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Hansen: Earth’s climate nears the tipping point

June 2008    Updated in my post Should scientists attack the cap and trade bill?

Like many who graze news stories about ways the United States might respond to global warming, I thought Congress would do well to pass any of the proposed bills to cap US emissions of carbon dioxide (C02), the principal greenhouse gas. I assumed that neither the specific level of reduction nor the exact timing mattered—so long as Congress acted soon.

But on June 23, I heard NASA scientist James E. Hansen argue that we’re approaching a point where planetary impacts will be irreversible.

The US “body politic” is aiming for too high a level of emissions, he said in a speech to a packed ballroom at the National Press Club, at a luncheon arranged by the WorldWatch Institute.  (1) If the United States does not lower emissions more drastically very soon—for our own sake and to get other nations on board— Earth will pass a tipping point, Hansen warned.

The leading cap-and-trade bills would have Washington set a “cap” on total US emissions or carbon dioxide equivalent (ccmte). Uncle Sam would sell or auction “permits” to those who emit this poison, such as utilities; the total of all allowances would equal the cap. Afterward, year  by year, fewer total emissions would be allowed, forcing permit holders to cut their emissions further or trade with others who had a surplus. As fewer total emissions were allowed, permits would have greater market value.  

But Hansen contends that current bills will not lower US emissions enough. Assuming that other nations follow our lead, the US legislation will allow global temperatures to rise 2° C (or 3.6° F).  Hansen says this rise “is a recipe for global disaster, not salvation.” And “frank assessment of scientific data” yields conclusions “shocking to the body politic.” 

Prophet of human-caused warming

Hansen was right back on June 23, 1988, when he testified before the Senate Energy Committee as a little-known NASA official. His message—that global warming was real and caused by humans—was so forceful and well-supported that it made the New York Times. (2)

Twenty years later, the well-attended lunch, followed by another appearance on Capitol Hill, was a tribute to the credibility Hansen has amassed.  He has continued to warn about global warming while serving as director of NASA’s Goddard Institute for Space Studies—even as the Bush administration muzzled other government scientists’ concerns on climate change. Columbia University hosts an archive of Hansen’s talks and his professional publications.

Since Hansen testified in 1988, Washington rejected the 1997 Kyoto Protocol whereby other industrial nations pledged to lower emissions and has done little to curb US emissions any other way.  Twenty years is a long time for the United States to let emissions go on climbing—we’re the source of one-fourth of humanity’s total greenhouse gas emissions, the vast majority of which is carbon dioxide.

Between 2001, when President Bush took office, and 2007, total US greenhouse gas emissions rose 4.7 percent (to 7,727.4 mmtce), according to the Energy Information Administration of the Department of Energy. (3) The EIA 2007 forecast put US greenhouse gas emissions a whopping 16.7 percent higher than in 1990.

Because of inaction by the Unites States and other countries, carbon dioxide concentrations in the Earth’s atmosphere are the highest in 100,000 years, at 387 parts per million of volume (ppmv)—and rising by 2 ppmv per year.

“A safe level” is 350 ppmv or less -

Earth is passing 387 ppmv—yet Hansen declares that “a safe level is at 350 ppmv and it may be less.” To stabilize CO2 at this level would take a century of reducing emissions growth already wafting upward from cars, power plants, industry and agriculture. But even if everyone stopped emitting carbon dioxide tomorrow, concentrations would go on rising because of what’s in the pipeline. Temperatures would also rise, but more slowly.

Another grim fact: Atmospheric CO2 takes thousands of years to degrade naturally, unlike most other pollution. So even if humanity leveled off emissions, it must bring off net absorption of CO2 for decades in order for a safe balance known as “stabilization” to kick in.

But Congress shoots for 450, 550 ppmv or higher

We can’t get to 350 ppmv via the leading climate bills before Congress [in 2008, when this article was written. It’s true for H.R. 2454 the House passed in June 2009. See my June 2008 post: "Should scientists attack the cap and trade bill?"] A November 2007 analysis by the Union of Concerned Scientists found that only two of the bills aim for a world stabilized at 450 ppmv or about 2° C or 2 to 4°F warmer on average. (4) Five other bills would leave the world near 550 ppmv of ccmte, or warmer by 1.5-3° C or 2.7-5° F. These include S. 280 cosponsored by presidential contender John McCain. And UCS notes that even if we got a global atmosphere with 450 ppmv of carbon equivalent, there would be a 50-50 chance that average global temperature will rise by more than 2° C.

UCS plotted the pathways of emissions of carbon dioxide equivalent in seven bills before the 110th Congress. (The authors assumed that other nations would begin lowering emissions, with the developed nations peaking in 2010 and developing nations in 2020.) Most bills require light reductions at first and put off big cuts for 30 to 40 years.  One of the report’s authors, Peter C. Frumhoff, Director of Science and Policy and Chief Scientist at UCS, told me: “You need best-case assumptions to get to 450 [ccmte]. Limiting temperature rise to 2º C is incredibly ambitious.”

