Past Temperature Changes Research Articles

Quantifying the variability of paleotemperature fluctuations on heat flow measurements

Climatically-driven surface temperature fluctuations disturb the steady state geotherm, and affect vertical heat flow measurements in shallow (<1000m deep) boreholes. We investigated the causes of variability in reconstructed paleotemperature recorded by boreholes with a well constrained regional dataset from Tasmania, and a global synthesis.Variability between reconstructed past temperature changes is lower at local rather than regional scales. Climatic factors influence the magnitude of variability between boreholes, with non-climatic factors including topography, lithology and land use representing secondary measurable influences. The magnitude of variability means that paleotemperature corrections for heat flow will generally increase the accuracy, but not the precision of heat flow measurements.

Impacts of the Last Glacial Cycle on ground surface temperature reconstructions over the last millennium

AbstractBorehole temperature profiles provide robust estimates of past ground surface temperature changes, in agreement with meteorological data. Nevertheless, past climatic changes such as the Last Glacial Cycle (LGC) generated thermal effects in the subsurface that affect estimates of recent climatic change from geothermal data. We use an ensemble of ice sheet simulations spanning the last 120 ka to assess the impact of the Laurentide Ice Sheet on recent ground surface temperature histories reconstructed from borehole temperature profiles over North America. When the thermal remnants of the LGC are removed, we find larger amounts of subsurface heat storage (2.8 times) and an increased warming of the ground surface over North America by 0.75 K, both relative to uncorrected borehole estimates.

Glacier‐based climate reconstructions for the last glacial–interglacial transition: Arthur's Pass, New Zealand (43°S)

ABSTRACTGeological records of mountain glacier fluctuations provide useful evidence for tracing the magnitude and rate of past temperature change. In this study, we present air temperature reconstructions for the last glacial termination in New Zealand derived using snowline reconstructions and numerical glacier modelling. We target the Arthur's Pass moraines in the Otira River catchment, which have previously been dated to the Lateglacial using cosmogenic 10Be. Recalculation of these exposure ages using a locally calibrated 10Be production rate indicates that these moraines formed ca. 16–14 ka. Our glacier modelling experiments and snowline reconstructions exhibit good agreement and show that the Arthur's Pass moraines formed in a climate that was 2.2–3.5 °C colder than present. Combining our results with other, proximal glacier records shows that ice in this catchment retreated ca. 50 km from the coastal plain to the main divide during the interval 17–15 ka, in response to a temperature increase of at least ca. 3 °C. Over half of this retreat occurred after the glacier had withdrawn from an overdeepened basin. Thus, we conclude that temperature increase was the primary driver of widespread and rapid glacier retreat in New Zealand at the onset of the last glacial termination.

Can stable oxygen and hydrogen isotopes from Australian subfossil Chironomus head capsules be used as proxies for past temperature change?

This paper presents the first systematic investigation of stable isotopes (δ18O and δ2H) from the subfossil chironomid head capsules (HCs) of a single taxon (Chironomus). The study focuses on sixteen south-eastern Australian lakes and investigates the potential of Chironomus spp. HC stable isotopes to reconstruct past temperature changes from these lakes. The relationship between δ18O values of Chironomus spp. HCs from Australian oligotrophic to mesotrophic lakes in humid areas and air temperature appears robust (r = 0.88) and in line with results from European lakes. Similar results were obtained for δ2H values and temperature (r = 0.94). For lakes that are located in semi-arid and sub-humid areas that have high evaporation compared to precipitation, and often long water residence time, the temperature relationship is not robust. This is due to the evaporative enrichment of δ18O values in lake water and the effect of salinity and higher nutrient status. Vital effects may also play a role. The overall findings of this study are that both Chironomus spp. HC δ18O and δ2H are potentially valuable tools for reconstructing temperature in cooler, low nutrient and low salinity lakes of Australia. In warmer, sub-humid to semi-arid regions, δ18O and δ2H may provide valuable information about past changes in hydrological conditions.

