How important is hydroxyl depletion?
Background: This post urges for more research to be done into possible causes of catastrophic climate change and ways to combat this. The role of hydroxyl (OH) depletion comes up in both cases. The IPCC is urged to look into the risk of large methane releases from clathrates more closely.
This post was started by Sam Carana at knol in 2009, and further edited over the following two years. The post is added here as is, for archival purposes, since knol has been discontinued by Google and it was seen as important to preserve some of the thoughts and discussions behind this post.
Arctic sea ice loss and feedbacks
Observations indicate that - with business as usual - Arctic sea ice extent is likely to disappear within a few decades, far earlier than predicted by even the worst-case models of the Intergovernmental Panel on Climate Change (IPCC), which did not incorporate feedback effects such as albedo changes that come with sea ice loss.
A rapid rise of Arctic temperatures could also lead to wildfires and the release of huge amounts of carbon dioxide and methane that are now stored in peat, permafrost, hydrates and clathrates. Heat produced by decomposition of organic matter is yet another feedback that leads to even deeper melting of permafrost.
The NSIDC image below shows that, at the end of the summer 2010, under 15% of the ice remaining in the Arctic was more than two years old, compared to 50 to 60% during the 1980s. There is virtually none of the oldest (at least five years old) ice remaining in the Arctic (less than 60,000 square kilometers [23,000 square miles] compared to 2 million square kilometers [722,000 square miles] during the 1980s).
The cumulative impact of multiple feedback processes and their interaction reinforces and accelerates Arctic warming, making straight line extrapolation of earlier data (blue line on the chart below) less appropriate than downward curved projections, such as the pink dotted line on above chart that shows a scenario reflecting the impact of a number of feedback processes.
Carbon releases from thawing permafrost
A 2008 study warns that Arctic sea ice loss is likely to in turn trigger rapid warming on land and subsequent permafrost degradation. Carbon uptake by new vegetation growth in these areas would give only little relief. A study by Edward Schuur concludes that such thawing would - over decades - overwhelmingly release more carbon than the uptake by new vegetation growth in these areas.
Hotspots in permafrost
Schuur estimates that, some 277 Gt of carbon is contained in peatlands alone. The East Siberian permafrost region alone contains 500 billion tonnes of carbon. East Siberia was at times 7°C warmer than normal during the summer of 2007, says Philippe Ciais, co-chair of the Global Carbon Project. Higher temperatures mean the seasonal melting of the upper layer of soil extends down deeper than normal, melting the permafrost below. Microbes can then break down any organic matter in the thawing layer, not only releasing carbon but alsogenerating heat that leads to even deeper melting. The heat produced by decomposition is yet another positive feedback that will accelerate melting, Ciais says.
Moreover, when summer melting depth exceeds the winter refreezing, a talik can form, a layer of permanently unfrozen soil sandwiched between the seasonally frozen layer above and the perennially frozen layer below. A talik allows heat to build more quickly in the soil, hastening the long-term thaw of permafrost, says David Lawrence of the National Center for Atmospheric Research in Boulder, Colorado.
Katie Walter Anthony, who has closely studied such hotspots, says: Methane hotspots in lake beds can emit so much gas that the convection caused by bubbling can prevent all but a thin skin of ice from forming above, leaving brittle openings the size of manhole covers even when the air temperature reaches -50 degrees C in the dark Siberian winter.
Methane releases from permafrost
Katie estimates that at least 50 billion tons of methane will escape from thermokarst lakes in Siberia alone during the next decades to centuries. Katie says releases could be up to 200 million tons of methane annually by 2100. This 200 million tons would constitute a significant addition to the total current amount of annual methane emissions for all sources worldwide (550 million tons). As indicated on the image below, current methane emissions already contribute significantly to global warming.
An image similar to the one on the left (no longer shown) illustrated a report in the LA Times based on Katie's article and on her earlier publications at the University of Alaska Fairbanks and in Nature. It predicts a 40% thaw of permafrost by 2100.
Apart from the methane from such permafrost areas, there is also methane from clathrates to consider. Katie quotes Russian scientists who estimate that some 1 trillion tons of methane may be stored beneath the Siberian shelf.
Katie quotes geophysicist Vladimir Romanovsky of the University of Alaska as saying: "One third to one half of permafrost in Alaska is already within one degree to one and a half degrees Celsius of thawing."
