Graphic Credit:  Johnny Selman

 

 

The New York Times, by James Hansen PhD, May 14, 2012  —  GLOBAL warming isn’t a prediction. It is happening. That is why I was so troubled to read a recent interview with President Obama in Rolling Stone in which he said that Canada would exploit the oil in its vast tar sands reserves “regardless of what we do.”

If Canada proceeds, and we do nothing, it will be game over for the climate.

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.

That is the long-term outlook. But near-term, things will be bad enough. Over the next several decades, the Western United States and the semi-arid region from North Dakota to Texas will develop semi-permanent drought, with rain, when it does come, occurring in extreme events with heavy flooding. Economic losses would be incalculable. More and more of the Midwest would be a dust bowl. California’s Central Valley could no longer be irrigated. Food prices would rise to unprecedented levels.

If this sounds apocalyptic, it is. This is why we need to reduce emissions dramatically. President Obama has the power not only to deny tar sands oil additional access to Gulf Coast refining, which Canada desires in part for export markets, but also to encourage economic incentives to leave tar sands and other dirty fuels in the ground.

The global warming signal is now louder than the noise of random weather, as I predicted would happen by now in the journal Science in 1981. Extremely hot summers have increased noticeably. We can say with high confidence that the recent heat waves in Texas and Russia, and the one in Europe in 2003, which killed tens of thousands, were not natural events — they were caused by human-induced climate change.

We have known since the 1800s that carbon dioxide traps heat in the atmosphere. The right amount keeps the climate conducive to human life. But add too much, as we are doing now, and temperatures will inevitably rise too high. This is not the result of natural variability, as some argue. The earth is currently in the part of its long-term orbit cycle where temperatures would normally be cooling. But they are rising — and it’s because we are forcing them higher with fossil fuel emissions.

The concentration of carbon dioxide in the atmosphere has risen from 280 parts per million to 393 p.p.m. over the last 150 years. The tar sands contain enough carbon — 240 gigatons — to add 120 p.p.m. Tar shale, a close cousin of tar sands found mainly in the United States, contains at least an additional 300 gigatons of carbon. If we turn to these dirtiest of fuels, instead of finding ways to phase out our addiction to fossil fuels, there is no hope of keeping carbon concentrations below 500 p.p.m. — a level that would, as earth’s history shows, leave our children a climate system that is out of their control.

We need to start reducing emissions significantly, not create new ways to increase them. We should impose a gradually rising carbon fee, collected from fossil fuel companies, then distribute 100 percent of the collections to all Americans on a per-capita basis every month. The government would not get a penny. This market-based approach would stimulate innovation, jobs and economic growth, avoid enlarging government or having it pick winners or losers. Most Americans, except the heaviest energy users, would get more back than they paid in increased prices. Not only that, the reduction in oil use resulting from the carbon price would be nearly six times as great as the oil supply from the proposed pipeline from Canada, rendering the pipeline superfluous, according to economic models driven by a slowly rising carbon price.

But instead of placing a rising fee on carbon emissions to make fossil fuels pay their true costs, leveling the energy playing field, the world’s governments are forcing the public to subsidize fossil fuels with hundreds of billions of dollars per year. This encourages a frantic stampede to extract every fossil fuel through mountaintop removal, longwall mining, hydraulic fracturing, tar sands and tar shale extraction, and deep ocean and Arctic drilling.

President Obama speaks of a “planet in peril,” but he does not provide the leadership needed to change the world’s course. Our leaders must speak candidly to the public — which yearns for open, honest discussion — explaining that our continued technological leadership and economic well-being demand a reasoned change of our energy course. History has shown that the American public can rise to the challenge, but leadership is essential.

The science of the situation is clear — it’s time for the politics to follow. This is a plan that can unify conservatives and liberals, environmentalists and business. Every major national science academy in the world has reported that global warming is real, caused mostly by humans, and requires urgent action. The cost of acting goes far higher the longer we wait — we can’t wait any longer to avoid the worst and be judged immoral by coming generations.

James Hansen directs the NASA Goddard Institute for Space Studies and is the author of “Storms of My Grandchildren.”

 

 

 

Global Warming & Climate Change

 

Photo Credit:  Steen Ulrik Johannessen/Agence France-Presse — Getty Images
Updated: March 27, 2012

 

 

The New York Times, May 14, 2012  —  Global warming has become perhaps the most complicated issue facing world leaders. Warnings from the scientific community are becoming louder, as an increasing body of science points to rising dangers from the ongoing buildup of human-related greenhouse gases — produced mainly by the burning of fossil fuels and forests.