Since the UCS report was compiled, the Lieberman-Warner bill, S. 2191, got to the Senate floor but failed in a vote of 48 to 36 on June 6. Pro cap-and-trade activists nonetheless called this progress. (5)

Fig. 1 Emissions Pathways Per Bills in Congress  (UCS 2007) (4)

(Permission requested)

All these bills were drafted some years back–eons in our fast-changing knowledge of impacts on the planet. Back then many scientists said humanity had time to let emissions rise on a “business as usual” slope before we needed to transform the power, transport, industrial and agriculture sectors to low/no greenhouse gas-emitting systems. Charts often showed the United States and the world stabilizing emissions in the 22nd century at 550 ppmv or 650 ppmv (which raise global temperature by 1.7-3.2°C or 3-5.76°F.) The debate was over when concentrations would double from pre-industrial levels and reach 550 ppmv. (6)

Even the Nobel-winning International Panel on Climate Change (IPCC), which compiles the consensus of scientists from 130 countries, didn’t say 450 ppmv or 550 ppmv was too high in its Fourth Assessment Synthesis Report released November 2008. (7)

So why should we believe Hansen’s promotion of 350 as la cause planetaire? He’s got followers: End of Nature author Bill McKibben has founded a new group,, whose war cry is “350 or Bust.”  But mainstream groups such as the Environmental Defense Fund (EDF) and the Natural Resources Defense Council (NRDC) supported the Lieberman-Warner bill.  

What on Earth has changed?

Fragile Earth is suffering from even the present warming brought on by our climbing emissions. A few years back, scientists correlated gradual warming with gradual effects. But now some alarming “nonlinear” effects are kicking in. These types of responses are shown in a chart below, adapted from “Global Warming: A Very Short Introduction,” a nifty pocket-sized primer by Mark Maslin. (8)

Fig. 2 Impacts of gradual warming on Earth systems per Mark Maslin

(Permission requested)

Hansen says, “Amplifying feedbacks spur large rapid changes.”  The UCS’ Frumhoff says:, “The planet is moving toward greater risk at lower temperatures.” Here are some examples of the changes.

• The sea ice that covers the Arctic Ocean melts each summer, reaching its minimal area in fall before winter refreezing expands its extent. But Arctic sea ice recently has been one-third of its average extent since measurements began in 1979. In September 2007, Arctic sea ice shrank to a record minimum. The floating ice gets a double whammy. As more dark ocean surface area is exposed, it is warmed by the sun. The warmer water shrinks the ice from below, while the sun’s direct heat melts it from above. Scientists now predict the Arctic could be ice-free in the summer as early as 2013. (9)

• Ten or twenty years ago, few thought the West Antarctic Ice Sheet (WAIS) could collapse anytime soon. Now there’s evidence of instability under the WAIS, which holds one-tenth of world’s ice, and under the Greenland ice sheet, which holds almost one-tenth of the world’s ice.

• Even before the IPCC’s Fourth Assessment Report was released, experts said in Science and the New York Times that the report’s forecast of sea level rise was too low. (10) 

Sea level rise could be speeding up. If emissions continue on their present path, Hansen says. “Sea level rise of at least two meters is likely this century. Hundreds of millions of people would become refugees. No stable shoreline would be reestablished in any time frame that humanity can conceive.”

Hansen concludes, “Climate is nearing dangerous tipping points.  Elements of a ‘perfect storm,’ a global cataclysm, are assembled.” Without drastic US and global action, “the planet upon which civilization developed” is at stake.

Does the IPCC disagree? Though its latest report did not spell out these alarms, participating scientists explained the report did not include new findings, such as evidence of rising emissions from melting permafrost. Also the IPCC’s mandate forbids inclusion of speculative impacts. So a faster-melting West Antarctica and Greenland was not factored into its forecasts, for example. (11) 

The head of the IPCC, Rajendra Pachauri, admits that “much stronger trends in climate change” had been observed since the December 2005 cutoff date for published papers the panel’s hundreds of experts could consider. Pachauri adds, “If there’s no action before 2012, that’s too late. What we do in the next two to three years will determine our future. This is the defining moment.” (12)

Political choices ahead

Should those who want US action on global warming support Hansen, McKibben, and the 350-or-bust crowd? Is it quixotic to work now towards such drastic US emissions cuts? One argument for  withholding support for Lieberman-Warner, or any current cap-and-trade bill, is that they’re riddled with loopholes for carbon-emitting big utilities.

