Citizen’s Climate Briefing  - Climate dialogues Seattle
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Citizen’s Climate Briefing - Climate dialogues Seattle


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Citizen’s Climate BriefingTemperature ChartFIG 1: This graph shows both historical and projected between multiple estimates. (Note that temperatures are temperatures for the time period 700 – 2100 AD. The relative to the 1961-1990 average, not to the 1980-1999 projection in orange is for a high emissions scenario, and average used in the rest of the guide.) Source: IPCC 4AR in gold is for a low emissions scenario. The historical data WG I, Chapter 6, Figure 6.10 and Chapter 10, Figure 10.26 is blurred to indicate the uncertainty about the exact (A1F1 and B1 scenarios).values, with darker values indicating better agreement Creative Commons Attribution-Noncommercial-No Derivative Works License 3.0 October 2007 Climate Dialogues / Seattlepage Climate Choices The Citizen’s Climate BriefingIntroductionThis briefing is divided in four sections:1. What’s happening to the climate?2. How serious are the impacts and risks?3. What are the solutions?4. What are our choices?At the outset, it’s helpful to preview the choices that you’ll be considering. These choices do not ask you about technology (for example, should we build more nuclear plants?) or policy (for example, should we have a cap-and-trade system?). They ask a more fundamental question: How should we balance the risks of climate change against the costs of addressing it? The choices are presented as four options:1. Minimize cost: voluntary actions only.2. Gradual steps: modest mandatory ...



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Published 07 December 2011
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Temperature Chart
FIG 1 : This graph shows both historical and projected between multiple estimates. (Note that temperatures are temperatures for the time period 700 – 2100 AD. The relative to the 1961-1990 average, not to the 1980-1999 projection in orange is for a high emissions scenario, and average used in the rest of the guide.) Source: IPCC 4AR in gold is for a low emissions scenario. The historical data WG I, Chapter 6, Figure 6.10 and Chapter 10, Figure 10.26 is blurred to indicate the uncertainty about the exact (A1F1 and B1 scenarios). values, with darker values indicating better agreement
Creative Commons Attribution-Noncommercial-No Derivative Works License 3.0 October 2007 Climate Dialogues / Seattle
Climate Choices The Citizen’s Climate Briefing Introduction This briefing is divided in four sections: 1. What’s happening to the climate? 2. How serious are the impacts and risks? 3. What are the solutions? 4. What are our choices? At the outset, it’s helpful to preview the choices that you’ll be considering. These choices do not ask you about technology (for example, should we build more nuclear plants?) or policy (for example, should we have a cap-and-trade system?). They ask a more fundamental question: How should we balance the risks of climate change against the costs of addressing it? The choices are presented as four options: 1. Minimize cost: voluntary actions only. 2. Gradual steps: modest mandatory action. 3. Larger steps: vigorous mandatory action. 4. Minimize risk: maximum practical response. In order to make an informed choice among these options, we need to understand both the risks of climate change and the costs of different approaches to dealing with it. That is what this briefing aims to provide. It’s important to bear in mind that climate change is an issue with many uncertainties. This briefing points out which facts are relatively certain and where there is significant uncertainty. However, we take as our starting point that there is now enough evidence to warrant action. That is the conclusion of our own National Academy of Sciences, along with the national academies of many other nations.
This briefing has been approved by the Joint Institute for the Study of the Atmosphere and Ocean (Dr. Tom Ackerman, Director) and the University of Washington Program on Climate Change (Dr. LuAnne Thompson, Acting Director).
