ONE TOWN SQUARE: at the intersection of peak oil, climate change, and land use

Imagery from the NSIDC Multisensor Analyzed Sea Ice Extent (MASIE) shows that the southern route of the Northwest Passage as well as the Northern Passage are now free of sea ice.

2011 is the fourth consecutive year – and the fourth time in recorded history – that both Arctic shipping routes have become open to navigation.

Arctic ice extent is declining at a brisk pace, but melt is slightly behind the pace set in 2007, the record low year – as seen in this image at the IJIS Web site provided by the Japan Aerospace Exploration Agency (JAXA).

The National Snow and Ice Data Center (NSIDC) reports weather conditions in late July spread the ice out, but that conditions are now again such that sea ice extent may decline rapidly:

During early summer, a high-pressure cell persisted over the northern Beaufort Sea, promoting ice loss. This weather pattern broke down toward the end of July, slowing ice loss but spreading out the ice pack, making it thinner on average. The weather has now changed again, bringing another high-pressure pattern. Winds associated with this pressure pattern generally bring warm temperatures, and tend to push the ice together and reduce overall extent. In the Kara Sea, the combination of a high-pressure cell with low pressure to the west has resulted in strong northward ice movement, pushing the ice pack away from the coast and reducing ice extent. The same weather pattern is also increasing the movement of ice out of Fram Strait, between Greenland and Spitsbergen.

Right now, there is a record divergence between area and extent, as Neven reports at Arctic Sea Ice Blog. The difference is often substantial, as can be seen by comparing the graph of sea ice extent, above, with that of sea ice area, below, posted by Joseph Romm at Climate Progress.

The ratio of sea ice area to sea ice extent is now at a record low, as seen in the graph below.

NSIDC also reports that Arctic sea ice volume is now showing record lows. Through July 20 this year, the ice surface was melting faster than the underside of the ice. As the Arctic days grow shorter surface melt will slow – but ocean waters warmed during the summer will continue to melt the ice from below, reducing ice thickness and extent into September.

The University of Washington’s Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) model projects that this year’s minimum volume in September will very likely finish below 2007, reaching a new record low volume.

Arctic sea ice extent is posting record lows in 2011. The Northern Sea Route is open, and sea ice in the Northwest Passage is melting rapidly.

Even more import than ice extent, Arctic sea ice volume is showing record lows.

The University of Washington’s Polar Science Center reports monthly averaged ice volume for July 2011 was 51% lower than the mean over the 1979-2010 period, 62% lower than the maximum in 1979, and 2.5 standard deviations below the trend.

New research from MIT finds that Arctic sea ice is thinning, on average, four times faster than the models used in the 2007 IPCC Forth Assessment Report indicate – and it’s drifting away twice as rapidly. The Fourth Assessment Report forecast an ice-free Arctic by 2100; we now expect it to happen several decades earlier.

Joseph Romm at Science Progress says we can expect Arctic sea ice to crash by two thirds by the 2030s and then collapse to near-zero shortly thereafter — unless we cut global GHG emissions about 60% to 70% almost immediately and then follow up with more cuts. That simply is not going to happen.

Not only will humans continue to spew GHG emissions. Mother Nature is starting to kick in, too.  Sea ice is just the canary in the coal mine.

Carbon emission (in billions of tons of carbon a year) from thawing permafrost.

In assessing the global warming impacts of melting permafrost, the NSIDC study that resulted in the graph above doesn’t even incorporate the CO2 released by the permafrost as feedback into its warming model, and further assumes that all of the permafrost carbon would be released as CO2 and none as methane. Methane is 25 times as potent a heat-trapping gas as CO2 over a 100 year time horizon, but 72 times as potent over 20 years.   The study warns:

The thaw and decay of permafrost carbon is irreversible and accounting for the PCF will require larger reductions in fossil fuel emissions to reach a target atmospheric CO2 concentration.

Setting atmospheric CO2 target – any target, no matter how inadequate to avert climate catastrophe – is no longer even on the international political agenda, is no longer even imaginable as part of the U.S. political agenda. Actually doing anything, voluntarily, to achieve any such target is inconceivable, as that would require that we begin to dismantle industrial civilization.

We’re approaching the end of the play. Time for the deus ex machina.

The National Snow and Ice Data Center (NSIDC) reports average Arctic sea ice extent for July 2011 was the lowest level for the month since satellite records began in 1979.

