"I think I missed the part where they discussed the Arctic melting," the environmentalist and author Bill McKibben recently quipped.

A tireless spokesman for a planet in rapid and, as he sees it, dangerous flux, McKibben had taken to his Twitter account in the aftermath of last week's presidential debate and, like many other Americans, he found the whole affair wanting -- though his reasons were singular. "Wasn't there some kind of drought or something this summer?" he continued. "Maybe I'm misremembering."

In the clipped and sardonic vernacular of the medium, he ended his Tweets "#oh-that."

McKibben was, of course, referring to climate change. His exasperation echoes a wider movement that by now has grown not just weary, but vaguely astounded at the lack of high-level dialogue on a topic that, as they see it, fundamentally influences -- and therefore ought to trump -- all others, particularly at a time when the nation is preparing to elect a president.

Earlier this month, two activist groups launched a website, ClimateSilence.org, which tracks the candidates' public statements on global warming over the years. By any measure, President Barack Obama fares far better than his Republican challenger, Mitt Romney, who has morphed from an early supporter of clean energy, fuel efficiency and emissions caps to a climate change agnostic given to openly ridiculing the issue.

But the activists also indict Obama, under whose leadership, they say, climate change has gone from an urgent matter to a mere afterthought.

In response to such assertions, White House and Obama campaign officials highlight numerous speeches and public statements over the last year in which the president has discussed the importance of tackling climate change. They also point to a raft of new measures aimed at curbing greenhouse gas emissions, including new fuel efficiency standards that will effectively cut in half the amount of greenhouse gas emissions from new cars and trucks by 2025, and proposed rules that would curb emissions from power plants, among other achievements.

"The Obama Administration has put in place smart, sensible steps to confront this issue," said White House spokesman Clark Stevens in an email message.

Other supporters of the president also suggested climate critics were being myopic, and that the administration's emissions reduction achievements ought to be viewed against the full complement of challenges facing a sitting president during a historically down economy.

McKibben concedes as much, though he adds that if a sympathetic figure like President Obama is unable to elevate climate change to the top of the nation's political agenda, activists may need to change tacks. He also says that, given the clear and present danger of global warming, a little single-mindedness is warranted.

"I plead guilty to tunnel vision around climate," McKibben said. "It's the biggest issue the planet has ever faced, and in 50 years the one thing we will be interested in knowing is how our leaders responded to it -- or didn't. I mean, the Arctic broke this summer, and we had the hottest month in American history," he added. "So it's perhaps just possible the Obama administration hasn't done quite enough."

A PLANET IN FLUX

The situation in the Arctic, where layers of ice and snow are disappearing at a rapid clip, has raised serious alarms among climate scientists. Last month, at the conclusion of the seasonal thaw, scientists discovered that the amount of sea ice covering the Arctic Ocean had reached its lowest point -- roughly 1.32 million square miles -- since satellite observation got underway more than 30 years ago.

Evidence also suggests that snowmelt across the Arctic is accelerating.

The implications here are myriad and, by now, familiar: Rising sea levels, inundation of communities in low-lying areas and potentially the wholesale obliteration of some island nations. What's more, the retreat of all this Arctic ice and snow -- important natural reflectors of the sun's heat -- could prove dangerously self-perpetuating. Bare land, after all, absorbs more heat. As more bare land is exposed for longer periods, the planetary thermostat gets nudged upward, causing yet more ice and snow to disappear.

bill mckibben

"It's the biggest issue the planet has ever faced," Bill McKibben said of climate change. Leaders in Washington, including President Obama, have simply proved ineffectual in addressing it, he says.

Many scientists fear a similarly dangerous feedback loop should large parts of the Arctic permafrost begin to thaw. This thick layer of soil, normally frozen year round, holds large stores of methane, a planet-warming gas significantly more potent, at least in the short term, than even carbon dioxide. Already researchers have begun to document increasing methane releases in the Arctic. Should enough methane enter the atmosphere, the Arctic itself, currently a natural "sink" for greenhouse gases, could become an aggregate -- and enormous -- source of the stuff.

Some observers have called it an Arctic "time bomb" that, after a certain melting point, will send a giant pulse of climate-altering methane into the atmosphere. Others suggest that the impacts will be dire but slow, measured in decades or centuries. Either way, the steady reduction in Arctic ice and snow, most scientists agree, is an expected byproduct of increased planet-warming gases in the atmosphere.