Global emissions of carbon dioxide jumped by the largest amount on record in 2010, upending the notion that the brief decline during the recession might persist through the recovery. Emissions rose 5.9 percent in 2010, according to the Global Carbon Project, an international collaboration of scientists. The increase solidified a trend of ever-rising emissions that scientists fear will make it difficult, if not impossible, to forestall severe climate change in coming decades.

However, the technological, economic and political issues that have to be resolved before a concerted worldwide effort to reduce emissions can begin have gotten no simpler, particularly in the face of a global economic slowdown.

For almost two decades, the United Nations has sponsored annual global talks, the United Nations Framework Convention on Climate Change, an international treaty signed by 194 countries to cooperatively discuss global climate change and its impact. The conferences operate on the principle of consensus, meaning that any of the participating nations can hold up an agreement.

The conflicts and controversies discussed are monotonously familiar: the differing obligations of industrialized and developing nations, the question of who will pay to help poor nations adapt, the urgency of protecting tropical forests and the need to rapidly develop and deploy clean energy technology.

But the meetings have often ended in disillusionment, with incremental political progress but little real impact on the climate. The negotiating process itself has come under fire from some quarters, including the poorest nations who believe their needs are being neglected in the fight among the major economic powers. Criticism has also come from a small but vocal band of climate-change skeptics, many of them members of the United States Congress, who doubt the existence of human influence on the climate and ridicule international efforts to deal with it.

A Global Initiative Led by the U.S.

In mid-February 2012, Secretary of State Hillary Rodham Clinton was expected to announce a new international effort focused on reducing emissions of common pollutants that contribute to rapid climate change and widespread health problems.

Impatient with the slow pace of international negotiations, the United States and a small group of countries — Bangladesh, Canada, Ghana, Mexico and Sweden as well as the United Nations Environment Program — are starting a program that will address short-lived pollutants like soot (also referred to as black carbon), methane and hydrofluorocarbons that have an outsize influence on global warming, accounting for 30 to 40 percent of global warming. Soot from diesel exhausts and the burning of wood, agricultural waste and dung for heating and cooking causes an estimated two million premature deaths a year, particularly in the poorest countries

Scientists say that concerted action on these substances can reduce global temperatures by 0.5 degrees Celsius by 2050 and prevent millions of cases of lung and heart disease by 2030.

The United States intends to contribute $12 million and Canada $3 million over two years to get the program off the ground and to help recruit other countries to participate. The United Nations Environment Program will run the project.

Officials hope that by tackling these fast-acting, climate-changing agents they can get results quicker than through the laborious and highly political negotiations conducted under the United Nations Framework Convention on Climate Change.

2011 Global Talks in Durban

At the 2011 conference delegates from about 200 nations gathered together in Durban, South Africa. One of the issues left unresolved was the future of the Kyoto Protocol, the 1997 agreement that requires major industrialized nations to meet targets on emissions reduction but imposes no mandates on developing countries, including emerging economic powers and sources of global greenhouse gas emissions like China, India, Brazil and South Africa.

The United States is not a party to the protocol, having refused to even consider ratifying it because of those asymmetrical obligations. Some major countries, including Canada, Japan and Russia, have said they will not agree to an extension of the protocol next year unless the unbalanced requirements of developing and developed countries are changed. That is similar to the United States’ position, which is that any successor treaty must apply equally to all major economies.

Expectations for the meeting were low, and it ended with modest accomplishments: the promise to work toward a new global treaty in coming years and the establishment of a new climate fund.

The deal on a future treaty renewed the Kyoto Protocol for several more years. But it also began a process for replacing the protocol with something that treats all countries — including the economic powerhouses China, India and Brazil — equally. The future treaty deal was the most highly contested element of a package of agreements that emerged from the extended talks among the nations here.

The expiration date of the protocol — 2017 or 2020 — and the terms of any agreement that replaces it will be negotiated at future sessions.

The delegates also agreed on the creation of a fund to help poor countries adapt to climate change — though the precise sources of the money have yet to be determined — and to measures involving the preservation of tropical forests and the development of clean-energy technology. The reserve, called the Green Climate Fund, would help mobilize a promised $100 billion a year in public and private financing by 2020 to assist developing countries in adapting to climate change and converting to clean energy sources.

