Foreword

This article first appeared on the Viva la Vegan website on 7th February, 2012 with the title “Solar or Soy, which is better for the planet, Part 2“. (This version has been amended slightly.) The title reflected the fact that it was an introduction to subsequent articles on the great elephant in the room of climate change, animal agriculture, but it did not deal with that issue specifically.

The contents of this article are very relevant to our current climate change crisis, which (not surprisingly) reflects a significant deterioration since the article was published. Awareness and concern about the issue seem to have increased enormously since then, but do we have the time or the political will to turn the juggernaut around and retain a habitable planet?

Should the deterioration in the state of our climate come as a surprise?

Perhaps not when you consider the existence of climate feedback mechanisms and the fact that, between 1998 and 2013, the oceans had been gaining heat at a rate equivalent to about four Hiroshima atomic bombs per second. Worse still, the rate had suddenly increased to around twelve per second during 2013.[1] Between 1998 and early 2015, those rates resulted in heat equivalent to more than two billion Hiroshima bombs being accumulated.[2]

Hiroshima-2

There are substantial year-on-year variations in heat uptake by the oceans, but even at a rate of four Hiroshima bombs per second, why wouldn’t the planet’s climate system move away from the relatively benign conditions that had been experienced during the 10,000 years of human civilisation? Of particular note is the fact that the current concentration of atmospheric greenhouse gases is more than thirty percent higher than at any time in at least the last one million years.[3]

Climate change author David Spratt, whose work is featured in the article, recently cited leading US climate scientist Dr Michael E. Mann, who has reported that new calculations “indicate that if the world continues to burn fossil fuels at the current rate, global warming will rise to 2C° by 2036”.[4] By the time that temperature has been reached, key climate change tipping points are likely to have been breached, creating a very real risk of even higher temperatures and runaway climate change over which humans will have little or no control.[5]

Our efforts to avoid such a scenario are limited by the fact that we have created a potentially tragic Catch-22 in the form of aerosols generated by the burning of fossil fuels. Aerosols are airborne particulates such as sulphates, nitrates, and dust from smoke and manufacturing. They have a cooling effect, sometimes referred to as “global dimming”, which has offset some of the warming effects of greenhouse gases. They only remain in the atmosphere for around ten days, so their cooling impact will be short-lived in any transition away from fossil fuels to less carbon-intensive energy sources. This dilemma is referred to by David Spratt and Dr James Hansen as a “Faustian bargain”, alluding to Doctor Faustus of folklore and legend, who sold his soul to the devil in exchange for knowledge and power. Based on research from organisations such as NASA and CSIRO, Spratt has suggested that aerosol cooling is in the range of 0.5-1.2°C.[6]

Introduction

In Part 1 of this series (Solar or Soy, Part 1), I wrote of the dramatic increase in atmospheric concentrations of carbon dioxide and other greenhouse gases since the beginning of the industrial revolution, and the accelerating pace of such increases in recent times.

In this article, I outline the impact of such changes in terms of tipping points, runaway climate change and the need for emergency action.

The current situation in regard to climate change could hardly be more dire. Paradoxically, the response from decision makers, relative to the dangers, could hardly be more muted. I will comment on the lack of an effective response in a future article.

I feel the need to report on these issues in the same way that I would feel the need to scream out to a friend who was about to be hit a truck careering towards her, which she was unaware of. Alerting her of the impending danger may enable her to save herself.

In addition to impacts on the current human population of our planet, we must also consider future generations and other species.

As a reminder of the rapid growth in greenhouse gases, here is a chart depicting the increase in carbon dioxide concentrations since 1960:

Figure 1: Levels of atmospheric carbon dioxide[7]

Mauna-Lao-emissions

Remember that carbon dioxide concentrations never exceeded 300 ppm (parts per million) in the previous 1,000,000 years. They have increased from around 315 ppm to around 390 ppm in just 50 years.

Over the past ten years, the average annual rate of increase was 2.07 ppm, which is more than double the rate of increase in the 1960s.[8]

On the Edge of a Precipice

David Spratt is a co-author (with Philip Sutton) of a groundbreaking book published in 2008, entitled “Climate Code Red: The case for emergency action”.

