new coal plants until their CO2 can be captured and stored, and a plan to tax CO2 emissions and fully rebate the tax revenues to citizens.
Hansen is unusual among climate scientists in drawing conclusions predominantly from empirical data rather than from computer simulations. Computer models can be valuable, but it's always difficult to know whether all relevant variables are included in the model, and some variables (such as clouds) are nearly impossible to compute. Empirical data come from mother nature, she includes all the variables, and she can do all the calculations.
For example, one of Hansen's figures graphs 65 million years of temperature history. The graph draws on evidence found in deep-ocean sediment "cores" (a long vertical pipe full of sediment inserted into the ocean bottom and then pulled up) and reported in 2001 by other scientists. Such a core contains evidence of the temperature and date of deposit at each position along the core.
Hansen draws several lessons from this graph and related evidence. One is that a long-term 9-degree (Fahrenheit) warming, during 59 to 50 million years ago (Mya), was caused by natural releases of CO2 into the atmosphere. Another lesson comes from the "Paleocene-Eocene thermal maximum" (PETM), a sudden 8-degree temperature spike 55 Mya. Hansen convincingly locates the cause. Rising ocean temperatures caused deposits of "methane ice" (a frozen mix of methane and water that gathers on the ocean floor) to melt and release large amounts of methane (a potent greenhouse gas) into the water, and the methane bubbled up to the atmosphere. Once methane release began it necessarily continued until essentially all the methane ice was melted, because the initial release warmed the atmosphere further, which caused further releases, and so forth in a vicious circle.
Hansen points out another lesson: The planet has generally cooled during the last 50 My, and new methane ices have had ample opportunity to spread over the ocean floor. CO2 and temperatures are again increasing. We're putting ourselves in danger of another PETM-like event. But unlike 55 Mya, Greenland and West Antarctica today hold huge ice sheets that would eventually melt under a massive methane release, causing catastrophic ocean rise.
Hansen's long-term perspective demonstrates the enormous rate of change that humans are imposing on the natural world. The warming 59 to 50 Mya was caused by an increase in atmospheric CO2 concentrations that averaged only one ppm every 10,000 years. By comparison, today's CO2 concentrations have increased by over 100 ppm in just two centuries! Wherever this is taking us, it's taking us mighty fast.
Today's CO2 concentration is nearly 390 ppm, 40 percent higher than it's been during at least the past 800,000 years. This CO2 spike occurred just since the beginning of the industrial age around 1800. As Hansen explains, this 390 ppm level is not sustainable: Marine species are suffering multiple stresses from warmer oceans; tropical regions are expanding, bringing spreading drought, deserts, and fires; the Greenland and West Antarctic ice sheets are losing mass at unacceptable rates; mountain glaciers are disappearing; and Arctic summer sea ice will soon vanish. It's "difficult to imagine how the Greenland ice sheet could survive if Arctic sea ice is lost entirely in the warm season."
Policy makers have talked for years about stabilizing the climate at 450 ppm, but in light of the trends, Hansen asserts that even 390 ppm is too high. What's the maximum safe level? Hansen is a proficient calculator of such problems. He calculates that a reduction from 390 to 350 ppm will restore planetary energy balance and stabilize the dangerous trends noted above. This won't happen overnight, and we'll be living dangerously until we get back to 350 ppm.
Hansen doesn't shrink from entering the policy debate. He advocates a moratorium on new coal-fired power plants until coal's CO2 emissions can be captured and stored underground. This is essential and needs to begin today, but corporate interests prevent it.
Hansen opposes the much-discussed cap-and-trade solution because it's complex and thus subject to corporate abuse. He instead supports a gradually increasing direct tax on carbon in order to reduce carbon's use, with the tax income rebated back to the public. The total amount collected each month would be divided equally among all legal adult residents, with half shares for children. For example, when the tax reaches $115 per ton of CO2, every family of four would receive a rebate of $8000 to $9000 per year. All economists seem to agree that tax-and-rebate is the simplest, cheapest, and most effective plan. Nevertheless, I disagree with Hansen's opposition to cap-and-trade, because it's the only plan that's been widely accepted, and most Americans will not support a carbon tax. Environmentalists should support both cap-and-trade and tax-and-rebate.
Check out Hansen's web site at www.columbia.edu/~jeh1/. Under "recent presentations," see his 10 December 2009 video interview on David Letterman's Late Night show. If you don't see this listed, try clicking on "older presentations."
Whether or not you agree with Hansen, do read his book.
Dept of Physics
Univ. of Arkansas, Fayetteville
These contributions haven not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the views of APS.