2010 Global Talks in Cancún

The United Nations conference on climate change in Cancún, Mexico, produced only modest achievements but ended with the toughest issues unresolved. The package that was approved, known as the Cancún Agreements, set up a new fund to help poor countries adapt to climate changes, created new mechanisms for transfer of clean energy technology, provided compensation for the preservation of tropical forests and strengthened the emissions reductions pledges that came out of the U.N. climate change meeting in Copenhagen in 2009.

The conference approved the agreement over the objections of Bolivia, which condemned the pact as too weak. But those protests did not block its acceptance. Delegates from island states and the least-developed countries warmly welcomed the pact because it would start the flow of billions of dollars to assist them in adopting cleaner energy systems and adapting to inevitable changes in the climate, like sea rise and drought.

But where the promised aid from wealthy nations — $100 billion — would come from was left unresolved.

The E.U. Gets Tough With Airline Emissions

In December 2011, the European Union’s highest court endorsed the bloc’s plan to begin charging the world’s biggest airlines for their greenhouse gas emissions from Jan. 1, 2012, setting the stage for a potentially costly trade war with the United States, China and other countries.

A group of United States airlines had argued that forcing them to participate in the potentially costly emissions-trading system infringed on national sovereignty and conflicted with existing international aviation treaties.

But in a final ruling , the European Court of Justice in Luxembourg affirmed an opinion issued in October by its advocate general, who had rejected their claim.

The court’s decision came amid increasing pressure from some of the biggest trading partners of the 27-member bloc to suspend or amend application of the legislation to expressly exclude non-E.U. countries — at least initially. Failing that, several governments have vowed to take their own legal action or retaliate with countervailing trade measures.

Although airlines initially will receive most of the permits they will need for free, the European Union estimates that ticket prices could rise by as much as €12, or nearly $16, on some long-haul flights to cover the cost of additional permits required.

Airlines for America, an industry lobby group and one of the plaintiffs in the case, said that its members would be required to pay more than $3.1 billion to the E.U. between 2012 and 2020. It said its members would comply with the system “under protest,” but would also review options for pursuing the case in Britain’s High Court, which had referred the original complaint to the European court in 2009.

The European initiative involves folding aviation into the Union’s six-year-old Emissions Trading System, in which polluters can buy and sell a limited quantity of permits, each representing a ton of carbon dioxide. The legislation mandates that airlines account for their emissions for the entirety of any flight that takes off from — or lands at — any airport in the 27-member bloc.

The goal, European officials have said, is to speed up the adoption of greener technologies at a time when air traffic, which represents about 3 percent of global carbon dioxide emissions, is growing much faster than gains in efficiency.

The U.S. and Climate Change

The United States has been criticized at the United Nations gatherings for years, in part because of its rejection of the Kyoto framework and in part because it has not adopted a comprehensive domestic program for reducing its own greenhouse gas emissions. President Obama has pledged to reduce American emissions 17 percent below 2005 levels by 2020, but his preferred approach, a nationwide cap-and-trade system for carbon pollution, was passed by the House in 2009 but died in the Senate the next year. United States emissions are down about 6 percent over the past five years, largely because of the drop in industrial and electricity production caused by the recession.

In January 2011, the Environmental Protection Agency began imposing regulations related to greenhouse gas emissions. The immediate effect on utilities, refiners and major manufacturers was minor, with the new rules applying only to those planning to build large new facilities or make major modifications to existing plants. Over the next decade, however, the agency plans to regulate virtually all sources of greenhouse gases, imposing efficiency and emissions requirements on nearly every industry and every region.

A Draft Rule Stands in the Way of New Coal-Fired Plants

In March 2012, the E.P.A. unveiled a draft rule that would limit carbon dioxide emissions from new power plants to 1,000 pounds per megawatt-hour.

Recently built power plants fired by natural gas already easily meet the new standards, so the rule presents little obstacle for new gas plants. But coal-fired plants face a far greater challenge, since no easily accessible technology can bring their emissions under the limit. Coal-fired plants are a major source emissions associated with global warming. The new rules do not apply to existing plants.

The declining price of natural gas has made it the fuel of choice in recent years for companies planning new plants. The E.P.A.’s move follows a shift that is already unfolding in the electric power market.

