"Spread in model climate sensitivity traced to atmospheric convective mixing," by S. C. Sherwood, S. Bony & J.-L. Dufresne, Nature 505 (2014); doi: 10.1038/nature12829

Nature, 505 (2 January 2014) 37-42; doi: 10.1038/nature12829

Spread in model climate sensitivity traced to atmospheric convective mixing

• Steven C. Sherwood,
• Sandrine Bony and
•  Jean-Louis Dufresne

Abstract

Equilibrium climate sensitivity refers to the ultimate change in global mean temperature in response to a change in external forcing. Despite decades of research attempting to narrow uncertainties, equilibrium climate sensitivity estimates from climate models still span roughly 1.5 to 5 degrees Celsius for a doubling of atmospheric carbon dioxide concentration, precluding accurate projections of future climate. The spread arises largely from differences in the feedback from low clouds, for reasons not yet understood. Here we show that differences in the simulated strength of convective mixing between the lower and middle tropical troposphere explain about half of the variance in climate sensitivity estimated by 43 climate models. The apparent mechanism is that such mixing dehydrates the low-cloud layer at a rate that increases as the climate warms, and this rate of increase depends on the initial mixing strength, linking the mixing to cloud feedback. The mixing inferred from observations appears to be sufficiently strong to imply a climate sensitivity of more than 3 degrees for a doubling of carbon dioxide. This is significantly higher than the currently accepted lower bound of 1.5 degrees, thereby constraining model projections towards relatively severe future warming.

See 10 figures at this link:  http://www.nature.com/nature/journal/v505/n7481/full/nature12829.html

Planet likely to warm by 4C by 2100, scientists warn

New climate model taking greater account of cloud changes indicates heating will be at higher end of expectations

by Damian Carrington, The Guardian, December 31, 2013

The role clouds play in climate change has been something of a mystery – until now. Photograph: Frank Rumpenhorst/ Frank Rumpenhorst/dpa/Corbis

Temperature rises resulting from unchecked climate change will be at the severe end of those projected, according to a new scientific study.

The scientist leading the research said that unless emissions of greenhouse gases were cut, the planet would heat up by a minimum of 4 degrees centigrade by 2100, twice the level the world's governments deem dangerous.

The research indicates that fewer clouds form as the planet warms, meaning less sunlight is reflected back into space, driving temperatures up further still. The way clouds affect global warming has been the biggest mystery surrounding future climate change.

Professor Steven Sherwood, at the University of New South Wales, in Australia, who led the new work, said: "This study breaks new ground twice: first by identifying what is controlling the cloud changes and second by strongly discounting the lowest estimates of future global warming in favour of the higher and more damaging estimates."

"4 C would likely be catastrophic rather than simply dangerous," Sherwood told the Guardian. "For example, it would make life difficult, if not impossible, in much of the tropics, and would guarantee the eventual melting of the Greenland ice sheet and some of the Antarctic ice sheet," with sea levels rising by many metres as a result.

The research is a "big advance" that halves the uncertainty about how much warming is caused by rises in carbon emissions, according to scientists commenting on the study, published in the journal Nature. Hideo Shiogama and Tomoo Ogura, at Japan's National Institute for Environmental Studies, said the explanation of how fewer clouds form as the world warms was "convincing," and agreed this indicated future climate would be greater than expected. But they said more challenges lay ahead to narrow down further the projections of future temperatures.

Scientists measure the sensitivity of the Earth's climate to greenhouse gases by estimating the temperature rise that would be caused by a doubling of CO2 in the atmosphere compared with pre-industrial levels – as is likely to happen within 50 years, on current trends. For two decades, those estimates have run from 1.5 to 5 C, a wide range; the new research narrowed that range to between 3 and 5 C, by closely examining the biggest cause of uncertainty: clouds.

The key was to ensure that the way clouds form in the real world was accurately represented in computer climate models, which are the only tool researchers have to predict future temperatures. When water evaporates from the oceans, the vapour can rise over 9 miles to form rain clouds that reflect sunlight; or it may rise just a few miles and drift back down without forming clouds. In reality, both processes occur, and climate models encompassing this complexity predicted significantly higher future temperatures than those only including the 9-mile-high clouds.

"Climate sceptics like to criticise climate models for getting things wrong, and we are the first to admit they are not perfect," said Sherwood. "But what we are finding is that the mistakes are being made by the models which predict less warming, not those that predict more."

