Shocker: The Hansen/GISS team paper that says: "we argue that rapid warming in recent decades has been driven mainly by non-CO2 greenhouse gases"

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No, this isn’t a joke, it isn’t a fake document, and it isn’t a misinterpretation. It is a paper published by Dr. James Hansen (and the GISS team) in PNAS (Proceedings of the National Academy of Sciences). In the paper (published in 2000, but long since buried) they make these two bold statements (emphasis mine):

..we argue that rapid warming in recent decades has been driven mainly by non-CO₂ greenhouse gases (GHGs), such as chlorofluorocarbons, CH₄, and N₂O, not by the products of fossil fuel burning, CO₂ and aerosols..

If sources of CH₄ and O₃ precursors were reduced in the future, the change in climate forcing by non-CO₂ GHGs in the next 50 years could be near zero. Combined with a reduction of black carbon emissions and plausible success in slowing CO₂ emissions, this reduction of non-CO₂ GHGs could lead to a decline in the rate of global warming, reducing the danger of dramatic climate change.

Basically what Hansen is saying is that we should focus on air pollution, and some CO₂ reduction, but not exclusively on CO₂ alone. This is of course at odds with his famous 350ppm CO₂ “safe level” upon which the activist organization 350.org is formed, along with many other pronouncements made by Hansen. I post the abstract and excerpts from the PNAS paper below. Be sure to note the item in red. – Anthony

Global warming in the twenty-first century: An alternative scenario

The global surface temperature has increased by about 0.5°C since 1975 (1, 2), a burst of warming that has taken the global temperature to its highest level in the past millennium (3). There is a growing consensus (4) that the warming is at least in part a consequence of increasing anthropogenic greenhouse gases (GHGs).

GHGs cause a global climate forcing, i.e., an imposed perturbation of the Earth’s energy balance with space (5). There are many competing natural and anthropogenic climate forcings, but increasing GHGs are estimated to be the largest forcing and to result in a net positive forcing, especially during the past few decades (4, 6). Evidence supporting this interpretation is provided by observed heat storage in the ocean (7), which is positive and of the magnitude of the energy imbalance estimated from climate forcings for recent decades (8).

The Intergovernmental Panel on Climate Change (IPCC) (4) has considered a range of scenarios for future GHGs, which is further expanded in its Special Report on Emissions Scenarios (9). Yet global warming simulations have focused on “business as usual” scenarios with rapidly increasing GHGs. These scenarios yield a steep, relentless increase in global temperature throughout the twenty-first century (4, 10) with warming of several degrees Celsius by 2100, if climate sensitivity is 2–4°C for doubled CO₂, as climate models suggest (4, 11–13). These figures can give the impression that curtailment of global warming is almost hopeless. The 1997 Kyoto Protocol, which calls for industrialized nations to reduce their CO₂ emissions to 95% of 1990 levels by 2012 (14), is itself considered a difficult target to achieve. Yet the climate simulations lead to the conclusion that the Kyoto reductions will have little effect in the twenty-first century (15), and “30 Kyotos” may be needed to reduce warming to an acceptable level (16).

We suggest equal emphasis on an alternative, more optimistic, scenario. This scenario focuses on reducing non-CO₂ GHGs and black carbon during the next 50 years. Our estimates of global climate forcings indicate that it is the non-CO₂ GHGs that have caused most observed global warming. This interpretation does not alter the desirability of limiting CO₂ emissions, because the future balance of forcings is likely to shift toward dominance of CO₂ over aerosols. However, we suggest that it is more practical to slow global warming than is sometimes assumed.

…

Climate forcing by CO₂ is the largest forcing, but it does not dwarf the others (Fig. 1). Forcing by CH₄ (0.7 W/m²) is half as large as that of CO₂, and the total forcing by non-CO₂ GHGs (1.4 W/m²) equals that of CO₂. Moreover, in comparing forcings due to different activities, we must note that the fossil fuels producing most of the CO₂ are also the main source of aerosols, especially sulfates, black carbon, and organic aerosols (4, 23). Fossil fuels contribute only a minor part of the non-CO₂ GHG growth via emissions that are not essential to energy production.