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page  I. WHAT’S HAPPENING TO THE CLIMATE? During the past century, the Earth warmed by about 1.3° F. Air temperatures rose, the oceans warmed, mountain glaciers melted, and snow cover declined. The average amount of warming was 1.3° F, but it wasn’t distributed evenly; some regions (such as the Arctic) warmed much more, and others warmed less. [I.1]* What has caused this warming? It is now widely agreed that most of the warming is due to heat-trapping gases released by hu -man activities. These gases act like a blanket around the Earth, trapping heat that would normally escape into space. Because this ef -fect is somewhat similar to the warming of air inside a greenhouse, these gases are known as “greenhouse gases” or simply “GHG.” [I.2] The most common greenhouse gases (carbon dioxide, methane, and nitrous oxide) also occur naturally. Along with water vapor, they provide a natural blanket around the Earth that keeps it warmer than if they weren’t there. Without this blanket, the Earth’s aver -age surface temperature would be like the Moon’s, about -4° F, instead of a livable 57° F. Global warming amplifies this natural effect, causing the temperature to rise. [I.3] How much further warming is expected? That depends on how much greenhouse gases we continue to add to the atmosphere. For a range of likely emissions, the Earth is likely to warm an additional 2°F to 12°F by the end of the century. Figure 1 (inside front cover) shows projected temperatures for high and low future emissions, compared to tempera -tures for the past 1,300 years. [I.4] Does this represent a large change for the Earth? Over the past million years, the largest temperature changes (affecting the entire globe) have been swings of about 10°F, when the Earth moved in and out of ice ages. A temperature change of that size implies large
hcnaeg sin ice cover and sea level: durni ght e
last ice age (about 20,000 years ago), Canada and the northern U.S. were under a mile-thick sheet of ice and sea level was about 400 feet lower than today. Thus, at the high end of projected warming, this represents a very large change. Furthermore, although the amount of change is comparable to the ice age cycle, the rate of change is much faster. The Earth takes thousands of years to move in and out of ice ages, but the projected warm -ing is in the next 100 years. That is likely to be an extremely unusual rate of change for the Earth’s climate. [I.5] Understanding the uncertainties There is little scientific uncertainty about whether the Earth has warmed — the evi -dence is now unequivocal. There is also little doubt that humans have increased the amount of greenhouse gases in the atmo -sphere. For example, carbon dioxide has increased about 35% over pre-industrial levels, exceeding by far its levels over the past 650,000 years. [I.6] As to the cause of the warming, there is room for some doubt -- but not much. There is very strong evidence that human GHG emissions are the main cause, and no good alternative explanation. The latest IPCC report (Feb. 2007) expressed “very high confidence” that the warming is human-caused. As is normal in science, there are some scientists who remain unconvinced, and continue to look for other “I am w t explanations. [I.7] orking o create safe and healthy human and How much uncertainty remains on this point? As one measure of scientific consensus, in environmental communities 2005, the national science academies of the for my daughter to grow up in.  United States, China, Russia, Brazil, France, It’s past time that each of us Canada, Germany, India, Italy, Japan, and the make changes in our lives, and Unite -ing thda tK tihneg devoimd eisnscue eisd  na ojowi nstt rsotantge emneonut gshay it is imperative that we come  to warrant prompt action. [I.8] together to address the Our estimates of future warming are uncer -climate issue.”  tain for two key reasons. First, we don’t know - Eric what future emissions will be. In a relatively
low emissions future, additional warming is likely to be between 2°F and 5°F by the end of the century. In a relatively high case, it is pro -jected to be between 4°F and 12°F. Second, even for a specific emissions amount there is uncertainty, and that’s because we don’t know precisely how sensitive the climate system is to greenhouse gases. This sensitiv -ity depends on numerous “feedback effects,” where warming itself causes more (and in a few cases, less) warming. †† These feedbacks make it much harder to predict exactly how much warming will occur for a given amount of gases. In particular, the extreme of high end projections cannot be ruled out. [I.9]
* All statements of fact are referenced in endnotes, by paragraph number. The endnotes are available at www. † The IPCC is the Intergovernmental Panel on Climate Change. See the endnote for more about the IPCC. † † For example, when warming melts frozen ground (permafrost), it releases large quantities of trapped greenhouse gases, which causes further warming.
