"One solution would be to abandon the term climate geoengineering and simply
assess the various methods for mitigating climate change on a case-by-case
basis."
You mean actually evaluate proposals for mitigating climate change and ocean
acidification based on impartially evaluating their individual merits rather
than automatically labeling as "scary geoengineering" those that threaten
conventional thinking? What a refreshing idea. In any case, as the article
asks, what are we waiting for?
Greg
From: Andrew Lockley <[email protected]>
To: geoengineering <[email protected]>
Sent: Wednesday, February 10, 2016 1:37 PM
Subject: [geo] Emissions reduction: Scrutinize CO2 removal methods : Nature
News & Comment
http://www.nature.com/news/emissions-reduction-scrutinize-co2-removal-methods-1.19318Emissions
reduction: Scrutinize CO2 removal methods
Phil Williamson10 February 2016The viability and environmental risks of
removing carbon dioxide from the air must be assessed if we are to achieve the
Paris goals, writes Phil Williamson.In Paris last December, the 196 parties to
the United Nations Framework Convention on Climate Change (UNFCCC) agreed to
balance the human-driven greenhouse-gas budget some time between 2050 and 2100.
This commitment is intended to limit the increase in global average temperature
above pre-industrial levels to “well below 2 °C” — and preferably to 1.5 °C.A
balanced greenhouse-gas budget either requires that industry and agriculture
produce zero emissions or necessitates the active removal of greenhouse gases
from the atmosphere (in addition to deep and rapid emissions cuts). In most
modelled scenarios that limit warming to 2 °C, several gigatonnes of carbon
dioxide have to be extracted and safely stored each year1. For more ambitious
targets, tens of gigatonnes per year must be removed2.Policy: Start research on
climate engineeringMany CO2-removal techniques have been proposed. Whether any
of them could work at the scale needed to deliver the goal of the Paris
agreement depends on three things: feasibility, cost and acceptability. A
crucial component of all of these approaches is the non-climatic impacts that
large-scale CO2-removal could have on ecosystems and biodiversity.Until now,
the UNFCCC's scientific advisory body, the Intergovernmental Panel on Climate
Change (IPCC), has paid relatively little attention to such impacts. It has
fallen to other groups to review insights and gaps in our understanding of the
influence of CO2-removal techniques on ecology3, 4, 5; to make broad
assessments of climate-engineering schemes6; and to carry out comparative
modelling studies7.It is time for the IPCC, governments and other
research-funding agencies to invest in new, internationally coordinated studies
to investigate the viability and relative safety of large-scale CO2
removal.Front-runnersSince its establishment in 1988, the IPCC has
predominantly involved physical scientists and modellers, rather than
ecologists. This, combined with the only relatively recent evidence that
emissions reduction alone is unlikely to avert dangerous climate change, could
account for why the IPCC's roughly 5,000-page Fifth Assessment Report, released
in 2013 and 2014, leaves out one crucial consideration: the environmental
impacts of large-scale CO2 removal.This omission is striking because the set of
IPCC emissions scenarios that are likely to limit the increase in global
surface temperature to 2 °C by 2100 (the aim of the RCP2.6 'representative
concentration pathway', the IPCC climate-change-response scenario that achieves
the lowest emissions) mostly relies on large-scale CO2 removal.Geoengineering:
Journey into geopoetryThese scenarios assume that two techniques could be
developed to balance the carbon budget later this century: bioenergy with
carbon capture and storage (BECCS), and afforestation. BECCS involves growing
bioenergy crops, from grasses to trees; burning them in power stations;
stripping the CO2 from the resulting waste gases; and compressing it into a
liquid for underground storage. Afforestation — planting trees — also relies on
photosynthesis to initially remove CO2from the atmosphere. Storage is achieved
naturally, in timber and soil.Limiting the global temperature rise to 2 °C,
with any confidence, would require the removal of some 600 gigatonnes of CO2
over this century (the median estimate of what is needed)8. Using BECCS, this
would probably require crops to be planted solely for the purpose of CO2
removal9 on between 430 million and 580 million hectares of land — around
one-third of the current total arable land on the planet, or about half the
land area of the United States.Unless there are remarkable increases in
agricultural productivity, greatly exceeding the needs of a growing global
population, the land requirements to make BECCS work would vastly accelerate
the loss of primary forest and natural grassland. Thus, such dependence on
BECCS could cause a loss of terrestrial species at the end of the century
perhaps worse than the losses resulting from a temperature increase of about
2.8 °C above pre-industrial levels10.A more fundamental concern is whether
BECCS would be as effective as it is widely assumed to be at stripping CO2 from
the atmosphere. Planting at such scale could involve more release than uptake
of greenhouse gases, at least initially, as a result of land clearance, soil
disturbance and increased use of fertilizer. When such effects are taken into
account, the maximum amount of CO2 that can be removed by BECCS (under the
RCP2.6 scenario) is estimated to be 391 gigatonnes by 2100. This is about 34%
less than the median amount assumed to be needed to keep the temperature rise
below 2 °C. If less optimistic but not unrealistic assumptions are made about
where the land for bioenergy crops would come from, a net release of 135
gigatonnes of CO2 could occur by 2100 (see 'Future unknown')8.Source: Ref.