Continuous measurements of isotopic composition of water vapour on the East Antarctic Plateau

Abstract. Water stable isotopes in central Antarctic ice cores are critical to quantify past temperature changes. Accurate temperature reconstructions require one to understand the processes controlling surface snow isotopic composition. Isotopic fractionation processes occurring in the atmosphere and controlling snowfall isotopic composition are well understood theoretically and implemented in atmospheric models. However, post-deposition processes are poorly documented and understood. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum between surface water vapour, precipitation, surface snow and buried snow. Here, we target the isotopic composition of water vapour at Concordia Station, where the oldest EPICA Dome C ice cores have been retrieved. While snowfall and surface snow sampling is routinely performed, accurate measurements of surface water vapour are challenging in such cold and dry conditions. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces. Two infrared spectrometers have been deployed at Concordia, allowing continuous, in situ measurements for 1 month in December 2014–January 2015. Comparison of the results from infrared spectroscopy with laboratory measurements of discrete samples trapped using cryogenic sampling validates the relevance of the method to measure isotopic composition in dry conditions. We observe very large diurnal cycles in isotopic composition well correlated with temperature diurnal cycles. Identification of different behaviours of isotopic composition in the water vapour associated with turbulent or stratified regime indicates a strong impact of meteorological processes in local vapour/snow interaction. Even if the vapour isotopic composition seems to be, at least part of the time, at equilibrium with the local snow, the slope of δD against δ18O prevents us from identifying a unique origin leading to this isotopic composition.

Cooling and drying in northeast Africa across the Pliocene

Terrestrial records suggest that Northeast Africa experienced drying during the Pliocene; however, these records are often incomplete in time and space, and questions about this shift in climate remain. Here, we use marine sediments from Deep Sea Drilling Project (DSDP) Site 231 in the Gulf of Aden to generate a multi-proxy organic geochemical record of northeast African climate spanning 5.3–2 Ma. This new record provides a regional perspective on climate and serves as context for the fossil record of early hominin evolution. We measured leaf wax carbon (δ13Cwax) and hydrogen (δDwax) isotopic composition and TEX86 (tetraether index of 86 carbons) to investigate past changes in vegetation, aridity, and ocean temperature, respectively. In the earliest Pliocene, we infer warm subsurface ocean temperatures from TEX86, semi-arid conditions on land and extensive C4 grasslands based on δDwax, δ13Cwax and previously published pollen. After 5 Ma, ocean temperatures gradually cooled, and at 4.3 Ma there was a transition to arid conditions on land based on δDwax and pollen. Grasslands yielded to a mid Pliocene landscape of dry shrublands. This drying appears to be an atmospheric response to cooling ocean temperatures, which may reflect changes in tropical ocean circulation, the intensification of Indian Monsoon winds or perhaps other changes associated with Pliocene cooling.

Radiative analysis of global mean temperature trends in the middle atmosphere: Effects of non-locality and secondary absorption bands

In this paper, we provide a refined and extended assignment of past and future temperature changes relative to previous analyses and describe and evaluate the relevance of vertical coupling and non-linear and secondary radiative mechanisms for the interpretation of climatic temperature variations in the middle atmosphere. Because of their nature, the latter mechanisms are not adequately accounted for in most regression analyses of temperature trends as a function of local constituent variations. These mechanisms are examined using (1) globally averaged profiles from transient simulations with the Canadian Middle Atmosphere Model (CMAM) forced by changes in greenhouse gases and ozone depleting substances and (2) a one-dimensional radiative-equilibrium model forced using the diagnosed global mean changes in radiatively active constituents as derived from the CMAM model runs. The conditions during the periods 1975 to 1995 and 2010 to 2040 (during which the rates of change in ozone and CO2 differ) provide a suitable contrast for the role of the non-linear and non-local mechanisms being evaluated in this paper to be clearly differentiated and evaluated. Vertical coupling of radiative transfer effects and the influence of secondary absorption bands are important enough to render the results of multiple linear regression analyses between the temperature response and constituent changes misleading. These effects are evaluated in detail using the 1D radiative-equilibrium model using profiles from the CMAM runs as inputs. In order to explain the differences in the CMAM temperature trends prior to and after 2000 these other radiative effects must be considered in addition to local changes in the radiatively active species. The middle atmosphere temperature cools in response to CO2 and water vapor increases, but past and future trends are modulated by ozone changes.