Subsequent to the book’s release, he commented as follows:

“ . . . the world stands . . . on the edge of a precipice . . . beyond which human actions will no longer be able to control in any meaningful way the trajectory of the climate system . . .” [9]

The precipice that David Spratt referred to derives from amplifying feedbacks in the climate system, causing us to approach tipping points beyond which catastrophic climate change is almost certain unless dramatic mitigation efforts commence without delay (assuming it is not already too late.)

In the words of Dr James Hansen, Director of NASA’s Goddard Institute for Space Studies and an adjunct professor in the Department of Earth and Environmental Sciences at Columbia University [Footnote 1]:

“Tipping points occur because of amplifying feedbacks – as when a microphone is placed too close to a speaker, which amplifies any little sound picked up by the microphone, which then picks up the amplification, which is again picked up by the speaker, until very quickly the noise becomes unbearable.” [10]

Figure 2: Feedbacks in a sound system[11] and in human-induced climate change[12]

acoustic_feedback_mechanism

Feedbacks-CSIRO

In the second image, the release of greenhouse gases (GHGs) increases temperatures, which in turn:

  1. increase the level of water vapour (a powerful greenhouse gas) through evaporation, along with the air’s capacity to hold that water vapour;
  2. reduce the area of ice sheets; and
  3. release GHGs from (for example) melting permafrost.

Each of those reactions (some of which I expand on below) then warms the atmosphere further, causing the process to continue and amplify.

Here are some further comments on the issue:

Dr James Hansen, 2009 [13]:

“How can we be on the precipice of such consequences while local climate change remains small compared to day-to-day weather fluctuations? The urgency derives from the nearness of climate tipping points, beyond which climate dynamics can cause rapid changes out of humanity’s control.”

Commonwealth Scientific and Industrial Research Organisation (CSIRO)

2010: “The further climate is pushed beyond the envelope of relative stability that has characterised the last several millennia, the greater becomes the risk of passing tipping points that will result in profound changes in climate, vegetation, ocean circulation or ice sheet stability.” [14]

2011: “Climate change does not proceed smoothly for a given change in radiative forcing from changing greenhouse gas levels. There is a risk of abrupt changes as the climate shifts from one state to another as a result of feedbacks in the climate system. . . . Their hazard lies in the fact that, once they have occurred, it may be hard for the planet to return to its previous steady state. For example, once Greenland’s ice cap is committed to melting it is unlikely to reform for thousands of years, leading eventually to sea level rises of several metres.[15]

International Energy Agency 2011(as reported by the Huffington Post):

The world is on the brink of irreversible climate change, according to a report released on Wednesday by the International Energy Agency (IEA). Called the World Energy Outlook 2011, the analysis is the most thorough ever produced on the effects of releasing fossil fuels into the atmosphere. According to the research, in five years global warming will hit a point of no return after which it will be impossible to reverse the process.”[16]

Professor Barry Brook, Sir Hubert Wilkins Chair of Climate Change, The University of Adelaide, as reported in 2008:

“Two degrees has the potential to lead to three or four degrees because of carbon-cycle feedbacks.”[17] [Footnote 2]

Shortcomings in some conventional measures of potential climate change impacts

The IPCC (Intergovernmental Panel on Climate Change) has considered fast feedbacks in establishing relatively conservative estimates of climate change impacts. Such feedbacks include: water vapour; cloud cover; snow cover; and sea ice extent; and are considered to modify the effects of increasing temperatures on short timescales.