Daily Arctic sea ice extent as of August 2, 2011, along with daily ice extents for previous low-ice-extent years. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, purple shows 2008, and dark gray shows the 1979 to 2000 average. The gray area around the average line shows the two standard deviation range of the data.

Ice loss slowed substantially over the latter half of the month as the weather changed. A high-pressure cell centered over the northern Beaufort Sea broke down and a series of low-pressure systems moved over the central Arctic Ocean, bringing cooler conditions and likely pushing the ice apart into a thinner but more extensive ice cover.

In the first week of August, with a month or more to go in the melt season, Arctic sea ice area has already dropped below not just the year-to-date values, but the annual low points of any satellite-era year before 2007.

Shipping routes in the Arctic have less ice than usual for this time of year, and more of the Arctic’s oldest ice has disappeared.

Sea ice concentration (left) and ice age (right) over the Arctic Ocean. In the Beaufort Sea off the coast of Alaska, ice has melted back to the edge of a tongue of older, thicker ice. In the "Ice Age" image, red shows ice 5 years old and older, green shows 4-year-old ice, light blue shows 3-year old ice, dark blue shows second-year ice, and purple shows first-year ice.

Over the past few weeks, the sea ice edge has retreated from the shores of Siberia and Eurasia, opening up much of the Northern Sea Route – the shipping lane that runs along the Eurasian Arctic coast from Murmansk on the Barents Sea, along Siberia, and through the Bering Strait. Some ice remains, particularly in the East Siberian Sea, but the reduced ice cover in the region has already made the route feasible this year. Taking advantage of the early retreat of sea ice in the Kara and Barents seas, the tanker Perseverance set sail on June 29, 2011 from Murmansk, Russia, aided by two icebreakers; and completed the passage on July 14. The company plans to send six to seven more ships through the Northern Sea Route this summer.

On the other side of the Arctic, the Northwest Passage is still choked with ice. However, ice loss in the Northwest Passage is well ahead of average, nearly matching last year when sea ice in the Parry Channel (the northern part of the Northwest Passage) reached the lowest levels in records dating back to 1968.

In an unusual mid-month update, the National Snow and Ice Data Center (NSIDC) reports Arctic sea ice is now disappearing faster than in 2007, the year that saw a record low for sea ice extent at the end of the melt season in September:

Arctic sea ice extent declined at a rapid pace through the first half of July, and is now tracking below the year 2007, which saw the record minimum September extent. The rapid decline in the past few weeks is related to persistent above-average temperatures and an early start to melt. Snow cover over Northern Eurasia was especially low in May and June, continuing the pattern seen in April.

To date in July, air temperatures over the North Pole (at the 925 millibar level, or roughly 1,000 meters or 3,000 feet above the surface) were 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) higher than normal.

NSIDC explains why the early ice melt is significant:

When sea ice starts to melt in spring, small ponds known as melt ponds form on its surface. The small pools create a darker surface (a lower albedo) that fosters further melt. How early sea ice melt starts is one indicator of how much the ice will melt in a given year. New research by Don Perovich and colleagues shows that an early start to sea ice melt increases the total amount of sunlight absorbed through the melt season.

Arctic sea ice volume continues to plunge to record lows, too . . .

. . . as older, multi-year ice is replaced by  younger, thinner ice more susceptible to melting in the summer.

The Arctic’s death spiral continues.

The National Oceanic and Atmospheric Administration (NOAA) has released its State of the Climate in 2010. The report tracks 41 climate indicators during 2010 (four more than in the previous year), and they all show show unequivocally that the world continues to warm.

Air samples collected weekly at NOAA’s Mauna Loa observatory continue to show a rise in the concentration of carbon dioxide.

Global surface temperatures continue to rise; 2010 was one of the two warmest years on record.

And in 2010, Greenland’s ice sheet lost more mass than at any time in the past ten years.

Multiple indicators lead to the same bottom line conclusion: there is a consistent and unmistakable signal of warming from the top of the atmosphere to the bottom of the oceans.

It’s been more than 300 months – that’s 25 years – since the average annual global temperature has been below the long-term average.

2010 saw a plethora of extreme weather events – a predicted consequence of global warming. Jeff Masters at Wunderblog catalogs the weather-related events that make 2010 the planet’s most extraordinary year for extreme weather, probably since 1816 – the devastating “year without a summer” caused by the massive climate-altering 1815 eruption of Indonesia’s Mt. Tambora, the largest volcanic eruption since at least 536 A.D. Earth in 2010 experienced a parade of record events: heat, drought, fire;  rains, winds, cold and snow, floods, ice melt.

