Commentary on:  Hsiang et al (2017) “Estimating economic damage from climate change in the United States.”

The authors of the above paper predict that by 2100 a good portion of the US will experience significant economic damage due to climate change. Their calculations assume a specific emissions trajectory known as Representative Concentration Pathway 8.5 (RCP8.5). 

RCP8.5 is one of four RCPs developed by the Intergovernmental Panel on Climate Change (IPCC). It is the “worst-case” RCP, projecting a global warming increase of 2.6° - 4.8°C by 2100.  RCP8.5 also comes with a storyline that would be consistent with such high GHG concentration levels by the end of this century.  The storyline is a set of socio-economic assumptions that provide a narrative for how we might get from here to there. The storylines aren’t carved in stone; different socio-economic developments could lead to the same climate change outcome – but to be taken seriously, a storyline has to be plausible.

In that spirit, let’s tackle the plausibility of the main storyline provided for RCP8.5 – aka the “business-as-usual” scenario referenced by Hsiang et al in their analysis of the economic effects of climate change.  Here are some key plot points of this storyline:

  • Delayed development of renewable energy technologies
  • Rebound of human population to 12 billion by 2100
  • Delayed improvements in agricultural land use
  • 10-fold increase in the use of coal as a power source
  • Move away from natural gas as an energy source

The RCP8.5 energy consumption picture could be summarized as delayed renewables, less natural gas, and a whole lot more coal. Overall energy use in 2100 would be 75% - 200% more than the other RCPs, per the following chart:

Source: van Vuuren, D. P., J. Edmonds, et al. (2011). "The representative concentration pathways: an overview." Climatic Change 109(1): 5.

So, how plausible is the RCP8.5 business-as-usual storyline for energy use? Not at all. Take coal, which the storyline has increasing ten-fold by 2100. Problem is, we’re already near peak coal. North American coal use peaked in 2005 and is down 25% since then. Europe’s coal consumption peaked in 2007.  Africa peaked in 2008 and Asia in 2011. The RCP8.5 storyline also has coal supplying 50% of the world’s energy needs in 2100. This is absurd. Coal is already down to 15% of the energy mix in the US and is projected to supply less than a third of the world’s energy consumption by 2050.  Coal is basically losing out to solar and wind, as per the following:

Note too that all of the RCP storylines underestimated how fast solar and wind would become major players in the energy game.

Next: Continuing interrogation of the “business-as-usual” RCP8.5 storyline, as part of critiquing Hsiang et al’s paper. Specifically: what are the chances the global population will reach 12 billion by 2100? And what are the trends in agricultural land use?

References:

"A closer look at scenario RCP8.5" Posted on December 13, 2015 by Larry Kummer  https://judithcurry.com/2015/12/13/a-closer-look-at-scenario-rcp8-5/

“Estimating economic damage from climate change in the United States.” By Solomon Hsiang, Robert Kopp, Amir Jina, James Rising, Michael Delgado, Shashank Mohan, D. J. Rasmussen, Robert Muir-Wood, Paul Wilson, Michael Oppenheimer, Kate Larsen, Trevor Houser Science 30 Jun 2017: 1362-1369.

“On RCP8.5 and "the Business as Usual" Scenario – Different beasts not to be confused” Posted on June 30, 2015 by Blair  https://achemistinlangley.wordpress.com/2015/06/30/on-rcp8-5-and-the-business-as-usual-scenario-different-beasts-not-to-be-confused/