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Review of Hansen et al.: Global Warming in the Twenty-First Century: An Alternative Scenario

As the scientific process takes its normal course of examining, assessing, and refining new scientific findings, there is likely to be an ongoing debate among scientists over the validity of the new model results and calculations. UCS will follow this debate as it unfolds and keep you informed of important new developments. In the meantime, however, the public discussion of a scientific issue in flux can result in premature judgments of findings and implications. Hence, in a first effort to assess Hansen et al.'s paper, UCS solicited peer-reviews of the paper from a number of climate change experts.

These first reactions from within the expert community call for a very careful review of Hansen et al.'s claims, findings, and policy suggestions before jumping to any conclusions. Atmospheric scientists Richard Gammon (University of Washington) and Don Wuebbles (University of Illinois), for example, emphasize the challenges in comparing warming and cooling effects at the global scale. They underline Hansen et al.'s own recognition of significant uncertainties in analyzing past and projecting future trends of aerosol and other GHG emission trends, suggesting that it is difficult to build a strong optimistic scenario on this uncertain basis.

Drs. Wuebbles and Gammon also highlight the difficulties in adding up climate forcings over time and space, given the widely differing properties of different GHGs - such as geographic distribution, timing of forcing over the last 150 years, and atmospheric lifetimes.

During a Science Friday live radio discussion on the Hansen et al article, Dr. Steve Schneider (Stanford) argued that he could find "nothing surprising" in the paper, but rather viewed it as a "very nice synthesis of a range of information that's been out there." That interpretation was echoed by IPCC Working Group II Co-Chair Dr. James McCarthy (Harvard) in pointing out that the paper's policy recommendations are entirely consistent with, and not really "alternatives" to, the provisions of the 1997 Kyoto Protocol.

In part, the alleged dichotomy between Hansen et al.'s and other GHG emission reduction strategies emerges from a key factual error or imprecision early in the paper, when the authors claim that the Kyoto Protocol calls for "CO2 reductions to 95% of 1990 levels by 2012." The Kyoto Protocol calls for GREENHOUSE GAS emission reductions, and explicitly includes a range of non-CO2 GHGs, largely due to pressure from US negotiators (and supported by UCS and SSI scientists at the time). Energy and climate change expert Dr. John Holdren (Harvard) thus correctly stressed in a New York Times article that reduction of CO2 and other non-CO2 greenhouse gases is not an "either/or but a both/and problem."

Policy Options Suggested In The "Alternative Strategy"  

While the scientific assessment continues, Hansen et al.'s paper has already produced some political fall-out - mostly through the "spin" climate contrarians have put on the news reports about this paper and the resulting confusion in the larger public. There is some potential for further, possibly more serious negative political effects in months to come. UCS is watching these developments carefully in the time leading up to the next round of international negotiations in The Hague (Netherlands, November 2000), and beyond.

Below we summarize Hansen et al.'s policy suggestion. Essentially, their "alternative scenario" is significantly more ambitious, but not fundamentally different from, other approaches currently discussed in research or policymaking circles. Rather, the suggested strategies and emission reduction options differ from current approaches by the degree of emphasis and timing, with a primary focus on air pollution in the near-term. The researchers suggest the following strategy for the next 25 years (2000-2025):

1. focus primarily on reducing emissions of non-CO2 emissions, achieving
   
   
   • CH4 emissions reductions through improvements in agricultural practices, closing of leaks in gas pipelines, and capturing from mining, landfills, and petroleum exploration operations;
     
     
   • CFC and other fluorocarbon compound reductions through strong enforcement and quicker and broader implementation of the provisions of the Montreal Protocol;
     
     
   • Smog (tropospheric O3) reductions through reductions of its pre-cursors (volatile organic compounds and nitrogen oxides) (which ultimately depend on reductions in fossil fuel burning in transportation, power production, and industrial processes);
   
   
2. achieve CO2 reductions (including black carbon or soot) through readily available technologies that improve energy efficiency and through decarbonization of energy sources (e.g., fuel switching from coal and oil to natural gas);
   
   
3. eliminate barriers that discourage such developments and market shifts; and
   
   
4. invest now in R&D to foster the development of low-carbon or carbon-free energy systems for the future.

In the long-term (2025-2050), they suggest to significantly reduce CO2 emissions through a greater use of energy sources that produce little or no CO2, building on the technologies developed through R&D until then.

UCS agrees with Hansen et al. on a number of points in their suggested strategy, including

• the multiple-gases approach they suggest, which is entirely consistent with the Kyoto Protocol;
  
  
• the desirability of reducing air pollution to reduce urban smog, human health, and ecological impacts;
  
  
• the necessity of strictly enforcing and implementing the Montreal Protocol; and
  
  
• the employment and development of cleaner, more efficient technologies in all aspects of energy production, use, and transportation.

The suggested "alternative scenario" calls for significant international commitments in order to implement its ambitious suggestions. While Hansen et al. claim that their approach offers a frame that would give developed and developing countries more grounds for cooperation than conflict, it is not at all clear that it is any less challenging to achieve than the ones currently under most active consideration. In particular, the strong focus on methane -- which in part stems from rice production and ruminants -- could make collaboration with developing, especially Asian, countries more challenging. While developed countries may quickly welcome the suggested view that we have more time to address fossil fuel issues, developing countries may react against what may be seen as yet another evasion of the developed world's responsibility.

