By Dennis Coyne

Note that non-Petroleum comments should mostly be in this thread.

A separate petroleum thread will be posted soon.

I created an optimistic scenario for future emissions based on low population growth (UN low fertility scenario) and energy intensity of real GDP that decreases by 0.93% until 2050 and then the rate of decrease gradually falls to 0.13% by 2100, other energy demand assumptions are similar to my previous high demand scenario in an earlier post (Energy Transition).

It is assumed that non-fossil fuel energy supply increases enough to satisfy demand until 2032 when the growth rate of non-fossil fuel energy(NFFE) supply has reached 5% per year. From that point the NFFE supply continues to increase at 5% per year and demand for fossil fuels is reduced as NFFE replaces fossil fuels. I assume for simplicity that any extra NFFE (that is greater than NFFE demand) replaces coal first, then oil, and finally natural gas until fossil fuel energy demand is zero in 2058.

The scenario is too optimistic because there will be some uses of fossil fuel which will be difficult or impossible to reduce completely by 2058.
The fossil fuel emissions scenario is shown in the chart that follows and can be downloaded at the link below.

https://www.dropbox.com/s/76hasvu73fmbv07/RCPMDB.SCEN?dl=0

An interactive version of the ‘Model for the Assessment of Greenhouse Gas Induced Climate Change’ (MAGICC) can be used with the scenario at the link above (registration required.) The model can also be used as a free download for a PC.

The “liveMAGICC” model can be accessed at http://live.magicc.org/

The emissions scenario is very similar to the RCP4.5 scenario, with the fossil fuel emissions changed to match the scenario in the chart above. My “RCPMDB.scen” must be downloaded to your computer and then uploaded to liveMagic to reproduce what I have done.

I ran two versions of the probabilistic models using live magicc and my emissions scenario.

The first is not actually probabilistic in reality, it is an ensemble that uses 19 different AOGCMs (Atmosphere-Ocean Global Circulation Models) and 9 different carbon cycle models (19*9=171 different possibilities) and assumes each is equally likely, then it shows results for the median, 17% chance that temperature will be lower, as well as 25%, 75%, and 83%.

CC/

The global temperature on the vertical scale is degrees Celsius above pre-industrial temperature.

The second scenario considers a true probabilistic historically constrained run using 600 different scenarios. Details can be found in the 2009 paper linked below:

https://www.ethz.ch/content/dam/ethz/special-interest/usys/iac/iac-dam/documents/group/climphys/knutti/publications/meinshausen09nat.pdf

Supplemental information at

http://www.nature.com/nature/journal/v458/n7242/extref/nature08017-s1.pdf

Using my low carbon emissions scenario we get the result below.

CC/

Does this suggest there is no reason for concern? No.

First, this is a very optimistic emissions scenario that is unlikely to be attained, total fossil fuel emissions are likely to be more than 1000 Pg C by 2100. In addition we don’t know if actual temperatures will be lower or higher than 2 C, we would be smart to reduce carbon emissions as quickly as is feasible due to uncertainty about climate sensitivity to increased carbon dioxide.

Works Cited

Meinshausen, M., S. C. B. Raper and T. M. L. Wigley (2011). “Emulating coupled atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6: Part I – Model Description and Calibration.” Atmospheric Chemistry and Physics 11: 1417-1456. doi:10.5194/acp-11-1417-2011.

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