page  II. HOW SERIOUS ARE THE IMPACTS AND RISKS? For those living in cold climates, one might think that global warming would simply make life a bit cozier. We now understand that raising the temperature of the planet causes many other changes, too, most of which are undesirable. There isn’t space to cover all expected impacts, but these are some of the most important. Figure 2 (inside back cover) provides an overview. [II.1] Gradual impacts: These effects increase gradually with increasing temperature. We’re already experiencing many of these impacts. The more warming we have, the more intense these effects will become. [II.2] • Heat waves: Heat waves have become more common and are very likely to con -tinue to become more frequent and more intense (hotter, for longer periods). [II.2a] • Droughts: More intense and longer droughts have been observed, over wider areas, since the 1970s. It is likely that this trend will worsen. [II.2a] • Heavy precipitation events: Heavy rain-storms (and flooding) have become more common over most land areas. It is very likely that this trend will worsen. [II.2a] • More intense tropical storms: It is likely that hurricanes will increase in intensity as the oceans warm. This increase has been observed in the North Atlantic since 1970. [II.2a] • Sea level rise: It is certain that sea levels will rise as the oceans warm, since water expands as it warms. Combined with meltwater from glaciers -- but excluding the contribution from the large ice sheets (see below) -- sea level rise is estimated to be between 7 and 23 inches for this century. Combined with the effect of increased storm surge, this amount of sea level rise will have severe impacts on coastal cities and regions (such as New York City and south Florida) that are at or near sea level. [II.2b]
page  • Species extinctions and ecosystem destruction: There are likely to be increasing extinctions with increased warming, with about 20-30% of plant and animal species at risk of extinction if further warming exceeds 2.5-4.5° F. Many ecosystems are likely to be pushed beyond their limits due to a combination of factors, including climate change and related effects (such as flooding, drought, wildfire, pest infestations, ocean acidifica -tion, etc.). For example, 30% of all coastal wetlands are expected to be lost with a warming of about 4.5° F. [II.2c] Tipping point impacts for societies or eco -systems: Some impacts occur when a point of no return is crossed, leading to large-scale, irreversible changes.  [II.3] • Melting of the large ice sheets: Warming brings with it the risk that the two large ice sheets that cover Greenland and West Antarctica will melt partially or completely. The process is expected to take centuries, but together they contain enough water to raise sea levels by about 40 feet. What temperature increase will cause large-scale melting? It is estimated that an additional 2° F to 7° F would cause enough melting for at least 13-20 feet of sea level rise (“me -dium confidence”). [II.3a]  Disruption of Arctic ecosystems and human communities: The Arctic is now experiencing some of the most rapid and severe climate change on earth, and this trend is expected to accelerate. Changes such as loss of sea ice and tundra are expected to put many species, including polar bears, ice-inhabiting seals, and Arctic-breeding shorebirds and waterfowl at risk. Indigenous communities that depend on these ecosystems, not only for food security but for cultural identity, are facing eradication. [II.3b] • Collapse of Amazon rainforest ecosys -tem: Although not certain, one of the plau -sible outcomes of global climate change is warmer, drier conditions in large parts of the Amazon basin. Under these condi -tions, much of the Amazon would likely be converted to grassland or desert. [II.3c]
Economic and social impacts [II.4] • Water: Regions at high latitudes (such as Alaska and Siberia) are expected to have increased water availability (10-40%). At mid-latitudes, the picture is mixed: for example, southern Europe and northern Africa will become drier, northern Europe wetter; the U.S. is likely to be drier in the summer (especially in the West). In the tropics, dry regions (such as India and Central America) will get drier, and wet regions (such as Central Africa) will tend to get wetter. Over a billion people live in regions where water is supplied from glaciers and snow cover. These regions are projected to have decreased water availability over the course of this cen -tury. [II.4a] Food: Globally, food production is pro -jected to increase slightly for additional local warming of 2 to 5 F, and beyond ° that it will decrease. However, in some re -gions, including large parts of Africa and Central and South Asia, even moderate warming is expected to severely decrease food production. [II.4b] Health: The greatest health impacts will be felt by those already most vulnerable: the poor in developing nations. Increased malnutrition, increased diarrhoeal diseases due to water supply problems, and increased deaths, disease, and injury from heat waves, floods, storms, fires, and drought. In cold regions, warming is expected to result in fewer deaths from cold exposure. [II.4c] Economy: For a warming of about 7° F, global economic losses are expected to be between 600 billion and 3 trillion dollars annually (1-5% of world GDP). It is very likely that these figures under -estimate damage costs, because many impacts are difficult or impossible to calculate. At lower amounts of warming, some regions are expected to have net benefits, and others will still have very significant net costs. [II.4d]
“Our main force for change is democracy in action. Change will only come from us. John Dewey said that “Democracy is born in conversation,” yet we’re increasingly failing to take the time to talk with one another. This is something we all can do. Let’s get involved with the climate change dialogues.”   - Cecile  
