Showing papers by "Kevin J. Anchukaitis published in 2015"

Tropical sea surface temperatures for the past four centuries reconstructed from coral archives

Abstract: 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 Nino–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.

Tree-ring reconstructed dry season rainfall in Guatemala

Abstract: Drought in Guatemala has negative consequences for agriculture and potable water supplies, particularly in regions of the country with highly seasonal rainfall. General circulation models suggest that a decrease in both winter and summer rainfall over Central America is likely and imminent as a consequence of anthropogenic influences on the climate system. However, precipitation observations over the last several decades are equivocal. Here, we use an Abies guatemalensis tree-ring chronology from the Sierra de los Cuchumatanes to estimate January through March rainfall since the late seventeenth century. Our reconstruction shows that recent winter–spring rainfall from the region is not yet exceptional in the context of the last several centuries, has a significant yet variable decadal component, is associated with large-scale modes of ocean–atmosphere variability, and reveals evidence of past multiyear droughts.

Multi-scale drought and ocean–atmosphere variability in monsoon Asia

Abstract: 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 Ni?o 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 Ni?o Modoki events.

Corrigendum: Continental-scale temperature variability during the past two millennia

Abstract: 339 During the current interglacial period, Earth’s climate has undergone significant climate variations that have yet to be quantified at the continental scale, where climate variability is arguably more relevant to ecosystems and societies than globally averaged conditions. Determining the magnitude of these changes is needed to distinguish anthropogenic impacts from the background range of natural variability1. Reconstructing spatiotemporal patterns of past climate variability helps us to understand and quantify the influence of externally forced and intrinsic dynamics of the global climate system2, and to understand natural climate variability, which needs to be considered in future climate scenarios3,4. Here we present a global data set of proxy records and associated temperature reconstructions for seven continental-scale regions. We describe the most prominent features of continental-scale temperature changes at multi-decadal to millennial timescales. In contrast to other recent global-scale reconstructions5,6, this study provides an inter-continental perspective of temperature evolution during the past one to two thousand years.

Tree‐ring reconstructed temperature index for coastal northern Japan: implications for western North Pacific variability

Abstract: While paleoclimatic studies have extended our understanding of North Pacific climate variability, these have been almost exclusively based on proxies from western North America. We present a tree-ring reconstruction of June to September coastal air temperatures for Nemuro, northeastern Japan for the past four centuries. It explains 36% of the variance in instrumental temperatures and correlates significantly with indices of the atmosphere–ocean circulation. Spectral analyses reveal robust bidecadal peaks that appear associated with regional modes of western North Pacific variability. At decadal time scales, Nemuro temperatures appear to be influenced by the confluence of the Kuroshio and Oyashio currents, a primary centre of action driving Pacific Decadal Variability. Regime shifts (e.g. 1976) are weakly expressed relative to western North America. These aspects of western North Pacific climate are regionally distinct relative to those elsewhere in the basin, with greater complexity than can be attributed to the Pacific Decadal Oscillation (PDO) alone.

Volcanic Eruptions and Climate

Abstract: Volcanic eruptions represent some of the most climatically important and societally disruptive short-term events in human history. Large eruptions inject ash, dust, sulfurous gases (e.g. SO2, H2S), halogens (e.g. Hcl and Hbr), and water vapor into the Earth's atmosphere. Sulfurous emissions principally interact with the climate by converting into sulfate aerosols that reduce incoming solar radiation, warming the stratosphere and altering ozone creation, reducing global mean surface temperature, and suppressing the hydrological cycle. In this issue, we focus on the history, processes, and consequences of these large eruptions that inject enough material into the stratosphere to significantly affect the climate system. In terms of the changes wrought on the energy balance of the Earth System, these transient events can temporarily have a radiative forcing magnitude larger than the range of solar, greenhouse gas, and land use variability over the last millennium. In simulations as well as modern and paleoclimate observations, volcanic eruptions cause large inter-annual to decadal-scale changes in climate. Active debates persist concerning their role in longer-term (multi-decadal to centennial) modification of the Earth System, however.

Reconstructed summer temperatures over the last 400 years based on larch ring widths: Sakhalin Island, Russian Far East

Abstract: A new ring-width record from the eastern flanks of the Eastern Sakhalin Range, Sakhalin Island, Russian Federation is significantly correlated with summer temperatures and allows for the reconstruction of May–July average temperatures for the past 400 years. The reconstruction explains 37 % of the variance in May–July temperatures and shows a strong cooling between 1680 and 1710 CE coincident with the Maunder solar minimum and in agreement with other independent tree-ring reconstructions and glacier histories from sites along the margin of the Sea of Okhotsk. While recent decades are among the warmest in the record they are rivaled by periods centered on 1650 and 1850 CE. Warming in the observational record and the reconstruction is consistent with the influence of the declining strength of the Siberian High and loss of sea ice over the same interval. Decadal (17–25 year) variability persists throughout the reconstruction. At interannual timescales the Sakhalin reconstruction is most strongly correlated with local and central North Pacific sea surface temperatures over the past 120 years, whereas at decadal timescales there is an additional association with Asian land surface temperatures.

A long-term context (931-2005 C.E.) for rapid warming over central Asia

Abstract: Warming over Mongolia and 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, 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 millenniallength, 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 (2000e2005) exceeds that from any other time and is concurrent with, and likely exacerbated, the impact of extreme drought (1999e2002) that resulted in massive livestock loss across Mongolia. © 2015 Elsevier Ltd. All rights reserved.