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  • 1
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    Comparing proxy and model estimates of hydroclimate variability and change over the Common Era (2017)
    Copernicus
    Details
    Publication Date: 2017-04-07
    Description: Water availability is fundamental to societies and ecosystems, but our understanding of variations in hydroclimate (including extreme events, flooding, and decadal periods of drought) is limited because of a paucity of modern instrumental observations that are distributed unevenly across the globe and only span parts of the 20th and 21st centuries. Such data coverage is insufficient for characterizing hydroclimate and its associated dynamics because of its multidecadal-to-centennial variability and highly regionalized spatial signature. High-resolution (seasonal to decadal) hydroclimatic proxies that span all or parts of the Common Era (CE) and paleoclimate model simulations are therefore important tools for augmenting our understanding of hydroclimate variability. In particular, the comparison of the two sources of information is critical for addressing the uncertainties and limitations of both, while enriching each of their interpretations. We review the principal proxy data available for hydroclimatic reconstructions over the CE and highlight contemporary understanding of how these proxies are interpreted as hydroclimate indicators. We also review the available last-millennium simulations from fully-coupled climate models and discuss several outstanding challenges associated with simulating hydroclimate variability and change over the CE. A specific review of simulated hydroclimatic changes forced by volcanic events is provided, as well as a discussion of expected improvements in estimated forcings, models and their implementation in the future. Our review of hydroclimatic proxies and last-millennium model simulations is used as the basis for articulating a variety of considerations and best practices for how to perform proxy-model comparisons of CE hydroclimate. This discussion provides a framework for how best to evaluate hydroclimate variability and its associated dynamics using these comparisons, as well as how they can better inform interpretations of both proxy data and model simulations. We subsequently explore means of using proxy-model comparisons to better constrain and characterize future hydroclimate risks. This is explored specifically in the context of several examples that demonstrate how proxy-model comparisons can be used to quantitatively constrain future hydroclimatic risks as estimated from climate model projections.
    Print ISSN: 1814-9340
    Electronic ISSN: 1814-9359
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
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    Blue Intensity based experiments for reconstructing North Pacific temperatures along the Gulf of Alaska (2017)
    Copernicus
    Details
    Publication Date: 2017-03-06
    Description: Climate in the Gulf of Alaska (GOA) reflects large-scale ocean-atmosphere variability of the North Pacific climate system. Ring-width (RW) records from the GOA have yielded a valuable long-term perspective for North Pacific changes on decadal to longer time scales in prior studies, but express a broad winter to late summer seasonal response. Similar to the highly climate-sensitive maximum latewood density (MXD) proxy, the Blue Intensity (BI) parameter has recently been shown to correlate well with year-to-year warm-season temperatures for a number of sites at northern latitudes. Since BI records are much less expensive and labor intensive to generate than MXD, such data hold great potential value for future tree-ring studies in the GOA and other regions at mid-to-high latitudes. Here we highlight the potential for improving tree-ring based reconstructions using combinations of RW and BI-related parameters (latewood BI (LWB) and delta BI (DB)) from an experimental sub-set of samples from eight mountain hemlock (Tsuga mertensiana) sites along the GOA. This is the first such study for the hemlock genus using BI data. We find that using either LWB or DB can improve the amount of explained temperature variance by 〉 10 % compared to RW alone although the optimal target season changes to June–September, which may have implications for studying ocean-atmosphere variability in the region. However, one challenge in building these BI records is that resin extraction did not remove colour differences between the heartwood and sapwood, so long term trend biases, expressed as relatively warm temperatures in the 18th century, were noted when using the LWB data. Using DB appeared to overcome these trend biases resulting in a reconstruction expressing 18th–19th century temperatures ca. 0.5 °C cooler than the 20th/21st centuries. This cool period agrees well with previous dendroclimatic studies and the glacial advance record in the region. Continuing BI measurement in the GOA region must focus on sampling more trees per site (〉 20) and more sites to overcome site specific factors effecting climate response while sub-fossil material will extend the reflectance records back over 1000 years. DB appears to capture long term secular trends that agree with other proxy archives in the region but great care is needed when implementing different detrending options. Finally, more experimentation is needed to assess the utility of DB for different conifer species around the Northern Hemisphere.
