Proistosescu, Huybers, and Maloof To Tune or not to Tune: Detecting Orbital Variability in Oligo-Miocene Climate Records, Earth and Planetary Science Letters, in press. pdf
Gebbie and Huybers, The mean age of ocean waters inferred from radiocarbon observations: upper and lower bounds, sensitivity to surface sources, and accounting for mixing histories, Journal of Physical Oceanography, in press.
pdf
Gomez, Pollard, Mitrovica, Huybers, and Clark, Evolution of a coupled marine ice sheet---sea level model, Journal of Geophysical Research,
in press.
Huybers, Combined obliquity and precession pacing of the
late Pleistocene glacial cycles, Nature, 2011. pdf and code.
Gebbie and Huybers, How is the ocean filled?, Geophysical Research Letters, 2011.
pdf
Rhines and Huybers, Estimation of spectral power laws in time-uncertain series of data with application to the GISP2 delta-18O record, Journal of Geophysical Research, 2011.
pdf
Huybers and Aharonsen, Orbital tuning, eccentricity, and the frequency modulation of climatic precession, Paleoceanography, 2010.
pdf
Gomez, Mitrovica, Huybers, and Clark, Sea level as a
stabilizing factor for marine ice-sheet grounding lines, Nature
Geoscience, 2010.
pdf
Gebbie and Huybers, Total Matrix Intercomparison: a method for determining the geometry of water-mass pathways, Journal of Physical Oceanography, 2010.
pdf
Huybers, Compensation between model feedbacks and curtailment of climate sensitivity, Journal of Climate, 2010.
pdf
Haam and Huybers, A test for the presence of covariance
between time-uncertain series of data with application to the Dongge
Cave speleothem and atmospheric radiocarbon records,
Paleoceanography, 2010.
pdf
Huybers and Wunsch, Paleo-Physical Oceanography with an
Emphasis on Transport Rates, Annual Review of Marine Science,
2010. pdf
Tingley and Huybers, A Bayesian Algorithm for
Reconstructing Climate Anomalies in Space and Time. Part 1:
Development and applications to paleoclimate reconstruction
problems, Journal of Climate, 2010
pdf
Tingley and Huybers, A Bayesian Algorithm for Reconstructing
Climate Anomalies in Space and Time. Part 2: Comparison with the
regularized expectation-maximization algorithm, Journal of
Climate,
2010.
pdf A zipped package of Matlab files that implements the method
can be downloaded
from Martin's
website.
Siddall, Hönisch, Waelbroeck, Huybers, Changes in deep Pacific temperature during the mid-Pleistocene transition and Quaternary, Quaternary Science Reviews,
2010.
pdf
Huybers, Pleistocene glacial variability as a chaotic
response to obliquity forcing , Climate of the Past,
2009.
pdf
Huybers, Antarctica's orbital beat, Science,
2009. pdf
Huybers and Langmuir, Feedback between deglaciation,
volcanism, and atmospheric CO2 , Earth and Planetary Science
Letters,
2009.
pdf
and supplementary
data
Clark and Huybers, Interglacial and future sea level, Nature news & views,
2009. pdf
Perron and Huybers, Is there an orbital signal in the
polar layered deposits on Mars? , Geology,
2009. pdf
and
a news
piece
Stine, Huybers, and Fung, Changes in the phase of the
annual cycle of surface temperature , Nature,
2009. pdf and supplementary information
Huybers and Denton, Antarctic temperature at orbital time
scales controlled by local summer duration, Nature Geoscience,
2008.
pdf
and
supplementary material
Huybers and Tziperman, Integrated summer insolation
forcing and 40,000 year glacial cycles: the perspective from an
icesheet/energy-balance model, Paleoceanography,
2008.
pdf and
code
Raymo and Huybers, Unlocking the mysteries of the ice
ages, Nature,
2008. pdf
Huybers and Molnar, Tropical cooling and the onset of
North American glaciation, Climate of the Past, 2007.
pdf
Huybers, Gebbie, and Marchal, Can paleoceanographic
tracers constrain meridional circulation rates?, Journal of Physical Oceanography, 2007.
