如果你关心全球变暖，那么一定不会陌生于媒体上层出不穷的应对招数，其中最抢眼球的一类可以成为“地球工程”（Geoengineering）：从在大洋上修建巨型导温管阵，将洋面热量引入洋底，到播撒含铁矿物质促进浮游生物生长，最让人惊叹的还是在平流层（大约距地面10千米以上的高空）大量的播撒二氧化硫反射太阳光。真是敢下五洋捉鳖，敢上九天揽月，没有做不到，只有想不到。难得有个拯救世界的机会，谁不想大显身手？这些东东，虽然没有具体的解释，也经不起仔细的推敲，但是因为抢眼球，适宜传播，所以一直会在眼前耳边晃悠。到后来，似乎还有一些科学家出来论证自己的方法的合理性，并在利益集团（主要是石油公司）的支持下，试图影响应对全球变暖的政策，淡化人们对于减少二氧化碳排放的注意力。美国气象学会09年7月开了一个关于地球工程对于气候变化作用的研讨会，给这些奇幻招数过了个堂，最后发表了一个学会的声明（原文在下），主要结论是认为地球工程策略不能取代对全球变暖的适应措施，是否能在全球暖化恶化时成为救急的吗啡也还难说，减排二氧化碳还是最务实与迫切的举措。这也给算是给政策圈提了个醒，（目前）除了减排，别无他路。

更多内容请参见 realclimate A biased economic analysis of geoengineering  and Why Levitt and Dubner like geo-engineering and why they are wrong, 顺便再推荐一下realclimate, 作者包括全球气候科学变化方面的资深专家（包括气候期刊的编辑，IPCC科学顾问等等）。如果遇到气候变化方面难断的是非，最好上去搜索一下相关文章，这里有热烈而高水平的讨论。如果国内的编辑记者们还有什么不明白也可以直接写信给作者，他们一般都很乐于帮忙。

Geoengineering the Climate System

A Policy Statement of the American Meteorological Society
(Adopted by the AMS Council on 20 July 2009)

PDF Version

Press Release: PROPOSALS TO GEOENGINEER CLIMATE REQUIRE MORE RESEARCH, CAUTIOUS CONSIDERATION, AND APPROPRIATE RESTRICTIONS (PDF)

Human responsibility for most of the well-documented increase in global average temperatures over the last half century is well established. Further greenhouse gas emissions, particularly of carbon dioxide from the burning of fossil fuels, will almost certainly contribute to additional widespread climate changes that can be expected to cause major negative consequences for most nations¹. 

Three proactive strategies could reduce the risks of climate change: 1) mitigation: reducing emissions; 2) adaptation: moderating climate impacts by increasing our capacity to cope with them; and 3) geoengineering: deliberately manipulating physical, chemical, or biological aspects of the Earth system². This policy statement focuses on large-scale efforts to geoengineer the climate system to counteract the consequences of increasing greenhouse gas emissions.

Geoengineering could lower greenhouse gas concentrations, provide options for reducing specific climate impacts, or offer strategies of last resort if abrupt, catastrophic, or otherwise unacceptable climate-change impacts become unavoidable by other means. However, research to date has not determined whether there are large-scale geoengineering approaches that would produce significant benefits, or whether those benefits would substantially outweigh the detriments. Indeed, geoengineering must be viewed with caution because manipulating the Earth system has considerable potential to trigger adverse and unpredictable consequences.

Geoengineering proposals fall into at least three broad categories: 1) reducing the levels of atmospheric greenhouse gases through large-scale manipulations (e.g., ocean fertilization or afforestation using non-native species); 2) exerting a cooling influence on Earth by reflecting sunlight (e.g., putting reflective particles into the atmosphere, putting mirrors in space, increasing surface reflectivity, or altering the amount or characteristics of clouds); and 3) other large-scale manipulations designed to diminish climate change or its impacts (e.g., constructing vertical pipes in the ocean that would increase downward heat transport).

Geoengineering proposals differ widely in their potential to reduce impacts, create new risks, and redistribute risk among nations. Techniques that remove CO₂ directly from the air would confer global benefits but could also create adverse local impacts. Reflecting sunlight would likely reduce Earth’s average temperature but could also change global circulation patterns with potentially serious consequences such as changing storm tracks and precipitation patterns. As with inadvertent human-induced climate change, the consequences of reflecting sunlight would almost certainly not be the same for all nations and peoples, thus raising legal, ethical, diplomatic, and national security concerns.

Exploration of geoengineering strategies also creates potential risks. The possibility of quick and seemingly inexpensive geoengineering fixes could distract the public and policy makers from critically needed efforts to reduce greenhouse gas emissions and build society’s capacity to deal with unavoidable climate impacts. Developing any new capacity, including geoengineering, requires resources that will possibly be drawn from more productive uses. Geoengineering technologies, once developed, may enable short-sighted and unwise deployment decisions, with potentially serious unforeseen consequences.

Even if reasonably effective and beneficial overall, geoengineering is unlikely to alleviate all of the serious impacts from increasing greenhouse gas emissions. For example, enhancing solar reflection would not diminish the direct effects of elevated CO₂ concentrations such as ocean acidification or changes to the structure and function of biological systems.

Still, the threat of climate change is serious. Mitigation efforts so far have been limited in magnitude, tentative in implementation, and insufficient for slowing climate change enough to avoid potentially serious impacts. Even aggressive mitigation of future emissions cannot avoid dangerous climate changes resulting from past emissions, because elevated atmospheric CO₂ concentrations persist in the atmosphere for a long time. Furthermore, it is unlikely that all of the expected climate-change impacts can be managed through adaptation. Thus, it is prudent to consider geoengineering’s potential benefits, to understand its limitations, and to avoid ill-considered deployment.

Therefore, the American Meteorological Society recommends:

1. Enhanced research on the scientific and technological potential for geoengineering the climate system, including research on intended and unintended environmental responses.
2. Coordinated study of historical, ethical, legal, and social implications of geoengineering that integrates international, interdisciplinary, and intergenerational issues and perspectives and includes lessons from past efforts to modify weather and climate.
3. Development and analysis of policy options to promote transparency and international cooperation in exploring geoengineering options along with restrictions on reckless efforts to manipulate the climate system.

Geoengineering will not substitute for either aggressive mitigation or proactive adaptation, but it could contribute to a comprehensive risk management strategy to slow climate change and alleviate some of its negative impacts. The potential to help society cope with climate change and the risks of adverse consequences imply a need for adequate research, appropriate regulation, and transparent deliberation.                                        

[This statement is considered in force until July 2012 unless superseded by a new statement issued by the AMS Council before this date]

© American Meteorological Society, 45 Beacon Street, Boston, MA 02108-3693

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¹For example, impacts are expected to include further global warming, continued sea level rise, greater rainfall intensity, more serious and pervasive droughts, enhanced heat stress episodes, ocean acidification, and the disruption of many biological systems. These impacts will likely lead to the inundation of coastal areas, severe weather, and the loss of ecosystem services, among other major negative consequences.

²These risk management strategies sometimes overlap and some specific actions are difficult to classify uniquely. To the extent that a geoengineering approach improves society’s capacity to cope with changes in the climate system, it could reasonably be considered adaptation. Similarly, geological carbon sequestration is considered by many to be mitigation even though it requires manipulation of the Earth system