    Print ISSN: 1814-9340
    Electronic ISSN: 1814-9359
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 3
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    Boreal forests and atmosphere - Biosphere exchange of carbon dioxide (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Two approaches to investigating the role of boreal forests in the global carbon cycle are presented. First, a tracer support model which incorporates the normalized-difference vegetation index obtained from advanced, very high resolution radiometer radiances was used to simulate the annual cycle of CO2 in the atmosphere. Results indicate that the seasonal growth of the combined boreal forests of North America and Eurasia accounts for about 50 percent of the mean seasonal CO2 amplitude recorded at Pt. Barrow, Alaska and about 30 percent of the more globally representative CO2 signal at Mauna Loa, Hawaii. Second, tree-ring width data from four boreal treeline sites in northern Canada were positively correlated with Pt. Barrow CO2 drawdown for the period 1971-1982. These results suggest that large-scale changes in the growth of boreal forests may be contributing to the observed increasing trend in CO2 amplitude. They further suggest that tree-ring data may be applicable as indices for CO2 uptake and remote sensing estimates of photosynthetic activity.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 329; 321-323
    Format: text
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  • 4
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    A Double Bootstrap Approach to Superposed Epoch Analysis to Evaluate Response Uncertainty (2019)
    In:  Other Sources
    Details
    Publication Date: 2019-05-25
    Description: The association between climate variability and episodic events, such as the antecedent moisture conditions prior to wildfire or the cooling following volcanic eruptions, is commonly assessed using Superposed Epoch Analysis (SEA). In SEA the epochal response is typically calculated as the average climate conditions prior to and following all event years or their deviation from climatology. However, the magnitude and significance of the inferred climate association may be sensitive to the selection or omission of individual key years, potentially resulting in a biased assessment of the relationship between these events and climate. Here we describe and test a modified double-bootstrap SEA that generates multiple unique draws of the key years and evaluates the sign, magnitude, and significance of event-climate relationships within a probabilistic framework. This multiple resampling helps quantify multiple uncertainties inherent in conventional applications of SEA within dendrochronology and paleoclimatology. We demonstrate our modified SEA by evaluating the volcanic cooling signal in a Northern Hemisphere tree-ring temperature reconstruction and the link between drought and wildfire events in the western United States. Finally, we make our Matlab and R code available to be adapted for future SEA applications.
    Keywords: Meteorology and Climatology
    Type: GSFC-E-DAA-TN68850 , Dendrochronologia (ISSN 1125-7865); 55; 119-124
    Format: text
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  • 5
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    The Anomalous Winter of 1783-1784: Was the Laki Eruption or an Analog of the 2009-2010 Winter to Blame? (2011)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The multi ]stage eruption of the Icelandic volcano Laki beginning in June, 1783 is speculated to have caused unusual dry fog and heat in western Europe and cold in North America during the 1783 summer, and record cold and snow the subsequent winter across the circum-North Atlantic. Despite the many indisputable impacts of the Laki eruption, however, its effect on climate, particularly during the 1783.1784 winter, may be the most poorly constrained. Here we test an alternative explanation for the unusual conditions during this time: that they were caused primarily by a combined negative phase of the North Atlantic Oscillation (NAO) and an El Nino ]Southern Oscillation (ENSO) warm event. A similar combination of NAO ]ENSO phases was identified as the cause of record cold and snowy conditions during the 2009.2010 winter in Europe and eastern North America. 600-year tree-ring reconstructions of NAO and ENSO indices reveal values in the 1783.1784 winter second only to their combined severity in 2009.2010. Data sources and model simulations support our hypothesis that a combined, negative NAO ]ENSO warm phase was the dominant cause of the anomalous winter of 1783.1784, and that these events likely resulted from natural variability unconnected to Laki.
    Keywords: Meteorology and Climatology
    Type: GSFC.JA.00420.2012 , Geophysical Research Letters; 38
    Format: text
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  • 6
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    Insensitivity of Tree-Ring Growth to Temperature and Precipitation Sharpens the Puzzle of Enhanced Pre-Eruption NDVI on Mt. Etna (Italy) (2018)
    Details
    Publication Date: 2018-03-26
    Description: On Mt. Etna (Italy), an enhanced Normalized Difference in Vegetation Index (NDVI) signature was detected in the summers of 2001 and 2002 along a distinct line where, in November 2002, a flank eruption subsequently occurred. These observations suggest that pre-eruptive volcanic activity may have enhanced photosynthesis along the future eruptive fissure. If a direct relation between NDVI and future volcanic eruptions could be established, it would provide a straightforward and low-cost method for early detection of upcoming eruptions. However, it is unclear if, or to what extent, the observed enhancement of NDVI can be attributed to volcanic activity prior to the subsequent eruption. We consequently aimed at determining whether an increase in ambient temperature or additional water availability owing to the rise of magma and degassing of water vapour prior to the eruption could have increased photosynthesis of Mt. Etna's trees. Using dendro-climatic analyses we quantified the sensitivity of tree ring widths to temperature and precipitation at high elevation stands on Mt. Etna. Our findings suggest that tree growth at high elevation on Mt. Etna is weakly influenced by climate, and that neither an increase in water availability nor an increase in temperature induced by pre-eruptive activity is a plausible mechanism for enhanced photosynthesis before the 2002/2003 flank eruption. Our findings thus imply that other, yet unknown, factors must be sought as causes of the pre-eruption enhancement of NDVI on Mt. Etna.