The Antarctic as well as the Arctic is thawing. A new paper titled Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf published in Nature Geoscience finds that the Pine Island Glacier in West Antarctica – one of the frozen continent’s largest glaciers – is being undermined the sea encroaching from below, and is melting more than 50% faster than it had been just 15 years ago.

Melting ice and warming temperatures are causing sea levels to rise. A newly-published reconstruction of sea level for the past 2000 years shows that 20th-Century sea-level rise on the U.S. Atlantic coast is faster than at any time in the past two millennia.

Just a couple of years ago, we could comfort ourselves with the thought we had two or three generations to turn things around – that the serious effects of global warming would not manifest themselves until around 2050. Humanity had time to change its ways before it was too late.

But suddenly, the predictions have started coming true. It’s too late. We’ve passed the environmental tipping point. Everthing will change, is already changing.

Skip Wentz reiterates at Peak Oil News that the human economy is a subsystem of the environment. He writes that the human economy is dependent upon and reflects the state of the environment. As the environment deteriorates, so will its dependent economies deteriorate.

Our character has been revealed, and character is fate. Oedipus Rex  solved the famous riddle with his brilliance, rose to power, became a man beyond all power. Who could behold his greatness without envy? Yet confronted with the reality of his crime, he blinded himself.

When he saw her, he cried out fearfully and cut the dangling noose. Then, as she lay, poor woman, on the ground, what happened after, was terrible to see. He tore the brooches – the gold chased brooches fastening her robe – away from her and lifting them up high dashed them on his own eyeballs, shrieking out such things as: they will never see the crime I have committed or had done upon me! Dark eyes, now in the days to come look on forbidden faces, do not recognize those whom you long for – with such imprecations he struck his eyes again and yet again with the brooches. And the bleeding eyeballs gushed and stained his beard – no sluggish oozing drops but a black rain and bloody hail poured down.

It’s not surprising that denial of global warming denial, and human responsibility for it, is so vociferous and emotionally charged. Humans are brilliant, have conquered the Earth and the stars, control power beyond imagination. Yet humans could not bear to recognize what they have wrought. I

In the world of the Greeks, retribution was inexorable. The gods will not be denied their due.

A new report just released by the International Program on the State of the Oceans finds the condition of the oceans is declining far more rapidly than even pessimists had expected. It’s bad enough that many marine species — including those that make coral reefs — could be extinct within a generation. Humans may have set Earth on track for a sixth mass extinction event.

The key findings of the International Earth system expert workshop on ocean stresses and impacts Summary Report should be enough to shake any cognizant being out of their lethargy:

• Human actions have resulted in warming and acidification of the oceans and are now causing increased hypoxia – symptoms that indicate disturbances of the carbon cycle associated with each of the previous five mass extinctions on Earth.
• The speeds of many negative changes to the ocean are near to or are tracking the worst-case scenarios from IPCC and other predictions. Consequences matching those predicted under the “worst case scenario” include decrease in Arctic Sea Ice, melting of the Greenland and Antarctic ice sheets, sea level rise, and release of trapped methane from the seabed.
• The magnitude of the cumulative impacts on the ocean is greater than previously understood, as interactions between different impacts can be negatively synergistic.
• Timelines for action are shrinking. Delays will mean increased environmental damage with greater socioeconomic impacts.
• Resilience of the ocean to climate change impacts is severely compromised by the other stressors from human activities, including fisheries, pollution and habitat destruction.
• Ecosystem collapse is occurring as a result of both current and emerging stressors including chemical pollutants, agriculture run-­off, sediment loads and over-­extraction of many components of food webs.
• The extinction threat to marine species is rapidly increasing due to overexploitation, habitat loss, and, increasingly, climate change.

But don’t count on any response from our political or economic elites, other than wanton disregard. They have proved to not be cognizant beings.

A press release quotes Dr. Alex Rogers, Scientific Director of the International Programme on the State of the Ocean (IPSO), which convened the workshop:

The findings are shocking. As we considered the cumulative effect of what humankind does to the ocean the implications became far worse than we had individually realized. This is a very serious situation demanding unequivocal action at every level. We are looking at consequences for humankind that will impact in our lifetime, and worse, our children’s, and generations beyond that.