On the other hand, activists could go along with mainstream environmental groups and support even John McCain’s S. 280. He’s the leading Republican pushing for US action. Come January he may be president. Why do mainstream groups like the Environmental Defense Fund support these flawed bills? Blogger-activist Ken Ward interviewed EDF President Fred Krupp for the online news service Grist, published June 19, 2008. (13) Ward got Krupp to admit that the US should shoot for drastically lower emissions by 2050 than in Lieberman-Warner bill. “But that’s not a live-or-die issue for us because Congress is going to amend this goal 10 times between now and 2050,” Krupp said.

Really? Can anyone believe that, once cap-and-trade emerges from the slings and arrows of utility lobbyists, some deus ex machina will ratchet down the total US cap on emissions again and again? More likely Krupp’s “adjustments” will come too little, too late, and too bad for melting ice caps and millions of people along swamped coasts.

Hansen ardently opposes cap-and-trade. Only a tax on all carbon-emitting fuels at their source—coal, oil, gas, and others—will raise prices enough to stop their use and keep coal in the ground forever. The revenue from this tax should be entirely passed through to taxpayers’ bank accounts, known as tax and 100 percent dividend so they gain funds during our nation’s massive, long-term shift in fuels. (14)

Hansen calculates that, if humanity could phase out existing coal plants and bar new ones by 2030 and change the energy defaults in agriculture and other sectors, it has a fighting chance to get the planet back to carbon dioxide concentrations of 350 ppmv. He was planning to go to Great Britain, to testify as a private citizen in defense of protesters known as the Kingsnorth Six, arrested while trying to block the first coal plant that may be built in Great Britain, in 30 years. (15)

Speaking to the reverent crowd at the press club, Hansen was moved to express moral urgency: “CEOs of fossil energy companies…are aware of long-term consequences of continued business as usual. In my opinion, these CEOs should be tried for high crimes against humanity and nature.”

Hansen even compares the trains carrying coal to power plants to the trains that ferried victims to Holocaust death camps. “Is it a God-given fact that all fossil fuels will be burned?” he asks. Do we as individuals have “free will” to do anything about the path Earth is on? 

Hansen’s moralizing made me wonder: When is it right to fling ourselves on the track to stop a train of calamity? Should citizens sacrifice the not-so-great goal of 450-550 ppmv in current bills to lobby for an airtight cap with a carbon tax—and with political chances now near zero?

The science of climate change is moving as fast as a whizzing ice sheet.  The challenge to the US political system is whether it can adjust nimbly enough to get in step with shifting data and forecasts. “There is very little time left,” Hansen predicts. A “path yielding energy independence and a healthier environment is, barely, still possible.”

© Deborah Shapley, June 2008   

Updated in June 2009 post "Should scientists attack the cap and trade bill?"


(1) James E. Hansen, “Global Warming Twenty Years Later: Tipping Points Near” at The WorldWatch Institute’s press release is at Speech based on paper at Supporting material at

(2) Hansen 1988 testimony in New York Times, June 24, 1988 at

(3) Chart “Greenhouse Gas Emissions in the United States 2007,” in Emissions of Greenhouse Gases Report DOE/EIA-0573 (2007), Energy Information Administration, DOE, shown at

(4) “How to Avoid Dangerous Climate Change,” 2007 Union of Concerned Scientists’ report on emissions targets at

The study analyzed these bills, known by their leading sponsors: Waxman (H.R. 1590);Sanders-Boxer (S. 309); Oliver-Gilchrist (H.R. 620); Bingaman-Specter (S. 1766); Kerry-Snowe (S. 485); Lieberman-Warner discussion draft (became S. 2191);Lieberman-McCain (S. 280).

(5) Details of the Lieberman-Warner bill per Wikipedia are here. A Pew Center summary is here with chart linked from this page. Claims of progress at

(6) See for example the IPCC Third Assessment Report (AR3) released October 2001 at

(7) IPCC Fourth Assessment Report (AR 4) released November 2007 at The New York Times November 17, 2007 at .

(8) Mark Maslin, “Global Warming: A Very Short Introduction,” a nifty pocket-sized primer.  Oxford University Press, 2004. Chart copyright Mark Maslin. Permission requested.

(9) Ice-free Arctic prediction and reference TK

(10) Science ref TK. New York Times, February 2, 2007 at

Sea level rise faster than predicted at Science (Feb 2 2007) and New York Times dot earth June 19, 2008. (11) New Scientist “What IPCC didn’t tell us.”

 (12) Pachauri quoted Nov 17, 2007 Also

(13) Grist interview of Fred Krupp by Ken Ward June 19 at

(14) Tax and 100% dividend spelled out in Peter Barnes, Climate Solutions, A Citizen’s Guide, Chelsea Green Publishing, White River Junction, Vermont (2008).

(15) Hansen’s testimony in Great Britain Sept 18, 2008 is at


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