The amount of future warming is predicated on the amount of emitted greenhouse gases and the sensitivity of earth’s surface temperature to changes in their concentrations. Here we take a look at the emissions component.
The U.N. currently entertains four emissions scenarios, all expressed as the change in downwelling radiation (in watts/meter-sq, nominal year 2100) towards the surface that results from an increase in the atmospheric concentration of certain greenhouse gases. They are called “representative concentration pathways,” or RCPs.
As can be seen in Figure 1, there are four, given as 2.6, 4.5, 6(.0) and 8.5. The ranges of associated warming for over 1000 total scenarios are given on the right axis.
Figure 1. Approximately 1000 scenario runs for four RCPs. From Fuss et al., 2014.
It’s not surprising that those making the case for climate action most frequently reference the highest (RCP8.5), embedding it in most climate scenarios, assessments, and international agreements (the Paris Agreement being a prime example). Here is a summary of Google Scholar citations for the different RCPs, published on February 9 by Eric Roston in Bloomberg:
Figure 2. Although increasingly untenable, RCP8.5 draws the most attention.
RCP8.5 is obsolete. It was obsolete when it was first published in the journal Climate Change by Riahi et al. in 2011. By then the shale gas revolution was underway, as can be seen from the plot below of shale gas production. By 2011, abundant shale gas had begun a wholesale displacement of coal for electrical generation, increasing natural gas’s portion of our energy portfolio and decreasing that of coal.
Figure 3. U.S. shale gas production, 2007–2016, according to the U.S. Energy Information Administration.
The Riahi et al. RCP 8.5 continues to be the favorite for analysts. It completely dominates the draft of the upcoming fourth “National Assessment” of climate change, created by our U.S. Global Change Research Program. Here is the fanciful “wedge chart” for various energy sources in RCP8.5:
Figure 4. Energy contributions (in Joules X 1018, or EJoules) in RCP 8.5.
There are at least two notable errors in RCP8.5, which both serve to exaggerate its radiative forcing. The first is an incorrectly modest growth in natural gas use, and the second is the massive growth in coal combustion. According to the International Energy Agency (2017):
The global natural gas market is undergoing a major transformation driven by new supplies coming from the United States to meet growing demand in developing countries and industry surpasses the power sector as the largest source of gas demand growth…[emphasis added]
The evolution of the role of natural gas in the global energy mix has far-reaching consequences on energy trade, air quality and carbon emissions…
Global gas demand is expected to grow by 1.6% a year…China will account for 40% of this growth.
British Petroleum (BP) recently estimated the global fuel mix through 2040 in its 2018 Energy Outlook. Under their “Evolving Transition” assumption, natural gas usage passes coal worldwide around 2030, and oil use levels off at the same time. A comparison to RCP 8.5 (above) shows how wrong it is, even in the near future.
Figure 5. British Petroleum’s fuel outlook from its most recent (2018) Energy Outlook. Note the color scheme is somewhat different than in Figure 4, with natural gas now red, instead of blue.
The substitution of shale gas for coal continues to drive down the “carbon (dioxide) intensity” of developing and developed economies. This is the amount of carbon (dioxide) emitted per unit of GDP, usually normalized to 2010 dollars adjusted for their purchasing power in a given economy. In the United States, in the quarter-century beginning in 1990, the drop was a remarkable: from 0.9kg of carbon dioxide/dollar to 0.35, or over 60%.
The imminent dethroning of King Coal is obvious in the BP data, which leads to another problem: Justin Ritchie and Hadi Dowlatabadi from University of British Columbia recently found there simply isn’t enough coal to support RCP8.5. Nor were they conservatively looking at so-called “recoverable” reserves; instead, they toted up all geologically identified coal around the planet.
They then adjusted RCP8.5 for the twin errors of increasing carbon (dioxide) intensity by a huge growth in coal use over natural gas (recall that IEA indicates large scale industrial as well as electrical switchover), and the fact that there isn’t enough coal, and modified RCP8.5 to look like this:
By comparing the contribution of oil, coal, and natural gas (the greenhouse gas sources) between RCP8.5 and what is likely to happen, we can estimate the total downwelling radiation change: it drops from 8.5 watts to roughly 5.1. (Recognizing there is a lot of fine print—this is certainly a ball-park number.)
It is the nature of climate models to scale global warming with percentage changes in emissions; i.e. a quadrupling of emissions has almost exactly the effect of doubling prospective warming over that forecast from an initial doubling of the concentration. Reducing emissions by 40%, which is the difference between Rihai’s RCP8.5 and Ritchie’s modification, similarly reduces total warming.
