Anchukaitis Kevin J.

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Anchukaitis

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Kevin J.

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Identifying coherent spatiotemporal modes in time-uncertain proxy paleoclimate records

( 2012-07) Anchukaitis, Kevin J. ; Tierney, Jessica E.

High-resolution sedimentary paleoclimate proxy records offer the potential to expand the detection and analysis of decadal- to centennial-scale climate variability during recent millennia, particularly within regions where traditional high-resolution proxies may be short, sparse, or absent. However, time uncertainty in these records potentially limits a straightforward objective identification of broad-scale patterns of climate variability. Here, we describe a procedure for identifying common patterns of spatiotemporal variability from time uncertain sedimentary records. This approach, which we term Monte Carlo Empirical Orthogonal Function (MCEOF) analysis, uses iterative age modeling and eigendecomposition of proxy time series to isolate common regional patterns and estimate uncertainties. As a test case, we apply this procedure to a diverse set of time-uncertain lacustrine proxy records from East Africa. We also perform a pseudoproxy experiment using climate model output to examine the ability of the method to extract shared anomalies given known signals. We discuss the advantages and disadvantages of our approach, including possible extensions of the technique.
A long-term context (931–2005 C.E.) for rapid warming over Central Asia

( 2014-11) Davi, Nicole K. ; D'Arrigo, Rosanne ; Jacoby, G. C. ; Cook, Edward R. ; Anchukaitis, Kevin J. ; Nachin, B. ; Rao, M. P. ; Leland, C.

Warming over Mongolia and adjacent Central Asia has been unusually rapid over the past few decades, particularly in the summer, with surface temperature anomalies higher than for much of the globe. With few temperature station records available in this remote region prior to the 1950s, paleoclimatic data must be used to understand annual-to-centennial scale climate variability, to local response to large-scale forcing mechanisms, and the significance of major features of the past millennium such as the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) both of which can vary globally. Here we use an extensive collection of living and subfossil wood samples from temperature-sensitive trees to produce a millennial-length, validated reconstruction of summer temperatures for Mongolia and Central Asia from 931 to 2005 CE. This tree-ring reconstruction shows general agreement with the MCA (warming) and LIA (cooling) trends, a significant volcanic signature, and warming in the 20th and 21st Century. Recent warming (2000-2005) exceeds that from any other time and is concurrent with, and likely exacerbated, the impact of extreme drought (1999-2002) that resulted in massive livestock loss across Mongolia.
Multivariate climate field reconstructions using tree rings for the northeastern United States

(American Geophysical Union, 2019-12-13) Pearl, Jessie K. ; Anchukaitis, Kevin J. ; Pederson, Neil ; Donnelly, Jeffrey P.

High‐resolution paleoclimate records are essential for improving our understanding of internal variability and the detection and attribution of forced climate system responses. The densely populated northeastern United States is at risk from increasing temperatures, severe droughts, and extreme precipitation, but the region has limited annual and seasonal‐resolution paleoclimate records beyond the instrumental record. Chamaecyparis thyoides, L. (B.S.P.), Atlantic white cedar, a wetland conifer found within 200 km of the Atlantic coastline of the United States, is a promising tree‐ring proxy that can fill in these data gaps. Here, we develop and analyze a new network of Atlantic white cedar tree‐ring chronologies across the northeastern United States and demonstrate that site selection is important for regional paleoclimate reconstructions. Ring width variability reflects winter through summer temperatures at inland and hydrologically stable sites in the northernmost section of the species' range. Ombrotrophic sites along the coast record hydrological signals and correlate with growing season precipitation. We demonstrate skillful regional climate field reconstructions for the last several centuries and show the increased skill from incorporating our moisture sensitive sites into broad‐scale products like the North American Drought Atlas. This comprehensive understanding of the species' climate responses leads to a tree‐ring network that provides the long‐term multivariate climate context at multidecadal and centennial time scales for the large‐scale ocean‐atmospheric processes that influence the climate of the region. We use this network to examine the covariance of temperature and drought across the New England area over the past two centuries.
Multi-scale drought and ocean–atmosphere variability in monsoon Asia

(IOP Science, 2015-07-17) Hernandez, Manuel ; Ummenhofer, Caroline C. ; Anchukaitis, Kevin J.