• National security: Climate change has the potential to create natural and hu -manitarian disasters on a large scale, and worsen already marginal living conditions in many developing nations, leading to widespread political instability and failed states. Unlike most conventional threats, it has the potential to trigger these im -pacts chronically and simultaneously in “It’s easy to feel hopeless in many locations around the world. [II.4e] the face of all this. What I like Understanding the uncertainties about the Dialogues is that it Different levels of certainty are indicated for connects me with other people different impacts, by terms such as “likely” and “very likely”. For example, increased heat who care. That gives me hope.”  waves are “very likely”, which means that sci - Andy entists are quite confident of this prediction. -Increased droughts are described as “likely”, which means there is somewhat less confi -dence in this prediction. See the endnote for the precise scientific usage. [II.5] Some impacts, such as the collapse of the Amazon, are more uncertain, in the sense that we’re not yet able to make precise predictions about them. However, it would be mislead -ing to omit them entirely. We do know that these types of large effects have occurred in the past, and the potential for them to occur in the near future is quite real. But we don’t understand them well enough yet to make specific predictions. [II.6] Predictions about economic and social im -pacts contain additional uncertainties. On the one hand, climate impacts such as sea level rise and extended drought can give rise to mass movement of refugees and social con -flict including wars. Predicting and determin -ing the probability and costs of such events is very difficult. On the other hand, we know that people will adapt to some degree to many of these impacts. At this point, however, we have very little information about how successfully they will do so, and at what cost. [II.7]
page  Local impacts: Pacific Northwest During the 20th century, the Puget Sound re -gion warmed by 2.3°F, significantly more than the global average. This trend is expected to continue, with a projected additional warm -ing of 1 to 5° F by the 2040s. [II.8] Water: Water availability is projected to increase in winter and decrease in summer -- when it is most needed for irrigation and electicity generation. For example, by 2050, the Columbia River is projected to have 30-50% less water during summer. These trends are already visible, and are expected to worsen. [II.8a] Salmon: Wild salmon in the Pacific Northwest are already at historically low numbers, and many populations are endangered. Salmon are expected to be further stressed by a warming climate. Warmer waters and reduced summer streamflows will cause increased mortality and make recovery efforts increas -ingly difficult. [II.8b] Wildfires: The number of large wildfires in Washington State has increased from an average of 6 per year in the 1970s to 21 per year today. Although other factors are also involved, it is likely that rising temperatures are a significant factor, and that this trend will worsen. [II.8c] Coasts: There is an increased likelihood of large, damaging coastal erosion and flooding events, due to a combination of sea level rise, increased winter precipitation, and increased winter storms. [II.8d]
page  . III WHAT ARE THE SOLUTIONS? Replace fossil fuels with cleaner energy sources: Numerous energy sources (such If we decide to limit the extent of climate as wind, nuclear, geothermal, hydro, solar change, we must reduce or halt the emission thermal and photovoltaic, etc.) produce zero of greenhouse gases. The largest source of or small amounts of greenhouse gases. Of these gases is the fossil fuels (coal, oil, and course, these have other tradeoffs, such as natural gas) we burn for electricity, heat, and cost, other environmental impacts, etc.. Solar transportation. The second largest source is energy is the most abundant form (more deforestation. Oth ches the Earth sources include: li than is con-conventional agric by the world all landfills, and indu , but as a source processes such as electricity is still cement and steel ignificantly more production. In expensive than addition to fossil fuels. With controlling our research, invest-own emissions, ment, and mass we will need production, this to exert cost is expected international to drop. [III.3] lea to ednesrsuhrie pt hat Develop cleaner emissions are ays to burn   reduced around t sil fuels (carbon world F ur a re and seques-. (inside bigack ecso 3ver) : For large, sta-the sources of lo gy sources such emissionsg .. as coal or gas-fired electric power Limiting .  [I e II. m 1] issions f om fossil fuels plants, it is possible to prevent 80-90% of r CO 2 emissions by capturing CO 2 before the Use energy more efficiently and avoid combustion gases are released. The CO 2  must then be transported and stored away waste: The most cost-effective way to lower emissions is to use energy more efficiently. from the atmosphere. Proposed storage sites Most sectors of the economy have significant include underground geological formations, potential to do so, avoiding pollution and the deep ocean, and conversion to inert min -often saving money. For example, about 30% eral carbonates. The main challenges with this of emissions from buildings could be avoided technology are the cost of capture and the through cost-saving measures such as high- potential for leakage of stored CO 2 . [III.4] efficiency lighting and appliances, better Put a price on global warming emissions: insulation, and passive solar design. Other Although greenhouse gases could be con -examples include more efficient vehicles, trolled by direct government regulation, it is compact communities for more efficient widely agreed that market-based approaches transport, improved electricity distribution, will do so more efficiently and at lower cost. and combined heat and power. [III.2] In market approaches, the cost of fuels and other products reflects the amount of green -house gases they contain. This encourages
