Tuesday, 9 February 2016

Fossil Carbon Safety Margin

by Dr. Susan P. Krumdieck, Professor in Mechanical Engineering, University of Canterbury

To me, as an engineer and a person with a family, the language of climate change action – for example setting “targets” for emissions – seems to be dangerously at odds with the science.

It seems obvious that the engineers of the world have a lot of work to do in changing everything that uses fossil fuel to use much less to no fossil fuel. However, this discussion is not really taking place. 

The science is clear, so I wanted to look at how we might use the language of engineering to understand the way forward. The latest IPCC Fifth Assessment Report gives conclusive modelling and science observation that profoundly affects every person on the planet. However, the general population doesn’t seem to understand the message. 

Everybody knows that it is not wise to exceed a safety limit, but we also know that we can probably get away with it. If the curve up ahead has a sign that says 65 km/hr, then I know it would be safe to take it at that speed. I also know I will “likely” make it through the curve if I do 70 or even 80 km/hr. 

If I do speed through the curve, however, the risk of losing control, drifting into the wrong lane or not being able to manoeuvre to avoid any unexpected obstacles is higher. A failure limit in this situation would be the speed in the curve where a crash occurs. This could be 70 km/hr if there is any water or loose gravel on the road or if my tires don’t have good tread. There is also a speed, say 130 km/hr, at which it is likely that a person will crash going around the curve. In the best car on the best day with the best road conditions, there is a speed, say 250 km/hr, beyond which it is not physically possible for a car to stay in contact with the road and there will be a crash. 

As a mechanical engineer, I can’t predict exactly at what speed a crash will occur. There are a lot of other factors. I also can’t predict exactly what will happen in the crash – whether it will involve rolling or hitting a tree or a fire – and I can’t predict whether you will live or what kind of injuries you will have. But – I can definitely recommend that you should not take that curve at more than 65 km/hr; this is the safety limit. I would call 130 km/hr the failure limit. I would call 250 km/hr suicide. 

Now, let’s translate the climate science of atmospheric carbon dioxide (CO2) loading into terms of a safety limit. Dr James Hansen, former director of the US NASA Goddard Institute for Space Studies, explained to the Bush administration that 350 parts per million (ppm) was the safe limit for atmospheric CO2 concentration. If the accumulation of CO2 in the atmosphere got to this level, there would definitely be climate change.  Going over this level would be likely to cause warming that could do more than just change the weather; it could melt polar and glacial ice, acidify the oceans, cause changes in ocean currents, and change the climate in unpredictable ways. There would, however, be certainty that more frequent and more extreme storm events would occur. This safety limit of 350 ppm atmospheric CO2 has been exceeded. Current atmospheric CO2 concentration is over 400 ppm, and evidence is mounting of unprecedented warming and ocean acidification.

Limiting the thermal imbalance, or warming, to less than 2oC above the 1860-1880 decadal average would require cumulative CO2 emissions to be kept below a certain level. CO2 emissions are caused primarily by burning solid and liquid fossil fuels; other major sources include industrial production and deforestation. The cumulative carbon loading limit likely to result in 2oC global warming is 1000 gigatonnes of carbon (GtC) (with a probability of greater than 66%) burned since the 1860’s. Accounting for forcings from additional greenhouse gases lowers the failure limit to 790 GtC.

As of 2011, over 500 GtC of fossil fuel had been extracted and burned. Just like with our driving speed analogy, the exact risks and the exact failure mechanisms can’t be predicted. But, we are now beyond the safe level for fossil fuel use, and we are pushing toward a failure limit.  I hope this is clear. If today we stopped extracting and burning fossil carbon, we would still be above the safety limit for having no risk of climate changes, and we would watch over the next 100 years to see how the climate settled into a new warmer equilibrium. If we were to extract and burn another 300 GtC in fossil fuel, then the energy balance on the planet would likely result in a temperature rise of over 5oC and the changes to the climate would be catastrophic.

According to the International Energy Agency, in 2012, global CO2 emissions from all sources totalled about 31.5 GtCO2 per year. I will do the analysis using this number, but be aware that the 2015 emissions are expected to top 40 GtCO2. Note that emissions are discussed in terms of CO2 emitted, but production is in terms of the carbon in the fuel. Burning of one GtC of fossil fuel produces 3.7 GtCO2.  If we did not increase our consumption of fossil fuels any further above the current 11 GtC/yr, we would have less than 30 years until we have burned the amount of fossil carbon that is likely to cause catastrophic climate change. If all nations of the world actually had achieved reductions called for in the Kyoto Protocol of reducing emissions to 1990 levels (14 GtCO2) or lower, then at 3.8 GtC/yr of fuel production it would take 80 years to go past the failure limit. Which is more acceptable: exceeding the climate failure limit in about 30 years by limiting growth, or exceeding the failure limit in 80 years by dramatic reduction of fossil fuel production?

The only intellectually acceptable answer is neither. It is not acceptable to exceed the failure limit.

This is the point where we usually start arguing over the numbers. Should the failure limit be 800 GtC, or 1000 GtC?  What should we count in current emissions rates? We also start questioning what the catastrophes would be. Would the sea level rise be 2 m or 17 m? This is like arguing about taking a 65 km/hr curve at 130 or 200 km/hr, and whether the car would skid into a tree or roll into a ditch. Once you have exceeded a safety limit, and you are pushing into the range of increasingly likely failure, it is really not the time to be arguing about the details.  It is TIME TO SLOW DOWN!

For reference, the amount of proven reserves (oil, gas and coal) that the energy companies plan to extract and bring to the market is more than 2800 GtC. This figure does not include the Arctic oil that Shell and other oil companies are scouting for at the moment. The best engineering terms I can find to describe the extraction and burning of these reserves are: unthinkable, irresponsible, negligent, reprehensible, criminal, and suicidal.

How can I explain to my future granddaughter that we had to preserve our economy so we accepted policy which would breach the climate failure limit in 20-30 years? Why does 30 years seem like a long time in the future? Why has this rather clear bit of science not caused radical change?

In the next part of my blog, I will turn to the personal interaction with the data to see if it sheds any light.


  1. Thank you for this cogent analysis. I like how clearly you outline the amount of carbon already 'burned' and that which the major fossil fuel companies intend to extract and burn. For an intelligent species, it is incomprehensible how the grave dangers of this are not seen but by only a few. And, almost always, when reading about global warming, the focus is on what will happen to Us as a species; what of the countless other species on earth, do they not also have a right to live and to thrive?

  2. Superb analysis and analogy! Thank you and please keep it up!