Co-author Dan Laffoley issued a call for action:

The world’s leading experts on oceans are surprised by the rate and magnitude of changes we are seeing. The challenges for the future of the ocean are vast, but unlike previous generations we know what now needs to happen. The time to protect the blue heart of our planet is now, today and urgent.

The chances of any significant action being taken are precisely zero. The sad reality is the ocean and its ecosystems are doomed to succumb to a constantly bombardment of multiple attacks.

Dan Allen at Energy Bulletin scathingly observes that humans have proved to be less than rational:

[A]ny sane society . . . when faced with such an overwhelming abundance of scientific evidence, would be gnashing its collective teeth and running for the powerdown-exits en masse at this point. No sane society would ignore the screaming warnings of every single Earth system. No sane society would knowingly doom their children and grandchildren to misery and starvation. No sane society would stand by and do NOTHING — NOT ONE DAMN THING!! — while their very life-support systems eroded away before their eyes.

But we are surely not sane.

Political solutions have failed us, are failing us, and will certainly continue to fail us. The only option we have – to slam on the brakes and to stop burning coal, tout de suite – won’t be undertaken voluntarily; to think otherwise is delusional. Climate catastrophe is where we are. As Allen says, that’s the bed we’ve made:

So, sadly, at this late hour, we just flat-out NEED the dark angel of economic collapse to swoop down onto the stage, ‘Deus ex Machina’ style, and save the day.

God help us.

Pray for the collapse of the global industrial economy. And do what you can to begin fashioning a replacement.

The National Snow and Ice Data Center (NSIDC) reports Arctic sea ice extent for May 2011 was the third lowest in the satellite data record since 1979, continuing its long-term decline.

The chart below shows the lowest year for May was 2004, followed by 2006. The long-term rate of decline for May now stands at -2.4% per decade.

During the month of May, sea ice declined at a near average rate, while air temperatures in the Arctic remained generally above average.

Although ice extent is low for this time of year, ice extent at the end of summer largely depends on Arctic weather over the next few months. Years with dramatic ice loss, such as 2007, have been associated with comparatively warm, calm, and clear conditions in summer that have encouraged ice melt. Summers with slow melt rates are opposite and tend to be stormier than average. The number of storms influences how warm, windy and cloudy the Arctic summer is.

The chart below compares this year to 2007, which saw dramatic, record-breaking ice loss in the Arctic.

NSIDC explains why

The last four summers have been dominated by an atmospheric pattern known as the Arctic dipole anomaly, which has been associated with low sea ice extent at the end of summer. This pattern features unusually high pressure over the Beaufort Sea and unusually low pressure over the Kara and Laptev Seas, which promote warm southerly winds along the Siberian coast, helping to melt ice and push it away from the coasts and out of the Arctic Basin through Fram Strait.

While the atmospheric pattern for May 2011 bears some resemblance to the Arctic dipole anomaly pattern, the centers of the pressure anomalies are in different locations this year, and it is not yet clear whether the pattern will persist through the summer and contribute to low ice extent.

Arctic sea ice volume continues to drop, too. In this chart published at the Polar Science Center, shaded areas represent one and two standard deviations of the anomaly from the trend.

Sea ice volume is an important climate indicator, as it depends on both ice thickness and extent and is therefore more directly tied to climate forcing than extent alone.

A recent post pointed to new scientific evidence suggesting that when the Earth starts to burn, the point of no return towards a rapid and catastrophic climate change event has already passed. 55.8 million years ago, climate change initiated the burning of terrestrial biomass over approximately a 50-year period, releasing huge amounts of organic carbon to the atmosphere. This carbon release was then followed by a second, catastrophic release of methane hydrate from terrestrial and marine sediments, again over a 50-year period. Result: the Paleocene-Eocene thermal maximum (PETM).

In late April, wildfires raged across eastern New Mexico and Western Texas. According to the Interagency Fire Center, wildfires in 2011 have already burned nearly 2.7 million acres in the U.S. This is the greatest acreage on record so early in the year, and is more area than burned all of last year. The largest U.S. acreage to burn since 1960 was the 9.9 million acres that burned in 2007, so we are already 27% of the way to breaking the all-time record fire year – with summer yet to come.

