Warwick Rowell, Tuesday 18 February 2014
Climate sensitivity, sea level and atmospheric carbon dioxide
James Hansen, Makiko Sato, Gary Russell and Pushker Kharecha
Phil. Trans. R. Soc. A 2013 371, 20120294, published 16 September 2013
Extract from the final section by Warwick Rowell:
(… indicates omissions, my spacing for emphasis.)
Global habitability
Burning all fossil fuels would produce a different, practically uninhabitable, planet.
Approximately 4.8 × CO2, correspond(s) to fossil fuel emissions as much as approximately 10,000 Gt C…
Our calculated global warming in this case is 16°C, with warming at the poles approximately 30°C. Calculated warming over land areas averages approximately 20°C. Such temperatures would eliminate grain production in almost all agricultural regions in the world [130].
… More ominously, global warming of that magnitude would make most of the planet uninhabitable by humans [132,133].
The human body generates about 100W of metabolic heat that must be carried away to maintain a core body temperature near 37°C, which implies that sustained wet bulb temperatures above 35°C can result in lethal hyperthermia [132,134]. Today, the summer temperature varies widely over the Earth’s surface, but wet bulb temperature is more narrowly confined by the effect of humidity, with the most common value of approximately 26–27°C and the highest approximately of 31°C. A warming of 10–12°C would put most of today’s world population in regions with a wet bulb temperature above 35°C [132]. Given the 20°C warming we find with 4.8 × CO2, it is clear that such a climate forcing would produce intolerable climatic conditions
… Note also that increased heat stress due to warming of the past few decades is already enough to affect health and workplace productivity at low latitudes, where the impact falls most heavily on low- and middle-income countries [135].
We conclude that the large climate change from burning all fossil fuels would threaten the biological health and survival of humanity, making policies that rely substantially on adaptation inadequate.
Let us now verify that our assumed fossil fuel climate forcing of 9Wm−2 is feasible.
If we assume that fossil fuel emissions increase by 3% per year, typical of the past decade and of the entire period since 1950, cumulative fossil fuel emissions will reach 10 000 Gt C in 118 years. However, with such large rapidly growing emissions the assumed 33% CO2 airborne fraction is surely too small. The airborne fraction, observed to have been 55% since 1950 [1], should increase because of well-known nonlinearity in ocean chemistry and saturation of carbon sinks, implying that the airborne fraction probably will be closer to two-thirds rather than one-third, at least for a century or more.
Thus, the fossil fuel source required to yield a 9Wm−2 forcing may be closer to 5000 Gt C, rather than 10 000 Gt C.
Are there sufficient fossil fuel reserves to yield 5000–10 000 Gt C?
Recent updates of potential reserves [114], including unconventional fossil fuels (such as tar sands, tar shale and hydrofracking-derived shale gas) in addition to conventional oil, gas and coal, suggest that 5 × CO2 (1400 ppm) is indeed feasible.
For instance, using the emission factor for coal from IPCC [48], coal resources given by the Global Energy Assessment [114] amount to 7300–11 000 Gt C. Similarly, using emission factors from IPCC [48], total recoverable fossil energy reserves and resources estimated by GEA [114] are approximately 15 000 Gt C. This does not include large ‘additional occurrences’ listed in ch. 7 of GEA [114].
Thus,.., there are ..more than enough available fossil fuels to cause a forcing of 9Wm−2 sustained for centuries. Most of the remaining fossil fuel carbon is in coal and unconventional oil and gas.
,, humanity stands at a fork in the road.
As conventional oil and gas are depleted, will we move to carbon-free energy and efficiency—or to unconventional fossil fuels and coal?
If fossil fuels were made to pay their costs to society, costs of pollution and climate change, carbon-free alternatives might supplant fossil fuels over a period of decades. However, if governments force the public to bear the external costs and even subsidize fossil fuels, carbon emissions are likely to continue to grow, with deleterious consequences for young people and future generations.
It seems implausible that humanity will not alter its energy course as consequences of burning all fossil fuels become clearer.
Yet strong evidence about the dangers of human-made climate change have so far had little effect.
Whether governments continue to be so foolhardy as to allow or encourage development of all fossil fuels may determine the fate of humanity.