Driving force behind global cooling in the Cenozoic: an ongoing mystery

The stepwise cooling marks the long-time global climate change during the Cenozoic, particularly since the Oligocene/Eocene boundary. This climatic evolution has been punctuated by several warming such as the peak Cenozoic warmth at 52Ma, the late Oligocene warming at ∼25Ma and the Mid-Miocene Climatic Optimum at 17–14Ma. Concurring with the global temperature changes, the Asian paleoenvironment has been modulated by the global cooling and the tectonic uplift during the Cenozoic, but what have driven the global climatic changes remains unresolved. In this review paper, I hypothesize that a threshold CO2 level in combination with favorable orbital configuration, ocean circulation, enhanced ice albedo and possible roles of silicate mineral and basalt weathering together facilitated the development of glaciations in the Cenozoic and the past temperature change. The synchronous variations between Earth’s surface temperature and atmospheric CO2 level may indicate that the atmospheric CO2 content is the direct driving force for the global climatic cooling, but this hypothesis needs testing by using high-resolution geological record and paleoclimatic modeling.

Interpretation of orbital scale variability in mid-latitude speleothem δ18O: Significance of growth rate controlled kinetic fractionation effects

Oxygen isotopes have been the most widely used climate indicator in stalagmites, applied to reconstruct past changes in rainfall δ18O and cave temperature. However, the δ18O signal in speleothems may also be influenced by variable kinetic fractionation effects, here conceived broadly as fractionation effects not arising from temperature variation. The regional reproducibility of speleothem δ18O signals has been proposed as a way to distinguish the δ18O variations arising directly from changes rainfall δ18O and cave temperature, from variations due to kinetic effects which may nonetheless be influenced by climate. Here, we compare isotopic records from 5 coeval stalagmites from two proximal caves in NW Spain covering the interval 140 to 70 ka, which experienced the same primary variations in temperature and rainfall δ18O, but exhibit a large range in growth rates and temporal trends in growth rate. Stalagmites growing at faster rates near 50 μm/yr have oxygen isotopic ratios over 1‰ more negative than coeval stalagmites with very slow (5 μm/yr) growth rates. Because growth rate variations also occur over time within any given stalagmite, the measured oxygen isotopic time series for a given stalagmite includes both climatic and kinetic components. Removal of the kinetic component of variation in each stalagmite, based on the dependence of the kinetic component on growth rate, is effective at distilling a common temporal evolution of among the oxygen isotopic records of the multiple stalagmites. However, this approach is limited by the quality of the age model. For time periods characterized by very slow growth and long durations between dates, the presence of crypto-hiatus may result in average growth rates which underestimate the instantaneous speleothem deposition rates and which therefore underestimate the magnitude of kinetic effects. The stacked growth rate-corrected speleothem δ18O is influenced by orbital scale variation in the cave temperature and the δ18O of the ocean moisture source, but also by temporally variable fractionation in the hydrological cycle. The most salient trend is increased hydrological fractionation during the GI-22 period, when warmer sea surface temperatures in the subtropical Atlantic moisture source region may have favored greater precipitation amounts.

Tree-Ring Amplification of the Early Nineteenth-Century Summer Cooling in Central Europea

Abstract Annually resolved and absolutely dated tree-ring chronologies are the most important proxy archives to reconstruct climate variability over centuries to millennia. However, the suitability of tree-ring chronologies to reflect the “true” spectral properties of past changes in temperature and hydroclimate has recently been debated. At issue is the accurate quantification of temperature differences between early nineteenth-century cooling and recent warming. In this regard, central Europe (CEU) offers the unique opportunity to compare evidence from instrumental measurements, paleomodel simulations, and proxy reconstructions covering both the exceptionally hot summer of 2003 and the year without summer in 1816. This study uses 565 Swiss stone pine (Pinus cembra) ring width samples from high-elevation sites in the Slovakian Tatra Mountains and Austrian Alps to reconstruct CEU summer temperatures over the past three centuries. This new temperature history is compared to different sets of instrumental measurements and state-of-the-art climate model simulations. All records independently reveal the coolest conditions in the 1810s and warmest after 1996, but the ring width–based reconstruction overestimates the intensity and duration of the early nineteenth-century summer cooling by approximately 1.5°C at decadal scales. This proxy-specific deviation is most likely triggered by inflated biological memory in response to reduced warm season temperature, together with changes in radiation and precipitation following the Tambora eruption in April 1815. While suggesting there exists a specific limitation in ring width chronologies to capture abrupt climate perturbations with increased climate system inertia, the results underline the importance of alternative dendrochronological and wood anatomical parameters, including stable isotopes and maximum density, to assess the frequency and severity of climatic extremes.

