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Ning
Zeng
Associate Professor
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In the News
Field work at
Antarctica
Earth System Dynamics
The 9th International CO2 Conference
Research
Opportunities
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My
general research interests are in
the field of climate change and
climate variability on time scales
ranging from seasonal-interannual
to glacial-interglacial cycles. My
approach is to study the Earth
system as a whole, focusing on the
interactions among various
components, in particular, the
atmosphere, the hydrosphere and
the biosphere. Currently my
research covers two different but
inter-connected areas: carbon
cycle-climate interaction and the
modeling of
atmosphere-land-vegetation-ocean
system. I also conduct research in
the technical solutions and policy
implications of climate change.
Research
Examples
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 Will
Amazonia dry out and
the rainforests die
back?
The fate of the
Amazon rainforest will
be determined by two key
factors: trends of
deforestation and
climate change. The
suggestion of a possible
climate change induced
forest dieback has
raised considerable
interest as well as
controversy. We analyzed
24 IPCC model future
climate projections
under the A1B scenario
and simulated their
impacts with a dynamic
vegetation model. Our
results suggest that the
core of the Amazon
rainforest should remain
largely stable as
rainfall in the core of
the basin is projected
to increase in nearly
all models. However, the
periphery, notably the
southern edge of
Amazonia and further
south into central
Brazil (SAB), are in
danger of soil moisture
loss and vegetation
change, driven by two
main processes: (1)
subtropical drying
during its dry season
due to a combination of
circulation and SST
changes, when vegetation
needs water most even
though the annual mean
rainfall may not change
significantly; (2)
evaporative soil
moisture loss in a
warmer world. Southern
Amazonia is currently
under intense human
influence as a result of
deforestation and land
use change. Should this
direct human impact
continue at present
rates, added pressure to
the region’s ecosystems
from climate change may
subject the region to
profound changes in the
21st century. Details can be found at Cook et al. (2012). Similar
Atlantic SST gradient
pattern has been shown
to cause the severe 2005
Amazon drought (Zeng,
et al., Best of the year 2008
at Environmental
Research Letters)
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Expansion of the
world's deserts due
to vegetation-albedo
feedback under
global warming
Many
subtropical regions are
expected to become drier
due to climate change.
This will lead to
reduced vegetation which
may in turn amplify the
initial drying. Using a
coupled
atmosphere-ocean-land
model with a dynamic
vegetation component
that predicts surface
albedo change, here we
simulate the climate
change from 1901 to 2099
with CO2 and other
forcings. In a standard
IPCC-style simulation,
the model simulated an
increase in the world's
‘warm desert’ area of
2.5 million km
squared or 10% at
the end of the 21st
century. In a more
realistic simulation
where the
vegetation-albedo
feedback was allowed to
interact, the ‘warm
desert’ area expands by
8.5 million km2 or 34%.
This occurs mostly as an
expansion of the world's
major subtropical
deserts such as the
Sahara, the Kalahari,
the Gobi, and the Great
Sandy Desert. It is
suggested that
vegetation-albedo
feedback should be fully
included in IPCC future
climate projections. Zeng
and Yoon (2009)
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 Carbon
sequestration via wood
harvest and storage
(WHS)
To mitigate
global climate change, a
portfolio of strategies
will be needed to keep
the atmospheric CO2
concentration below a
dangerous level. I
propose a carbon
sequestration strategy in
which certain dead or
live trees are harvested
via collection or
selective cutting, then
buried in trenches or
stowed away in
above-ground shelters. The largely anaerobic condition under a
sufficiently thick layer
of soil will prevent the
decomposition of the
buried  wood. Because a
large flux of CO2 is
constantly being assimilated
into the world’s forests
via photosynthesis, cutting off its
return pathway to the
atmosphere forms an effective
carbon sink. I estimated
that a theoretical
potential for sustainable
long-term carbon
sequestration using WHS is 10 GtC/y, but the
practical potential is
likely between 1-3
GtC/y. The cost is lower
than the typical cost
for power plant CO2
capture with geological
storage. The technique
is low tech, distributed,
easy to monitor, safe,
and reversible, thus
providing an option in
the 'toolbox' of climate
mitigation and
adaptation strategies. Zeng (2008). See In
the
News for
media stories and
comments. Further
discussion can be found
at biocarbonsinks.org.
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 Midlatitude
drought and
anomalous CO2 growth
A rare drought
occurred from 1998 to
2002 across much of the
Northern Hemisphere midlatitude regions.
Using observational data
and numerical models, we
analyze the impact of
this event on
terrestrial ecosystem
and the global carbon
cycle. The biological
productivity in these
regions were found to
decrease by 0.9 PgC/y or 5%
compared to the average
of the previous two
decades, in conjunction
with significantly
reduced vegetation
greenness. The drought
led to a land carbon
release that is large
enough to significantly
modify the canonical
tropically dominated
ENSO response.
This large CO2 source
explains the consecutive
large increase in
atmospheric CO2 growth
rate of
about 2 ppmv/y in recent
years, as well as the
anomalous timing of
events. Zeng,
Qian, Roedenbeck and Heimann
(2005).
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 Glacial-interglacial
Cycles
Only 21,000
years ago, large parts
of the Northern
Hemisphere were covered
under giant icesheets. Today, the
mystery of the
glacial-interglacial
cycles remains unsolved.
Apart from important
roles astronomical
orbital forcing may
play, it is becoming
increasingly clear that
CO2-climate interaction
is a key component. Zeng
(2003)
hypothesized a mechanism
in which organic carbon
buried under the icesheets may be a
`missing link' in the
ice-age story. Zeng
(2007) further
proposed a mechanism
where internally
generated quasi-100ky
cycles could be
triggered by subglacial burial carbon
release as large icesheets such as the Laurentide grow long and
large enough and the
basal melting ejects
burial carbon into the
atmosphere, thus
starting a
carbon-climate-icesheet feedback that
could explain such as
the deglaciation at Termination
II.
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 Drought
in
the
Sahel
The Sahel,
a semiarid region in West
Africa between the Sahara
desert and the Guinea coast
rainforest, has
experienced an
unprecedented drought in
recorded history since
the late 1960s. The
drought had a
devastating impact on
this ecologically
vulnerable region and
was a major impetus in
the establishment of the
United Nations
Convention on Combating
Desertification and
Drought. In a
perspective article in
the journal Science, Zeng
(2003) explains
our current
understanding of the
problem, while Zeng
et al. (1999)
explores the relative
roles of sea surface
temperature, land and
vegetation feedbacks.
Additionally, a series
of papers explore the
nonlinear dyanmics of
vegetation-atmosphere
interaction in
desert-forest
transitions.
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