8Incomplete understanding throws other assumptions of the BECCS-based scenarios
into question9. For instance, little is known about the effect of future
climatic conditions on the yields of bioenergy crops; what the water
requirements of such crops may be in a warmer world; the implications for food
security if bioenergy production directly competes with food production; and
the feasibility (including commercial viability) of the associated carbon
capture and storage infrastructure.Is the 2 °C world a fantasy?Less is expected
of afforestation in terms of its ability to take CO2 out of the atmosphere. Yet
there is a near-universal assumption that increased forest cover is
environmentally desirable. This is true in most cases of reforestation,
particularly if a mixture of native trees is planted or re-planted, rather than
an exotic monoculture. But afforestation can also involve the loss of natural
ecosystems. And planting swathes of forest will cause complex changes in cloud
cover, albedo (reflectance) and the soil–water balance (through changes to
evaporation and plant transpiration), all of which affect Earth's surface
temperature.Counter-intuitively, afforestation at mid-latitudes and in
northern, boreal forests may have a net warming effect, despite increasing the
storage of carbon7. Also, as with bioenergy crops, it is difficult, if not
impossible, to reliably quantify the effects of future climate change during
2050–2100. Increased fires, droughts, pests and disease could jeopardize the
stability of carbon storage in newly planted forests.Other optionsThere is no
shortage of other ideas for CO2 removal by biological, geochemical and chemical
means (see 'Take your pick'). For all such schemes, modelling the theoretical
potential of a proposed approach can give a completely different picture from
that obtained when environmental impacts — not to mention practicalities,
governance and acceptability — are considered.The roughly 25 years of
discussion, research and policymaking on ocean fertilization, another
CO2-removal technique, is a case in point. Since the link was first made
between natural changes in the input of dust to the ocean, ocean productivity
and climatic conditions, there has been a dramatic scaling-down of expectations
of how effective ocean fertilization might be as a way to avoid human-driven
global warming11.During the 1990s, researchers postulated that for every tonne
of iron added to seawater, tens of thousands of tonnes of carbon (and hence
CO2) could be fixed by the resulting blooms of phytoplankton. This quantity has
been whittled down over the years with the realization that most of the CO2
absorbed by such blooms — stimulated either by adding iron or other nutrients
to seawater, or by enhancing upwelling through mechanical means — would be
released back into the atmosphere when the phytoplankton decomposed. Moreover,
a large-scale increase in plankton productivity in one region (across the
Southern Ocean, say) could reduce the yields of fisheries elsewhere by
depleting other nutrients, or increase the likelihood of mid-water
deoxygenation. Such risks have resulted in the near-universal rejection of
ocean fertilization as a climate intervention, through bodies such as the
Convention on Biological Diversity (CBD)3.More recently, other, potentially
more controllable, ocean-based CO2-removal techniques have been suggested, such
as the cultivation of seaweed to cover up to 9% of the global ocean12. The
specific environmental implications of this method have yet to be assessed. Yet
such an approach would clearly affect, and potentially displace, existing
marine ecosystems that have high economic value. (Shallow and coastal waters
currently provide around 90% of global fish catches.)Back on land, other
techniques include those to increase the amount of carbon sequestered in the
soil, for example by ploughing in organic material such as straw, reducing
ploughing (to limit soil disturbance) or adding biochar (a form of charcoal).