He added: "Sceptics may also point to the 'hiatus' of temperatures since the end of the 20th century, but there is increasing evidence that this inaptly named hiatus is not seen in other measures of the climate system, and is almost certainly temporary."

Global average air temperatures have increased relatively slowly since a high point in 1998 caused by the ocean phenomenon El Niño, but observations show that heat is continuing to be trapped in increasing amounts by greenhouse gases, with over 90% disappearing into the oceans. Furthermore, a study in November suggested the "pause" may be largely an illusion resulting from the lack of temperature readings from polar regions, where warming is greatest.

Sherwood accepts his team's work on the role of clouds cannot definitively rule out that future temperature rises will lie at the lower end of projections. "But," he said, for that to be the case, "one would need to invoke some new dimension to the problem involving a major missing ingredient for which we currently have no evidence. Such a thing is not out of the question but requires a lot of faith."

He added: "Rises in global average temperatures of [at least 4 C by 2100] will have profound impacts on the world and the economies of many countries, if we don't urgently start to curb our emissions."

http://www.theguardian.com/environment/2013/dec/31/planet-will-warm-4c-2100-climate

Climate change by the numbers: The worst is yet to come

CO2 levels went through the roof in 2013, as the world tried — and mostly failed — to slow down warming

by Lindsey Abrams, Salon, December 30, 2013

EnlargeFirefighters battle the Rim Fire near Yosemite National Park, Calif., on Aug. 25, 2013. (Credit: AP/Jae C. Hong/Salon)

“We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations,” President Obama announced back in January at his second-term inauguration. Thus began another year of steady climate change, continued pollution of the atmosphere and half-hearted attempts at changing the world’s dire trajectory.

By many measures, 2013 wasn’t particularly extreme: it it wasn’t the hottest we’ve ever seen; its storms, by and large, weren’t the most devastating. Much of what occurred can best be seen as a sign of things to come. Droughts, believed to be exacerbated by climate change, will become more widespread. Wildfires are expected to get bigger, longer and smokier by 2050. Twelve months, after all, is but a short moment in Earth’s history. Only in the future, looking back, will we be able to recognize the true significance of many of this year’s big numbers:

7: Where 2013 ranks among the warmest years in history, according to the World Meteorological Association. Tied with 2003, the ranking is based on the year’s first nine months, during which average temperatures were 0.86 °F above the 1960-1991 global average.

395.5: The average concentration levels of CO2 in parts per million (ppm) observed in the atmosphere through November.

400: The ”milestone,” in parts per million of atmospheric CO2, that was temporarily crossed in May. It was the first time carbon levels crossed that boundary in 55 years of record-keeping — and possibly in 3 million years of history on Earth.

95: Percent certainty with which IPCC scientists say climate change is caused by human activity, a confidence level up from 90% in 1997.

1,100: Amount by which EPA regulations proposed in September would limit emissions from new coal-fired power plants, in pounds of CO2 per hour. The average plant currently emits CO2 at a rate of 1,800 pounds per hour.

25: The factor by which the concentration of PM 2.5 — the part of air pollution most harmful to human health — exceeded the amount considered safe in the U.S. when Beijing’s first “airpocalypse” occurred in January

1,000: Air pollution levels in the Chinese city of Harbin, in micrograms per cubic meter of PM 2.5, during October’s smog emergency. According to the World Health Organization, it shouldn’t exceed 20; anything higher than 300 is considered hazardous.

8: Age of girl in Harbin who contracted lung cancer.

3.8: Percent by which Japan said it would try to reduce its emissions by 2020, down from its  previous pledge of 25%.

1.97 million: The annual minimum extent of Arctic sea ice, in square miles. Melting this year wasn’t as severe as it was in 2012, but the remaining area was still 17% below average — and the sixth lowest on record.

3.2: Current average sea level rise, in millimeters per year. Sea levels reached a record high in March.

104.6: The average country-wide temperature, in degrees Fahrenheit, on January 7 in Australia — the continent’s hottest day on record, in its hottest month on record.

121.3: The temperature reading, in degrees Fahrenheit, in the South Australian town of Moomba on January 12.

90: Percent confidence with which researchers at the University of Melbourne concluded, in July, that “human influences on the Australian atmosphere had dramatically increased the odds of extreme temperatures.”

