To recap, EPA estimates that by 2100, unchecked global warming will kill 57,000 Americans by intensifying air pollution and 12,000 Americans by intensifying heat waves. The agency also claims “significant global action” to limit future warming to 3.6ºF (2ºC) would avert those deaths.
EPA’s ‘methodology’ is GIGO from top to bottom.
To begin with, EPA assumes unchecked warming will add 9ºF to average global temperatures by 2100. That implies a warming rate of 1.058ºF/decade during the next 85 years. The actual warming rate over the past 36 years is 0.205ºF (0.114ºC)/decade, according to the latest University of Alabama in Hunstville (UAH) satellite dataset — less than one-fifth the rate in EPA’s projection.
EPA then models the impact of that implausible 9ºF warming on current U.S. air pollutant emissions, even though emissions and concentrations have declined, decade-by-decade, since 1980. All significant domestic air pollution sources will likely be gone long before 2100.
As for heat-related mortality, EPA bizarrely assumes that in 2100, 49 major U.S. cities either have the same adaptive capabilities they do today (12,000 fatalities), or at best have the adaptive capabilities of present-day Dallas (6,500 fatalities). Yet Centers for Disease Control data indicate that heat stress currently kills fewer than 650 Americans per year, and heat-related mortality rates in U.S. cities have declined, decade-by-decade since the 1960s. The most reasonable expectation is that such progress will continue.
Today’s post takes another look at EPA’s 9ºF warming projection. Turns out, EPA’s so-called business-as-usual scenario is actually a high-end emissions scenario.
Two speculative inputs in particular drive global warming guesstimates: total net radiative forcing from anthropogenic emissions and climate sensitivity. Let’s examine climate sensitivity first.
Climate sensitivity is the equilibrium (very long-term) temperature increase from a doubling of atmospheric greenhouse gas (GHG) concentrations. Climate sensitivity is a speculative quantity because the relative strengths of the feedbacks, positive and negative, that amplify or damp down the direct heating or cooling effects of anthropogenic emissions are largely unknown.
As noted in the earlier post, EPA’s 9ºF (5ºC) business-as-usual warming projection assumes a climate sensitity of 3ºC — the “best” estimate in the IPCC’s 2007 Fourth Assessment Report (AR4). EPA thus turns a blind eye to numerous post-AR4 studies that estimate significantly lower climate sensitivities.
Indeed, according to UAH atmospheric scientist Roy Spencer, global temperature data over the past 50 years indicate that climate sensitivity may be “well below 1.3ºC” — less than half of what EPA assumes.
The other key input in any global warming forecast is a projection of the total GHG emissions, concentrations, and associated radiative forcing over a particular time period. Such projections are called “Representative Concentration Pathways” (RCPs).
EPA’s business-as-usual and global-action scenarios are based on RCPs developed by Paltsev et al. (2013), researchers at MIT. A few words of clarification may be helpful.
RCPs are called “pathways” because they plot the trajectory of GHG emissions and concentrations, and the resulting changes in radiative forcing, over a period of decades to centuries, usually from pre-industrial times to 2100 and beyond.
“Radiative forcing” may be defined as the difference between the amount of solar energy absorbed by the Earth and the amount radiated back to space. Forcing can be both positive (warming) or negative (cooling). If incoming and outgoing radiation exactly balance, the net forcing is zero. Any global warming or cooling would then be due solely to “unforced” internal variability, and such changes would be cyclical or oscillatory rather than linear.
If, on the other hand, anthropogenic emissions exert a net positive forcing, the Earth will warm until radiative balance is restored at a higher average global temperature.
Forcing is expressed in watts per square meter (W/m2). Accordingly, RCPs are typically identified by their respective W/m2 forcings. For example, current IPCC climate models use four RCPs to project future global temperatures: RCP8.5, RCP6, RCP4.5, and RCP2.6. In the warmest RCP, the concentration pathway leads to a positive forcing of 8.5 W/m2 in 2100.
Finally, RCPs are called “representative” because several socio-economic development scenarios in the literature have similar forcing characteristics.
