The hodgepodge of information available on global warming and climate change can be bewildering, sometimes intentionally so.  Let me see if I can clear away some of the clutter and boil it down to a couple of numbers that you need to keep track of to understand global warming.  I do need to warn you though; this column does not have a happy ending.

Last week in Part I, I reviewed the scientific and technical background on methane hydrate.  This week, I’ll explain why I’m using methane hydrate as the lens through which to view the future of our climate.  But first, here is a refresher on the Green House Effect.
When the sun’s rays hit the earth, a portion of their energy is reflected back as infrared radiation.  Oxygen and nitrogen, which account for almost 99% of our atmosphere, are transparent to infrared radiation.  Therefore, if the air was comprised exclusively of oxygen and nitrogen, the infrared radiation would escape into outer space and, as a result, the average temperature of the Earth would hover around the freezing point of water.  Fortunately for us, water vapor and carbon dioxide molecules, which make up part of the remaining 1% of the atmosphere, absorb some of the infrared rays before they escape (the Green House Effect).  This warms the atmosphere to its current global average temperature of approximately 14 oC (57.2 oF).  Although water vapor absorbs infrared radiation and is, therefore, a green house gas, it is not generally included in the discussion of the Green House Effect since it cannot accumulate in the atmosphere.  Once the water vapor concentration in the air reaches saturation – 100% relative humidity – it falls as rain.  In contrast, the carbon dioxide (CO2) concentration in our atmosphere can increase without limits.
You might be tempted to think that since the Green House Effect is important in keeping us “warm enough” today, a little more of it should not be such a big deal.  As it turns out, what may appear to us as a “small” change in global average temperature can have dramatic effects.  For example, during the last ice age which covered most of North America and Europe in massive glaciers, the global average temperature was only 4 oC cooler than today. 
In addition to water and CO2, methane is a potent green house gas.  It is twenty times more effective in absorbing infrared radiation than CO2.  Therefore, an accumulation of methane in the atmosphere would have a disproportionate impact on global temperatures. This effect would be mitigated over time since methane in the atmosphere is slowly converted to carbon dioxide.
The key to understanding the future of the Green House Effect is to keep track of where all the carbon atoms are.  They reside in five main reservoirs:

  • CO2 in the atmosphere,
  • CO2 dissolved in the oceans,
  • hydrocarbons in plants and animals,
  • hydrocarbons in the near-surface soils, and
  • hydrocarbons in fossil fuels buried deep underground. 

The first four of these reservoirs comprise the biosphere.  Human-caused global warming results from the transfer of the carbon atoms from deeply burried fossil fuels up into the biosphere.  When a fossil fuel, like coal for a power plant or gasoline for your car, is burned, the resulting CO2 initially enters just the first of the five carbon reservoirs, the atmosphere.  With time, some of this CO2 is distributed among the other carbon reservoirs in the biosphere.  At present, about half of the carbon emitted from burning fossil fuels remains in the atmosphere.  However, since the oceans are approaching their limits in their capacity to dissolve CO2, the fraction of newly emitted carbon dioxide which remains in the atmosphere is going to increase in the coming decades. 
OK, now for the numbers.  In the year 1850, just prior to the Industrial Revolution, the Earth’s atmosphere contained approximately 280 ppm of carbon dioxide, which corresponded to there being 574 gigatons of carbon in the atmophere.  Today the concentration is 390 ppm, which corresponds to 800 gigatons of carbon.  So over the course of the Industrial Age we have added 226 gigatons of carbon to the atmosphere.
The increase in the CO2 concentration from 280 to 390 ppm has resulted in an increase of 0.7 oC in the global average temperature since 1850.  Again, while this may not sound like a lot, this seemingly minor increase is already having a measurable impact on our global climate, with stronger storms, rising sea levels and more frequent droughts.  The United Nations Intergovernmental Panel on Climate Change has concluded that the largest temperature rise we could endure while still maintaining some semblance of our current lifestyles and population is 2 oC.  A 2 oC temperature rise above the 1850 level corresponds to an atmospheric CO2 concentration of 450 ppm.  Increasing from the current level of 390 ppm to 450 ppm would correspond to adding 123 additional gigatons of carbon to the atmosphere.  Since approximately half of the carbon we introduce to the atmosphere remains there, the most we can burn (our “fossil fuel allowance”) is twice that, or 246 gigatons. (1)  
While the 450 ppm/2 oC case is considered survivable, an increase of 4 oC, which corresponds to a concentration of 800 ppm of CO2 in the atmosphere, is predicted to have catastrophic consequences, with rising sea levels inundating coastal cities around the world and scorching temperatures converting our farm lands to deserts.  Using the same math as in the paragraph above, the 800 ppm scenario would result in a fossil fuel allowance 1680 gigatons.