Research led by Natalia Shakhova detected significant methane emissions from the East Siberian Arctic Shelf, a methane-rich area of more than 2 million km² located about 50 meters (164 feet) or less below the surface of the Arctic Ocean. Emissions equalled total emissions from all other world oceans.
The study, published in Science, found that more than 80% of the deep water and more than 50% of surface water had methane levels more than eight times that of normal seawater. In some areas, saturation levels reached more than 250 times that of background levels in the summer and 1,400 times higher in the winter.
"The release to the atmosphere of only one percent of the methane assumed to be stored in shallow hydrate deposits might alter the current atmospheric burden of methane up to 3 to 4 times," Shakhova said.
As the IPCC image below shows, methane levels have already been rising dramatically since the industrial revolution.
Global methane levels are currently rising, as shown on the edited NOAA image on the left, due to rapidly growing industrialization in Asia, increased numbers of livestock and rising wetland emissions in the Arctic and tropics.
To understand why these methane releases are so worrying, methane's lifetime and warming potential as a greenhouse gas need to be looked at more closely.
Currently, methane's chemical lifetime in the atmosphere is about 12 years, after which it will have oxidized into carbon dioxide and water vapor. Methane oxidizes in a reaction with hydroxyl radicals (OH). The IPCC in AR4 pointed at studies suggesting no significant long-term change in the global abundance of OH.
However, much of the methane released from permafrost may remain in the atmosphere longer, due to OH depletion. The more methane there is to be oxidized, the more chance there is of OH depletion, and the longer it will take for methane to oxidize. A study by Drew Shindell, accompanied by the NASA image below, concludes that chemical interactions between emissions cause more global warming than previously estimated by the IPCC.
The study shows that increases in global methane emissions have caused a 26% OH decrease. Because of this, methane now persists longer in the atmosphere, before getting transformed into the less potent carbon dioxide.
A Centre for Atmospheric Science study suggests that sea ice loss may amplify permafrost warming, with an ice-free Arctic featuring a decrease in OH of up to 60% and an increase of tropospheric ozone (another greenhouse gas) of up to 60% over the Arctic.
Methane's warming potential
An extension of methane's lifetime would strongly amplify the greenhouse effect, due to methane's strong initial potency as a greenhouse gas, compared to carbon dioxide. The figure used by the IPCC for methane's global warming potential (GWP) was 21, indicating that methane is 21 times more powerful than carbon dioxide (CO2) by weight, when calculated over a period of 100 years.
A Centre for Atmospheric Science study suggests that sea ice loss may amplify permafrost warming, with an ice-free Arctic featuring a decrease in OH of up to 60% and an increase of tropospheric ozone (another greenhouse gas) of up to 60% over the Arctic.
Methane's warming potential
An extension of methane's lifetime would strongly amplify the greenhouse effect, due to methane's strong initial potency as a greenhouse gas, compared to carbon dioxide. The figure used by the IPCC for methane's global warming potential (GWP) was 21, indicating that methane is 21 times more powerful than carbon dioxide (CO2) by weight, when calculated over a period of 100 years.
Methane's potent short-term impact
Over a long period, methane's impact looks less threatening, but over a short period from its release, methane’s impact will be dramatic. In the first five years after its release, methane will have an impact more than 100 times as potent as a greenhouse gas compared to carbon dioxide.
In the absence of OH to oxidize methane, much methane could persist locally with its full GWP for years, causing a dramatic greenhouse effect and thus warming locally. This and all the above-mentioned feedback mechanisms can dramatically amplify local warming in the Arctic, causing large-scale thawing and melting over a period of years, rather than centuries. Arctic amplification is largely overlooked by the IPCC which uses a period of a century to calculate methane's impact.
Climate change in the past
The IPCC, in AR4, says that global average sea level in the last interglacial period (about 125,000 years ago) was likely 4 to 6 m higher than today, mainly due to the retreat of polar ice. Currently, we're in such an interglacial period, so there is a good chance of similar retreat of polar ice. In the past, however, such climate changes took place over long periods of time. What's different today is that greenhouse gas levels exceed anything seen over the past 800,000 years or more, as shown on the Wikipedia image below.
In the past, climate change followed orbital changes of Earth. Long periods of weathering and natural adaptation may have helped the planet overcome peak levels. In our case, we're already at a historic temperature peak and our current levels of greenhouse gases look set to push temperature much higher yet. We do not have thousands of years to wait and hope for carbon dioxide levels to fall. Current greenhouse gas levels far exceed any earlier levels showing up on ice core data.