It is also important to note that the author team did not undertake an economic cost-benefit analysis or assess the technical or political feasibility of implementation and monitoring (important for accountability in international treaties) of their optimistic policy options. On the other hand, the author team seems unduly convinced that reducing fossil fuel emissions would be economically wrenching to the United States. Based on analyses undertaken by UCS and other organizations, however, we do know that many CO2 reduction strategies can be implemented today in a cost-effective manner and with multiple co-benefits.

In addition to questions about the practicality of Hansen et al.'s suggestions, UCS is concerned about the potential misuse of the paper's findings by those who stand to defend the status quo, and about the implied "either-or" approach to addressing the climate problem. While the paper provides useful arguments for stronger domestic clean air legislation and for more R&D to develop cleaner, more efficient transportation and energy technologies, UCS continues to support a properly designed Kyoto Protocol that calls for reductions in all GHG emissions through source reductions and employment of sinks.

Misuse by Climate Contrarians 

The article has already received press coverage in major national papers, is causing a significant stir among climate contrarians, and is likely to fuel greater confusion about global warming among the wider public. Climate skeptics, using their usual tactics of selective quoting and misleading interpretation of the findings, claim that Hansen, the scientist who first put global warming on the political agenda before the US Congress in 1988, now admits that CO2 is not the major culprit.

Making Hansen the finally-converted champion of their cause, they also highlight the article's more optimistic stance that global warming can be prevented 'without any economically wrenching actions' because "of the growing realization that too much emphasis has been placed on the effects of burning fossil fuels."

UCS anticipates that climate contrarians will continue to draw on this article, and on the mis-portrayal of its lead author, at a variety of upcoming opportunities -- including, for example, the release of the final National Assessment Synthesis report, the next round of international negotiations of the climate treaty (COP-6) in The Hague, and the release of the IPCC's Third Assessment Report in spring 2001.

Talking Points To Respond To Contrarians 
Claims as to the unimportance of CO2 in causing global warming, the benign impacts of fossil fuel burning, and the alleged feasibility of achieving GHG reductions without the Kyoto Protocol are likely to resurface over the coming months.

We suggest that scientists be alert to such claims in the media, in public discussions, and in policy forums, and be prepared to counteract and proactively avert such false claims by pointing to important messages actually reaffirmed in Hansen et al.'s article. These messages are quite contrary to what climate contrarians portray as the messages of the article.

• Global warming is real, underway, and likely to accelerate if no action is taken to slow the emissions of GHGs.
  
• Recent climate change is at least in part caused by human action.
  
• In order to avert dramatic climate change, these human causes need to and can be addressed immediately.
  

• The Kyoto Protocol, negotiated in 1997, covers both CO2 and non-CO2 GHGs, and thus provides an important policy mechanism through which all GHG emission reductions can be addressed.
  
• A variety of flexibility mechanisms are included in the Kyoto Protocol in order to allow for the most efficient and effective ways to address the climate problem. If designed properly, developed and developing countries can make use of these mechanisms to reduce global GHG emissions.
  
• Reducing CO2 emissions is both feasible and affordable today. Both governmental and independent studies show that adopting practices and technologies that would reduce US emissions of carbon dioxide -- like energy efficiency, renewable energy sources, and clean transportation -- would save billions of dollars and generate hundreds of thousands of jobs. Efficiency and renewable energy sources reduce both -- emissions of CO2 and air pollution.
  
• Climate change and air pollution have a common source: fossil fuel burning. Ultimately, there is no way around reducing our use of fossil fuels if we are serious about limiting global warming.
  
• The Montreal Protocol of 1988, which focuses on the reduction and elimination of stratospheric ozone-depleting substances (some of which are also enormously powerful GHGs), should be more strongly and swiftly implemented by all countries.

1. The original research article by Hansen et al.: 
   James Hansen, Makiko Sato, Reto Ruedy, Andrew Lacis, and Valdar Oinas. 2000. Global warming in the twenty-first century: An alternative scenario. Proceedings of the National Academy of Science (PNAS), published August 15, 2000, 10.1073/pnas.170278997.

   Abstract:  
   A common view is that the current global warming rate will continue or accelerate. But we argue that rapid warming in recent decades has been driven mainly by non-CO2 greenhouse gases (GHGs), such as chloro-fluorocarbons, CH4, and N2O, not by the products of fossil fuel burning, CO2 and aerosols, the positive and negative climate forcings of which are partially offsetting. The growth rate of non-CO2 GHGs has declined in the past decade. 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. Such a focus on air pollution has practical benefits that unite the interests of developed and developing countries. However, assessment of ongoing and future climate change requires composition-specific long-term global monitoring of aerosol properties.

   The full text can only be accessed with a subscription to PNAS. Alternatively, contact Eleni Palmos (epalmos@giss.nasa.gov) to request a copy.

2. Abbreviated version of the article: 
   The research article is also available in an abbreviated version on the NASA web site at http://www.giss.nasa.gov by clicking on "Spotlight." This article is shorter and not fully referenced, but the basic argument is fully captured.

3. Science Friday Discussion with Jim Hansen and other scientists 
   National Public Radio's Science Friday show on August 25, 2000 focused on two recent global warming related issues: the uncommon occurrence of open water at the North Pole, and on Dr. Hansen's controversial article. The discussion can be heard by accessing the archives at the NPR Science Friday web site at http://www.sciencefriday.com (streaming RealAudio accessible with the appropriate web technology).
   

September 2000

This Information Update was prepared by UCS staff scientist Susi Moser and reviewed by Peter Frumhoff, Richard Gammon, Michael Oppenheimer, and Don Wuebbles.