All climate scenarios in early IPCC reports
yielded global warming of well over 2C, which led us to define an
alternative scenario[13] in 2000 with equal emphasis on air pollution
and CO2. We thought it would probably take more than half a century to phase off fossil fuel CO2 emissions. By focusing on air pollutants methane, black carbon, and tropospheric ozone, as well as CO2,
we concluded that it was still possible to keep global warming from
exceeding 2°C. The alternative scenario had constant fossil fuel
emissions in the first half of this century – which required an increase
of carbon-free energies such as renewables and nuclear power – and
declining fossil fuel emissions in the second half of the century. As
described on page 13 of Bright Future,10 this paper irritated
the scientific community. A decade and a half later, the fifth IPCC
Assessment Report (AR5) defined four scenarios: RCP (Representative
Concentration Pathways) 2.6, 4.5, 6 and 8.5, where the number is the
greenhouse gas forcing in 2100. RCP2.6 was defined so as to keep global
warming below 2°C; however, emissions growth after 2000 meant that the
2°C limit could be met only by inserting a large dose of negative
emissions.[14]
Now let’s compare the real world with RCP2.6. Actual annual growth of
the climate forcing – the upper edge of the red area in Fig. 5 – has
increased in the past decade. Negative emissions required in 2021 to
match the RCP2.6 scenario must reduce the annual growth of greenhouse
gas climate forcing by 0.022 W/m2. This gap between reality
and the 2°C scenario can readily be converted – using accurate formulae
in Table 1 of the alternative scenario paper13 – to the atmospheric CO2
reduction required to close the gap in added climate forcing during the
single year 2021. However, as is well known, the required negative
emissions (CO2 extracted from the air and placed in permanent
storage (which alternatively could have been reduced emissions) must be
larger than the desired atmospheric CO2 reduction by a factor of about 1.7 (see Fig. 10 of Young People’s Burden[15]). Using the factor 1.7, the required CO2 extraction (negative emissions) is 1.55 ppm atmospheric CO2, which is 5.58 GtC.
What is the annual cost of this CO2 extraction? In Young People’s Burden
– co-authors include carbon cycle experts Pete Smith and David Beerling
– the unit cost is estimated as low as $150-350 per tC. The cost of
extraction in that case is $0.84-1.95 trillion in 2021. The annual cost
increases rapidly to stay on the RCP2.6 scenario. Moreover, the cost
estimate of $150-350 per tC (which is $41-95 per tCO2) is
optimistic. Based on a pilot carbon capture plant built in Canada,
David Keith[16] estimates an extraction cost of $450-920 per tC, as
clarified elsewhere.[17] Keith’s cost range yields an extraction cost
of $2.5-5.1 trillion for the single year 2021.
The United Nations struggles to come up with a $100 billion climate fund
for innocent nations suffering climate change. It’s inconceivable that
trillions of dollars per year will be found for CO2
extraction. We conclude that the 1.5°C target certainly will be
exceeded, and the world will almost certainly blow through the 2°C
ceiling. Of course, one can devise a scenario that stays under 2°C via a
miraculous transition to zero emissions within a few decades, but the
real world pays no attention to imaginary scenarios. Instead, the real
world responds to the actual growth of greenhouse gas climate forcings,
shown by the top edge of the red area in Fig. 5.
Continue reading ↓↓↓
|
|
No comments:
Post a Comment