However, Hansen and others argue that slow feedbacks must also be considered, which greatly increase the potential impacts. They include: ice sheet growth and decay; changes in vegetation cover; permafrost melting; and carbon-cycle feedbacks.[18]

In relation to the IPCC’s reports, Australia’s Chief Climate Commissioner, Professor Tim Flannery, has stated that they are “painfully conservative” because the IPPC “works by consensus and includes government representatives from the United States, China and Saudi Arabia, all of whom must assent to every word of every finding.”[19]

Writing in the Scientific American in 2008, Michael D Lemonick commented as follows on the issue (with my emphasis and underline):[20]

“The problem is that conventional projections for how warm things will get come out of a calculation everyone knows is wrong. Called the Charney sensitivity, it estimates how much the global mean temperature will rise if atmospheric CO2 is doubled from its preindustrial levels, before people began burning coal and oil on a grand scale”

 “The calculation does take into account some feedback mechanisms that can modify the effects of increasing temperatures on short timescales – changes in water vapor, clouds and sea ice, for example. But for the sake of simplicity, it assumes no change in other, longer-term factors, including changes in glaciation and vegetation; in particulates, such as dust; and in the ability of the ocean to absorb carbon dioxide, which diminishes as sea temperature rises.”

Many, and possibly all, of the fast and slow feedbacks are interrelated.

Examples of feedbacks and potential tipping points

Reduction in area and volume of Arctic sea ice

Sea ice is defined as “Any form of ice found at sea which has originated from the freezing of sea water”[21] It is floating, rather than fixed to land. As described in “Scientific American”, “As ice retreats in a warming world, more dark surface is exposed to absorb solar radiation, which makes the world even warmer, melting more ice.”[22]Atmospheric or ocean warming leads to a loss of sea ice, which in turn causes more warming, then more melting, more warming and so on. For a time, the melting ice may reduce the surrounding ocean temperature, partly offsetting the impact of increased absorption of solar radiation. However, the effect is relatively short-lived, and the higher melting rate soon returns.

That process may be exemplified by the dramatic reduction in Arctic summer sea ice in 2007. In that and the previous year combined, the area of sea ice declined by 22 per cent, compared to an average reduction of 7 per cent per decade between 1979 and 2005.[23] The situation improved over the next three years, but in 2011 the area of sea ice again reduced dramatically.[24]

A key factor in the melting of Arctic sea ice and polar ice caps (refer below) is the non-uniformity of temperature changes. The temperature changes at the poles are around double the global average and about three times the change at the equator.[25]

According to David Spratt:

“ . . . average temperatures in Siberia, Alaska and western Canada are now 3ºC to 4ºC warmer than 50 years ago.”
[26]

“The danger is that an ice-free state in the Arctic summer will kick the climate system into run-on warming and create an aberrant new climate state many, many degrees hotter. The Arctic sea-ice is the first domino and it is falling fast. Other dominos will inevitably fall unless we stop emitting greenhouse gases and cool the planet to get the Arctic sea-ice back. Those dominoes include the Greenland ice sheet.”
[27]

Disintegration of Greenland and Antarctic ice sheets

The Greenland ice sheet is almost 2,400 kilometres long, 1,100 kilometres across at its widest point and more than 2 kilometres thick.[28] James Hansen has reported that, as recently as the 1990’s, it was neither gaining nor losing mass at a substantial rate. As of 2009 it was losing around 250 cubic kilometres of ice per year in a dynamic wet melting process, while Antarctica was losing around half that amount. “The rate of ice sheet mass loss has doubled during the present decade [commencing in 2000].”

Dr Hansen has also stated, “Sea level is going up at a rate of about 3 centimetres (about 1 and 1/5 inches) per decade. But if ice sheet disintegration continues to double every decade, we will be faced with sea level rise of several meters this century. IPCC has estimated only modest rates of sea level rise this century, much less than one meter. But IPCC treats sea level change basically as a linear process. It is more realistic, I believe, that ice sheet disintegration will be non-linear, which is typical of a system that can collapse.”[29]

Figure 3: Greenland’s ice sheet’s diminishing reflectiveness

Greenland_Albedo465

The National Oceanic and Atmospheric Administration (NOAA) reported in December 2011 that in the past decade, satellite observations show a drop in Greenland’s reflectiveness. The darker surface absorbs more sunlight, accelerating melting. They have stated, “The map above shows the difference between the percent of sunlight Greenland reflected in the summer of 2011 and the average percent it reflected between 2000 and 2006. Virtually the entire ice sheet is colored in shades of blue, indicating that the ice sheet reflected as much as 20% less light this summer than it did in the early part of the last decade.”[30]