“The Climate Dialogues serve as an exciting new platform, bringing a broad community together not just to talk, but to take concrete steps toward mitigating climate change. It’s exciting to see this action taking shape.   - Gabriel
people to find cost-effective ways to avoid GHG emissions, and fosters the development of low or zero-emission alternatives. Pricing emissions can be done either through a cap-and-trade system (tradable emissions per -mits), or by a direct tax based on greenhouse gas content (“carbon tax”). [III.5] Emissions pricing does not necessarily create a net cost to society. The economic impact depends strongly on what is done with the revenues that are generated. For example, if revenues from a carbon tax were used to reduce income taxes, or to pay down the defi -cit, the net effect on the economy as a whole could be beneficial. [III.6] Invest in technology research and develop -ment (R&D): The cost of addressing global warming will depend to a large extent on what technology is available. Current invest -ment in energy technology R&D is only half of what it was in 1980, and is unlikely to be adequate for achieving large reductions in greenhouse gas emissions. [III.7] Limiting emissions from deforestation Forests are cut down for a variety of reasons, including logging, cattle ranching, commer -cial agriculture, and slash-and-burn cultiva -tion by subsistence farmers. In many cases, forests could be preserved through measures that are relatively low-cost, with substantial co-benefits in terms of employment, income generation, biodiversity and watershed conservation, renewable energy supply and poverty alleviation. [III.8] Limiting other emissions of greenhouse gases In the U.S., about 14% of our emissions comes from non-fossil fuel sources such as landfills, manure lagoons, nitrogen fertilizers, soil tillage, and cement and steel production. Each type of source requires its own solution: methane capture at landfills; no-till agricul -
page  ture; and so on. In some cases, research will be needed to find and develop viable substi - tutes. [III.9] Addressing the global scope of emissions Global warming is a global problem that requires international cooperation to solve. It is essential that all major emitters participate in reductions, and global cooperation will lower total costs. The biggest challenge in this area lies with developing nations, whose growing economies are expected to produce most of the growth in emissions in the com -ing decades. There are many opportunities for these countries to develop economically while lowering global emissions, and it will be critical to support these choices. [III.10] Understanding the uncertainties There is no doubt that fossil fuels and defor -estation are the main sources of greenhouse gases. There is uncertainty about the exact contribution of deforestation, since its mea -surement is difficult. [III.11] There is general agreement that many oppor -tunities for energy efficiency improvements exist in our economy, and that these improve -ments often offer substantial money savings. But there is disagreement about how large these opportunities are, and what amount of financial and pollution savings they could provide. [III.12] Some of the technology solutions needed to avoid fossil fuel emissions are currently available (such as wind power, which now provides about 20% of Denmark’s and 10% of Spain’s electricity needs). Other technologies (such as capture and storage of emissions from coal plants) still require substantial re -search and development. This creates un -certainty about the costs, timeline, and best technology mix as we move forward. There is also some uncertainty about the total global warming impact of some energy sources, especially nuclear and hydroelectric. [III.13]
page  IV. WHAT ARE OUR CHOICES? lenge, and could be costly. If we had time, a We’ve seen that global warming is happen - very gradual transition would be preferable. ing, and that it has potentially very serious [IV.2] consequences. According to the U.S. National Academy of Sciences (2005), “The scientific Omiunr icmhiozic es, then, are about cost and risk. To understanding of climate change is now suf -slowly. Teo tmhien ciomsitz eo ft hace triiosnk,  owf es esvheoruel id mmpoacvtes , ficiently clear to justify nations taking prompt we should move quickly. The table below action. ... [D]elayed action will increase the risk shows a range of options. There are many of adverse environmental effects and will likely certaint s h in terms of cost and of incur a greater cost.”  [IV.1]ruisnk. But thieese,  baroet the best estimates that we Fortunately, the actions that are needed to have, based on the work of thousands of the reduce GHG emissions bring many co-ben - world’s top scientists and economists. At the efits, such as jobs, cleaner air, energy security end of this section, you will find a more de -and conservation of biodiversity. The problem tailed discussion of the uncertainties in these is that adopting them rapidly will be a chal - estimates. [IV.3]
Option Slowing of U.S Annual increase economic growth in gasoline and per year electricity prices* Minimize cost None** None**
Gradual steps < $8 billion ¢ / gal 3/100 ¢ / kWh Larger steps < $6 billion 4¢ / gal ¢ / kWh Minimize risk > $6 billion? > 4¢ / gal ? > ¢ / kWh ? Table 1. Overview of options, costs, and risks  
*: These prices are mid-estimates. See text for the full range of estimates. **: It’s important to note that the costs given here are the economic costs of government policies. They do not include economic costs imposed by climate change itself. Of course, gasoline and electricity prices, as well as economic growth, are affected by many other factors, too.
