STATEMENT OF

DR. P. PATRICK LEAHY

ASSOCIATE DIRECTOR FOR GEOLOGY

U.S. GEOLOGICAL SURVEY

U.S. DEPARTMENT OF THE INTERIOR

BEFORE THE

COMMITTEE ON NATURAL RESOURCES

SUBCOMMITTE ON ENERGY AND MINERAL RESOURCES

AND

SUBCOMMITTEE ON NATIONAL PARKS, FORESTS, AND PUBLIC LANDS

U.S. HOUSE OF REPRESENTATIVES

HEARING ON

THE FUTURE OF FOSSIL FUELS:

GEOLOGICAL AND TERRESTRIAL SEQUESTRATION OF CARBON DIOXIDE

MAY 1, 2007

Messrs. Chairmen and Members of the Subcommittees, thank you for the
opportunity to present testimony on terrestrial sequestration and
geologic capture and storage of carbon dioxide and their role in
reducing atmospheric carbon. In addition to these topics, I also plan to
discuss in my statement today the role of science in evaluating the
potential geologic storage capacity for industrial carbon dioxide and in
furthering our understanding of the carbon cycle.

**Introduction**

Let me begin by saying that the challenges of addressing carbon dioxide
accumulation in the atmosphere are significant. Fossil fuel usage, a
major source of carbon dioxide emissions to the atmosphere, will
continue in both industrialized and developing nations. Therefore, a
variety of strategies are being investigated to reduce emissions and
remove carbon dioxide from the atmosphere. Such strategies include the
facilitated sequestration of carbon from the air to terrestrial biomass,
including soils and the capture and storage of carbon dioxide in
geologic formations.

The current atmospheric carbon dioxide concentration is approximately
380 parts per million volume and rising at a rate of approximately 2
parts per million volume annually, according to the most recent
information from the Intergovernmental Panel on Climate Change (IPCC).
 The fraction of carbon emissions from all sources that must be
eliminated or sequestered to impact the magnitude of climate change is
large.  For example, to stabilize carbon dioxide concentrations at about
550 parts per million volume, the extent to which carbon dioxide
emissions would need to be reduced may be as much as 70 percent.
Reductions of this magnitude could involve implementation of several
mechanisms, including geologic storage and biological sequestration,
fuel shifts from fossil sources to renewable biological sources,
increased electricity generation from solar and wind systems and nuclear
power, and increased efficiency of power generation, transmission, and
end use.  Each of these mechanisms has distinct geological,
hydrological, ecological, economic and social implications that should
be assessed on a wide range of scales, from molecular to basin scales,
to allow informed policy discussions and decisions on implementation and
deployment of technologies.  

**Geologic Storage of Carbon**

The 2005 IPCC Special Report on *Carbon Dioxide Capture and Storage*
concluded that, in emissions reductions scenarios striving to stabilize
global atmospheric carbon dioxide concentrations at targets ranging from
450 to 750 parts per million volume, the global storage capacity of
geologic formations may be able to accommodate most of the captured
carbon dioxide.  However, geologic storage capacity may vary on a
regional and national scale, and a more refined understanding of
geologic storage capacity is needed to address this knowledge gap.

Geological storage of carbon dioxide in porous and permeable rocks
involves injection of carbon dioxide into a subsurface rock unit and
displacement of the fluid or formation water that initially occupied the
pore space.  This principle operates in all types of potential
geological storage formations such as oil and gas fields, deep saline
water-bearing formations, or coal beds.  Because the density of injected
carbon dioxide is less than the density of formation water, carbon
dioxide will be buoyant in pore space filled with water and rise
vertically until it is retained beneath a nonpermeable barrier (seal).
 A critical issue for evaluation of storage capacity is the integrity
and effectiveness of these seals.

