'Worst-case' CO2 emissions scenario is best for assessing climate risk
and impacts to 2050
RCP 8.5 tracks within 1% of actual emissions

Date:
August 4, 2020
Source:
Woods Hole Research Center
Summary:
The RCP 8.5 carbon emissions pathway is the most appropriate
for conducting assessments of climate change impacts by 2050,
according to a new article. Long dismissed as an alarmist
or misleading worst-case scenario, the authors argue that is
actually the closest approximation of both historical emissions
and anticipated outcomes of current global climate policies,
tracking within 1% of actual emissions.



FULL STORY ==========================================================================
The RCP 8.5 C02 emissions pathway, long considered a "worst case scenario"
by the international science community, is the most appropriate for
conducting assessments of climate change impacts by 2050, according to
a new article published today in the Proceedings of the National Academy
of Sciences. The work was authored by Woods Hole Research Center (WHRC)
Risk Program Director Dr. Christopher Schwalm, Dr. Spencer Glendon,
a Senior Fellow at WHRC and founder of Probable Futures, and by WHRC
President Dr. Philip Duffy. Long dismissed as alarmist or misleading,
the paper argues that is actually the closest approximation of both
historical emissions and anticipated outcomes of current global climate policies, tracking within 1% of actual emissions.


==========================================================================
"Not only are the emissions consistent with RCP 8.5 in close agreement
with historical total cumulative CO2 emissions (within 1%), but
RCP8.5 is also the best match out to mid-century under current and
stated policies with still highly plausible levels of CO2 emissions
in 2100," the authors wrote. ." ..Not using RCP8.5 to describe the
previous 15 years assumes a level of mitigation that did not occur,
thereby skewing subsequent assessments by lessening the severity of
warming and associated physical climate risk." Four scenarios known as Representative Concentration Pathways (RCPs) were developed in 2005 for
the most recent Intergovernmental Panel on Climate Change Assessment
Report (AR5). The RCP scenarios are used in global climate models, and
include historical greenhouse gas emissions until 2005, and projected
emissions subsequently. RCP 8.5 assumes the greatest fossil fuel use,
and a resulting additional 8.5 watts per square meter of radiative
forcing by 2100.

The commentary also emphasizes that while there are signs of progress
on bending the global emissions curve and that our emissions picture may
change significantly by 2100, focusing on the unknowable, distant future
may distort the current debate on these issues. "For purposes of informing societal decisions, shorter time horizons are highly relevant, and it is important to have scenarios which are useful on those horizons. Looking
at mid-century and sooner, RCP8.5 is clearly the most useful choice,"
they wrote.

The article also notes that RCP 8.5 would not be significantly impacted
by the COVID-19 pandemic, adding that "we note that the usefulness of
RCP 8.5 is not changed due to the ongoing COVID-19 pandemic. Assuming
pandemic restrictions remain in place until the end of 2020 would
entail a reduction in emissions of -4.7 Gt CO2. This represents less
than 1% of total cumulative CO2 emissions since 2005 for all RCPs and observations." "Given the agreement of 2005-2020 historical and RCP8.5
total CO2 emissions and the congruence between current policies and
RCP8.5 emission levels to mid- century, RCP8.5 has continued utility,
both as an instrument to explore mean outcomes as well as risk," they concluded. "Indeed, if RCP8.5 did not exist, we'd have to create it."

========================================================================== Story Source: Materials provided by Woods_Hole_Research_Center. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Christopher R. Schwalm, Spencer Glendon, Philip B. Duffy. RCP8.5
tracks
cumulative CO2 emissions. Proceedings of the National Academy of
Sciences, 2020; 202007117 DOI: 10.1073/pnas.2007117117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200804085912.htm

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