The age of large termite mounds—radiocarbon dating of Macrotermes falciger mounds of the Miombo woodland of Katanga, DR Congo

Abstract The age of four large termite mounds has been determined by 14C-dating the acid-insoluble organic carbon fraction of samples taken along the central vertical axis of two active and two abandoned mounds. The age sequence in the active mounds is erratic, but the results for the abandoned mounds show a logical increase of 14C-age with depth. The ages measured at 50 cm above ground level were 2335–2119 cal yr BP for the large abandoned mound (630 cm high), and 796–684 cal yr BP for the small abandoned mound (320 cm high). Cold-water-extractable organic carbon (CWEOC) measurements combined with spectroscopic analysis revealed that the lower parts of the active mounds may have been contaminated with recent carbon that leached from the active nest. Nonetheless, this method appears to provide reliable age estimates of large, abandoned termite mounds, which are older than previously estimated. Furthermore, historical mound growth rates seem to correspond to past temperature changes, suggesting a relation between past environmental conditions and mound occupancy.

Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology, Lake Vuoksjávrátje, NW Sweden

In this paper, we show the potential of combining multi‐proxy analysis of lake sediments with catchment geomorphology to better understand palaeoenvironmental changes. Previous studies have suggested that alpine lakes in N Sweden may be highly sensitive to variations in catchment erosion and precipitation, and that this sensitivity may influence ecologically based reconstructions of past temperature changes. We analysed lake sediments covering the last 5100 years from the alpine Lake Vuoksjávrátje in NW Sweden in order to identify different erosional regimes in the lake catchment, sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. The measured proxies include elemental geochemistry from XRF core scanning, grain size, sediment accumulation rates, fraction of terrestrial organic carbon and geomorphological mapping, supported by previously published chironomid and total organic carbon data. From the integrated results we identified time intervals when increased intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event occurred c. 2900 cal. a BP and is interpreted to be the result of excessive precipitation, possibly related to the climatic shift towards cooler and wetter conditions referred to as the 2.8 ka event.

North American extreme temperature events and related large scale meteorological patterns: a review of statistical methods, dynamics, modeling, and trends

The objective of this paper is to review statistical methods, dynamics, modeling efforts, and trends related to temperature extremes, with a focus upon extreme events of short duration that affect parts of North America. These events are associated with large scale meteorological patterns (LSMPs). The statistics, dynamics, and modeling sections of this paper are written to be autonomous and so can be read separately. Methods to define extreme events statistics and to identify and connect LSMPs to extreme temperature events are presented. Recent advances in statistical techniques connect LSMPs to extreme temperatures through appropriately defined covariates that supplement more straightforward analyses. Various LSMPs, ranging from synoptic to planetary scale structures, are associated with extreme temperature events. Current knowledge about the synoptics and the dynamical mechanisms leading to the associated LSMPs is incomplete. Systematic studies of: the physics of LSMP life cycles, comprehensive model assessment of LSMP-extreme temperature event linkages, and LSMP properties are needed. Generally, climate models capture observed properties of heat waves and cold air outbreaks with some fidelity. However they overestimate warm wave frequency and underestimate cold air outbreak frequency, and underestimate the collective influence of low-frequency modes on temperature extremes. Modeling studies have identified the impact of large-scale circulation anomalies and land–atmosphere interactions on changes in extreme temperatures. However, few studies have examined changes in LSMPs to more specifically understand the role of LSMPs on past and future extreme temperature changes. Even though LSMPs are resolvable by global and regional climate models, they are not necessarily well simulated. The paper concludes with unresolved issues and research questions.

