Posts
1.5C
of global warming already baked in – “The window of opportunity
on a 1.5-degree target is closing”
26
November, 2014
Estimates
of committed warming under five different sets of assumptions. Cases
a (black) and b (red) are the equilibria with and without aerosol
cooling, whereas case c (purple) includes the effect of removing
short-lived climate forcers. Cases d (blue) and e (orange) are scaled
with the transient climate response. Graphic: Mauritsen and Pincus,
2017 / Nature Climate Change
31
July 2017 (CU Boulder Today) – Even if humans could instantly turn
off all emissions of greenhouse gases, Earth would continue to heat
up about two more degrees Fahrenheit by the turn of the century,
according to a sophisticated new analysis published today in the
journal Nature Climate Change.
If
current emission rates continue for 15 years, the research shows,
odds are good that the planet will see nearly three degrees
Fahrenheit (1.5 Celsius) of warming by then.
“This
‘committed warming’ is critical to understand because it can tell
us and policymakers how long we have, at current emission rates,
before the planet will warm to certain thresholds,” said Robert
Pincus, a scientist with the Cooperative Institute for Research in
Environmental Sciences (CIRES), a partnership of the University of
Colorado Boulder and NOAA. “The window of opportunity on a
1.5-degree [C] target is closing.”
During
United Nations meetings in Paris last year, 195 countries including
the United States signed an agreement to keep global temperature rise
less than 3.5 degrees F (2 C) above pre-industrial levels, and pursue
efforts that would limit it further, to less than 3 degrees
Fahrenheit (1.5 C) by 2100.
The
new assessment, co-authored by Pincus and Thorsten Mauritsen of the
Max Planck Institute for Meteorology, is unique in that it does not
rely on computer model simulations, but rather on observations of the
climate system to calculate Earth’s climate commitment. Their work
accounts for the capacity of oceans to absorb carbon, detailed data
on the planet’s energy imbalance, the climate-relevant behavior of
fine particles in the atmosphere and other factors.
Among
Pincus and Mauritsen’s findings:
Even
if all fossil fuel emissions stopped in 2017, warming by 2100 is very
likely to reach about 2.3 F (range: 1.6-4.1) or 1.3 degrees C (range:
0.9-2.3).
Oceans
could reduce that figure a bit. Carbon naturally captured and stored
in the deep ocean could cut committed warming by 0.4 degrees F (0.2
C).
There
is some risk that warming this century cannot be kept to 1.5 degrees
C beyond pre-industrial temperatures. In fact, there is a 13 percent
chance we are already committed to 1.5-C warming by 2100.
“Our
estimates are based on things that have already happened, things we
can observe, and they point to the part of future warming that is
already committed to by past emissions,” said Mauritsen. "Future
carbon dioxide emissions will then add extra warming on top of that
commitment.”
The
research was funded by the Max-Planck-Gesellschaft, the U.S.
Department of Energy and the National Science Foundation.
31
July 2017 (Max Planck Institute for Meteorology ) – Concerted
efforts around the world are now being made to limit global warming
to less than 1.5 to 2 degrees Celsius. But how far are we from
passing these thresholds? Climate models have been used to estimate
this emission headroom, but a new study by Thorsten Mauritsen from
the Max Planck Institute for Meteorology (MPI-M) and Robert Pincus
from University of Colorado published in Nature Climate Change
instead uses observations of global warming at the Earth's surface
and in the oceans to infer the future warming to which the planet is
already committed by past emissions, and find that the window of
opportunity on the 1.5 degrees target is closing.
The
Earth is about 0.8 degrees Celsius warmer today than at the dawn of
industrialization. This warming is due mainly to human emissions of
the greenhouse gas carbon dioxide through burning of fossil coal, oil
and gas. Because the oceans have such an enormous capacity to absorb
heat they are out of balance with even current concentrations of CO2
and balance would be reached only after hundreds or thousands of
years. Because CO2 is removed from the atmosphere at the same long
time scales, human influence on Earth's climate will continue long
after emissions from fossil fuel burning eventually stop. The
influence of past emissions on future temperature is often called
"committed warming."
Carbon
dioxide is not the only influence on future temperature changes. Some
amount of warming is masked by polluting aerosol particles also
associated with fossil fuel burning. These aerosols reflect sunlight
back to space, cooling the planet's climate. But in contrast to CO2
their lifetime in the atmosphere is very short, so that a short burst
of rapid warming is expected when emissions stop. Working in the
opposite direction are various short-lived greenhouse gas pollutants
such as methane, nitrogen oxides and carbon monoxide. All these gases
contribute to warming but have short lifetimes -- less than a decade
- leading to a somewhat cooler future after emissions are stopped.
After
considering these effects the authors estimate that warming at the
end of the century would probably reach 1.3 degrees Celsius (0.9-2.3)
in the hypothetical case that all fossil fuel emissions would
suddenly stop in year 2017. This leaves fairly little headroom until
the 1.5 degrees target is surpassed: about 15 years at the current
rate of emissions until the risk of exceeding the 1.5 degrees target
reaches 50 percent.
Nature
might help a bit, though, by removing some of the CO2 from the
atmosphere and upper ocean and burying it in the deeper oceans. It is
still too early to estimate how strong the removal is using
observations, but climate models suggest the effect is important. By
accounting for such an effect in their study Mauritsen and Pincus
find that committed warming is 1.1 degrees Celsius (0.7-1.8) at the
end of the century.
By
considering the error bars in each factor the authors are able to put
error bars on their estimates. The error bars imply that for example,
there is some risk that the 1.5 degrees target is already
impractical. This uncertainty will decrease quickly in the coming
years as observations improve and the warming signal becomes
stronger.
Original
publication:
Mauritsen,
T. and Pincus, R. (2017), Committed warming inferred from
observations, Nature Climate Change, doi: 10.1038/nclimate3357.
Contact
Dr
Thorsten Mauritsen
Max
Planck Institute for Meteorology
Phone:
+49 40-41173-182
ABSTRACT:
Due to the lifetime of CO2, the thermal inertia of the oceans1, 2,
and the temporary impacts of short-lived aerosols3, 4, 5 and reactive
greenhouse gases6, the Earth’s climate is not equilibrated with
anthropogenic forcing. As a result, even if fossil-fuel emissions
were to suddenly cease, some level of committed warming is expected
due to past emissions as studied previously using climate models6, 7,
8, 9, 10, 11. Here, we provide an observational-based quantification
of this committed warming using the instrument record of global-mean
warming12, recently improved estimates of Earth’s energy
imbalance13, and estimates of radiative forcing from the Fifth
Assessment Report of the Intergovernmental Panel on Climate Change14.
Compared with pre-industrial levels, we find a committed warming of
1.5 K (0.9–3.6, 5th–95th percentile) at equilibrium, and of
1.3 K (0.9–2.3) within this century. However, when assuming that
ocean carbon uptake cancels remnant greenhouse gas-induced warming on
centennial timescales, committed warming is reduced to 1.1 K
(0.7–1.8). In the latter case there is a 13% risk that committed
warming already exceeds the 1.5 K target set in Paris15. Regular
updates of these observationally constrained committed warming
estimates, although simplistic, can provide transparent guidance as
uncertainty regarding transient climate sensitivity inevitably
narrows16 and the understanding of the limitations of the
framework11, 17, 18, 19, 20, 21 is advanced.
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