Potential signs of a changing climate are multiplying elsewhere. In the lower 48 states of the U.S., for example, the month of July was the hottest month ever recorded -- that is, since official record-keeping began nearly 125 years ago. As noted in a recent compilation of data prepared by Democratic Reps. Ed Markey of Massachusetts and Henry Waxman of California, ranking minority members of the House Natural Resources and Energy and Commerce committees, respectively, some 64 percent of the continental United States was experiencing drought in recent months. Wildfires have burned through huge swaths of the West.

During the first half of this year, surface temperatures in the northeastern Atlantic Ocean shattered a record dating back to 1854.

From the analysis:

The number of natural disasters has increased steadily over the past 30 years with natural disasters in 2011 resulting in the most costly toll in history -- $154 billion worth of worldwide losses from floods, tornadoes, hurricanes, wildfires, and other extreme weather events. In the United States alone, 2011 extreme weather events caused almost $60 billion in damages. This total does not include expenses associated with sickness or injuries triggered by the disasters. Given the number and severity of extreme events that have thus far occurred this year, weather-related costs in 2012 could equal or exceed those in 2011. According to Aon Benfield, a global reinsurance company, insured losses associated with natural disasters have totaled at least $22 billion through August 2012.

While no single incident can be unequivocally tied to climate change, these are precisely the sorts of outcomes that scientists have long suggested would arise if atmospheric concentrations of carbon dioxide continue to rise unchecked.

"This is what global warming looks like at the regional or personal level," said Dr. Jonathan Overpeck, a professor of geo- and atmospheric sciences at The University of Arizona, in the Markey-Waxman report. "The extra heat increases the odds of worse heat waves, droughts, storms and wildfire. This is certainly what I and many other climate scientists have been warning about."

BROKENHEARTED

Against such a dire backdrop, Obama has pursued what some critics would call an equivocal, and others a politically expedient path. The Obama administration has made historic investments in clean energy and fuel efficiency, for example, and emissions from the energy sector overall have declined in four out of the last six years, according to the Energy Information Administration.

lisa jackson

The president has also received high marks for quickly appointing a slate of tough, science-minded agency heads, including Lisa Jackson at the EPA.

Much of this drop is attributable to a sluggish economy and diminished industrial activity, however, and the administration has also advocated for expanded domestic oil and gas production, including in the Arctic. The president's clean energy achievements, critics say, have also been somewhat offset by continued investment in things like "clean coal" technology (an oxymoron to environmentalists) and an increasing aversion to discussing climate change unless it is couched in terms of energy production or green jobs.

To be sure, after taking office in January 2009, Obama and his team began pursuing numerous measures that would, directly or indirectly, reduce the amount of carbon dioxide being released into the atmosphere. One month into office he signed a $787 billion economic stimulus bill, which was loaded with investments and incentives for clean energy, weatherization and other energy efficiency programs, advanced battery and smart grid development, among other "green" projects.

The president has also received high marks for quickly appointing a slate of tough, science-minded agency heads with influence over climate policy. These included Steven Chu, the physicist and Nobel laureate at the Department of Energy, Jane Lubchenco at the National Oceanic and Atmospheric Administration, and Lisa Jackson at the Environmental Protection Agency.

The EPA's aggressive pursuit of tougher regulation of planet-warming emissions from power plants and vehicles -- driven in large part by the agency's historic determination that greenhouse gases are a threat to public health and therefore subject to oversight under the Clean Air Act -- has greatly angered industry and conservatives in Congress. Not surprisingly, the agency was quickly sued over that finding, though the courts have upheld it to date, most recently a federal appeals court in June.

For many supporters, these achievements cannot be underestimated. "Just take the vehicle standards," says Daniel J. Weiss, a senior fellow and director of climate strategy at the Center for American Progress Action Fund. "By the time they are fully implemented, they will reduce carbon pollution by 6 billion tons for the cars built from 2017 to 2025. That's like removing a year's worth of carbon pollution from the U.S. This administration has proposed the very first carbon pollution standard for coal-fired power plants. That's a historic step as well. Under his watch, we've doubled the generation of clean, renewable electricity from sources like solar and wind power.

"President Obama," Weiss added, "has done more to reduce carbon pollution than all of his predecessors put together."

Clark Stevens, the White House spokesman, also pointed to what he called "historic international agreements" brokered by the president, including the December 2009 accord reached at the United Nations climate conference in Copenhagen. "All told," Stevens said, "the Obama administration has taken unprecedented action to confront this issue."