Estimates of future warming‐induced methane emissions from hydrate offshore west Svalbard for a range of climate models

AbstractMethane hydrate close to the hydrate stability limit in seafloor sediment could represent an important source of methane to the oceans and atmosphere as the oceans warm. We investigate the extent to which patterns of past and future ocean‐temperature fluctuations influence hydrate stability in a region offshore West Svalbard where active gas venting has been observed. We model the transient behavior of the gas hydrate stability zone at 400–500 m water depth (mwd) in response to past temperature changes inferred from historical measurements and proxy data and we model future changes predicted by seven climate models and two climate‐forcing scenarios (Representative Concentration Pathways RCPs 2.6 and 8.5). We show that over the past 2000 year, a combination of annual and decadal temperature fluctuations could have triggered multiple hydrate‐sourced methane emissions from seabed shallower than 400 mwd during episodes when the multidecadal average temperature was similar to that over the last century (∼2.6°C). These temperature fluctuations can explain current methane emissions at 400 mwd, but decades to centuries of ocean warming are required to generate emissions in water deeper than 420 m. In the venting area, future methane emissions are relatively insensitive to the choice of climate model and RCP scenario until 2050 year, but are more sensitive to the RCP scenario after 2050 year. By 2100 CE, we estimate an ocean uptake of 97–1050 TgC from marine Arctic hydrate‐sourced methane emissions, which is 0.06–0.67% of the ocean uptake from anthropogenic CO2 emissions for the period 1750–2011.

Montane bias in lowland Amazonian peatlands: Plant assembly on heterogeneous landscapes and potential significance to palynological inference

Abstract Past temperature changes in tropical mountain regions are commonly inferred from vertical elevational shifts of montane indicator taxa in the palynological record. However temperature is one of several abiotic factors driving the low-elevational limits of species and many montane taxa can occur in warmer lowlands by tracking appropriate habitat types, especially highly flooded wetlands. In this paper we explore ways in which lowland habitat heterogeneity might introduce error into paleo-temperature reconstructions, based on field data of seven modern peatland vegetation communities in the southern Peruvian Amazon (~ 200 masl). Peat-rich substrates are common edaphic transitions in pollen cores and provide detailed records of past vegetation change. The data show that indicators of modern peatlands include genera with montane as well as lowland distributions, while indicators of surrounding forests on mineral substrates have predominantly lowland distributions. Based on family-level analyses we find that modern peatland vegetation communities have taxonomic compositions appearing to be 389 m to 1557 m (mean = 1050 ± 391 m) above their actual elevations due to a high abundance and number of families with high elevation optima. We interpret the relatively higher prevalence of montane elements in modern peatlands as habitat tracking of a conserved montane niche on heterogeneous lowland landscapes. We suggest that both high moisture availability and stressful edaphic conditions of peatland habitat may explain the montane bias observed. To the extent that fossilization provides a better record of past vegetation that occurred proximate to the site of deposition, we suggest that habitat tracking of montane elements may introduce a cool bias in lowland paleo-temperature reconstructions based on pollen proxies.

River water temperature in the United Kingdom

Change in river water temperature has important consequences for the environment and people. This review provides a new perspective on the topic by evaluating changes in river water temperature for the UK over the 20th century and possible changes over the 21st century. There is limited knowledge of space-time variability in, and controls on, river temperature at the region scale and beyond over the 20th century. There is historical evidence that UK river temperature has increased in the latter part of the 20th century, but low agreement on the attribution of changes to climatic warming because river temperature is a complex, dynamic response to climate and hydrological patterns moderated by basin properties and anthropogenic impacts. Literature is scarce to evaluate changes to UK river temperature in the 21st century, but it appears as likely as not that UK river temperature will increase in the future. However, there are a number of interlinked sources of uncertainty (related to observations, scenarios, process interactions and feedback) that make estimating direction and rate of temperature change for rivers across the UK with confidence very challenging. Priority knowledge gaps are identified that must be addressed to improve understanding of past, contemporary and future river temperature change.