**Terrestrial Carbon Sequestration**

Terrestrial carbon sequestration practices seek to effect the transfer
of carbon between the atmosphere and terrestrial biosphere (the earth
and the living organisms that inhabit it) to reduce atmospheric carbon
dioxide concentrations. Land management practices in the United States
can affect the transfer of carbon from terrestrial systems into the
atmosphere. Land conversion, especially deforestation, continues to be a
significant source of global carbon dioxide emissions. Good land
stewardship practices can reverse this and enhance biological uptake of
carbon dioxide from the atmosphere, an approach termed terrestrial
sequestration. Many of these practices, including tree planting and
conservation tillage, are widely adopted and well understood. The
Department of Agriculture is promoting the adoption of these practices
through conservation programs implemented under the Farm Bill. The
knowledge gained on the benefits of terrestrial sequestration will
improve our understanding of the duration and extent to which the
biological uptake of atmospheric carbon dioxide can be enhanced to
reduce atmospheric concentration of carbon dioxide.

**Role of the U.S. Geological Survey**

While the USGS currently has no experience assessing the national
geologic storage capacity, USGS-generated data and information were
included in the Carbon Sequestration Atlas of the United States and
Canada developed by the Department of Energy. In addition, our
experience with national and international assessments of natural
resources could allow USGS to develop geologically based methodologies
to assess the National capacity for geologic storage of carbon dioxide.
 We envision the national geologic carbon dioxide storage assessment
methodology would be largely analogous to the peer-reviewed
methodologies used in USGS oil, gas, and coal resource assessments.  In
addition, the USGS' knowledge of regional groundwater aquifer systems
and groundwater chemistry would allow USGS to develop methods to assess
potential carbon storage in saline aquifers.  Previous studies have
postulated the existence of very large carbon dioxide storage capacities
in saline aquifers, but the extent to which these capacities can be
utilized remains unknown.  

The USGS could create a scientifically based, multi-disciplinary
methodology for geologic carbon dioxide storage assessment that can be
consistently applied on a national scale. Some potential areas for
further study include understanding the capabilities of seals to retain
carbon dioxide and the role of abandoned wells that may act as migration
pathways for carbon dioxide and formation water; defining the potential
for mobilization of trace metals and organic materials by carbon dioxide
reactions with minerals or dissolution of organic compounds; and
understanding the role of bacteria and other microorganisms in
water-rock-carbon dioxide interactions relevant to storage.

There are also a number of potential issues for further study pertaining
to terrestrial sequestration, including the natural processes that
affect carbon cycling. It is now widely recognized that the global
carbon cycle and climate varied together, before human influence, as
interactive components in a highly complex system of global feedbacks.
These feedbacks have profound implications for the response of climate
to anthropogenic carbon dioxide emissions, and for the potential
response of the carbon cycle to changes in climate.

Along with our partners in the Department of Agriculture and other
agencies, ongoing USGS research addresses these issues. In particular,
USGS research on soil carbon dynamics focuses on soil development and
the buildup and stabilization of soil organic matter, a large carbon
reservoir in the terrestrial biosphere, which play key roles in water
distribution, and in turn control both sediment transport and carbon
production and respiration. This research is critically important in
explaining the processes affecting the flow of carbon dioxide from
soils. The response of soils to human land use is a significant
component in the global carbon dioxide budget, and their response to
climate change may cause significant feedback on a global scale. Land
use -- particularly agriculture -- significantly alters patterns of
terrestrial carbon storage and transport, nutrient cycles, and erosion
and sedimentation. Current models of the terrestrial carbon cycle do not
adequately account for the interactions among changes in erosion,
sedimentation, and soil dynamics. Additional research on variable scales
(local to global) of carbon flow would provide a more thorough
understanding of the carbon cycle.

**Conclusion**

It is clear that addressing the challenge of reducing atmospheric carbon
dioxide and understanding the effect of global climate change is a
complex issue with many interrelated components. A better understanding
of geologic storage potential for carbon dioxide combined with research
to understand the implications of terrestrial carbon sequestration on
the carbon cycle would provide a scientific foundation for future
decisions regarding carbon management. We believe additional study of
geologic and terrestrial opportunities will better prepare decision
makers as they deal with these issues. Thank you for the opportunity to
present this testimony.  I am pleased to answer questions you and other
Members of the Committee might have.