129.2: The temperature, in degrees Fahrenheit, recorded in California’s Death Valley on June 30, setting a record for the hottest temperature ever recorded on Earth for that month.

2: The weather emergency level declared by officials in China during this summer’s heat wave — a number normally reserved for typhoons and floods.

1.7 billion: The estimated cost, in USD, of New Zealand’s drought — its worst in 30 years.

10: The number of consecutive months during which over half of the contiguous U.S. experienced moderate or severe drought, which finally fell below 50% in mid-April 2013.

72: Percent of land area in 10 Western states in drought conditions after a record-breaking heat wave in June.

3.95: Inches of rain that fell from January to November in San Francisco. When the final numbers come in, it’s likely that California will be found to have had its driest year on record.

257,000: Acres of land burned by the California Rim Fire, the biggest wildfire in Sierra’s recorded history, which caused over $50 million in damage. It was caused by a number of factors, drought and abnormal seasons included.

5.9–7.9: The amount of rain, in inches, that normally falls over two and a half months and instead pummeled central Europe between May 30 and June 1. Floodwaters in Germany rose to their highest levels in over 500 years.

1.3: The width, in miles, of the tornado that struck Moore, Oklahoma on May 20. Sen. Sheldon Whitehouse, D-R.I., caused controversy when he invoked the storm during a speech criticizing climate deniers. While researchers cannot be sure there was a link between climate change and the twister, they believe that a warming planet may host more frequent, stronger storms.

2.6: The width, in miles, of the tornado that struck El Reno, Oklahoma, 10 days later. It was the widest ever measured on Earth.

20 billion: Cost, in dollars, of plans laid out by NYC Mayor Bloomberg in June to make infrastructure improvements, including floodwalls and storm barriers, in preparation for the effects of climate change.

6,100: The most recent death count from Typhoon Haiyan, which officially became the deadliest storm in Philippines’ history. Bodies continue to be recovered.

132: The number of countries that walked out of the U.N. climate talks in Warsaw in protest over rich nations’ refusal to entertain the idea of compensation for extreme climate events

90: The number of global companies that together account for two-thirds of greenhouse gas emissions, according to a report in the journal Climactic Change.

7 billion: The number of “key individuals” responsible for climate change. The Onion, as always, is spot on.

http://www.salon.com/2013/12/29/climate_change_by_the_numbers_the_worst_is_yet_to_come/

Public Outrage Over Climate Inaction Reaches Fever Pitch in 2013

After years of silence, the climate conversation is now happening on many levels—from the White House to Wall Street and from classrooms to the streets.

by Katherine Bagley, InsideClimate News, December 30, 2013

Activists protest against the Keystone XL pipeline during President Obama's visit to New York City on May 13, 2013. Credit: maisa_nyc, flickr

Frustrated by years of waiting on politicians to reduce American dependence on climate-changing fossil fuels, an unprecedented number of citizen activists rallied to send a message in 2013: Enough is enough.  

Thousands of chanting marchers took to the streets, from Washington, D.C., to San Francisco, urging policymakers to take action against global warming. They wanted Congress to end the inertia that has built-up over climate policy. They wanted help protecting themselves from climate threats like Superstorm Sandy. They also wanted President Obama to reject the Keystone XL pipeline—which would funnel as much as 830,000 barrels per day of Canadian tar sands oil across America's midsection. The controversial project has become a symbol of the battle over the nation's energy policy.

Some activists took a more aggressive tack. Dozens chained themselves to construction equipment used to build the southern leg of the Keystone XL—which runs from Oklahoma to Texas and is now complete. Still others stormed government agencies and fossil fuel company headquarters, getting themselves arrested in the process.  

All together, this widespread action represented the reemergence of an environmental movement on par with that of the 1960s. This time the goal was to make global warming the moral issue of this generation.

A divestment campaign with roots in the South African apartheid protests of the 1980s was a catalyst for the reinvigorated movement. Led by Bill McKibben, an environmental writer-turned-activist, and his organization 350.org, the campaign sought to convince colleges and other institutions to withdraw holdings in coal, oil and gas companies in an effort to force climate change onto the political agenda. Some 400 divestment campaigns are now underway at universities across North America—with 9 colleges having agreed to divest their endowments. Dozens of cities and religious institutions have also pledged to make their portfolios fossil fuel-free.

Green groups weren't the only ones calling for action this year. Scientists—historically known for staying out of political issues—became more vocal about the need to address global warming. They issued report after report in the lead-up to December's international climate talks in Warsaw asking global leaders to dramatically curb emissions.

