Paris Climate Agreement goal still within reach, suggests new study


Date:
February 11, 2022
Source:
University of Colorado at Boulder
Summary:
A new study suggests some cautiously optimistic good news: The
2015 Paris Climate Agreement goal is still within reach, while
apocalyptic, worst- case scenarios are no longer plausible.



FULL STORY ==========================================================================
The Paris Climate Agreement goal to limit global warming this century
to 3.6 degrees Fahrenheit (2 degrees Celsius) over pre-industrial
temperatures is still within reach, while apocalyptic, worst-case
scenarios are no longer plausible, suggests a new CU Boulder analysis.


==========================================================================
Out today in Environmental Research Letters, the new study finds that a
subset of climate scenarios from the Intergovernmental Panel on Climate
Change (IPCC) most in line with recent data and International Energy
Agency (IEA) forecasts to 2050 project between 3.6 and 5.4 degrees F (2
and 3 C) of warming by 2100, with a median of 3.96 F (2.2 C) degrees. In comparison, some implausible, worst-case scenarios have projected as much
as 7.2 or 9 F (4 or 5 C) degrees of warming by the end of the century.

"This is cautiously optimistic good news with respect to where the world
is today, compared to where we thought we might be," said lead author
Roger Pielke Jr., professor of environmental studies. "The two-degree
target from Paris remains within reach." In order to explore and plan for possible futures, the climate research community uses scenarios: forecasts
of how the future might evolve based on factors such as projected
greenhouse gas emissions and different possible climate policies.

The most commonly used scenarios, called the Representative Concentration Pathways (RCPs), were developed by the IPCC starting in 2005. The
Shared Socioeconomic Pathways (SSPs) that followed, starting in 2010,
were meant as an update. Together, the two sets of scenarios inform the
IPCC's Fifth and forthcoming Sixth Assessment Reports.

For their study, Pielke Jr. and his co-authors started with a total of
1,311 climate scenarios from which the climate research community selected
the 11 RCPs and SSPs. Pielke and colleagues compared the scenarios to
the projected 2005-2050 fossil fuel and industry carbon dioxide emissions growth rates most consistent with real-life observations from 2005-2020,
and IEA projections to 2050. The number of scenarios which most closely
matched up to data from the past 15 years and subsequent emissions
projections ranged from less than 100 to almost 500, depending upon the
method applied. These scenarios represent what futures are plausible if
current trends continue and countries adopt the climate policies they
have already announced to reduce carbon emissions.



========================================================================== Additional, more optimistic or pessimistic futures could also exist,
the authors said.

"Because we haven't updated our [IPCC] scenarios [for many years],
there are also some futures which are plausible but haven't yet been envisioned," said Pielke Jr.

Pathways and plausibility The analysis joins a growing consensus
of independent groups around the world whose work finds that the
most extreme climate scenarios are unlikely to occur this century,
and mid-range scenarios are more likely. A report from the IPCC Sixth Assessment Report (AR6) released in 2021 also notes that the likelihood
of high emissions scenarios is considered low.

Why are these worst-case scenarios now less plausible? Mainly, they were
all developed more than a decade ago, and a lot has happened since.



==========================================================================
For example, renewable energy has become more affordable and, thus, more
common faster than expected, said Matthew Burgess, co-author and fellow
in the Cooperative Institute for Research in Environmental Sciences
(CIRES) at CU Boulder.

These fast-moving changes are captured in the scenarios drafted by the
IEA, a Paris-based intergovernmental organization, which provides updates
each year.

Climate scenarios also tend to overestimate economic growth, especially
in poorer countries, according to Burgess, assistant professor of
environmental studies.

In addition, while the 2010 scenarios were supposed to serve as updates
to the socio-economic assumptions of the initial RCPs, the RCPs have
continued to be used heavily by scientists. And the commonly used
"worst-case" scenario, RCP8.5 (named for 8.5 watts per meter squared,
a measure of solar irradiance) projects an increase of 7.2 to 9 F (4 to
5 C) by 2100.

"It's hard to overstate how much the [climate] research has focused on
the four- and five- degree scenarios, RCP 8.5 being one of them. And
those are looking less and less plausible by the year," said Burgess.

Relying on not only outdated scenarios, but scenarios which are no longer plausible, for research and policy has big implications for how we think
about, act and spend money on climate change issues, the authors said.

"There's a need for these scenarios to be updated more
frequently. Researchers may be using a 2005 scenario, but we need a 2022 perspective," said Pielke Jr.

"You're going to have better policies if you have a more accurate
understanding of the problem, whatever the political implications are
for one side or the other." The authors stress that 3.6 degrees F (2 C)
of warming will still take a dramatic toll on the planet, and this is
no time for complacency.

"We're getting close to our two-degree target, but we definitely have
a lot more work to do if we're going to get to 1.5," said Burgess.

special promotion Explore the latest scientific research on sleep and
dreams in this free online course from New Scientist -- Sign_up_now_>>> ========================================================================== Story Source: Materials provided by
University_of_Colorado_at_Boulder. Original written by Kelsey
Simpkins. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Roger Pielke Jr, Matthew G Burgess, Justin Ritchie. Plausible
2005-2050
emissions scenarios project between 2 DEGC and 3 DEGC of warming
by 2100.

Environmental Research Letters, 2022; 17 (2): 024027 DOI:
10.1088/1748- 9326/ac4ebf ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220211161325.htm

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