Not everyone buys this, and the president has drawn sharp criticism for simultaneously embracing policies that, critics say, prolong the nation's addiction to fossil fuels and fail to reduce carbon emissions as quickly and dramatically as possible. At the same time, they charge Obama with giving too much rhetorical slack in his public statements to those who continue to deny years of climate science, thereby muddying the case for dramatic action.

Michael Mann, a prominent climate scientist and the director of the Earth System Science Center at Penn State University, for example, criticized the president for doing precisely this during his 2010 State of the Union speech. "I know that there are those who disagree with the overwhelming scientific evidence on climate change," Obama said at the time. "But even if you doubt the evidence, providing incentives for energy efficiency and clean energy are the right thing to do for our future."

Mann was unimpressed. "How far we had regressed in the 10 years since President Bill Clinton's 2000 State of the Union address, in which he issued a call to arms in confronting the climate change threat based on the strength of the science, not in spite of a conceded potential weakness in it."

Other critics were quick to point out that it was only a few months after that State of the Union address that Obama unveiled historic plans to expand oil and gas drilling up and down the Atlantic coast, as well as in the eastern Gulf of Mexico and the northern coast of Alaska. Those plans, which raised the ire of environmentalists, were quickly shelved when the well under BP's Deepwater Horizon drill rig began unleashing an unprecedented torrent of oil into the Gulf.

The administration quickly reformed federal oversight of offshore oil and gas drilling, but critics say the administration has since made haste to burnish its record as a friend to oil and gas, touting historic expansions of land-based domestic oil and gas development and approving new forays for oil in the icy and environmentally sensitive waters off the coast of Alaska.

"Instead of ramping up fossil fuel exploration, we should be doing the opposite," wrote J. Mijin Cha, a senior policy analyst with the nonpartisan research and policy organization Demos, in an essay last month. "It will take some time to have a renewable energy infrastructure in place and instead of spending time and money on extreme energy sources, we should be investing in our future."

Whether such ambitions might have been better realized through legislation, as opposed to executive action, is an open question, but here too Obama has drawn criticism -- partly for spending his early political capital in pursuit of health care and immigration reform, while failing to adequately support efforts to find consensus on climate legislation in Congress.

As it was, the House did manage to pass such legislation -- albeit by a very narrow margin -- in June 2009. But a few short months later, after conservative groups and big business lobbies had managed to characterize the measure as a big-government tax scheme, Democrats took a shellacking in the midterm elections, losing 63 seats in the House.

The drubbing undermined the president's ability to agree to concrete terms with other major polluting nations at the Copenhagen conference that year. The accord that was reached -- at its heart an agreement to continue pursuing an international agreement -- has proved all but meaningless.

A Senate version of a climate bill fell apart a few months later, at roughly the same time that Obama was announcing his plan to expand offshore oil and gas exploration.

"On the climate bill, the president was just stepping back and not leading," said Phil Radford, the executive director of Greenpeace USA, in a recent phone call. "And in that absence of that leadership, the bill just became a piñata for polluters.

"I had senior members of Congress say to me, 'I'm all alone here,'" Radford added. "They said, 'I'm not getting any help from the White House.'"

In the minds of those who would argue that there is no longer time to waste in addressing the looming threat of global warming, all of this has left Obama's first-term climate legacy as something of a patchwork of high and low moments. The last four years, they say, have sometimes been punctuated by lofty, if brief, assertions that climate change is a real threat. But the president has also hobbled himself, they say, by too often seeking the middle on energy, and by refusing to present the threat of climate change as a problem so real and so immediate that the nation can no longer afford to dither over whether and when to make drastic cuts in the amount of fossil fuel it burns, and make much more aggressive investments in clean energy.

In an email message last week, Mann said he thought the president had been "more forceful in the way he's framed the issue in recent months," and that he held out hope that Obama will make it higher priority in a prospective second term.

"I'd like to see the administration put forward an energy plan for Congress to vote on," Mann said, "which meaningfully addresses climate change risks through incentives for non-fossil fuel energy combined with some means of internalizing the costs associated with the damages caused by fossil fuel burning."

Greenpeace's Radford, asked prior to last week's debate what question he might put to the president, said, "I would ask him if in his heart he believes that the policies he's pursuing are enough to really make the world his children are inheriting a safer place."

