Past warming events suggest
climate models fail to capture true warming under business-as-usual scenarios
July 5, 2018
University of New South Wales
Future global warming may
eventually be twice as warm as projected by climate models under
business-as-usual scenarios and even if the world meets the 2°C target sea
levels may rise six meters or more, according to an international team of
researchers from 17 countries.
Future global warming may
eventually be twice as warm as projected by climate models under
business-as-usual scenarios and even if the world meets the 2°C target sea
levels may rise six metres or more, according to an international team of
researchers from 17 countries.
The findings published last
week in Nature Geoscience are based on observational evidence from
three warm periods over the past 3.5 million years when the world was 0.5°C-2°C
warmer than the pre-industrial temperatures of the 19th Century.
The research also revealed how
large areas of the polar ice caps could collapse and significant changes to
ecosystems could see the Sahara Desert become green and the edges of tropical
forests turn into fire dominated savanna. "Observations of past warming
periods suggest that a number of amplifying mechanisms, which are poorly
represented in climate models, increase long-term warming beyond climate model
projections," said lead author, Prof Hubertus Fischer of the University of
Bern.
"This suggests the carbon
budget to avoid 2°C of global warming may be far smaller than estimated,
leaving very little margin for error to meet the Paris targets."
To get their results, the
researchers looked at three of the best-documented warm periods, the Holocene
thermal maximum (5000-9000 years ago), the last interglacial (129,000-116,000
years ago) and the mid-Pliocene warm period (3.3-3 million years ago).
The warming of the first two
periods was caused by predictable changes in the Earth's orbit, while the
mid-Pliocene event was the result of atmospheric carbon dioxide concentrations
that were 350-450ppm -- much the same as today.
Combining a wide range of
measurements from ice cores, sediment layers, fossil records, dating using
atomic isotopes and a host of other established paleoclimate methods, the
researchers pieced together the impact of these climatic changes.
In combination, these periods
give strong evidence of how a warmer Earth would appear once the climate had
stabilized. By contrast, today our planet is warming much faster than any of
these periods as human caused carbon dioxide emissions continue to grow. Even
if our emissions stopped today, it would take centuries to millennia to reach
equilibrium.
The changes to the Earth under
these past conditions were profound -- there were substantial retreats of the
Antarctic and Greenland ice sheets and as a consequence sea-levels rose by at
least six metres; marine plankton ranges shifted reorganising entire marine
ecosystems; the Sahara became greener and forest species shifted 200 km towards
the poles, as did tundra; high altitude species declined, temperate tropical
forests were reduced and in Mediterranean areas fire-maintained vegetation
dominated.
"Even with just 2°C of
warming -- and potentially just 1.5°C -- significant impacts on the Earth
system are profound," said co-author Prof Alan Mix of Oregon State
University.
"We can expect that
sea-level rise could become unstoppable for millennia, impacting much of the
world's population, infrastructure and economic activity."
Yet these significant observed
changes are generally underestimated in climate model projections that focus on
the near term. Compared to these past observations, climate models appear to
underestimate long term warming and the amplification of warmth in Polar
Regions.
"Climate models appear to
be trustworthy for small changes, such as for low emission scenarios over short
periods, say over the next few decades out to 2100. But as the change gets
larger or more persistent, either because of higher emissions, for example a
business-as-usual-scenario, or because we are interested in the long term
response of a low emission scenario, it appears they underestimate climate
change.," said co-author Prof Katrin Meissner, Director of the University
of New South Wales Climate Change Research Centre.
"This research is a
powerful call to act. It tells us that if today's leaders don't urgently
address our emissions, global warming will bring profound changes to our planet
and way of life -- not just for this century but well beyond."
Story Source:
Materials provided by University of New South Wales. Note:
Content may be edited for style and length.
Journal Reference:
Hubertus Fischer, Katrin J.
Meissner, Alan C. Mix, Nerilie J. Abram, Jacqueline Austermann, Victor Brovkin,
Emilie Capron, Daniele Colombaroli, Anne-Laure Daniau, Kelsey A. Dyez, Thomas
Felis, Sarah A. Finkelstein, Samuel L. Jaccard, Erin L. McClymont, Alessio Rovere,
Johannes Sutter, Eric W. Wolff, Stéphane Affolter, Pepijn Bakker, Juan Antonio
Ballesteros-Cánovas, Carlo Barbante, Thibaut Caley, Anders E. Carlson, Olga
Churakova, Giuseppe Cortese, Brian F. Cumming, Basil A. S. Davis, Anne de
Vernal, Julien Emile-Geay, Sherilyn C. Fritz, Paul Gierz, Julia Gottschalk, Max
D. Holloway, Fortunat Joos, Michal Kucera, Marie-France Loutre, Daniel J. Lunt,
Katarzyna Marcisz, Jennifer R. Marlon, Philippe Martinez, Valerie
Masson-Delmotte, Christoph Nehrbass-Ahles, Bette L. Otto-Bliesner, Christoph C.
Raible, Bjørg Risebrobakken, María F. Sánchez Goñi, Jennifer Saleem Arrigo,
Michael Sarnthein, Jesper Sjolte, Thomas F. Stocker, Patricio A. Velasquez
Alvárez, Willy Tinner, Paul J. Valdes, Hendrik Vogel, Heinz Wanner, Qing Yan, Zicheng
Yu, Martin Ziegler, Liping Zhou. Palaeoclimate constraints on the impact
of 2 °C anthropogenic warming and beyond. Nature Geoscience, 2018; 11 (7):
474 DOI: 10.1038/s41561-018-0146-0
No comments:
Post a Comment