The risk of rapid global warming
A sudden rise in global temperatures is likely to cause all kinds of havoc, such as wildfires, since the vegetation will be out of sync with such temperatures and - over a short period - has too little time to adapt. This would turn the Amazon from a carbon sink into an area of high emissions of carbon dioxide and aerosols (causing further OH depletion) and escalating global warming elsewhere.
The U.K. Met also warns that, without drastic action, this worst-scenario rise of 7.2°F (4°C) rise will actuallybe reached by 2070, and possibly as early as 2060.
Above image illustrates the vulnerability of the Amazon rain forest and the Arctic. The Met study concludes that, by the end of the century, the Arctic could warm by up to 27°F (15.2°C) for a high-emissions scenario, enhanced by melting of snow and ice causing more of the Sun’s radiation to be absorbed.
Obviously, reducing greenhouse gases is imperative, but at the same time we should realize that - despite the best efforts - there still is a chance of runaway global warming. Once such a runaway greenhouse effect takes off, it will be too hard to stop.
Humans and other mammals cannot survive prolonged exposure to temperatures exceeding 95°F (35°C), saysSteven Sherwood. Heat stress would make many parts of the globe uninhabitable with global-mean warming of about 7°C (12.6°F).
Some therefore advocate geoengineering methods to reflect some sunlight back into space. The risk analysis below is by John Nissen.
One such method in the Space Hose, proposed by Nathan Myhrvold who suggests to pump sulfur dioxide into the stratosphere above the Arctic by means of a hose attached to balloons.
As Myhrvold says, it's important to ensure that large buildings have fire detectors, alarms, fire escape routes, sprinklers and fire extinguishers, complete with fire drills, trained people to handle fires, etc. There is an entire infrastructure to prevent and handle possible disasters, including fire engines with all the bells and whistles, ambulances and hospitals to deal with the eventuality of a fire, even though a particular building will never experience a fire in its lifetime.
Back to hydroxyl depletion
Even if the risk is of runaway greenhouse effect was small, and even if we never needed things such this space hose, we need to be better prepared, as part of a comprehensive Global Warming Action Plan. In the case of catastrophic global warming, we don't know much about possible tipping points and there isn't much of an comprehensive action plan what to do. We may be crossing tipping points that could lead to global firestorms, yet nobody is even practicing how to hold the fire hose.
In preparation if its Fifth Assessment Report, the IPCC, in Working Group III, is assessing options for mitigating climate change, through limiting or preventing greenhouse gas emissions, and through enhancing activities that remove them from the atmosphere. Approaches such as this Space Hose are not included in these options, though.
The space hose that Myhrvold proposes could well be part of the solution, perhaps even a vital part, but why aren't such approaches looked into by the IPCC? It doesn't appear to fix ocean acidification and it could be more difficult than Myhrvold may think. Which brings us back to hydroxyl depletion. Such a Space Hose would pump sulfur dioxide into the stratoshphere. This sulfur dioxide will react with hydroxyl to produce sulfates. How much additional hydroxyl depletion would oxidation of sulphur dioxide cause? Would this mean that ever more sulfur dixode would have to be released? Would the decrease of sunlight cause a decrease in photolysis and thus also reduce hydroxyl formation? If OH reductions were dramatic, what impact would that have on methane, on cloud formation, etc? Injecting sulphur dioxide into the stratosphere could result in less precipitation and less evaporation.
Tri-Air Developments has developed a technology that combines UV light with extremely low levels of ozone and mixes it with volatile hydrocarbons, to produce hydroxyls.
This technology is used in Cirrus3 devices that emit hydroxyls in rooms of less than 25m3 up to rooms in excess of 500m3 (image below). Perhaps such technology could be used at large scale in the Arctic to combat the methane menace. The IPCC should be looking into research on this.
Another method may be to use UV light for photolysis of hydrogen peroxide. Such methods are discussed in places such as this geoengineering group.
Using UV light to break down methane in the Arctic could possibly be achieved by model airplanes, equipped with LiPo batteries and with solar thin film mounted both on top of and underneath the wings. Numerous such planes could navigate the Arctic by autopilot in summer, when there are high concentrations of hydrogen peroxide and when the sun shines 24-hours a day. Flying figure-8 patterns with the wings under an angle could optimize capture of sunlight, keeping the planes in the air, while using surplus energy to power UV lights. At the end of summer, the planes could return home for a check-up and possible upgrade of the technology, to be launched again early summer the next year.
If you have any thoughts on all this, feel welcome to post a comment below!