Limit of additional warming no limit
° F 6.5° F 2.5° F
Risk of ice sheet loss and other severe impacts Very high
High Medium Low
The Choices in Detail These choices are meant to be representative, not exhaustive. You may want to consider other possibilities not included here. [IV.4] q OPTION 1: Minimize cost: voluntary actions only: This approach aims to minimize “Increasing publi understand-the cost of taking action. It does not regulate c greenhouse gas emissions, but encourages ing of environmental and voluntary reductions. It makes modest social issues is something that investments in energy R&D, and creates modest incentives for energy efficiency and is intrinsic to my work and my other voluntary actions such as avoiding life journey. The Dialogues are deforestation and managing agriculture more a great way to become well sustainably. [IV.5] versed on these issues and to Costs due to policies: minimal. connect with concerned citi-Temperature target: no limit on temperature zens and leaders who want to rise find solutions to these pressing GHG stabilization goal*: no limit dilemmas.”  Risk of ice sheet loss and other severe im -- Brittany pacts: very high Rationale: More certainty about the science is needed before we take mandatory action. It would be foolhardy to make a major change in our economy and spend large sums of money when we are not yet certain about the cause or about how serious the effects will be. Furthermore, warming is likely to bring not only harm but some benefits as well. Let’s wait until we’re sure there’s a crisis, then we can take bold action. [IV.6] Critique : The longer we wait to take action, the more costly it will be to act, and it’s likely that the lowest temperature targets will become unattainable. Our understanding of the climate is far from complete, which is why we should be cautious about tampering with it. We know the possibility of catastrophic impacts is real. Although there may be small benefits from small amounts of warming, these benefits are likely to be swamped by damages as the warming increases. [IV.7]
page  q  OPTION 2: Gradual steps: modest mandatory action: This approach recognizes the need for mandatory action, but sets modest targets to ensure that costs are low. It regulates greenhouse gas emissions, but with the goal of slowing their growth rather than reducing the absolute amount, and with strict cost limits in place. It recognizes that more stringent action will eventually be necessary, but should only be pursued if the other major emitters (countries) agree. This approach also increases investment in energy technology (and related) research. [IV.8] Costs due to policies: • Slowing of GDP** growth: up to 0.06% per year ($8 billion in 2006). By 2030, the cumulative effect of this slowing could lower GDP by up to 1.2%. • Gasoline prices: increase 0.2 to 1.5 ¢/gal per year. • Electricity prices: increase 0.016 ¢/kWh to 0.108 ¢/kWh ($0.14 to $0.96 for average household monthly bill in 2001) per year. Temperature target: likely to stay below 10° F of additional warming GHG stabilization goal: 700 ppm CO 2 e Risk of ice sheet loss and other severe impacts : high Rationale: It is politically pragmatic to start with a modest goal that can be gradually tightened as needed. We should only adopt more ambitious goals if the rest of the world also does so, therefore we link tightening of these controls to international efforts. It may be more cost-effective to adapt to some cli -mate change, rather than attempting to hold it to low levels. [IV.9] Critique: Of course, every policy must be phased in to allow time for us to adjust. But this approach is too gradual. By the time it * The GHG stabilization goal is the total amount of greenhouse gases that we will permit in the atmosphere. It is measured in units of “carbon dioxide equivalent”, CO 2 e. **GDP, or Gross Domestic Product, represents the total value of goods and services produced in the economy.