The proposed rule is rooted in a 2007 directive from the Supreme Court instructing the E.P.A. to decide whether carbon dioxide was a pollutant under the Clean Air Act. In late 2009, the agency declared that it was, and so had to be regulated.

It took more than two years for the agency to work out the regulatory details.

To open an avenue to companies still planning to build coal plants, for example, the E.P.A. said it would allow new ones to begin operating with higher levels of emissions as long as the average annual emissions over a period of 30 years met the standard.

Environmental groups generally applauded the standards, although some expressed disappointment with the agency’s decision not to regulate existing power plants for the moment.

Steps Toward a Response

The debate over climate questions pales next to the fight over what to do, or not do, in a world where fossil fuels still underpin both rich and emerging economies.

With the completion of the United Nations Framework Convention on Climate Change at the Earth Summit in 1992, the world’s nations pledged to avoid dangerously disrupting the climate through the buildup of greenhouse gases, but they never defined how much warming was too much.

Nonetheless, recognizing that the original climate treaty was proving ineffective, all of the world’s industrialized countries except for the United States accepted binding restrictions on their greenhouse gas emissions under the Kyoto Protocol, which was negotiated in Japan in 1997. That accord took effect in 2005 and its gas restrictions expire in 2012. The United States signed the treaty, but it was never submitted for ratification in the face of overwhelming opposition in the Senate because the pact required no steps by China or other fast-growing developing countries.

It took until 2009 for the leaders of the world’s largest economic powers to agree on a dangerous climate threshold: an increase of 2 degrees Celsius (3.6 degrees Fahrenheit) from the average global temperature recorded just before the Industrial Revolution kicked into gear. (This translates into an increase of 1.3 degrees Fahrenheit above the Earth’s current average temperature, about 59 degrees.)

The Group of 8 industrial powers also agreed in 2009 to a goal of reducing global emissions 50 percent by 2050, with the richest countries leading the way by cutting their emissions 80 percent. But they did not set a baseline from which to measure that reduction, and so far firm interim targets — which many climate scientists say would be more meaningful — have not been defined.

At the same time, fast-growing emerging economic powerhouses, led by China and India, opposed taking on mandatory obligations to curb their emissions. They said they will do what they can to rein in growth in emissions — as long as their economies do not suffer.

In many ways, the debate over global climate policy is a result of a global “climate divide.’’ Emissions of carbon dioxide per person range from less than 2 tons per year in India, where 400 million people lack access to electricity, to more than 20 in the United States. The richest countries are also best able to use wealth and technology to insulate themselves from climate hazards, while the poorest, which have done the least to cause the problem, are the most exposed.

Background

Scientists learned long ago that the earth’s climate has powerfully shaped the history of the human species — biologically, culturally and geographically. But only in the last few decades has research revealed that humans can be a powerful influence on the climate, as well.

A growing body of scientific evidence indicates that since 1950, the world’s climate has been warming, primarily as a result of emissions from unfettered burning of fossil fuels and the razing of tropical forests. Such activity adds to the atmosphere’s invisible blanket of carbon dioxide and other heat-trapping “greenhouse” gases. Recent research has shown that methane, which flows from landfills, livestock and oil and gas facilities, is a close second to carbon dioxide as an impact on the atmosphere.

That conclusion has emerged through a broad body of analysis in fields as disparate as glaciology, the study of glacial formations, and palynology, the study of the distribution of pollen grains in lake mud. It is based on a host of assessments by the world’s leading organizations of climate and earth scientists.

In the last several years, the scientific case that the rising human influence on climate could become disruptive has become particularly robust.

Some fluctuations in the earth’s temperature are inevitable regardless of human activity — because of decades-long ocean cycles, for example. But centuries of rising temperatures and seas lie ahead if the release of emissions from the burning of fossil fuels and deforestation continues unabated, according to the Intergovernmental Panel on Climate Change, a group that shared the 2007 Nobel Peace Prize with former Vice President Al Gore.

In addition, a report released by the I.P.C.C. in November 2011 predicted that global warming will cause more dangerous and “unprecedented extreme weather” in the future.

Despite the scientific consensus on these basic conclusions, enormously important details remain murky. That reality has been seized upon by some groups and scientists disputing the overall consensus and opposing changes in energy policies.

