2011 - Cooperative Institute for Research in Environmental Sciences ...

change is to what extent have El Niño-
Southern Oscillation-related (ENSO)
variations contributed to the observed
trends. Isolating such contributions is
challenging for several reasons, including
ambiguities arising from how ENSO itself
is defined. In particular, defining ENSO in
terms of a single index and ENSO-related
variations in terms of regressions on that
index, as done in many studies, can lead to
wrong conclusions. In a recently published
study, we argued that ENSO is best
viewed not as a number but as an evolving
dynamical process for this purpose.
Specifically, ENSO was identified with the
four dynamical eigenvectors of tropical
sea surface temperature (SST) evolution
that are most important in the observed
evolution of ENSO events. This definition
was used to isolate the ENSO-related
component of global SST variations on a month-by-month
basis in the 136-year (1871–2006) HadISST (Hadley Centre
Global Sea Ice and Sea Surface Temperature) data set. The
analysis showed that previously identified multidecadal
variations in the Pacific, Indian and Atlantic Oceans all
have substantial ENSO components. The long-term warming
trends over these oceans were also found to have
appreciable ENSO components, in some instances up to 40
percent of the total trend. The ENSO-unrelated component
of five-year average SST variations, obtained by removing
the ENSO-related component, was interpreted as a combination
of anthropogenic, naturally forced and natural
coherent multidecadal variations. Two surprising aspects
of these ENSO-unrelated variations were emphasized:
1) a strong cooling trend in the eastern equatorial Pacific
Ocean and 2) a nearly zonally symmetric multidecadal
tropical–extratropical seesaw that has amplified in recent
decades.
Product: Compo, GP, and PD Sardeshmukh (2010), Removing
ENSO-related variations from the climate record,
J. Clim., 23, 1957-1978, DOI: 10.1175/2009JCLI2735.1.
Figure 1: Time series of the near-global ocean average surface temperature
anomalies (black curve), and after their ENSO-related components
are removed (red curve). A 10-year running mean has been applied to
both time series. Anomalies are relative to a 1949 to 2004 average. Note
that after removing the contributions associated with ENSO, the 1871
to 2006 trend of 0.5 K per century is reduced to 0.3 K per century, a 40%
reduction. From Compo and Sardeshmukh (Journal of Climate, 2010).
Figure 2: Locations of cave (orange) and ice core (blue) records added to
the data set of climate time series spanning the period between the Last
Glacial Maximum and today.
NGDC-04Paleoclimatology:Understanding
DecadaltoMillennial-ScaleClimateVariability
FEDERAL LEAD: DAVE M. ANDERSON
CIRES LEAD: CARRIE MORRILL
NOAA Goal 2: Climate
Project Goal: Improve the understanding of observed longterm
climate variations through compilation and analysis of
data from the pre-instrumental record, and provide access to
data and information from the paleoclimatic record.
Milestone 1: Expand the database of transient climate
change during the last 21,000 years to include terrestrial
temperature reconstructions and stable isotope records
from speleothems and ice cores. Also, add raw age model
data to the database to allow users to generate new age
models as dating and calibration methods are refined.
We added more than 100 marine and terrestrial records to
the data set of climate time-series since the Last Glacial Maximum
(21,000 years ago). The majority of these records came
from cave deposits and ice cores and provided information
about terrestrial temperature and hydrology. Refinements to
our database structure and in standardizing variable names
within and between proxy types permitted us to ingest these
data into a common database. These advances allowed users
for the first time to easily download consistently formatted
data grouped into science-relevant themes. In addition, we
gathered missing age model information, including raw
radiocarbon dates, for more than 30 new and existing marine
time-series. Incorporating this information into the database
gave users the opportunity to recalibrate radiocarbon
dates for each time-series and to eliminate discrepancies in
age models caused by using different calibration methods.
This research database of the last 21,000 years will enable
extensive comparisons between climate models and paleoclimate
data planned for the next Intergovernmental Panel on
Climate Change (IPCC) assessment report.
Milestone 2: Expand the last millennium temperature
database to include gridded climate reconstructions.
These gridded reconstructions will complement the point
reconstructions already included in the database and will
provide a template for the eventual addition of climate
model simulations.
CIRES Annual Report 2011 107