There’s the further problem of model overprediction of warming that we recently documented in our public comments on the upcoming Fourth National Assessment of Climate Change. Generally speaking, we find the data-based sensitivity of temperature to be about 56% of the average of the 105 climate models in the UN’s most (2013) science summary.
Multiplying everything through, we take the mean 20th and 21st century RCP8.5 warming of 4.3⁰C, adjust by 60% to get the difference with the modified RCP, and then adjust for the 56% sensitivity and we find a 21st century warming a teense under 1.5⁰C—very, very close to the sensitivity just calculated by University of Alabama-Huntsville’s Roy Spencer.
REFERENCES
British Petroleum 2018 Energy Outlook at https://www.bp.com/content/dam/bp/en/corporate/pdf/energy-economics/energy-outlook/bp-energy-outlook-2018.pdf
Fuss, S., et al, 2014. Betting on Negative Emissions. Nature Climate Change 4, 850-853
IEA, 2017. IEA Sees Global Gas Demand Rising to 2022 as US Drives Market Transformation. https://www.iea.org/newsroom/news/2017/july/iea-sees-global-gas-demand-rising-to-2022-as-us-drives-markettransformation.html
Riahi, K., Rao, S., Krey, V. et al. Climatic Change (2011) 109: 33. https://doi.org/10.1007/s10584-011-0149-y
Ritchie J and Dowlatabadi H 2017. The 1000 GtC coal question: are cases of vastly expanded future coal combustion still plausible? Energy Econ. 65 16–31.
Roston, E., 2017, at: https://www.bloomberg.com/news/articles/2017-05-24/misleading-coal-estimates-may-have-skewed-climate-projections
Ryan Maue of Cato’s Center for the Study of Science provided important background material for this post.
When uncertainty is taken into account, not much remains of the ECS (climate sensitivity) parameter in the Hadley Center temperature reconstructions. Thus no evidence of the Lacis Control Knob that determines surface temperature according to atmospheric CO2.
https://ssrn.com/abstract=3117385
What is the science behind climate sensitivity?
The many wild guesses do not seem like
real science to me.
Just one assumption after another,
and haphazard, inaccurate average temperature
compilations.
And after the assumption that CO2 is a greenhouse
gas that should cause warming, how would one
distinguish between greenhouse warming from
CO2 versus water vapor, methane, CFCs, etc>
If you start with the measured warming, and
work backwards, by assuming CO2 is the cause,
or the primary cause of the warming,
which are only unproven assumptions,
then how about the HUGE potential errors
in the surface average temperature
compilation, where a majority of grids
are wild guesses,
with no thermometer data,
and the actual thermometers
on land have been warmed
by nearby economic growth (UHI) ?
So, with the haphazard temperature measurements,
that must be at least +/- one degree C., and I’m being kind
with that proposed margin of error, how can anyone claim
to know, or calculate, the climate sensitivity to CO2?
There is NOTHING in the measured climate of the second half
of the 20th century that even suggests natural climate
change has stopped — not much different than the
first half of the 20th century, in fact — perhaps the
climate sensitivity to CO2 is zero?
If you want to be a “CO2 is evil believer”,
then you have to believe
4.5 billion years of natural climate change
suddenly stopped in 1940,
then “aerosols” took over as the
climate controller until 1975,
then all the aerosols
suddenly fell out of the air in 1975
and CO2 took over
as the climate controller
from 1975 to 2000,
then CO2 suddenly lost
it’s mojo from 2000 to 2015,
and nothing controlled the climate,
(the flat trend)
and then a late 2015 / early 2016
El Nino became
the climate controller
for those two years,
and in 2017 — your guess is as
good as mine, for who got the
job as “climate controller” in
2017 and 2018.
Only an imbecile,
or a leftist,
(I repeat myself)
would believe that tale tale of
so many different “climate
controllers” since 1940 …
but that is exactly what the
warmists believe in
… and now are
we are supposed to believe
ANY estimate of climate
sensitivity to CO2, when so little
is known about climate change ?
Climate blog for people with common sense:
http://www.elOnionBloggle.Blogspot.com
The U.N. Green Climate Fund is failing.
The U.N. and its minions the World Meteorological Organization (WTO), the UN Framework Convention on Change Change (UN FCCC) and their darling of darlings the Intergovernmental Panel on Climate Change (IPCC) must ratchet up the rhetoric. Else, all is fail and the lifestyles of 100,000 bureaucrats is in jeopardy.
Through Toil, Sweat, Blood And Tears the lifestyles of the blessed 100,000 bureaucrats will be supreme … supreme … SUPREME.
Ha ha
Really great post. Thank you. I would like to add that the much hyped correlation between cumulative emissions and cumulative warming is spurious.
Here is the proof of that.
https://ssrn.com/abstract=3000932