For example, estimates of the amount of warming that would result from a doubling of greenhouse gas concentrations (compared to the level just before the Industrial Revolution got under way in the early 19th century) range from 3.6 degrees to 8 degrees Fahrenheit. The intergovernmental climate panel said it could not rule out even higher temperatures. While the low end could probably be tolerated, the high end would almost certainly result in calamitous, long-lasting disruptions of ecosystems and economies, a host of studies have concluded. A wide range of economists and earth scientists say that level of risk justifies an aggressive response.

Other questions have persisted despite a century-long accumulation of studies pointing to human-driven warming. The rate and extent at which sea levels will rise in this century as ice sheets erode remains highly uncertain, even as the long-term forecast of centuries of retreating shorelines remains intact. Scientists are struggling more than ever to disentangle how the heat building in the seas and atmosphere will affect the strength and number of tropical cyclones. The latest science suggests there will be more hurricanes and typhoons that reach the most dangerous categories of intensity, but fewer storms overall.

Impatient with the slow pace of international negotiations, the United States and a small group of countries — Bangladesh, Canada, Ghana, Mexico and Sweden as well as the United Nations Environment Program — are starting a program that will address short-lived pollutants like soot (also referred to as black carbon), methane and hydrofluorocarbons that have an outsize influence on global warming, accounting for 30 to 40 percent of global warming. Soot from diesel exhausts and the burning of wood, agricultural waste and dung for heating and cooking causes an estimated two million premature deaths a year, particularly in the poorest countries

Scientists say that concerted action on these substances can reduce global temperatures by 0.5 degrees Celsius by 2050 and prevent millions of cases of lung and heart disease by 2030.

The United States intends to contribute $12 million and Canada $3 million over two years to get the program off the ground and to help recruit other countries to participate. The United Nations Environment Program will run the project.

Officials hope that by tackling these fast-acting, climate-changing agents they can get results quicker than through the laborious and highly political negotiations conducted under the United Nations Framework Convention on Climate Change.

2011 Global Talks in Durban

At the 2011 conference delegates from about 200 nations gathered together in Durban, South Africa. One of the issues left unresolved was the future of the Kyoto Protocol, the 1997 agreement that requires major industrialized nations to meet targets on emissions reduction but imposes no mandates on developing countries, including emerging economic powers and sources of global greenhouse gas emissions like China, India, Brazil and South Africa.

The United States is not a party to the protocol, having refused to even consider ratifying it because of those asymmetrical obligations. Some major countries, including Canada, Japan and Russia, have said they will not agree to an extension of the protocol next year unless the unbalanced requirements of developing and developed countries are changed. That is similar to the United States’ position, which is that any successor treaty must apply equally to all major economies.

Expectations for the meeting were low, and it ended with modest accomplishments: the promise to work toward a new global treaty in coming years and the establishment of a new climate fund.

The deal on a future treaty renewed the Kyoto Protocol for several more years. But it also began a process for replacing the protocol with something that treats all countries — including the economic powerhouses China, India and Brazil — equally. The future treaty deal was the most highly contested element of a package of agreements that emerged from the extended talks among the nations here.

The expiration date of the protocol — 2017 or 2020 — and the terms of any agreement that replaces it will be negotiated at future sessions.

The delegates also agreed on the creation of a fund to help poor countries adapt to climate change — though the precise sources of the money have yet to be determined — and to measures involving the preservation of tropical forests and the development of clean-energy technology. The reserve, called the Green Climate Fund, would help mobilize a promised $100 billion a year in public and private financing by 2020 to assist developing countries in adapting to climate change and converting to clean energy sources.

2010 Global Talks in Cancún

The United Nations conference on climate change in Cancún, Mexico, produced only modest achievements but ended with the toughest issues unresolved. The package that was approved, known as the Cancún Agreements, set up a new fund to help poor countries adapt to climate changes, created new mechanisms for transfer of clean energy technology, provided compensation for the preservation of tropical forests and strengthened the emissions reductions pledges that came out of the U.N. climate change meeting in Copenhagen in 2009.

The conference approved the agreement over the objections of Bolivia, which condemned the pact as too weak. But those protests did not block its acceptance. Delegates from island states and the least-developed countries warmly welcomed the pact because it would start the flow of billions of dollars to assist them in adopting cleaner energy systems and adapting to inevitable changes in the climate, like sea rise and drought.