Climate reconstruction based on GDGT-based proxies in a paleosol sequence in Japan: Postdepositional effect on the estimation of air temperature

We investigated branched and isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) in surface soils and a paleosol sequence to understand the effects of environmental and postdepositional factors on branched GDGT composition in different soil types and to reconstruct the past changes in the mean annual air temperature (MAAT) in southwestern Japan during the last 15 ka. The estimated MAAT was overestimated by 6 °C and 2 °C when the global and regional soil calibrations were applied, respectively. Additionally, the estimated MAAT increased downward by a maximum of 4 °C in the upper 30 cm of the soil sequence. This is likely to reflect the addition of newly produced branched GDGTs in subsurface soils. The estimated MAATs in a paleosol sequence are thus ∼10 °C and ∼6 °C higher than those expected when the global and regional soil calibrations were applied, respectively, but the variation agrees with the Holocene variation in the MAAT estimated by the pollen assemblage. This indicates that the MBT'/CBT-derived MAAT is biased, but the variation reflects the past changes in MAAT.

Differential effects of temperature change and human impact on European Late Quaternary mammalian extinctions.

Species that inhabited Europe during the Late Quaternary were impacted by temperature changes and early humans, resulting in the disappearance of half of the European large mammals. However, quantifying the relative importance that each factor had in the extinction risk of species has been challenging, mostly due to the spatio-temporal biases of fossil records, which complicate the calibration of realistic and accurate ecological niche modeling. Here, we overcome this problem by using ecotypes, and not real species, to run our models. We created 40 ecotypes with different temperature requirements (mean temperature from -20°C to 25°C and temperature range from 10°C to 40°C) and used them to quantify the effect of climate change and human impact. Our results show that cold-adapted ecotypes would have been highly affected by past temperature changes in Europe, whereas temperate and warm-adapted ecotypes would have been positively affected by temperature change. Human impact affected all ecotypes negatively, and temperate ecotypes suffered the greatest impacts. Based on these results, the extinction of cold-adapted species like Mammuthus primigenius may be related to temperature change, while the extinction of temperate species, like Crocuta crocuta, may be related to human impact. Our results suggest that temperature change and human impact affected different ecotypes in distinct ways, and that the interaction of both impacts may have shaped species extinctions in Europe.

末次冰盛期以来我国气候环境变化及人类适应

Based on various geological records of high-resolutions, this project aims at addressing the climate and environmental histories in China since the Last Glacial Maximum (LGM) and human impacts on the Holocene environmental changes. Significant progresses have been obtained with regards to the impacts of past temperature changes to Asian monsoon and to the arid/semi-arid ecosystems in China. The results also suggest that changes in the concentrations of greenhouse gases in the pre-industrial era were mainly attributable to natural driven forces although early agriculture had significantly affected the landscapes.

The modern distribution of chironomid sub-fossils (Insecta: Diptera) in Costa Rica and the development of a regional chironomid-based temperature inference model

Chironomids have been shown to provide robust reconstructions of past temperature change and variability. This is the first study to assess the contemporaneous relationship between the distribution of sub-fossil chironomids and limnological and climatic parameters in Central America. Here, we describe the distribution of chironomids in a suite of 51 lakes in Costa Rica. We identify environmental variables that account for a statistically significant amount of variance in midge distribution, and develop a quantitative chironomid-based inference model for mean annual air temperature (MAT). Psectrocladius, which is documented for the first time in Costa Rica, dominate high-elevation lakes characterized by low MAT and relatively dilute water. Canonical correspondence analysis (CCA) revealed that MAT and conductivity account for large, statistically significant amounts of variance in the distribution of chironomids. A chironomid-based inference model for MAT, developed using a partial least squares approach, provided robust performance statistics with a high coefficient of determination and a relatively low root-mean square error. Application of the chironomid-based inference model for MAT to chironomid stratigraphies spanning the Holocene, together with the ecological information provided by this study, will enable us to address many outstanding questions relating to long-term climate and environmental change in the region.