pdf
Huybers, Glacial variability over the last 2Ma: an
extended depth-derived agemodel, continuous obliquity pacing, and
the Pleistocene progression, Quaternary Science Reviews,
2007.
pdf
and supplemental
material
(also posted at NCDC)
Gebbie and Huybers, Meridional
circulation during the Last Glacial Maximum explored through a
combination of South Atlantic d18O observations and a geostrophic
inverse model, G-cubed, 2006.
pdf
Tziperman, Raymo, Huybers, and Wunsch, Consequences of
pacing the Pleistocene 100 kyr ice ages by nonlinear phase locking to
Milankovitch forcing, Paleoceanography,
2006. pdf
Huybers and Curry, Links between annual, Milankovitch,
and continuum temperature variability, Nature,
2006. pdf
and supplemental
material
Huybers and Wunsch, Obliquity pacing of the late Pleistocene
glacial terminations, Nature,
2005. pdf
Huybers, comment on ``Hockey sticks, principal
components, and spurious significance'' by McIntyre and McKitrick
[2005], Geophysical Research Letters,
2005. pdf
and supplemental
material (An edited version of this paper was
published by AGU. Copyright 2005 American Geophysical Union.)
Huybers, Comments on: 'Coupling of the hemispheres in
observations and simulations of glacial climate change': by
A. Schmittner, O.A. Saenko, and A.J. Weaver [Quaternary Science
Reviews 22 (2003) 659-671], Quaternary Science Reviews,
2004. pdf
Huybers and Wunsch, A depth-derived Pleistocene
age-model: uncertainty estimates, sedimentation variability, and
nonlinear climate change, Paleoceanography,
2004. pdf
Huybers and Wunsch, Rectification and precession-period
signals in the climate system, Geophysical Research Letters,
2003. pdf
Manuscripts
Butler and Huybers Adaptation of US Maize to Temperature Variations,
submitted. pdf and supplemental information
Stine and Huybers Changes in the seasonal cycle of temperature and atmospheric circulation ,
submitted. pdf
Lin and Huybers, Reckoning the leveling of wheat yields,
submitted. pdf
Research
Glaciation, insolation, and CO2: During the last million years,
Northern Hemisphere continental ice has alternately covered much of
northern North America and Fennoscandia and then retreated to today's
relatively ice-free conditions at approximately 100,000 year
intervals. Various models have been proposed throughout the last
century that call on changes in the obliquity of Earth's spin axis,
precession of the equinoxes, or eccentricity of Earth's orbit to
determine when the Northern Hemisphere glaciates. Yet the cause of
these massive shifts in climate remain unclear---not for lack of
hypotheses, but for lack of a means to choose between them. Thus, one
aim is to distinguish between the many competing glacial hypotheses by
testing the extent to which obliquity
(2005)
and precession (manuscript in press) control the timing of deglaciation. Another
is to explore the causes of glaciation during the Pliocene and early
Pleistocene---an earlier epoch between 2.7 and 1 million years ago
that is characterized by 40,000 year glacial cycles
(2006,
2008). High resolution imagery and topography from Mars offers
another perspective for understanding the orbital influence on
glaciation, though positively identifying orbital variability appears
challenging given currently available data
(2009).
It has become increasingly clear that understanding the glacial cycles
requires an understand of the accompanying changes in the
concentration of atmospheric CO2. These glacial/interglacial changes
in CO2 are generally ascribed to variations in marine carbon pools but
may also involve the vast reservoir of carbon in Earth's interior. In
particular, glacial unloading appears to have roughly tripled global
volcanic activity during the last deglaciation and, presumably, also
increased the volcanic emission of
CO2
(2009). More needs to be done to test this hypothesis, and we're
working on it. Further examples of interactions between glaciation and
other parts of Earth's climate include that long term cooling in the
Eastern Equatorial Pacific may have initiated Northern Hemisphere
glaciation
(e.g. 2007),
and that Antarctica's response to insolation forcing seems to mirror
and may reinforce the Northern response
(2008).