Another idea is to enhance weathering, which involves the absorption of CO2
from the atmosphere by certain silicate rocks. Existing insights from
agriculture, geoscience and mineral extraction enable more informed assessments
of the feasibility and acceptability3, 4, 5, 6 of these approaches. Yet it is
crucial to know more about the permanence of carbon storage for biologically
based methods, and the environmental impacts that might result if such
approaches are used at vast scale4, 5, 6.“Action should focus on urgent
emissions reductions.”For example, the use of biochar raises land-use issues.
In addition, millions of hectares of soil darkened by the application of
biochar would decrease albedo, increasing heat absorption. The addition of
pulverized rock to the soil surface, by contrast, would increase reflectivity.
Yet to reduce the amount of CO2 in the atmosphere by around 50 parts per
million (a roughly 12% decrease from current levels), 1–5 kilograms per square
metre of silicate rock would need to be applied each year to 2 billion to 6.9
billion hectares of land (15–45% of Earth's land surface area), mostly in the
tropics13. The volume of rock mined and processed would exceed the amount of
coal currently produced worldwide, with the total costs of implementation
estimated to be between US$60 trillion and $600 trillion. And the chemistry and
biology of rivers and adjacent ocean areas would be radically altered.The most
environmentally benign option for large-scale CO2 removal may be direct air
capture (DAC). This can be done by passing air through anion-exchange resins
that contain hydroxide or carbonate groups, which, when dry, absorb CO2, and
release it when moist. The extracted CO2 can then be compressed, stored in
liquid form and deposited underground using carbon capture and storage
technologies6.The operational costs for DAC cover a similar range to those
estimated for enhanced weathering. The extraction process would also need land
and probably water, and, as for BECCS, there is a risk of CO2 leaking out of
geological reservoirs. Such risks can be minimized by storing the liquid CO2
beneath the sea or by using geochemical transformation, which involves in situ
reactions between CO2 and certain rock types. In theory, cooling (rather than
chemistry) to liquefy out the CO2 could also be used to remove CO2 from ambient
air14. The technical feasibility, costs and potential environmental impacts of
this approach — which could involve setting up plants in remote places such as
Antarctica — have yet to be investigated.Urgent actionAs well as a major step
up in research, urgent attention must be given to clarification at the UN level
of what is considered geoengineering and what is climate mitigation. Once
considered distinct approaches, the meaning of these terms has become fuzzier
in recent years. CO2 removal is frequently included in both categories,
generating confusion and contradiction.This is crucial to resolve because
mitigation and geoengineering have very different psychological connotations.
Mitigation is universally considered to be a good thing that reduces risk or
damage. Geoengineering frequently elicits suspicion, or is dismissed as a
'high-risk, high-tech' approach that may itself be harmful.CO2 removal was not
specifically discussed in Paris. However, the large-scale extraction of CO2
does seem to be a requirement to meet the goal of the Paris agreement. The CBD
considers most, if not all, techniques for CO2 removal to be climate
geoengineering, which it has repeatedly rejected as a policy option for
addressing climate change. With a few exceptions, the same 195 or so
governments make up both the UNFCCC and the CBD.One solution would be to
abandon the term climate geoengineering and simply assess the various methods
for mitigating climate change on a case-by-case basis.The Paris agreement shows
where we want to go — the brave new world of a balanced carbon budget — but not
how to get there. For now, action should focus on urgent emissions reductions
and not on an unproven 'emit now, remove later' strategy. But the unwelcome
truth is that, unless a lot more effort is made to cut emissions, significant
CO2 removal will need to begin around 2020, with up to 20 gigatonnes of CO2
extracted each year by 2100 to keep the global temperature increase “well below
2 °C”2.Is that feasible? What environmental risks and constraints are involved?
We need to know.Nature 530, 153–155 (11 February 2016)doi:10.1038/530153a
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contextRelated stories and linksFrom nature.comNature special: 2015 Paris
climate talksFrom elsewhereIPCCAuthor informationAffiliationsPhil Williamson is
a science coordinator for the Natural Environment Research Council and an
associate fellow in the School of Environmental Sciences at the University of
East Anglia in Norwich, UK.Corresponding authorCorrespondence to: Phil
Williamson
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