Spatially extensive and persistent drought episodes have repeatedly influenced human history, including the 'Strange Parallels' drought event in monsoon Asia during the mid-18th century. Here we explore the dynamics of sustained monsoon failure using observed and tree-ring reconstructed drought patterns and a 1300-year pre-industrial community earth system model control run. Both modern observational and climate model drought patterns during years with extremely weakened South Asian monsoon resemble those reconstructed for the Strange Parallels drought. Model analysis reveals that this pattern arises during boreal spring over Southeast Asia, with decreased precipitation and moisture flux, while related summertime climate anomalies are confined to the Indian subcontinent. Years with simulated South Asian drying exhibit canonical El Niño conditions over the Pacific and associated shifts in the Walker circulation. In contrast, multi-year drought periods, resembling those sustained during the Strange Parallels drought, feature anomalous Pacific warming around the dateline, typical of El Niño Modoki events.
Dendroclimatology in the Eastern Mediterranean

(University of Arizona Libraries, 2014) Touchan, Ramzi ; Meko, David M. ; Anchukaitis, Kevin J.

Dendroclimatology in the Eastern Mediterranean (EM) region has made important contributions to the understanding of climate variability on timescales of decades to centuries. These contributions, beginning in the mid-20th century, have value for resource management, archaeology, and climatology. A gradually expanding tree-ring network developed by the first author over the past 15 years has been the framework for some of the most important recent advances in EM dendroclimatology. The network, now consisting of 79 sites, has been widely applied in large-scale climatic reconstruction and in helping to identify drivers of climatic variation on regional to global spatial scales. This article reviews EM dendroclimatology and highlights contributions on the national and international scale.
Reconstructing Northeastern United States temperatures using Atlantic white cedar tree rings

(IOP Publishing, 2017-11-02) Pearl, Jessie K. ; Anchukaitis, Kevin J. ; Pederson, Neil ; Donnelly, Jeffrey P.

Our knowledge of climate variability in the densely populated Northeastern United States is limited to instrumental data of the last century. Most regional paleoclimate proxies reflect a mix of climate responses, which makes reconstructing historical climate a challenge. Here we analyze tree-ring chronologies from Atlantic white cedar (Chamaecyparis thyoides) as a potential regional paleotemperature proxy. We evaluate our tree-ring network for spatiotemporal climate signal strength and reconstruction skill across New England. Atlantic white cedar sites in the northern section of the species' range exhibit positive significant annual growth relationships with local and regional temperatures. Chronologies constructed from northern sites yield skillful reconstructions of temperature that reproduce centennial, multidecadal, and interannual variability in the instrumental record, providing a novel paleotemperature record for New England.
Volcanic cooling signal in tree ring temperature records for the past millennium

(John Wiley & Sons, 2013-08-29) D'Arrigo, Rosanne ; Wilson, Rob ; Anchukaitis, Kevin J.

Tree rings are an important proxy for understanding the timing and environmental consequences of volcanic eruptions as they are precisely dated at annual resolution and, particularly in tree line regions of the world, sensitive to cold extremes that can result from climatically significant volcanic episodes. Volcanic signals have been detected in ring widths and by the presence of frost-damaged rings, yet are often most clearly and quantitatively represented within maximum latewood density series. Ring width and density reconstructions provide quantitative information for inferring the variability and sensitivity of the Earth's climate system on local to hemispheric scales. After a century of dendrochronological science, there is no evidence, as recently theorized, that volcanic or other adverse events cause such severely cold conditions near latitudinal tree line that rings might be missing in all trees at a given site in a volcanic year (“stand-wide” missing rings), resulting in misdating of the chronology. Rather, there is a clear indication of precise dating and development of rings in at least some trees at any given site, even under adverse cold conditions, based on both actual tree ring observations and modeling analyses. The muted evidence for volcanic cooling in large-scale temperature reconstructions based at least partly on ring widths reflects several factors that are completely unrelated to any misdating. These include biological persistence of such records, as well as varying spatial patterns of response of the climate system to volcanic events, such that regional cooling, particularly for ring widths rather than density, can be masked in the large-scale reconstruction average.
Applications of proxy system modeling in high resolution paleoclimatology

(Elsevier B.V., 2013-05-29) Evans, Michael N. ; Tolwinski-Ward, S. E. ; Thompson, D. M. ; Anchukaitis, Kevin J.