British glaciologists have recorded water pouring down one of hundreds (possibly thousands) of moulins (craters) on Greenland’s ice cap at an estimated rate of 42 million litres per day. It was reported that Greenland is losing enough water each year to cover Germany to a depth of one metre.[31]

Melting Permafrost

Permafrost is frozen soil (once considered to be permanently frozen), tens of metres deep. It covers twenty per cent of the world’s land mass, with half of it being in Siberia.[32]

The permafrost extends from the mainland into the seabed of the relatively shallow sea of the East Siberian Arctic Shelf. It stores massive amounts of carbon, which can be released in the form of carbon dioxide and methane as the permafrost melts. The IPCC estimates that methane is 72 times more potent than carbon dioxide as a greenhouse gas over a 20 year period. [See Footnote 3 for a more recent estimate.]

David Spratt has reported as follows (with my underlines):[33]

  • The rapid regional warming consequent to the sea-ice loss also has grave repercussions for the permafrost.
  • The National Centre for Atmospheric Research in Boulder predicts that half of the permafrost in the Arctic north will thaw to a depth of 3 metres by 2050.
  • Glaciologist Ted Scambos says, ‘That’s a serious runaway … a catastrophe lies buried under the permafrost.’
  • Permafrost specialist Sergei Zimov says: ‘Permafrost areas hold 500 billion tonnes of carbon, which can fast turn into greenhouse gases … If you don’t stop emissions of greenhouse gases into the atmosphere … the Kyoto Protocol will seem like childish prattle.’
  • The western Siberian peat bog is amongst the fastest-warming places on the planet, and Sergei Kirpotin of Tomsk State University calls the melting of frozen bogs an ‘ecological landslide that is probably irreversible’.
  • In August 2008, Örjan Gustafsson, the Swedish leader of the International Siberian Shelf Study confirmed that methane was now also bubbling through seawater from permafrost on the seabed.
  • So the question is no longer whether the permafrost will start to melt, but if and when the time-bomb will go off. When it does, it will sweep the climate system away from our capacity to stop further dramatic ‘tipping points’ being passed.
  • All the carbon in the permafrost is equivalent to twice the total amount of all carbon dioxide in the atmosphere, so losing even a significant portion of it will create a very different planet from the one we know.
  • Scientists are warning that the temperature at which it will be triggered is closer that think. Research published in mid-2008 by Dmitry Khvorostyanov shows the trigger is warming in the Arctic of around 9ºC, and that once initiated it will maintain itself, leading to three-quarters of the carbon being released within a century. It could happen as early as mid-century. [Footnote 4]

In The Independent of 13 December, 2011, Steve Connor reported as follows in relation to methane being released from permafrost in the seabed of the East Siberian Arctic Shelf (with my underlines):[34]

  • Dramatic and unprecedented plumes of methane . . . have been seen bubbling to the surface of the Arctic Ocean by scientists undertaking an extensive survey of the region.
  • The scale and volume of the methane release has astonished the head of the Russian research team who has been surveying the seabed of the east Siberian Arctic Shelf off northern Russia for nearly 20 years.
  • Igor Semiletov of the International Arctic Research Centre at the University of Alaska Fairbanks . . . said that he has never before witnessed the scale and force of the methane being released from beneath the Arctic seabed.
  • He said, “We carried out checks at about 115 stationary points and discovered methane fields of a fantastic scale – I think on a scale not seen before. Some of the plumes were a kilometre or more wide and the emissions went directly into the atmosphere – the concentration was a hundred times higher than normal.”

Activation of methane hydrates/clathrates

The potential activation of methane hydrates or clathrates sitting below sediment on the ocean floor represents a similar threat to that of carbon stored in permafrost. Clathrates are frozen water molecules containing frozen methane or carbon dioxide molecules. Warming oceans can potentially cause those ice crystals to thaw and release the carbon dioxide and methane.

