Limiting Global
Warming Is Not Enough
So
far, international climate targets have been restricted to limiting the
increase in temperature. But if we are to stop the rising sea levels, ocean
acidification and the loss of production from agriculture, CO2 emissions
will have to fall even more sharply.
This
is demonstrated by a study published in Nature that has been
carried out at the University of Bern.
The
ultimate objective of international climate policy is to prevent dangerous
anthropogenic interference with the climate system. To do this, greenhouse
gases are to be stabilised at a level that is acceptable for humans and for the
environment.
This climate goal is commonly expressed as an increase in the global mean temperature by a maximum of two degrees since pre-industrial times. This general direction is recognised by the majority of the world’s governments.
But
now, a study carried out by climate researchers based in Bern shows that the
focus on the temperature increase alone is by no means enough to meet the
ultimate, overarching objective – to protect the climate system from dangerous
anthropogenic interference.
This
is because, according to the United Nations Framework Convention on Climate
Change from 1992, the climate system comprises the "totality of the
atmosphere, hydrosphere, biosphere, geosphere and their interactions." The
Framework Convention also calls for the sustainability of ecosystems and food
production. All of this can scarcely be realised by the two-degree target
alone.
Six targets proposed
This
is why Dr. Marco Steinacher, Prof. Fortunat Joos and Prof. Thomas Stocker are
proposing a combination of six different specific global and regional climate
targets in their work, which has just been published in the «Nature» journal.
They
say that a global temperature target is «neither sufficient nor suitable» to
avoid further damage that is relevant for communities and ecosystem services. These
include in particular: rising sea levels, ocean acidification – which threatens
coral reefs – and production on agricultural land.
Realistic development paths
The
main culprit in relation to these environmental changes is the emission of the
greenhouse gas CO2, which is produced when fossil fuels are burned.
The researchers have now used extensive model calculations to show which levels
of CO2emissions would still be allowable in order to meet the
proposed combined targets.
The
basis for the calculations is provided by a wide range of greenhouse gas
scenarios that are based on realistic economic trajectories. "We can now
show which total CO2 emissions would be tolerable in the coming
decades in order to meet each and every one of the additional climate targets –
for example stable production on agricultural land and limitation of ocean
acidification," says Marco Steinacher, the leading author of the study.
And
the researchers ask the crucial question of what would be required in order for
all of the climate targets to be met. Their unambiguous answer is that CO2 emissions
have to be lowered even more radically than provided for by the two-degree
target. "When we consider all targets jointly, CO2 emissions
have to be cut by twice as much than if we only want to meet the two-degree
target," explains Steinacher.
The
objective of limiting ocean acidification proved particularly challenging and
is achievable only through a massive reduction in the emissions of CO2.
Important basis for informing policy
The
three researchers, all of whom are members of the Oeschger Centre for Climate
Change Research at the University of Bern, recommend that further studies of
this type be carried out. However, further relevant climate targets need to be
set out by policy makers and by society, they say.
"Ultimately,
the magnitude of environmental changes we are able to cope with and the amount
of risks we are prepared to take is a social and political question. But the
constant rise in CO2emissions is increasingly limiting our options
to act," says Fortunat Joos.
The
climate physicists emphasise the fact that it is important for political
decision-makers to link different climate targets to anthropogenic greenhouse
gas emissions in a quantitative manner.
According
to the study, in the future more detailed simulations will have to be carried
out which inform about local and regional consequences of climate change. For
example, these include extreme occurrences such as flooding and heatwaves.
However, we do not yet have sufficient computing power to operate the complex
Earth System Models needed for such probabilistic simulations.
Laborious computing work
The
study was made possible by using the Bern3D-LPJ Earth System Model developed at
the University of Bern. The model is able to simulate a large number of
important physical and biogeochemical processes and their interactions on a
regional scale. This information is needed to formulate many additional climate
targets – for example to prevent the acidification of the oceans in the
Tropics.
The
Bern Model is so efficient that it only took a few weeks to calculate the
roughly 65,000 simulations needed for the study. From this rich set of
simulations, the researchers have estimated probabilities of meeting specific
climate targets. This is not possible with most of the other Earth System
Models currently in existence.
Story Source:
The
above story is reprinted from materials provided by University of Bern.
Note: Materials may be edited for content and length. For further
information, please contact the source cited above.
Journal Reference:
1.
Marco Steinacher,
Fortunat Joos, Thomas F. Stocker. Allowable carbon emissions lowered by
multiple climate targets. Nature, 2013; DOI: 10.1038/nature12269
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