In September, the United Nations-run Intergovernmental Panel on Climate Change concluded with 95% certainty—the highest yet—that human activities caused most of the earth's temperature rise since the 1950s, and will continue to do so in coming decades. For the first time, the report's authors declared that the world is in serious danger of exhausting its "carbon budget," or the amount of fossil fuels countries can safely burn before triggering catastrophic climatic changes.

Meanwhile, Wall Street investors started demanding that top fossil fuel producers calculate the financial risks of pouring billions of dollars into oil, coal and gas projects. They worry that carbon emission limits and market factors could prevent companies from selling all of their fossil fuel reserves—leaving stockpiles of "unburnable" carbon energy that would batter firms' stock prices and harm investors.

Educators also took a stance. Twenty-six states representing more than half of America's youth wrote new science standards that for the first time require K-12 students learn about human-driven climate change.

Acceptance of climate change grew on both sides of the voting ballot in 2013, as people connected the dots between extreme weather events such as Sandy and record-breaking wildfires and global warming. According to an October poll by the Pew Research Center, half of Republicans, 62% of independents and 88% of Democrats say there is solid evidence of climate change. In comparison, only 35% of Republicans, 53% of independents, and 75% of Democrats believed that 4 years ago.

http://insideclimatenews.org/news/20131230/public-outrage-over-climate-inaction-reaches-fever-pitch-2013

Two Subglacial Lakes Discovered in Greenland

by Sci-News.com, November 28, 2013

A team of researchers from the University of Cambridge’s Scott Polar Research Institute has discovered two lakes about 800 m below the ice sheet near the town of Qaanaaq in northwestern Greenland.

This map shows the location of two subglacial lakes near the town of Qaanaaq in northwestern Greenland.

Subglacial lakes are likely to influence the flow of the ice sheet, impacting global sea level change. The discovery of the lakes in Greenland will help researchers to understand how the ice will respond to changing environmental conditions.

The Cambridge scientists used airborne radar measurements to reveal the lakes underneath the ice sheet.

The two lakes are roughly 8-10 km2, and at one point may have been up to 3 times larger than their current size.

They are found in the northwest sector of the Greenland Ice Sheet, about 40 km from the ice margin, and below 757 and 809 m of ice, respectively.

“Our results show that subglacial lakes exist in Greenland, and that they form an important part of the ice sheet’s plumbing system. Because the way in which water moves beneath ice sheets strongly affects ice flow speeds, improved understanding of these lakes will allow us to predict more accurately how the ice sheet will respond to anticipated future warming,” said Dr Steven Palmer, the lead author of the study published online in the journal Geophysical Research Letters.

The lakes are unusual compared with those detected beneath Antarctic ice sheets, suggesting that they formed in a different manner.

This radar map shows subglacial bed elevations near the town of Qaanaaq; lines show contours of the newly discovered subglacial lakes; dashed lines show possible previous larger contours. Image credit: S. J. Palmer et al.

The scientists propose that, unlike in Antarctica where surface temperatures remain below freezing all year round, the newly discovered lakes are most likely fed by melting surface water draining through cracks in the ice. A surface lake situated nearby may also replenish the subglacial lakes during warm summers. This means that the lakes are part of an open system and are connected to the surface, which is different from Antarctic lakes that are most often isolated ecosystems.

While nearly 400 lakes have been detected beneath the Antarctic ice sheets, the two newly discovered lakes are the first to be identified in Greenland.

Bibliographic information: Palmer SJ et al. 2013. Greenland subglacial lakes detected by radar. Geophysical Research Letters, published online; doi: 10.1002/2013GL058383

http://www.sci-news.com/othersciences/geography/science-subglacial-lakes-greenland-01581.html

The Climate Champions Of 2013

BY JOANNA M. FOSTER CLIMATE PROGRESS, DECEMBER 23, 2013

"The Climate Champions Of 2013"

 

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In a year that saw carbon pollution levels hit the milestone of 400 parts per million in the atmosphere and brought record-breaking drought, fires, typhoons, and air pollution, it can be easy to forget there are climate champions out there, pushing back on those climate grinches. Here are a few of the climate heroes that made progress, inspired, or otherwise made an impact in 2013:

Naderev “Yeb” Saño

CREDIT: AP

Three days after Typhoon Haiyan made landfall, Philippines climate negotiator Naderev “Yeb” Saño told the delegation at the 19th United Nations Framework Convention on Climate Change (COP19) that his island nation had run out of time for failed climate negotiations. Saño vowed to go on a hunger strike until “clear progress was made.” Saño challenged climate change deniers and countries less impacted by the effects of global warming, saying, “I dare them, I dare them to get off their ivory towers and away from the comfort of their armchairs. I dare them to go to the islands of the Pacific, the Caribbean, the Indian ocean and see the impacts of rising sea levels; to the mountainous regions of the Himalayas and the Andes to see communities confronting glacial floods, to the Arctic where communities grapple with the fast dwindling sea ice caps, to the large deltas of the Mekong, the Ganges, the Amazon, the Nile where lives and livelihoods are drowned, to the hills of Central America that confronts similar monstrous hurricanes, to the vast savannas of Africa where climate change has likewise become a matter of life and death as food and water become scarce. … And if that is not enough, you may want to pay a visit to the Philippines right now.”

Michael Mann

CREDIT: MICHAEL MANN

Michael Mann, who directs Penn State University’s Earth System Science Center and is the creator of the “hockey-stick” graph, which illustrates the recent spike in global temperatures, has been the target of legal battles for years. He has been investigated by Penn after his email was hacked during so-called “climategate” and in 2010 was accused of defrauding Virginia taxpayers while he was a faculty member at the University of Virginia. Virginia attorney general Ken Cuccinelli demanded access to every document relating to his research during that time. Mann has never been convicted of any wrong-doing and now, Cuccinelli has been defeated in the 2013 Virginia gubernatorial race. Climate denial was a central issue in the race with fossil fuel companies backing Cuccinelli, while climate activists spent millions for Terry McAullife. Cuccinelli’s “witch hunt” after Mann was held up as an example of Cuccinelli prioritizing his own radically conservative agenda over the concerns of his constituents. McAuliffe said that “the fact that UVA was forced to spend $600,000 to defend itself from its own Attorney General is outrageous.”

LA Times

CREDIT: AP

The Los Angeles Times announced in 2013 that it will no longer publish letters from climate change deniers.

“Simply put, I do my best to keep errors of fact off the letters page; when one does run, a correction is published,” wrote letters editor Paul Thornton explaining his decision. “Saying ‘there’s no sign humans have caused climate change’ is not stating an opinion, it’s asserting a factual inaccuracy.”

Climate change deniers have long argued that the extent of man-made global warming has been wildly exaggerated in order to advance an agenda that includes more government control and decried the decision by the LA Times as taking a political side. The LA Times has chosen to listen to the 97% of scientists who believe that climate change is happening and that it is in large part the result of human actions. Many in the scientific community applauded the decision by the LA Times, hoping the decision would give other outlets the courage to stop “appeasing the climate change denial noise machine.” The Times was followed by Popular Science’s decision to shut off its comments and Reddit’s science forum prohibiting posts and comments by people who deny the realities of man-made climate change.

Sheldon Whitehouse

On November 13, 2013, Senator Sheldon Whitehouse (D-RI) went to the floor of the Senate for the 50th time in 50 weeks to push for congressional action to address climate change.

“We are a great country, but not when we’re lying and denying what’s real,” he said. “The atmosphere is warming; ice is melting; seas are warming, rising, and acidifying. It is time for the misleading fantasies to end.”

Whitehouse started delivering the speeches in April 2012 to counteract the Senate’s practical avoidance of the issue. While the Senator often addresses a nearly-empty Senate floor, he is determined to not settle for silence on this huge issue and will keep on talking, hoping that more people will soon listen.

Barbara Kingsolver

CREDIT: SHUTTERSTOCK

Not many top novelists have tackled climate change as subject matter, despite the wide variety of apocalyptic and inspiring plot lines it offers. In her 2013 novel “Flight Behavior” Kingsolver does just this — using the story of a restless young mother in rural Tennessee to shed new light on the story of a planet out of balance. Kingsolver’s protagonist, Dellarobia Turnbow, discovers a colony of monarch butterflies on her family’s property. Soon these butterflies, mysteriously far from their ancient migration route have caught the attention of scientists, tourists, activists and journalists around the world — all of whom collide in rural Tennessee, understanding nothing about each other and ready to fight about what has caused the butterflies to wander so far. The novel dives deep into how identity determines people’s willingness or refusal to accept the reality of climate change, and offers readers exhausted by scientific studies and government reports a fresh and entertaining way to consider the changing climate and society’s response.