A proxy system model may be defined as the complete set of forward and mechanistic processes by which the response of a sensor to environmental forcing is recorded and subsequently observed in a material archive. Proxy system modeling complements and sharpens signal interpretations based solely on statistical analyses and transformations; provides the basis for observing network optimization, hypothesis testing, and data-model comparisons for uncertainty estimation; and may be incorporated as weak but mechanistically-plausible constraints into paleoclimatic reconstruction algorithms. Following a review illustrating these applications, we recommend future research pathways, including development of intermediate proxy system models for important sensors, archives, and observations; linking proxy system models to climate system models; hypothesis development and evaluation; more realistic multi-archive, multi-observation network design; examination of proxy system behavior under extreme conditions; and generalized modeling of the total uncertainty in paleoclimate reconstructions derived from paleo-observations.
How unusual is the 2012–2014 California drought?

(John Wiley & Sons, 2014-12-30) Griffin, Daniel ; Anchukaitis, Kevin J.

For the past three years (2012–2014), California has experienced the most severe drought conditions in its last century. But how unusual is this event? Here we use two paleoclimate reconstructions of drought and precipitation for Central and Southern California to place this current event in the context of the last millennium. We demonstrate that while 3 year periods of persistent below-average soil moisture are not uncommon, the current event is the most severe drought in the last 1200 years, with single year (2014) and accumulated moisture deficits worse than any previous continuous span of dry years. Tree ring chronologies extended through the 2014 growing season reveal that precipitation during the drought has been anomalously low but not outside the range of natural variability. The current California drought is exceptionally severe in the context of at least the last millennium and is driven by reduced though not unprecedented precipitation and record high temperatures.
Bayesian parameter estimation and interpretation for an intermediate model of tree-ring width

(Copernicus Publications on behalf of the European Geosciences Union, 2013-07-15) Tolwinski-Ward, S. E. ; Anchukaitis, Kevin J. ; Evans, Michael N.

We present a Bayesian model for estimating the parameters of the VS-Lite forward model of tree-ring width for a particular chronology and its local climatology. The scheme also provides information about the uncertainty of the parameter estimates, as well as the model error in representing the observed proxy time series. By inferring VS-Lite's parameters independently for synthetically generated ring-width series at several hundred sites across the United States, we show that the algorithm is skillful. We also infer optimal parameter values for modeling observed ring-width data at the same network of sites. The estimated parameter values covary in physical space, and their locations in multidimensional parameter space provide insight into the dominant climatic controls on modeled tree-ring growth at each site as well as the stability of those controls. The estimation procedure is useful for forward and inverse modeling studies using VS-Lite to quantify the full range of model uncertainty stemming from its parameterization.
Tropical sea surface temperatures for the past four centuries reconstructed from coral archives

(John Wiley & Sons, 2015-03-18) Tierney, Jessica E. ; Abram, Nerilie J. ; Anchukaitis, Kevin J. ; Evans, Michael N. ; Giry, Cyril ; Kilbourne, K. Halimeda ; Saenger, Casey P. ; Wu, Henry C. ; Zinke, Jens

Most annually resolved climate reconstructions of the Common Era are based on terrestrial data, making it a challenge to independently assess how recent climate changes have affected the oceans. Here as part of the Past Global Changes Ocean2K project, we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics, based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives. Validation exercises suggest that our reconstructions are interpretable for much of the past 400 years, depending on the availability of paleoclimate data within, and the reconstruction validation statistics for, each target region. Analysis of the trends in the data suggests that the Indian, western Pacific, and western Atlantic Ocean regions were cooling until modern warming began around the 1830s. The early 1800s were an exceptionally cool period in the Indo-Pacific region, likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century. Decadal-scale variability is a quasi-persistent feature of all basins. Twentieth century warming associated with greenhouse gas emissions is apparent in the Indian, West Pacific, and western Atlantic Oceans, but we find no evidence that either natural or anthropogenic forcings have altered El Niño–Southern Oscillation-related variance in tropical sea surface temperatures. Our marine-based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change.

Anchukaitis Kevin J.

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