How much methane is stored as clathrates on the ocean floor?

Speaking on ABC Radio National’s Ockham’s Razor program on 24 May, 2009[35], Melbourne computer specialist Geoff Hudson cited a report by Bruce Buffet and David Archer of the University of Chicago’s Department of Geophysical Sciences[36], in which they estimated the stores of methane to weigh 3,000 billion tonnes. That is six times the weight of carbon estimated to be stored in permafrost, as referred to above.

Hudson reported, “releasing all that methane would be like raising the carbon dioxide level to 70,000 parts per million, more than 100 times worse than the 540 ppm said to the point of no return.” (Hudson’s estimate is significantly higher than potential impact of carbon released from permafrost, as referred to above. The reason may be the application of: (a) methane’s “global warming potential” (GWP) [Footnote 3]; and (b) differences between atmospheric and sea level pressures; in his calculations.)

Hudson nominated a slowing in the flow of the Gulf Stream as a potential trigger for what is known as the “Clathrate Gun”, involving a process of amplifying feedbacks resulting from some initial thawing of methane clathrates of other warming mechanisms. The Gulf Stream is the massive flow of warm water from the Gulf of Mexico to the North Atlantic.

If the flow were to slow sufficiently, there would be excess warm water remaining in the Gulf of Mexico, potentially thawing clathrates that exist on the sea floor there. He stated:

“Once the temperature gets too high, the ices melt. That will release hundreds of cubic kilometres of methane presently sitting on the floor of the Gulf. The trigger for the Clathrate Gun might be just south of New Orleans.”

Hudson noted that Dr Bill Turrell of the Marine Laboratory in Aberdeen, Scotland observed a 20% slowing in the flow of the Gulf Stream five years prior to the Ockham’s Razor broadcast. (As an important aside, with the impact of warming oceans on storm activity, he noted, “Armed with this information, the origin of the strength of Hurricane Katrina is obvious.”)

The need for emergency action

With climate feedbacks seemingly leading to exponential growth in greenhouse gas concentrations, it is essential that key decision makers treat the issue as the emergency that it is. We need to urgently transform our energy systems to be emissions free, draw down existing atmospheric carbon dioxide through massive levels of reforestation, and reduce emissions of non-carbon dioxide climate forcing agents, such as methane, nitrous oxide, tropospheric ozone and black carbon. Those issues will be referred to in future articles.

In recent years, governments have spent trillions of dollars to save financial institutions and struggling economies. During World War 2, military expenditures as a percentage of GDP in the US, UK, Germany and Japan were as high as 42%, 55%, 70% and 76% respectively.[37] However, governments are yet to tackle climate change in a meaningful way. Emission reduction targets such as Australia’s figure of 5% are miniscule relative to what is required.

In his article “As emission rise, we may be heading for an ice-free planet”, earth and paleoclimate scientist at Australian National University, Dr Andrew Glikson, stated as follows (with my underline):[38]

“Contrarian claims by sceptics, misrepresenting direct observations in nature and ignoring the laws of physics, have been adopted by neo-conservative political parties. A corporate media maintains a ‘balance’ between facts and fiction. The best that governments seem to do is devise cosmetic solutions, or promise further discussions, while time is running out. 

Good planets are hard to come by.”

A final word from James Hansen on tipping points

“Animal and plant species are already being stressed by climate change. Species can migrate in response to movement of their climatic zone, but some species in polar and alpine regions will be pushed off the planet. As climate zones move farther and faster, climate change will become the primary cause of species extinction. The tipping point for life on the planet will occur when so many interdependent species are lost that ecosystems collapse.”[39]

Footnotes:

  1. Dr Hansen has since retired from NASA’s Goddard Institute for Space Studies so as to more freely campaign on climate change.
  2. In 2014, Barry Brook became Professor of Environmental Sustainability at the University of Tasmania.
  3. The emissions of different gases can be aggregated by converting them to carbon dioxide equivalents (CO2-e).  They are converted by multiplying the mass of emissions by the appropriate global warming potentials (GWPs).  GWPs represent the relative warming effect of a unit mass of the gas when compared with the same mass of CO2 over a specific period.  For methane, at the date of this republication, the GWPs used by the UN’s Intergovernmental Panel on Climate Change (IPCC), allowing for climate-carbon feedbacks, are 34 for 100 years and 86 for 20 years.
  4. Temperature increases at the poles to date have been multiples of the global average.