EPA’s business-as-usual emission scenario, based on the MIT study, is substantially similar to RCP8.5 (Benefits of Global Action, p. 85, fn. 6).
This week on her blog, Georgia Tech atmospheric scientist Judith Curry cites a recent essay by the “Chemist in Langley” (Blair King) challenging the plausibility of RCP8.5 as a business-as-usual scenario.
King quotes van Nuuren et al. 2011, who note that RCP8.5 “leads to a forcing level near the 90th percentile for baseline [no policy action] scenarios,” which means that it projects more forcing in 2100 than about 90% of all baseline scenarios in the literature.
Unlike the emission scenarios used in AR4, RCPs do not assume a specific socio-economic development path. The purpose of RPCs is to enable climate modelers to work from a standardized set of forcing trajectories, not to derive those trajectories from alternative “story lines” of future socio-economic development. Nonetheless, RCP developers cannot avoid offering some socio-economic narrative, or else the “pathway” has no plausibility.
King notes that RCP8.5 was originally based on an AR4 scenario called A2 developed by Keywan Riahi and colleagues in 2007. According to Riahi et al. (2011), the A2 “story line” contains the following elements:
- Coal use increases almost 10-fold by 2100 and there is a continued reliance on oil in the transportation sector.
- Population increases continuously (does not peak) in the 21st century, resulting in a global population of 12 billion by 2100.
- Per capita income growth is slow and both internationally as well as regionally there is only little convergence between high and low income countries.
- The slow economic development implies little progress in energy efficiency. Combined with the high population growth, this leads to rapid energy demand growth.
- Despite high energy demand, international trade in energy and technology is limited and overall rates of technological progress are modest.
- Reflecting the assumption of slow technological change, the long-term reduction in the energy-intensity of production slows to 0.5% per year — well below the historical average (about 1% per year between 1940 and 2000).
- A growing population and economy combined with assumptions about slow improvements in energy efficiency and non-fossil energy technologies lead to a tripling of energy demand, met primarily by fossil fuels.
Source: Riahi et al. (2011). RCP8.5 projects a 10-fold increase in coal consumption during 2000-2100 (graph on left).
King comments: “Looking at what the activists have labelled the ‘Business as Usual’ scenario we see a slew of assumptions that are anything but business as usual.” A real-world business-as-usual baseline would reflect the following information:
- In the UN’s mid-range population growth projection, global population levels off at 10 billion in 2100, it does not keep growing past 12 billion, as in A2.
- “Rather than trade blocs hoarding technologies, we are living in an increasingly international world where technological improvements move at the speed of the internet and new and improved renewable energy technologies are both being developed and shared worldwide,” King observes.
- BP Statistical Review of World Energy 2015 projects a slowdown in the growth of coal consumption over the next 20 years, partly due to plentiful supplies of natural gas for power generation, and partly due to air pollution regulations in China and the United States.
- In the U.S. Energy Information Administration’s International Energy Outlook 2013 reference case, world coal consumption rises afrom 147 quadrillion Btu in 2010 to 180 quadrillion Btu in 2020 and 220 quadrillion Btu in 2040 — a 49% increase. That is impressive, but nobody has a clue how competitive new coal generation will be compared to new gas, nuclear, and renewables during 2040-2100.
In short, every part of the A2 storyline that would make RCP8.5 a plausible emission concentration pathway is itself either implausible or sheer conjecture.
To repeat, EPA’s so-called business-as-usual RCP is virtually identical to RCP8.5, which projects greater emissions and concentrations than 9 out of 10 baseline scenarios. EPA offers no socio-economic narrative that might make its “no action” RCP a plausible projection of the next 85 years.
On the flip side, the emission reductions envisioned in EPA’s “global action” scenario appear to require politically-unsustainable cutbacks in developing countries’ access to affordable energy.
So EPA’s Benefits of Global Action report compares the hypothetical health effects of two virtually impossible futures. Seems a giant waste of time. Your gov’t at work.