  PPM Carbon Dioxide Gigatons Carbon in Atmosphere Fossil Fuel Allowance
1850 280 574  
2012 390 800  
U.N. Targets 450 923 246
Catastrophe 800 1641 1680

 What do all those number tell us?  Humanity has already increased the global average temperature by 0.7 oC.  To maintain a reasonable climate for mankind, we need to burn no more than 246 additional gigatons of carbon from fossil fuels.  Burning 1680 gigatons of carbon from fossil fuels could bring down civilization.  So what does methane hyrdrate have to do with this you ask?  The answer lies in some more numbers.
The table below shows the carbon content equivalents of the fossil fuel reserves on Earth.(2)

  Gigatons of Carbon
Petroleum 140
Natural Gas 150
Oil Sands 160
Coal 800
Subtotal from Traditional Fossil Fuels 1250
Methane Hydrate 1500
Total 2750

Look at this table for a moment and focus on the subtotal of 1250 gigaton equivalents of carbon in traditional fossil fuel reserves.  Then consider that both presidential candidates in the recent election called for increased exploitation of fossil fuels.  Consider that the global economy, at its very foundation, is built on the energy of fossil fuels. 
At the moment, we are adding approximately a net of 10 gigatons of carbon to the atmosphere per year, and the global rate of fossil fuel use is on the rise.  Absent a global economic collapse or nearly apocalyptic epidemic to slow our carbon emissions, I see no possible way that we are going to limit ourselves to our fossil fuel allowance of 246 gigatons.  The U.N. targets will be exceeded sometime in the next 20 to 30 years.  (Interestingly, during the time I have been working on this column, the World Bank released a report with the same conclusion.)
So if we are destined to blow right by the target of 450 ppm, where are we headed?  Without methane hydrate, we would be limited to the 1250 gigaton equivalents of carbon in the traditional fossil fuel reserves.  While burning all of this would still put humanity at great risk, it would leave us short of the 1680 gigatons of carbon that we would need to destroy ourselves by hitting 800 ppm.  If we start to use methane hydrates for fuel, we could reach 800 ppm fairly quickly. 
This data makes it clear that we should not even consider an attempt to recover the methane in the methane hydrate.  But even if we don’t there’s a catch, and it’s a big one.  Recall from last week’s column that methane hydrate is a methane-containing lattice of ice which resides primarily on the ocean floors.  As we warm the atmosphere, we warm the oceans.  As the oceans continue to warm, some of the methane hydrate will melt, releasing methane into the atmosphere.  Since methane is a much more efficient green house gas than CO2, any sizable release of methane would rapidly increase global temperatures which would, in turn, melt more methane hydrate.  This self-reinforcing release of methane from methane hydrates is thought to be responsible for past episodes of rapid global temperature rise.
At this point of the analysis, most authors would include the “how we can act now to avoid this disaster” paragraph.  Although I am certainly capable of laying out the technical path to a rapid global conversion to renewable energy, I feel that to do so would be dishonestly optimistic.  Barring potental miraculous technical breakthroughs (one of which I will discuss next week), any of these possible technical solutions would require global consensus on how to proceed, sustained efforts on the agreed upon plan, and a universal human commitment to shared sacrifice.  In a world where we still kill one another over differences in skin color or varying interpretations of the branches of Abrahamic faiths, this level of cooperation is not going to happen, at least not until it is far too late.  We’re going to blow it.  We’re already blowing it.  May our children forgive us.
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(1) As I pointed out, the capacity of the oceans to absorb CO2 is running out.  Therefore, the actual fossil fuel allowance to raise the amount of carbon in the atmosphere by 123 gigatons is somewhat less than 246 gigatons.  In the original draft of this column I included a section on this.  In the end, I did not think a lengthy discussion of this point was needed for this analysis.  I may revisit this issue in a stand-alone column.
(2) There are no universally accepted values for the size of either traditional fossil fuel reserves or methane hydrates.  The fossil fuel reserve numbers are clouded by secrecy and varying approaches to determining which deposits are economically viable. Difficulties in estimating the global reserve of methane hydrates stem from their relative inaccessibility.  I have done my best to use an average of the numbers which are publically available.  Bear in mind though, that the variability in the ranges of estimates for these numbers are not large enough to change the conclusions.