Author: 

Paul Mahony (also on Twitter, Scribd, Slideshare and Viva la Vegan)

References:

[1]     Painting, R., “The Oceans Warmed up Sharply in 2013: We’re Going to Need a Bigger Graph”, Skeptical Science, 31 January 2014, http://www.skepticalscience.com/The-Oceans-Warmed-up-Sharply-in-2013-We-are-Going-to-Need-a-Bigger-Graph.html

[2]       Skeptical Science, “Global Warming at 4 Hiroshima Atomic Bombs per Second”, https://4hiroshimas.com/

[3]       Miller, C., quoted at NASA, “Global Climate Change: Vital Signs for the Planet”, http://climate.nasa.gov/400ppmquotes/

[4]       Mann, M.E., “Earth Will Cross the Climate Danger Threshold by 2036”, Scientific American, 18th March, 2014, http://www.scientificamerican.com/article/earth-will-cross-the-climate-danger-threshold-by-2036/, cited in Spratt, D., “Two degrees of warming closer than you may think”, Climate Code Red, 6th February, 2015, http://www.climatecodered.org/2015/02/two-degrees-of-warming-closer-than-you.html#more

[5]       Spratt, D. and Dunlop, I., “Dangerous Climate Warming: Myth, reality and risk management”, Oct 2014, p. 5, http://www.climatecodered.org/p/myth-and-reality.html

[6]       Spratt, D., “Two degrees of warming closer than you may think”, Climate Code Red, 6th February, 2015, http://www.climatecodered.org/2015/02/two-degrees-of-warming-closer-than-you.html#more

[7]       Scripps Institution of Oceanography, National Oceanic and Atmospheric Administration (NOAA) Monthly Data for the Atmospheric CO2 Since 1958, via http://co2now.org/Current-CO2/CO2-Trend/ (Accessed 4 February 2012)

[8]       Data is calculated by CO2Now using annual growth rates published by NOAA-ESRL based on its measurements of the CO2 concentration in the atmosphere (Mauna Loa Observatory).  Refer to http://co2now.org/Current-CO2/CO2-Trend/ (Accessed 4 February 2012)

[9]       Spratt, D.,“Global Warming – No more business as usual: This is an emergency!”, Environmental Activists’ Conference 2008: Climate Emergency – No More Business as Usual, 10 October, 2008, reproduced in Links International Journal of Socialist Renewal, http://links.org.au/node/683 (Accessed 4 February 2012)

[10]      Hansen, J, “Storms of my Grandchildren”, Bloomsbury, 2009, p. IX

[11]     Sound system image courtesy of TOA Corporation, http://www.toa.jp/soundoh_wiki/index.php?Soundindex%2FAcoustic%20feedback

[12]      CSIRO, “Science and Solutions for Australia: Climate Change”, 2011, Extract of Fig. 2.3, p. 22, http://www.csiro.au/Outcomes/Climate/Climate-Change-Book.aspx

[13]      Hansen, J, op cit.

[14]      CSIRO, op cit., p. 15

[15]      Whetton, P, “Future Australian Climate Scenarios”, Chapter 3, p. 43 “Climate Change”, CSIRO Publishing, 2011, Cleugh, H; Stafford Smith, M; Battaglia, M; Graham, P (Editors), http://www.publish.csiro.au/Books/download.cfm?ID=6558 (Accessed 4 February 2012)

[16]      Vale, P,“Climate Change: World Reaches Point Of No Return In Five Years, Say Scientists”, The Huffington Post UK, 9 Nov, 2011, http://www.huffingtonpost.co.uk/2011/11/09/climate-change-five-years_n_1084052.html (Accessed 4 February 2012)

[17]      Spratt, D, 2008, op cit.

