"Carbon dioxide removal from the atmosphere allows to
separate emissions control from the time and location of the actual emissions.
This flexibility can be important for climate protection," says
lead-author Elmar Kriegler.
"You don't have to prevent emissions in every factory
or truck, but could for instance plant grasses that suck CO2 out of the air to
grow – and later get processed in bioenergy plants where the CO2 gets stored
How it will lower
In economic terms, this flexibility allows to lower costs by
compensating for emissions which would be most costly to eliminate. "This
means that a phase-out of global emissions by the end of the century - that we
would need to hold the 2 degree line adopted by the international community -
does not necessarily require to eliminate each and every source of emissions,"
"Decisions whether and how to protect future
generations from the risks of climate change have to be made today, but the
burden of achieving these targets will increase over time. The costs for future
generations can be substantially reduced if carbon dioxide removal technologies
become available in the long run."
financial burden across generations
The study now published is the first to quantify this. If
bioenergy plus CCS is available, aggregate mitigation costs over the 21st
century might be halved. In the absence of such a carbon dioxide removal
strategy, costs for future generations rise significantly, up to a quadrupling
of mitigation costs in the period of 2070 to 2090.
The calculation was carried out using a computer simulation
of the economic system, energy markets, and climate, covering a range of
Options for carbon dioxide removal from the atmosphere
include afforestation and chemical approaches like direct air capture of CO2
from the atmosphere or reactions of CO2 with minerals to form carbonates. But
the use of biomass for energy generation combined with carbon capture and
storage is less costly than chemical options, as long as sufficient biomass
feedstock is available, the scientists point out.
Serious concerns about large-scale biomass use combined with
"Of course, there are serious concerns about the
sustainability of large-scale biomass use for energy," says co-author
Ottmar Edenhofer, chief-economist of PIK. "We therefore considered the
bioenergy with CCS option only as an example of the role that carbon dioxide
removal could play for climate change mitigation." The exploitation of
bioenergy can conflict with land-use for food production or ecosystem
protection. To account for sustainability concerns, the study restricts the
bioenergy production to a medium level, that may be realized mostly on
abandoned agricultural land.
Still, global population growth and changing dietary habits,
associated with an increased demand for land, as well as improvements of
agricultural productivity, associated with a decreased demand for land, are
important uncertainties here. Furthermore, CCS technology is not yet available
for industrial-scale use and, due to environmental concerns, is controversial
in countries like Germany. Yet in this study it is assumed that it will become
available in the near future.
"CO2 removal from the atmosphere could enable humankind
to keep the window of opportunity open for low-stabilization targets despite of
a likely delay in international cooperation, but only under certain
requirements," says Edenhofer.
"The risks of
scaling up bioenergy use need to be better understood, and safety concerns
about CCS have to be thoroughly investigated. Still, carbon dioxide removal
technologies are no science fiction and need to be further explored." In
no way should they be seen as a pretext to neglect emissions reductions now,
notes Edenhofer. "By far the biggest share of climate change mitigation
has to come from a large effort to reduce greenhouse-gas emissions