Massachusetts

CREDIT: AP PHOTO/MICHAEL DWYER

For the third year running, Massachusetts won the coveted top spot on the annual energy efficiency state scorecard released every year by the American Council for an Energy-Efficient Economy. Massachusetts has held onto its lead due in large part to the continued implementation and growth of the programs put in place in 2008 with the passage of the Green Communities Act. This landmark law required utilities to increase investment in energy efficiency measures, mandated the design and implementation of three-year energy efficiency plans for gas and electric utilities, required that 15 percent of electricity be supplied by new renewable power facilities by 2020, established a pilot program for utilities to enter into long-term contracts with renewable energy developers and encouraged green building design through updated codes, training, and assistance.

Al Jazeera America

CREDIT: AP PHOTO/BEBETO MATTHEWS

On its first day on air, Al Jazeera America devoted a full half-hour to an expert panel discussing climate change. The panel included Michael Mann from Penn State University, Heidi Cullen from Climate Central, and Klaus Jacob from the Lamont-Doherty Earth Observatory at Columbia. This first-day coverage is nearly half as much time as all network news programs gave climate change during all of 2012, and as Media Matters noted, “all while avoiding common pitfalls like providing false balance to those that deny the science and leaving the crisis’ manmade origins ambiguous.”

Josh Fox

CREDIT: AP

In his 2010 Emmy-winning and Oscar-nominated documentary GasLand, Josh Fox took his banjo, camera and dark sense of humor on a road trip to explore the affects of the natural gas boom. In doing so, he galvanized the U.S. anti-fracking movement and made flaming tap water a symbol of the fight. In 2013, Fox continued his crusade to educate Americans about what is happening on their public lands and in their backyards with the release of his sequel, Gasland 2. His latest documentary focuses special attention on industry’s efforts to silence protesters and examines the potentially corrupting influence of industry on politicians and regulators.

“I felt like I could see it: a horizontal well bore, drilled down into the earth, snaking underneath the Congress, shooting money up through the chamber at such high pressure that it blew the top off of our democracy,” Fox narrates in Gasland 2. “Another layer of contamination due to fracking, not the water, not the air, but our government.”

Michael Bloomberg

CREDIT: SHUTTERSTOCK

After 12 years as mayor of New York City, Michael Bloomberg is now counting down his last days in office, while commentators and ordinary New Yorkers tally up his achievements, controversies, and attempt to summarize his legacy. One thing is for sure, Bloomberg will leave the nation’s largest city more sustainable and more prepared to meet the future challenges of climate change. In 2007, Bloomberg released PlaNYC, a sweeping sustainable program including 127 initiatives that would transform New York into a greener city and a leader in the fight against climate change. The program helped restore wetlands, create new open space and created miles of new bike lanes. It also significantly reduced pollution in the city. Post-Sandy, Bloomberg has pledged $20 billion to rebuild New York City to be a more resilient, climate ready metropolis.

John Kerry

CREDIT: AP

John Kerry has been beloved by the environmentally-minded for decades. And unlike some, he hasn’t abandoned his green record as he has risen in the political world. Now as Secretary of State, Kerry still speaks frankly about the global threat of climate change. Climate was a major talking point during Kerry’s trip to India earlier this year. And touring the devastation caused by Typhoon Haiyan last week, Kerry called the storm a warning of extreme weather in a warming world as he pledged more U.S. support to the Philippines.

Bill McKibben

Bill McKibben used to be a mild-mannered journalist. Today, he is the leader of one of the biggest grassroots environmental movements in decades. In 2007, McKibben and a group of graduates from Middlebury College founded the organization 350.org. The name refers to scientist James Hansen’s quantification of the maximum concentration of carbon dioxide (350 parts per million) the atmosphere can contain while still offering “a safe operating space for humanity.” McKibben’s “Do The Math” tour this year has taken his message on the road. Speaking at sold-out venues across the country, McKibben does the math for his audiences — we can only emit 565 more gigatons of carbon dioxide and stay below 2 °C of warming. That’s just a tiny fraction of the 2,795 gigatons of carbon dioxide that will be emitted if corporations bring to market what they have in their reserves.

http://thinkprogress.org/climate/2013/12/23/3073901/climate-champs-2013/