But where the promised aid from wealthy nations — $100 billion — would come from was left unresolved.

The E.U. Gets Tough With Airline Emissions

In December 2011, the European Union’s highest court endorsed the bloc’s plan to begin charging the world’s biggest airlines for their greenhouse gas emissions from Jan. 1, 2012, setting the stage for a potentially costly trade war with the United States, China and other countries.

A group of United States airlines had argued that forcing them to participate in the potentially costly emissions-trading system infringed on national sovereignty and conflicted with existing international aviation treaties.

But in a final ruling , the European Court of Justice in Luxembourg affirmed an opinion issued in October by its advocate general, who had rejected their claim.

The court’s decision came amid increasing pressure from some of the biggest trading partners of the 27-member bloc to suspend or amend application of the legislation to expressly exclude non-E.U. countries — at least initially. Failing that, several governments have vowed to take their own legal action or retaliate with countervailing trade measures.

Although airlines initially will receive most of the permits they will need for free, the European Union estimates that ticket prices could rise by as much as €12, or nearly $16, on some long-haul flights to cover the cost of additional permits required.

Airlines for America, an industry lobby group and one of the plaintiffs in the case, said that its members would be required to pay more than $3.1 billion to the E.U. between 2012 and 2020. It said its members would comply with the system “under protest,” but would also review options for pursuing the case in Britain’s High Court, which had referred the original complaint to the European court in 2009.

The European initiative involves folding aviation into the Union’s six-year-old Emissions Trading System, in which polluters can buy and sell a limited quantity of permits, each representing a ton of carbon dioxide. The legislation mandates that airlines account for their emissions for the entirety of any flight that takes off from — or lands at — any airport in the 27-member bloc.

The goal, European officials have said, is to speed up the adoption of greener technologies at a time when air traffic, which represents about 3 percent of global carbon dioxide emissions, is growing much faster than gains in efficiency.

The U.S. and Climate Change

The United States has been criticized at the United Nations gatherings for years, in part because of its rejection of the Kyoto framework and in part because it has not adopted a comprehensive domestic program for reducing its own greenhouse gas emissions. President Obama has pledged to reduce American emissions 17 percent below 2005 levels by 2020, but his preferred approach, a nationwide cap-and-trade system for carbon pollution, was passed by the House in 2009 but died in the Senate the next year. United States emissions are down about 6 percent over the past five years, largely because of the drop in industrial and electricity production caused by the recession.

In January 2011, the Environmental Protection Agency began imposing regulations related to greenhouse gas emissions. The immediate effect on utilities, refiners and major manufacturers was minor, with the new rules applying only to those planning to build large new facilities or make major modifications to existing plants. Over the next decade, however, the agency plans to regulate virtually all sources of greenhouse gases, imposing efficiency and emissions requirements on nearly every industry and every region.

A Draft Rule Stands in the Way of New Coal-Fired Plants

In March 2012, the E.P.A. unveiled a draft rule that would limit carbon dioxide emissions from new power plants to 1,000 pounds per megawatt-hour.

Recently built power plants fired by natural gas already easily meet the new standards, so the rule presents little obstacle for new gas plants. But coal-fired plants face a far greater challenge, since no easily accessible technology can bring their emissions under the limit. Coal-fired plants are a major source emissions associated with global warming. The new rules do not apply to existing plants.

The declining price of natural gas has made it the fuel of choice in recent years for companies planning new plants. The E.P.A.’s move follows a shift that is already unfolding in the electric power market.

The proposed rule is rooted in a 2007 directive from the Supreme Court instructing the E.P.A. to decide whether carbon dioxide was a pollutant under the Clean Air Act. In late 2009, the agency declared that it was, and so had to be regulated.

It took more than two years for the agency to work out the regulatory details.

To open an avenue to companies still planning to build coal plants, for example, the E.P.A. said it would allow new ones to begin operating with higher levels of emissions as long as the average annual emissions over a period of 30 years met the standard.

Environmental groups generally applauded the standards, although some expressed disappointment with the agency’s decision not to regulate existing power plants for the moment.

Steps Toward a Response

The debate over climate questions pales next to the fight over what to do, or not do, in a world where fossil fuels still underpin both rich and emerging economies.

With the completion of the United Nations Framework Convention on Climate Change at the Earth Summit in 1992, the world’s nations pledged to avoid dangerously disrupting the climate through the buildup of greenhouse gases, but they never defined how much warming was too much.