Annual cycles: The annual cycle in surface temperature
is larger than the temperature change between glacial and interglacial
climates at most places on Earth. Even small changes in the amplitude
and timing of the seasonal cycle can have large consequences. Zan
Stine showed that the annual cycle on land has been trending earlier
over the last fifty years
(2009),
and hypothesized this as a result of surface drying, changes in
Earth's orbital configuration, changes in the absorptivity of the
atmosphere, or shifts in atmospheric circulation. We now argue that
these trends in seasonality are almost entirely result from variations
in the Northern Annular Mode and Pacific/North-American patterns of
atmospheric variaiblity
(submitted).
Also of note is that variations in Earth's orbital configuration act
almost entirely through modifying the seasonal cycle of insolation
(e.g., 2006),
and that the power-law relationship of temperature variations between
monthly and centennial timescales is proportional to the amplitude of
the annual cycle
(2006).
Overall, it seems that a thorough understanding of the annual cycle is
needed if we are to also understand longer term changes.
Reconstruction of past climate states: Instrumental
records of climate are increasingly sparse back in time, and tracing
out the history of past temperature variability requires the use of
climate proxies, such as those derived from ice, rock, sediment, and
biological records. How best to determine spatial average quantities,
such as temperature, from these proxies has been the subject of some
debate
(e.g. 2005).
Martin Tingley constructed a Bayesian Hierarchical model to estimate
spatial average temperature from noisy proxies of local temperature
variability (2010
part
1,
part
2). We are now looking to apply this technique to reconstructions
of rainfall. A related line of work is to reconstruct past ocean
states, allowing us to better gage the natural range and modes of
ocean circulation and, in principle, permits for testing of our models
under different climate conditions
(e.g. 2006, 2007
and as reviewed here
2010).
Jake Gebbie developed a new technique for tracing out ocean water
masses and we've applied it to modern observations to quantify the
amounts of different water masses
(2010),
how they are filled from surface ocean
(2011a),
and to better interpret radiocarbon observations
(2011b).
This approach appears promising for providing statistically strong
constraints upon past changes in ocean water masses, carbon storage,
and shifts in past circulation.
Time and its uncertainty: Time-uncertainty is
ubiquitous and of a degree that cannot be ignored in many paleoclimate
and geologic applications. One theme has been to develop a chronology
of Pleistocene glaciation which is independent of orbital assumptions
(2004,
2007),
along with estimates of the associated time-uncertainty. Recent work
shows why the amplitude modulation of precession variability in tuned
records is a poor test of time accuracy
(2010),
whereas tuning to obliquity and precession independently and then
comparing the results against one another provides a good test
(draft).
Another theme is to explore how time-uncertainty influences
statistical analysis of the climate record
(2004,
2009).
Eddie Haam developed an extreme value method to test for the
relationship between time-uncertain records
(2010),
and is now adapting and applying this technique to collections of
paleoclimate data. Andy Rhines showed that, unlike its influence upon
narrow-band components of Fourier spectral estimates, time uncertainty
has minimal influence upon power-law continua
(2011).
And Cristi Proistosescu has developed a framework to better understand
when tuning helps
(submitted).
The handling of time-uncertainty seems one of the more pressing, yet
less developed, problems in paleoclimate.
Crop yield: A more recent area of interest is how we should
go about predicting future crop yields. The first-order question is
whether historical trends toward increased yield can be sustained.
Marena Lin developed a technique to statistically identify whether
yield trends have plateaued, and argues that the regional patterns of
plateauing in wheat yields found across the globe is more consistent
with local socio-economic conditions, as opposed to being indicative
of intrinsic limits in yield
(submitted).
Ethan Butler has analyzed the sensitivity of maize yield in the
U.S. to variations in temperature and has demonstrated strong regional
adaptation. Using this spatial adapatation as a proxy for future
adaptability gives different predictions for the response to
modest warming: adaptation decreases yield loss by half
(submitted).
Research Staff:Zan Stine (Environment Fellow),
Martin Tingley
(research associate), Marena Lin (research assistant), and
Jeremy Shakun (visiting fellow).
Graduate
students:
Ethan Butler, Cristian
Proistosescu, Andrew
Rhines, Octavia Crompton, and Karen McKinnon.
Former students and research
staff:Martin
Tingley (PhD, 2009), Eddie Haam (PhD,
2011 now a post-doc at UW), and Jake
Gebbie (now a research scientist at WHOI).
