A review of terrestrial and marine climates in the Cretaceous with implications for modelling the ‘Greenhouse Earth (original) (raw)
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Marine rapid environmental/climatic change in the Cretaceous greenhouse world
Cretaceous Research, 2012
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Southern high latitude climate variability in the Late Cretaceous greenhouse world
Global and Planetary Change v. 60, p. 351–364, 2008
A palynological study of oil exploration wells in the Gippsland Basin southeastern Australia has provided a record of southern high latitude climate variability for the last 12 million years of the Cretaceous greenhouse world. During this time, the vegetation was dominated by a cool to temperate flora of Podocarpaceae, Proteaceae and Nothofagidites spp. at a latitude of 60°S. Milankovitch forced cyclic alternations fromdrier towetter climatic periods caused vegetation variability from72 to 77Ma. This climate change was probably related to the waxing and waning of ephemeral (100 ky) small ice sheets in Antarctica during times of insolation minima and maxima. Drying and cooling after 72Ma culminated from 68 to 66Ma, mirroring trends in global δ18O data. Quantitative palynofloral analyses have the potential to provide realistic proxies for small-scale climate variability in the predominantly ice-free Late Cretaceous.
Special Topic: Cretaceous greenhouse palaeoclimate and sea-level changes
Science China Earth Sciences, 2016
Earth's climate has oscillated between greenhouse (warm) and icehouse (cold) modes throughout Earth history. At present, Earth is in the midst of an icehouse climate interval, despite the anthropogenic contribution to global warming and sea-level rise due to industrialization during the past two centuries. This led to a dramatic increase in atmospheric CO 2 , mainly caused by the extensive burning of fossils fuels. The Cretaceous (145 to 66 million years ago) is the youngest prolonged greenhouse climate interval in the Phanerozoic, marked by very high global mean temperatures with some extreme warming peaks ('hothouse' or 'supergreenhouse'), largely absence of permanent continental ice sheets, a mean global sea-level having been some 250 m higher than that of today, and levels of carbon dioxide 4 to 10 times higher than those of the pre-industrial era. If temperature will continue to rise as quickly as in the last three decades, we are close to being at the cusp to a new greenhouse climate interval facing quickly rising global sea-level and reaching atmospheric CO 2 levels of the 'Cretaceous supergreenhouse' in about the years 2190-2260 (Hay, 2011). Evidence from Earth's history indicates that glacial-interglacial climate mode changes as well as past sea-level changes such as in the Cretaceous greenhouse occurred at rates orders of magnitude slower than observed at present. The recent rise in global sea-level in response to rising levels of atmospheric greenhouse gases, the associated global warming, and the waning of continental ice shields is a primary concern for human society. To predict future sea-levels we need a better understanding of the record of past sea-level changes, especially in the greenhouse palaeoclimate modes. Therefore, understanding the Cretaceous palaeoclimate is essential for a more accurate prediction of future global climate, sea-level rise and environmental changes in a prospective 'Cretaceous-like' greenhouse Earth.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2012
To date, many general circulation model (GCM) experiments have failed to reproduce the warm, high latitude temperatures suggested for the Cretaceous by geological proxy climate indicators, especially for the Northern Hemisphere and within continental interiors. The vast majority of these proxies are biologically based, and it is important to determine whether alternative sedimentologically based proxies indicate similar cold biases in models. Therefore, we have performed an evaluation of the very latest generation of climate model predictions for terrestrial sites using climatically sensitive sediments as palaeoclimate indicators. Evidence from the geological record, comprising coal/peat, evaporites, bauxite and laterite deposits, are portrayed on a series of palaeoclimate-data maps. These are then compared with the global distributions of potential deposits generated from model simulations of the Maastrichtian using versions of the Hadley Centre climate model. The Maastrichtian was chosen because of the greater range and sophistication of GCMs adapted for its climate simulation and sediment prediction than for other Cretaceous stages. This thus represents the first attempt at comparing such state-of-the-art models to lithological climate indicators and quantifying their relative performances. For peat/coal, there is generally good correspondence between Maastrichtian model predictions for predicted potential deposits and the observed record. For evaporites, there is also very close agreement between predictions by the models and the geological record, minor differences between the individual model versions resulting from their differing levels of atmospheric CO 2 and the different palaeogeographical representations of intracontinental seaways in the Northern Hemisphere. For bauxites and laterites, the models predict less than half of the documented deposits, successfully portraying equatorial accumulations but omitting the majority of mid to high latitude deposits. The main discrepancy is therefore identified as the failure of all models to predict bauxite and laterite deposits corresponding with recorded accumulations within the mid to high latitudes of Europe and Asia. In many cases, the effects of CO 2 have minimal impact on the skill of model prediction. However, for evaporite distributions, the low CO 2 model is appreciably worse. In general, the best match across the geological data and models is achieved by the simulation with open Northern Hemisphere seaways. Overall, these results confirm those inferred from biological proxies, showing that climate models have a serious cold bias in high latitudes and continental interiors during the Cretaceous and that the latest generation of climate models still produces results which are incompatible with the geological data. Levels of atmospheric CO 2 and uncertainties in palaeogeography cannot explain the discrepancy. The cold bias is common to many climate models, and suggests that a process or mechanism is poorly represented or omitted in the current generation of climate models, or that we are failing to recognise a major boundary condition change in the Cretaceous. If the former, this implies that we may be underestimating the extent of extreme future climate change at high latitudes and in continental interiors.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2011