Wildfires in Canada have burned 909 percent more than the average number of acres this year, mainly due to a number of blazes in northern Alberta that have been described as “freakish firestorms.” The unusually large fires are linked with global warming and the pine beetle infestation that has spread through millions of acres of boreal forests – and Mountain pine beetles have now successfully colonized stands of jack pine, previously considered to be unsuitable habitat for the insects. Canadian government scientists are saying the fires are consistent with expected climate change impacts. Temperatures in northern Canada have climbed two to three degrees in the past three decades, mainly due to warmer winters and springs. The acreage burned by wildfires has already doubled since the 1970s. Models predict that fires in Alaska, the Yukon and B.C. could increase fivefold in the next few decades.

The Amazon rainforest  is under withering assault from climate change. As the tropical Atlantic warms, large parts of the Amazon suffer higher temperatures and less rainfall. The rainfall-starved tropical forests lose massive amounts of carbon due to reduced plant growth, dying trees, and associated fire. If that’s not enough, the loss of the Amazon rain forest to slash-and-burn clearing for farming and ranching is accelerating, too, prompted by rising demand for soy and cattle.

Indonesia is home to the most extensive rainforests in Asia – rainforests that over the past fifty years have become increasingly vulnerable to fire during El Niño-induced drought events. Global warming is projected to make dry conditions worse during the dry season due to increased interannual climate variability, exacerbating the risk of fire. Fires in the region in 1997 released ~2.7 billion tons of carbon dioxide, the largest single release since records began in 1957, and equivalent to about 40% of annual global emissions from burning fossil fuels. Some burning takes place every year in Indonesia, but the number and intensity of fires depend largely on rainfall and soil moisture conditions during the fire season, which usually runs September through November. Since then, Indonesia experienced drought conditions and corresponding forest fires in 2002, 2006 & 2009.

This year, the waters around Indonesia are only slightly warmer than normal.

Although it’s only May, rainfall in Sumatra has been scarce and the fires have already started to burn.

2011 could prove to be a hot year, and the harbinger of many more to come.

A new worldwide analysis of agricultural trends just published in the journal Science blames our warming global climate for a 3-5% decline in corn and wheat production during the last 30 years, to such an extent that it may be a factor in rising food prices that are now causing worldwide stress. The study is the first to demonstrate a link between global crop yields and climate change.

Corn yields were 5.5% lower than they would have been if the environmental factors remained constant, and wheat yields were 3.8% lower. Wheat production in Russia showed the biggest drop, with yields off by 15%. Soybeans and rice were relatively unaffected, due respectively to being grown in areas not experiencing as much warming and thriving in higher temperatures. The United States has been lucky so far: temperatures in the midwestern corn and soybean belt during the summer crop-growing season have not yet shown an increase.

John Cox at Discovery News has posted a map from the study showing global temperature and precipitation changes.

The authors of the study — David Lobell and Justin Costa-Roberts of Stanford University, and Wolfram Schlenker of Columbia University — warn that as temperature increases accelerate in coming decades, the negative impacts on food production will also increase.

A new assessment of the impacts of climate change in the Arctic finds that the changes in the sea ice on the Arctic Ocean and in the mass of the Greenland Ice Sheet and Arctic ice caps and glaciers over the past ten years have been dramatic and  and represent an obvious departure from the long-term patterns. The study is titled Snow, Water, Ice and Permafrost in the Arctic.

The assessment finds that the past six years (2005–2010) have been the warmest period ever recorded in the Arctic. The higher surface air temperature are driving changes in the cryosphere. Two components of the Arctic cryosphere – snow and sea ice – are interacting with the climate system to accelerate warming in a feedback loop. Loss of ice and snow in the Arctic enhances climate warming by increasing absorption of the sun’s energy at the surface of the planet. Temperatures in the permafrost have risen by up to 2 °C and the southern limit of permafrost has moved northward in Russia and Canada- a trend which could result in dramatically increased emissions of carbon dioxide and methane. Melting ice could change large-scale ocean currents. Melting glaciers and ice sheets worldwide have become the biggest contributor to global sea level rise. Arctic glaciers, ice caps, and the Greenland Ice Sheet are contributing much more to global sea level rise than previously measured. High uncertainty surrounds estimates of future global sea level, with latest models predicting a rise of 0.9 to 1.6 m above the 1990 level by 2100. But, the assessment cautions, the combined outcome of these effects is not yet known. Interactions (‘feedbacks’) between elements of the cryosphere and climate system are particularly uncertain.

