Environmental Engineering Reference
In-Depth Information
century, in the absence of intervention (EMF 22, 2009). The study attributes
much of the growth to developing countries.
Even if wealthier countries like the United States were to reduce their
emissions to zero immediately, it is unlikely that global CO
2
emissions
would be stabilized, much less global atmospheric concentrations (Blanford
et al., 2009). Being in their post-industrial phase of development, the eco-
nomic growth rates in developed countries are expected to be lower than
those of developing countries and their mix of goods and services less
carbon intensive. The cumulative reductions of developed countries, even
with aggressive emissions reduction programs, are expected to be low when
compared to those of developing countries.
One important contribution that developed countries can make to
global emissions reductions is to develop the technological wherewithal
that would not only be necessary for their own emission reductions, but
also would be essential for developing countries to meet their economic
development goals with affordable climate-friendly technologies.
As noted above, both the existing capital stock and that put in place in
the future are critical to understanding the difficulty of transitioning away
from the current path of growth in greenhouse gas emissions. Figure 2.6
shows representative carbon pathways (RCPs) for limiting radiative forcing
(watts per m
2
) at two alternative levels. These are referred to as the RCP
2.6
1
and RCP 4.5 scenarios. These are among a suite of pathways being
developed for use in the IPCC 5th Assessment. The pathways shown in the
figure were developed by the IMAGE and MiniCAM models, respectively
(Moss et al., 2010).
Figure 2.6 highlights the importance of the carbon budget, that is, the
area under the allowable emissions curve associated with a particular radia-
tive forcing target. Being much lower in the RCP 2.6 scenario than in the RCP
4.5 scenario, we see the rate of growth first slows and then rapidly decline
beginning in 2020. In the case of the higher CO
2
budget, emissions rise for
another two decades before peaking. Notice that the maximum rate of de-
cline is comparable in the two scenarios (about 3.5% per year); however, in
the latter it is shifted out in time. The reasons for this shift are both the higher
1
Although Moss et al. (2010) refers to this as the RCP 2.6 scenario, this is the one RCP sce-
nario that peaks and then declines. For this reason it is also referred to as the RC P3-PD sce-
nario. The RCP 3-PD has a unique shape. The radiative forcing of RCP 3-PD peaks and declines
(PD), while the radiative forcing of the other RCPs stabilize or rise towards their higher 2100
levels. Specifically, the final RCP 3-PD prepared for climate modeling peaks at 2.99 W/m
2
in
2050 and then declines to 2.71 W/m
2
in 2100 with the decline continuing beyond 2100. The
decline is due to the availability later in the century of a negative-emitting technology, biomass
with carbon capture and storage (BECs).