This study aims to investigate the global hydrologic cycle during the mid-Cretaceous greenhouse by utilizing the oxygen isotopic composition of pedogenic carbonates (calcite and siderite) as proxies for the oxygen isotopic composition of precipitation. The data set builds on the Aptian-Albian sphaerosiderite δ 18 O data set presented by Ufnar et al. (2002) by incorporating additional low latitude data including pedogenic and early meteoric diagenetic calcite δ 18 O. Ufnar et al. (2002) used the proxy data derived from the North American Cretaceous Western Interior Basin (KWIB) in a mass balance model to estimate precipitation-evaporation fluxes. We have revised this mass balance model to handle sphaerosiderite and calcite proxies, and to account for longitudinal travel by tropical air masses. We use empirical and general circulation model (GCM) temperature gradients for the mid-Cretaceous, and the empirically derived δ 18 O composition of groundwater as constraints in our mass balance model. Precipitation flux, evaporation flux, relative humidity, seawater composition, and continental feedback are adjusted to generate model calculated groundwater δ 18 O compositions (proxy for precipitation δ 18 O) that match the empirically-derived groundwater δ 18 O compositions to within ±0.5‰. The model is calibrated against modern precipitation data sets. Four different Cretaceous temperature estimates were used: the leaf physiognomy estimates of Wolfe and Upchurch (1987) and Spicer and Corfield (1992), the coolest and warmest Cretaceous estimates compiled by Barron (1983) and model outputs from the GENESIS-MOM GCM by Zhou et al. (2008). Precipitation and evaporation fluxes for all the Cretaceous temperature gradients utilized in the model are greater than modern precipitation and evaporation fluxes. Balancing the model also requires relative humidity in the subtropical dry belt to be significantly reduced. As expected calculated precipitation rates are all greater than modern precipitation rates. Calculated global average precipitation rates range from 371 mm/year to 1196 mm/year greater than modern precipitation rates. Model results support the hypothesis that increased rainout produces δ 18 O-depleted precipitation. Sensitivity testing of the model indicates that the amount of water vapor in the air mass, and its origin and pathway, significantly affect the oxygen isotopic composition of precipitation. Precipitation δ 18 O is also sensitive to seawater δ 18 O and enriched tropical seawater was necessary to simulate proxy data (consistent with fossil and geologic evidence for a warmer and evaporatively enriched Tethys). Improved constraints in variables such as seawater δ 18 O can help improve boundary conditions for mid-Cretaceous climate simulations.
Vegetation-atmosphere interactions and their role in global warming during the latest Cretaceous
1998
Forest vegetation has the ability to warm Recent climate by its e¡ects on albedo and atmospheric water vapour, but the role of vegetation in warming climates of the geologic past is poorly understood. This study evaluates the role of forest vegetation in maintaining warm climates of the Late Cretaceous by (1) reconstructing global palaeovegetation for the latest Cretaceous (Maastrichtian); (2) modelling latest Cretaceous climate under unvegetated conditions and di¡erent distributions of palaeovegetation; and (3) comparing model output with a global database of palaeoclimatic indicators. Simulation of Maastrichtian climate with the land surface coded as bare soil produces high-latitude temperatures that are too cold to explain the documented palaeogeographic distribution of forest and woodland vegetation. In contrast, simulations that include forest vegetation at high latitudes show signi¢cantly warmer temperatures that are su¤cient to explain the widespread geographic distribution of high-latitude deciduous forests. These warmer temperatures result from decreased albedo and feedbacks between the land surface and adjacent oceans. Prescribing a realistic distribution of palaeovegetation in model simulations produces the best agreement between simulated climate and the geologic record of palaeoclimatic indicators. Positive feedbacks between high-latitude forests, the atmosphere, and ocean contributed signi¢cantly to high-latitude warming during the latest Cretaceous, and imply that high-latitude forest vegetation was an important source of polar warmth during other warm periods of geologic history.
Geology, 2015
A major challenge in paleoclimatology is disagreement between data and models for periods of warm climate. Data generally indicate equable conditions and reduced latitudinal temperature gradients, while models generally produce colder conditions and steeper latitudinal gradients except when using very high CO 2 . Here we show congruence between temperature indicators and climate model output for the cool greenhouse interval of the latest Cretaceous (Maastrichtian) using a global database of terrestrial and marine indicators and fully coupled simulations with the Community Climate System Model version 3. In these simulations we explore potential roles of greenhouse gases and properties of pre-anthropogenic liquid clouds in creating warm conditions. Our model simulations successfully reproduce warm polar temperatures and the latitudinal temperature gradient without overheating the tropics. Best fits for mean annual temperature are simulations that use 6× preindustrial levels of atmospheric CO 2 , or 2× preindustrial levels of atmospheric CO 2 and liquid cloud properties that may reflect pre-anthropogenic levels of cloud condensation nuclei. The Siberian interior is problematic, but this may relate to reconstructed elevation and the presence of lakes. Data and models together indicate tropical sea-surface temperatures ~5 °C above modern, an equator-to-pole temperature difference of 25-30 °C, and a mid-latitudinal temperature gradient of ~0.4 °C per 1° latitude, similar to the Eocene. Modified liquid cloud properties allow successful simulation of Maastrichtian climate at the relatively low levels of atmospheric CO 2 indicated by proxies and carbon cycle modeling. This supports the suggestion that altered properties of liquid clouds may be an important mechanism of warming during past greenhouse intervals.