But perhaps the most pointed criticism of the last four years came from Rena Steinzor, a professor of law at the University of Maryland and the president of the Center for Progressive Reform, a Washington-based research organization focused on health, safety and environmental issues. "I'm brokenhearted," she said.

"In a big picture way, I would say it was a fundamental mistake to talk about climate change, as the president has, in terms of foreign oil and green jobs. I think you need to talk about climate change itself," Steinzor said in a phone call. "I think he missed the opportunity to use the bully pulpit of the presidency to explain to the American people exactly what's going to happen if we don't act."

LOOKING AHEAD

Virtually no one believes that Romney and his running mate, Rep. Paul Ryan of Wisconsin, would do more than Obama to tackle climate change. Romney himself has vacillated on the subject over the years, most recently suggesting that while it seems likely that humans are contributing to planetary warming, it remains unclear just how dire the situation really is. Ryan, meanwhile, has in the past suggested that climate scientists have manipulated data to satisfy a green agenda -- a view that has little merit.

keystone protestors

Demonstrators protest the Keystone XL pipeline and the Canadian oil patch it would tap. They'd prefer that these sorts of fossil fuels stay in the ground.

On Obama's record, analysts like Kevin Book, the managing director of research at ClearView Energy Partners, a Washington-based consulting and research firm, argues that the impacts of some policy victories will prove substantial over time. He points in particular to EPA's conclusion that greenhouse gases are a danger to public health and the agency's aggressive efforts to regulate them under the Clean Air Act.

"You can say the president hasn't done as much maybe as he set out to do on climate, or as he had been expected to," Book said. "But what he has done is introduce one of the most ground-shifting policies in a generation. The endangerment finding is altering everything right now.

"The administration isn't out there advertising it, which makes sense," he added. "You don't lead with your chin."

To be sure, addressing climate is a tall order given the politics at play. The president has been saddled with a flagging economy at home even as he faces a challenge with intrinsically global dimensions, particularly given that nations like China and India -- up-and-coming economies that now directly compete with the U.S. -- aren't willing to take on dramatic greenhouse gas limitations of their own. And of course, however sound the science, prominent skeptics continue to sow doubt among some American voters.

Congressional Republicans have also put forward dozens of environmentally regressive bills, including several aimed at preventing the EPA from regulating greenhouse gases at all. Fossil fuel companies, meanwhile, have invested more than $150 million in an effort to unseat the president.

Pointing to the combination of Republican opposition and high unemployment, Daniel Weiss said it was unfair to criticize the Obama administration for, say, failing to help nudge a climate bill through Congress. "It's Monday morning quarterbacking in the extreme to say he could have done or should have done more when it was never in the cards," Weiss said.

McKibben seems to concede as much. "My sense is, [Obama] thought he was walking a very fine tightrope and judged that he had little room for error or the right would take him down," McKibben said. "So while there's a long list of things I would have liked to have seen -- a drumbeat of attention from the presidential podium on the climate challenge, a real pre-Copenhagen push of serious climate diplomacy, and so on -- I don't waste my time crying about it. It's clear that we failed to open up the space he thought he needed to act, so there are failings here on all sides."

McKibben says he's given up trying to nudge leadership in Washington to act. Last fall, his organization, 350.org, mounted some of the largest demonstrations in a generation in an effort to forestall administration approval of the Keystone pipeline, the contentious project that would bring a particularly dirty and greenhouse gas-intensive form of oil known as oil sands from Canada to refineries in Texas. NASA's James Hansen has described development of the Canadian oil patch as "game over" for the climate.

Almost every sign suggested that the administration would approve the project, but at the 11th hour, and amid the crowds protesting outside the White House, Obama announced a delay in the decision-making process -- until after this November's election.

McKibben has no faith that the project won't ultimately be built, and he has set his sights on promoting an apartheid-like disinvestment campaign aimed at producers of fossil fuels. Until their influence is diminished, he suggests, there's little reason to expect leadership in Washington really to tackle the climate problem.

"Clearly there's been a failure of leadership, because we haven't gotten anywhere," he said. "The key thing is to start figuring out where that failure lies, and if we keep endlessly hoping that politicians will solve the problem for us, it seems unlikely that they are going to.

"I don't think we're going to elect a more progressive president, whatever that means, than Obama in the years to come," he added, "So you could say, 'Well, he hasn't solved it, so it's insoluble and let's go away and watch everything melt.' The other option is to say, 'Let's figure out how to open up the kind of space that our leaders need to do their work.'"

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