    Description: Published
    Description: e0169297
    Description: 4V. Dinamica dei processi pre-eruttivi
    Description: JCR Journal
    Keywords: Mt. Etna ; Normalized Difference in Vegetation Index (NDVI) ; photosynthesis ; eruption ; relation between NDVI and future volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Inter-decadal climate variability in the Southern Hemisphere: evidence from Tasmanian tree rings over the past three millennia (2021)
    In:  http://aquaticcommons.org/id/eprint/15715 | 8 | 2014-11-25 21:15:51 | 15715
    Details
    Publication Date: 2021-07-09
    Description: EXTRACT (SEE PDF FOR FULL ABSTRACT):The characterization of inter-decadal climate variability in the Southern Hemisphere is severely constrained by the shortness of the instrumental climate records. To help relieve this constraint, we have developed and analyzed a reconstruction of warm-season (November-April) temperatures from Tasmanian tree rings that now extends back to 800 BC. A detailed analysis of this reconstruction in the time and frequency domains indicates that much of the inter-decadal variability is principally confined to four frequency bands with mean periods of 31, 57, 77, and 200 years. ... In so doing, we show how a future greenhouse warming signal over Tasmania could be masked by these natural oscillations unless they are taken into account.
    Keywords: Atmospheric Sciences ; PACLIM ; dendrochronology
    Repository Name: AquaDocs
    Type: conference_item
    Format: application/pdf
    Format: application/pdf
    Format: 7-20
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  • 8
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    Modeling North Pacific temperature and pressure changes from coastal tree-ring chronologies (2021)
    In:  http://aquaticcommons.org/id/eprint/15747 | 8 | 2014-11-25 22:22:18 | 15747
    Details
    Publication Date: 2021-07-10
    Description: Climate modeling using coastal tree-ring chronologies has yielded the first summer temperature reconstructions for coastal stations along the Gulf of Alaska and the Pacific Northwest. These land temperature reconstructions are strongly correlated with nearby sea surface temperatures, indicating large-scale ocean-atmospheric influences. Significant progress has also been made in modeling winter land temperatures and sea surface temperatures from coastal and shipboard stations. In addition to temperature, the pressure variability center over the central North Pacific Ocean (PAC), which is related to the strength and location of the Aleutian Low pressure system, could be extended using coastal tree rings.
    Keywords: Atmospheric Sciences ; Oceanography ; PACLIM ; dendrochronology
    Repository Name: AquaDocs
    Type: conference_item
    Format: application/pdf
    Format: application/pdf
    Format: 67-78
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  • 9
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    Tree-ring records as indicators of air-sea interaction in the northeast Pacific sector (2021)
    In:  http://aquaticcommons.org/id/eprint/15629 | 8 | 2014-11-13 19:41:53 | 15629
    Details
    Publication Date: 2021-07-09
    Description: Climate conditions in land areas of the Pacific Northwest are strongly influenced by atmosphere/ocean variability, including fluctuations in the Aleutian Low, Pacific-North American (PNA) atmospheric circulation modes, and the El Niño-Southern Oscillation (ENSO). It thus seems likely that climatically sensitive tree-ring data from these coastal land areas would likewise reflect such climatic parameters. In this paper, tree-ring width and maximum lakewood density chronologies from northwestern Washington State and near Vancouver Island, British Columbia, are compared to surface air temperature and precipitation from nearby coastal and near-coastal land stations and to monthly sea surface temperature (SST) and sea level pressure (SLP) data from the northeast Pacific sector. Results show much promise for eventual reconstruction of these parameters, potentially extending available instrumental records for the northeastern Pacific by several hundred years or more.
    Keywords: Atmospheric Sciences ; Environment ; Oceanography ; PACLIM ; dendrochronology
    Repository Name: AquaDocs
    Type: conference_item
    Format: application/pdf
    Format: application/pdf
    Format: 35-45
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  • 10
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    A long-term context (931–2005 C.E.) for rapid warming over Central Asia (2015)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Quaternary Science Reviews 121 (2015): 89-97, doi:10.1016/j.quascirev.2015.05.020.
    Description: 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.
    Description: This research was supported by the National Science Foundation under grants AGS-PRF #1137729, ATM0117442, and AGS0402474.
    Keywords: Mongolia ; Temperature ; Tree-ring ; Dendrochronology ; Reconstruction ; Global warming
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: application/pdf
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