[18]      Spratt, D and Sutton, P, “Climate Code Red: The case for emergency action”, Scribe, 2008, p. 47

[19]      Spratt, D, 2008, op cit.

[20]      Lemonick, Michael D, “Beyond the Tipping Point”, Scientific American Earth 3.0, 6 October 2008, http://www.scientificamerican.com/article.cfm?id=global-warming-beyond-the-co2 <http://www.scientificamerican.com/article.cfm?id=global-warming-beyond-the-co2>  (Preview) (Full article accessed 4 February 2012)

[21]      Data Buoy Cooperation Panel, http://www.dbcp.noaa.gov/seashelp/HtmlIceGlossary.htm (Accessed 4 February 2012)

[22]      Lemonick, Michael D, op cit.

[23]      Spratt, D and Sutton, P, op cit., p. 13

[24]      Raloff, J., “Science News of the Year 2011 – Environment”, Science News, 31 December 2011, Vol. 180 Issue 14, p 25, http://www.sciencenews.org/view/feature/id/336997/title/2011_Science_News_of_the_Year_Environment

[25]      Hansen, J., op cit., p. 38.

[26]      Spratt, D and Lawson, D, “Bubbling our way to the Apocalypse”, Rolling Stone, November 2008, pp. 53-55

[27]      Spratt, D. 2008, op cit.

[28]      Spratt, D and Sutton, P, op cit., p. 20.

[29]      Hansen, J., op cit., pp. 255-256 and p. 287. (An alternative ice loss figure to the quoted figure of 250 cubic km from p. 287 had been shown on p. 255 but the correct figure has been confirmed as 250 cubic km in emails of 15/6/11 and 16/6/11.)

[30]      Lyndsey, R, “Greenland Ice Sheet Getting Darker”, Climate Watch Magazine, NOAA Climate Services, 30 December 2011, http://www.climatewatch.noaa.gov/article/2011/greenland-ice-sheet-getting-darker-2 (including map) (Accessed 4 February 2012)

[31]      Salter, J. “Scientists capture dramatic footage of Arctic glaciers melting in hours”, The Telegraph, 20 February 2009, http://www.telegraph.co.uk/earth/environment/climatechange/4734859/Scientists-capture-dramatic-footage-of-Arctic-glaciers-melting-in-hours.html (Accessed 4 February 2012)

[32]      Spratt, D and Lawson, D, op cit.

[33]      Spratt, D, 2008, op cit.

[34]      Connor, S, “Vast methane ‘plumes’ seen in Arctic ocean as sea ice retreats”, The Independent, 13 December, 2011, http://www.independent.co.uk/news/science/vast-methane-plumes-seen-in-arctic-ocean-as-sea-ice-retreats-6276278.html (Accessed 4 February 2012)

[35]      Hudson, G, “The trigger for the clathrate gun” Ockham’s Razor, ABC Radio National, 24 May, 2009, http://www.abc.net.au/radionational/programs/ockhamsrazor/the-trigger-for-the-clathrate-gun/3152002 (Accessed 4 February 2012)

[36]      Buffet, B and Archer, D, “Global inventory of methane clathrate: sensitivity to changes in the deep ocean”, Earth and Planetary Science Letters 227 (2004) 185 – 199, http://geosci.uchicago.edu/~archer/reprints/buffett.2004.clathrates.pdf (Accessed 4 February 2012)

[37]      Spratt, D and Sutton, P, op cit., p. 252

[38]      Glikson, A, “As emissions rise, we may be heading for an ice-free planet”, The Conversation, 18 January, 2012, http://theconversation.edu.au/as-emissions-rise-we-may-be-heading-for-an-ice-free-planet-4893 (Accessed 4 February 2012)

[39]      Hansen, J, “Twenty Years Later: Tipping Points Near on Global Warming”, Huffington Post, 23/6/08, http://www.huffingtonpost.com/dr-james-hansen/twenty-years-later-tippin_b_108766.html (Accessed 4 February 2012)