Nonetheless, recognizing that the original climate treaty was proving ineffective, all of the world’s industrialized countries except for the United States accepted binding restrictions on their greenhouse gas emissions under the Kyoto Protocol, which was negotiated in Japan in 1997. That accord took effect in 2005 and its gas restrictions expire in 2012. The United States signed the treaty, but it was never submitted for ratification in the face of overwhelming opposition in the Senate because the pact required no steps by China or other fast-growing developing countries.

It took until 2009 for the leaders of the world’s largest economic powers to agree on a dangerous climate threshold: an increase of 2 degrees Celsius (3.6 degrees Fahrenheit) from the average global temperature recorded just before the Industrial Revolution kicked into gear. (This translates into an increase of 1.3 degrees Fahrenheit above the Earth’s current average temperature, about 59 degrees.)

The Group of 8 industrial powers also agreed in 2009 to a goal of reducing global emissions 50 percent by 2050, with the richest countries leading the way by cutting their emissions 80 percent. But they did not set a baseline from which to measure that reduction, and so far firm interim targets — which many climate scientists say would be more meaningful — have not been defined.

At the same time, fast-growing emerging economic powerhouses, led by China and India, opposed taking on mandatory obligations to curb their emissions. They said they will do what they can to rein in growth in emissions — as long as their economies do not suffer.

In many ways, the debate over global climate policy is a result of a global “climate divide.’’ Emissions of carbon dioxide per person range from less than 2 tons per year in India, where 400 million people lack access to electricity, to more than 20 in the United States. The richest countries are also best able to use wealth and technology to insulate themselves from climate hazards, while the poorest, which have done the least to cause the problem, are the most exposed.

Background

Scientists learned long ago that the earth’s climate has powerfully shaped the history of the human species — biologically, culturally and geographically. But only in the last few decades has research revealed that humans can be a powerful influence on the climate, as well.

A growing body of scientific evidence indicates that since 1950, the world’s climate has been warming, primarily as a result of emissions from unfettered burning of fossil fuels and the razing of tropical forests. Such activity adds to the atmosphere’s invisible blanket of carbon dioxide and other heat-trapping “greenhouse” gases. Recent research has shown that methane, which flows from landfills, livestock and oil and gas facilities, is a close second to carbon dioxide as an impact on the atmosphere.

That conclusion has emerged through a broad body of analysis in fields as disparate as glaciology, the study of glacial formations, and palynology, the study of the distribution of pollen grains in lake mud. It is based on a host of assessments by the world’s leading organizations of climate and earth scientists.

In the last several years, the scientific case that the rising human influence on climate could become disruptive has become particularly robust.

Some fluctuations in the earth’s temperature are inevitable regardless of human activity — because of decades-long ocean cycles, for example. But centuries of rising temperatures and seas lie ahead if the release of emissions from the burning of fossil fuels and deforestation continues unabated, according to the Intergovernmental Panel on Climate Change, a group that shared the 2007 Nobel Peace Prize with former Vice President Al Gore.

In addition, a report released by the I.P.C.C. in November 2011 predicted that global warming will cause more dangerous and “unprecedented extreme weather” in the future.

Despite the scientific consensus on these basic conclusions, enormously important details remain murky. That reality has been seized upon by some groups and scientists disputing the overall consensus and opposing changes in energy policies.

For example, estimates of the amount of warming that would result from a doubling of greenhouse gas concentrations (compared to the level just before the Industrial Revolution got under way in the early 19th century) range from 3.6 degrees to 8 degrees Fahrenheit. The intergovernmental climate panel said it could not rule out even higher temperatures. While the low end could probably be tolerated, the high end would almost certainly result in calamitous, long-lasting disruptions of ecosystems and economies, a host of studies have concluded. A wide range of economists and earth scientists say that level of risk justifies an aggressive response.

Other questions have persisted despite a century-long accumulation of studies pointing to human-driven warming. The rate and extent at which sea levels will rise in this century as ice sheets erode remains highly uncertain, even as the long-term forecast of centuries of retreating shorelines remains intact. Scientists are struggling more than ever to disentangle how the heat building in the seas and atmosphere will affect the strength and number of tropical cyclones. The latest science suggests there will be more hurricanes and typhoons that reach the most dangerous categories of intensity, but fewer storms overall.

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