Aerosols cause a climate forcing directly by reflecting sunlight and indirectly by modifying cloud properties. The indirect effect includes increased cloud brightness, as aerosols lead to a larger number and smaller size of cloud droplets (24), and increased cloud cover, as smaller droplets inhibit rainfall and increase cloud lifetime (25). Absorbing aerosols cause a semidirect forcing by heating the atmosphere, thus reducing large-scale cloud cover (5). In addition, absorbing aerosols within cloud drops and in interstitial air decrease cloud brightness.

Forcing by atmospheric aerosols is uncertain, but research of the past decade indicates that it is substantial (4, 26–28). The aerosol forcing that we estimate (6) has the same magnitude (1.4 W/m²) but a sign that is opposite that of the CO₂ forcing. Fossil fuel use is the main source of both CO₂ and aerosols, with land conversion and biomass burning also contributing to both forcings. Although fossil fuels contribute to growth of some of the other GHGs, it follows that the net global climate forcing due to processes that produced CO₂ in the past century probably is much less than 1.4 W/m². This partial offsetting of aerosol and greenhouse forcings has been discussed (29–31). Offsetting of global mean forcings does not imply that climate effects are negligible.

A corollary following from Fig. 1 is that climate forcing by non-CO₂ GHGs (1.4 W/m²) is nearly equal to the net value of all known forcings for the period 1850–2000 (1.6 W/m²). Thus, assuming only that our estimates are approximately correct, we assert that the processes producing the non-CO₂ GHGs have been the primary drive for climate change in the past century.

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An Alternative Scenario

Let us propose a climate forcing scenario for the next 50 years that adds little forcing (Fig. 5), less than or about 1 W/m², and then ask whether the elements of the scenario are plausible. The next 50 years is the most difficult time to affect CO₂ emissions, because of the inertia of global energy systems, as evidenced by Fig. 4. The essence of the strategy is to halt and even reverse the growth of non-CO₂ GHGs and to reduce black carbon emissions. Such a strategy would mitigate an inevitable, even if slowing, growth of CO₂. By midcentury improved energy efficiency and advanced technologies, perhaps including hydrogen-powered fuel cells, should allow policy options with reduced reliance on fossil fuels and, if necessary, CO₂ sequestration.

…

Summary

Business-as-usual scenarios provide a useful warning about the potential for human-made climate change. Our analysis of climate forcings suggests, as a strategy to slow global warming, an alternative scenario focused on reducing non-CO₂ GHGs and black carbon (soot) aerosols. Investments in technology to improve energy efficiency and develop nonfossil energy sources are also needed to slow the growth of CO₂ emissions and expand future policy options.

A key feature of this strategy is its focus on air pollution, especially aerosols and tropospheric ozone, which have human health and ecological impacts. If the World Bank were to support investments in modern technology and air quality control in India and China, for example, the reductions in tropospheric ozone and black carbon would not only improve local health and agricultural productivity but also benefit global climate and air quality.

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So the strategy should be to focus on air pollution, not CO₂

Think I made all this up? Read the paper at PNAS here.

(Big hat tip to WUWT reader Nick.)

Backup link in case it disappears like so many other things is here.

Now for the other shocker. This paper was published in the year 2000. So what happened to Hansen since then? He’s totally lost the plot from then, which from my perspective, seems reasonable, and one I could get behind.

Instead we have pronouncements like this:

2008 from a non peer reviewed paper published on Hansen’s personal website –

If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm.

2009 in a article in the UK Guardian. Hansen says –

“The trains carrying coal to power plants are death trains. Coal-fired power plants are factories of death.”

And this:

Clearly, if we burn all fossil fuels, we will destroy the planet we know. Carbon dioxide would increase to 500 ppm or more.