The assessment was done by the Arctic Monitoring and Assessment Programme (AMAP), an international organization headquartered in Norway. Member nations include the eight Arctic rim countries: Canada, Denmark/Greenland, Finland, Iceland, Norway, Russia, Sweden, and the United States. Other nations and organizations participate as well.

The National Snow and Ice Data Center (NSIDC) reports Arctic sea ice extent declined through April more slowly than usual, as cool conditions helped retain ice in Baffin Bay, between Canada and Greenland. Still, April 2011 continued the overall downward trend of the past thirty years, ranking fifth lowest in the satellite record. The two lowest years for April were 2007 and 2006.

University of Washington’s Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) model of sea ice volume shows continued very low ice mass in the Arctic compared to previous decades.

Joseph Romm at Climate Progress reports on a study showing the Greenland ice sheet has been losing mass over the last decade.

A new study finds that natural global warming during the Paleocene-Eocene thermal maximum (PETM), 55.8 million years ago, can be best explained as occurring in 2 stages – both of which took place extremely rapidly, much more rapidly than previously thought. The study, titled Methane and environmental change during the Paleocene-Eocene thermal maximum (PETM): Modeling the PETM onset as a two-stage event, is published in the March 2011 edition of the journal Geophysical Research Letters (and conveniently posted at NASA’s website).

In the first stage, a global warming of 3° to 9° C was accompanied by a large release of organic carbon to the atmosphere through the burning of terrestrial biomass over approximately a 50-year period. This carbon release was then followed by a second, catastrophic release of methane hydrate from terrestrial and marine sediments, followed by the oxidation of a part of this methane gas in the water column and the escape of the remaining CH₄ to the atmosphere, again over a 50-year period.

55 million years ago, land masses were distributed on Earth something like this (graphic from Christopher Scotese’s Paleomap Project.

The major difference between the PETM and present global warming is that the PETM warming was initiated by increased exposure to solar radiation causing carbon feedbacks and rapid global warming.  Today’s global warming is caused by the on-going burning of fossil fuels, which yearly inject a massive amount of CO₂ in the atmosphere, initiating further carbon feedbacks.

Methane from Siberia is already leaking into atmosphere at alarming rate.

Top left: Bubble plumes (probably dominated by CH4) rising from the seafloor registered by geophysical instrumentation. Top right: Seismic image showing gas charged sediments and gas release from the bottom. Bottom left: Positions of oceanographic stations with bathymetry lines. Bottom right: Fluxes of CH4 venting to the atmosphere over the ESAS. Source: Shakhova et al.

It may be much later than we think. When the Earth starts to burn, that’s a sign we may have already entered Stage 1.

The National Snow and Ice Data Center (NSIDC) reports sea ice reached its maximum extent on March 7 this year. Sea ice extent on this date tied for the lowest winter maximum extent in the satellite record. Arctic sea ice extent for the month of March 2011 was the second lowest in the satellite record.

The amount of older, thicker ice has increased slightly over last year. Older ice that has survived several summer melt seasons tends to be thicker, while newer ice is thinner and more vulnerable to melt in summer. The trend of spring ice cover becoming increasingly dominated by younger and generally thinner ice (because of strong summer melting reducing the amount of ice surviving into winter) remains striking.

There is still almost none of the oldest ice, older than four years old, that used to dominate much of the Arctic Ocean.

We recently posted about a new study that concluded natural gas – especially from fracking – might be worse than other fossil fuels, even worse than coal, for climate change.

Calculating the net climate impact of an activity is complex and fraught with uncertainties, requiring tracking many different emissions (not just CO2) and accounting for their (time-varying) impacts. Gavin at RealClimate notes a couple of caveats about the results of the study.

For shale gas extraction (and indeed for most fossil fuel extraction), a big issue is fugitive emissions. The estimates for fugitive emissions are uncertain because they are not being reported, either voluntarily by the industry or through regulation from the states. Fugitive emissions mostly consist of methane, which is relatively more important for a 20 year time frame than it is for a 100 year time frame by a factor of ~3. For lack of anything better, the Howarth study had to rely on admittedly poor observations.

Another problem is that, for other fossil fuels, fugitive emissions weren’t considered.

For an apples-to-apples life cycle comparison, one would need to also update the impacts of coal and oil to include their fugitive emissions, their impact on other short-lived components (black carbon, CO, etc). The Howarth study compared apples to oranges.

Still, the main point of the study remains valid: natural gas, conventional or fracked, isn’t the energy or climate panacea we hoped it was.