May 10th, 2012 Game over on Climate, New York Times op-ed –

Canada’s tar sands, deposits of sand saturated with bitumen, contain twice the amount of carbon dioxide emitted by global oil use in our entire history. If we were to fully exploit this new oil source, and continue to burn our conventional oil, gas and coal supplies, concentrations of carbon dioxide in the atmosphere eventually would reach levels higher than in the Pliocene era, more than 2.5 million years ago, when sea level was at least 50 feet higher than it is now. That level of heat-trapping gases would assure that the disintegration of the ice sheets would accelerate out of control. Sea levels would rise and destroy coastal cities. Global temperatures would become intolerable. Twenty to 50 percent of the planet’s species would be driven to extinction. Civilization would be at risk.

No mention of the other GHG’s, carbon soot, and aersols in that op-ed.

Clearly he seems to have abandoned the idea that seemed so reasonable and workable in his 2000 paper for the idea that CO₂ reduction and removal of fossil fuels from the energy equation is the only possible scenario.

I think he was affected by the money, power, and hoopla surrounding Al Gore’s success with the alarming fabrications in An Inconvenient Truth as well as the hoopla and fame associated with the Nobel prize for the 2007 IPCC report. (Added: it is important to note that all of this backpedaling occurred after Hansen’s 1988 Senate testimony  where he and sponsoring Senator Tim Wirth were so sure of the science blaming CO2 saying “that it was 99 percent certain that the warming trend was not a natural variation but was caused by a buildup of carbon dioxide and other artificial gases in the atmosphere.” that they had a thermostat malfunction in the hearing room, it came after Rio Earth Summit 1992, and the subsequent Kyoto protocol. Now Hansen has flip-flopped again with more recent CO2 pronouncements.)

When you go from scientist to arrested activist, the reasonable path just doesn’t get people stirred up. It seems Dr. Hansen has gone over to the dark side of the forcings.

Ask Dr. Hansen’s acolyte Bill McKibben how well reasonable approaches work in all the wailing hippie protests he organizes. You can connect the dots.

UPDATE: graph added, thanks to Joshua Halpern of Howard University who says:

Eli Rabett on 2012/06/03 at 10:42 am says:

That was 2000, this is 2012. As that paper said, the alternative strategy would buy time, not solve the problem. We didn’t follow it and are now running out of time. Twelve years is a while.

REPLY: Yes as noted clearly in red, that was 2000. Twelve years without warming is a while.

http://www.woodfortrees.org/plot/hadcrut3vgl/from:2000/plot/hadcrut3vgl/from:2000/trend

What’s the rush? Meanwhile:

NOAA: Carbon dioxide levels reach milestone at Arctic sites

NOAA cooperative measurements in remote, northern sites hit greenhouse gas milestone in April

– Anthony

UPDATE2: It gets stranger. WUWT reader Jimbo points out in comments, that Hansen wrote a paper blaming soot for the Arctic ice melt, calling it twice as effective as CO2.

Soot climate forcing via snow and ice albedos  James Hansen*  †‡  and Larissa Nazarenko*  †

Plausible estimates for the effect of soot on snow and ice albedos (1.5% in the Arctic and 3% in Northern Hemisphere land areas) yield a climate forcing of
0.3 W
m2 in the Northern Hemisphere. The ‘‘efficacy’’ of this forcing is
2, i.e., for a given forcing it is twice as effective as CO2 in altering global surface air temperature.

Global Warming. Soot snow
ice albedo climate forcing is not included in Intergovernmental Panel on Climate Change evaluations.  This forcing is unusually effective, causing twice as much global  warming as a CO2 forcing of the same magnitude. This high efficacy  is a straight-forward consequence of positive albedo feedbacks and  atmospheric stability at high latitudes.  Our estimate for the mean soot effect on spectrally integrated  albedos in the Arctic (1.5%) and Northern Hemisphere land areas  (3%) yields a Northern Hemisphere forcing of 0.3 W
m2  or an  effective hemispheric forcing of 0.6 W
m2  . The calculated global  warming in an 1880–2000 simulation is about one quarter of  observed global warming

Source: pubs.giss.nasa.gov/docs/2004/2004_Hansen_Nazarenko.pdf