Dana Royer - Academia.edu (original) (raw)

Papers by Dana Royer

Geology, 2000

Abstract An analysis of 1168 modern soil profiles from the US Natural Resources Conservation Serv... more Abstract An analysis of 1168 modern soil profiles from the US Natural Resources Conservation Service yields no correlation between mean annual precipitation and depth to the top of the carbonate horizon (r 2= 0.03; p&amp;amp;amp;lt; 0.001). Parent material and soil texture both play negligible roles in this regression. When combined with similar published studies (n= 1481), r 2 improves slightly (r 2= 0.31; p&amp;amp;amp;lt; 0.001). Caution is therefore advised in using this or any previously published regression for inferring paleoprecipitation from paleosols. ...

Nature communications, Jan 4, 2017

The evolution of Earth's climate on geological timescales is largely driven by variations in ... more The evolution of Earth's climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow ∼50 Wm(-2) increase in TSI over the last ∼420 million years (an increase of ∼9 Wm(-2) of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO2. This was likely due to the silicate weathering-negative feedback and the expansion of land plants that together ensured Earth's long-term habitability. Humanity's fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO2 not seen since the early Eocene (50 million years ago). If CO2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.

Proceedings of the National Academy of Sciences of the United States of America, Jan 15, 2008

Palaios, 2008

... The leaf on the slow-return end of the spectrum (left side) is modern Hakea dactyloides (Prot... more ... The leaf on the slow-return end of the spectrum (left side) is modern Hakea dactyloides (Proteaceae), collected near Sydney, New South Wales, Australia. ... (2007) applied this method to two well-known fossil floras: Republic (Washington, USA; 49 Ma) and Bonanza (Utah, USA ...

Most modern C3 seed plants show an inverse relationship between PCO2 and stomatal index (SI), whe... more Most modern C3 seed plants show an inverse relationship between PCO2 and stomatal index (SI), where SI is the proportion of epidermal cells that are stomatal packages. This plant-atmosphere response therefore provides a reliable approach for estimating paleo-CO2 levels. Since stomatal responses to CO2 are generally species-specific, one is limited in paleo-reconstructions to species that exist both in the fossil record and living today. Fossils morphologically similar to living Ginkgo biloba and Metasequoia glyptostroboides extend back to the early and late Cretaceous, respectively, indicating that the fossil and living forms are very closely related. Measurements of SI made on fossil Ginkgo and Metasequoia were calibrated with historical collections of G. biloba and M. glyptostroboides leaves from sites that developed during the anthropogenically-driven CO2 increases of the past 145 years (288-369 ppmv) and with saplings of G. biloba and M. glyptostroboides grown in CO2 controlled growth chambers (350-800 ppmv). Both nonlinear regressions are highly significant (Ginkgo: n = 40, r2 = 0.91; Metasequoia: n = 18; r2 = 0.85). Results from a sequence of 23 latest Cretaceous to early Eocene-aged Ginkgo-bearing sites indicate that CO2 remained between 300 and 450 ppmv with the exception of one high estimate ( ~800 ppmv) near the Paleocene/Eocene boundary, and results from 4 middle Miocene-aged Ginkgo- and Metasequoia-bearing sites indicate that CO2 was between 320 and 400 ppmv. If correct, the CO2 values estimated here are too low to explain via the CO2 greenhouse effect alone the higher global mean temperatures (e.g., 3-4 ° C for the early Eocene) inferred from models and geological data for these two intervals.

Special Paper 369: Causes and consequences of globally warm climates in the early Paleogene, 2003

The role of atmospheric CO 2 in determining climate is important for understanding patterns in th... more The role of atmospheric CO 2 in determining climate is important for understanding patterns in the geologic record and predicting future climate. Because of the recent anthropogenic rise in temperatures, the role of CO 2 in globally warm periods is particularly important for any predictions of future climate change. Here, I reconstruct the concentration of atmospheric CO 2 using patterns of stomatal index in the plant cuticles of Ginkgo and Metasequoia for two globally warm intervals, the latest Cretaceous to early Eocene (66-53 Ma) and the middle Miocene (17-15 Ma).

Leaf physiognomy (size and shape) in fossils is commonly used to reconstruct terrestrial paleocli... more Leaf physiognomy (size and shape) in fossils is commonly used to reconstruct terrestrial paleoclimate. Physiognomic leaf-climate methods are underpinned mostly by the covariation between toothed margins and mean annual temperature (MAT) and between leaf size and mean annual precipitation. Digital leaf physiognomy, a multivariate method based largely on variables that are functionally linked to climate and that can be measured by computer algorithm, minimizes many of the deficiencies present in other approaches. Nevertheless, the relationships between MAT and many physiognomic variables, especially tooth-related variables, are confounded by leaf thickness, leaf habit (deciduous vs. evergreen), and phylogenetic history. Until these factors are properly accounted for, a minimum error in MAT of ±4 °C for digital leaf physiognomy and ±5 °C for other methods should be assumed.

Review of Palaeobotany and Palynology, 2001

A growing number of studies use the plant species-speci®c inverse relationship between atmospheri... more A growing number of studies use the plant species-speci®c inverse relationship between atmospheric CO 2 concentration and stomatal density (SD) or stomatal index (SI) as a proxy for paleo-CO 2 levels. A total of 285 previously published SD and 145 SI responses to variable CO 2 concentrations from a pool of 176 C 3 plant species are analyzed here to test the reliability of this method. The percentage of responses inversely responding to CO 2 rises from 40 and 36% (for SD and SI, respectively) in experimental studies to 88 and 94% (for SD and SI, respectively) in fossil studies. The inconsistent experimental responses verify previous concerns involving this method, however the high percentage of fossil responses showing an inverse relationship clearly validates the method when applied over time scales of similar length. Furthermore, for all groups of observations, a positive relationship between CO 2 and SD/SI is found in only #12% of cases. Thus, CO 2 appears to inversely affect stomatal initiation, although the mechanism may involve genetic adaptation and therefore is often not clearly expressed under short CO 2 exposure times.

Proceedings of the Royal Society B: Biological Sciences, 2013

Models generally predict a response in species richness to climate, but strong climate-diversity ... more Models generally predict a response in species richness to climate, but strong climate-diversity associations are seldom observed in long-term (more than 10(6) years) fossil records. Moreover, fossil studies rarely distinguish between the effects of atmospheric CO2 and temperature, which limits their ability to identify the causal controls on biodiversity. Plants are excellent organisms for testing climate-diversity hypotheses owing to their strong sensitivity to CO2, temperature and moisture. We find that pollen morphospecies richness in an angiosperm-dominated record from the Palaeogene and early Neogene (65-20 Ma) of Colombia and Venezuela correlates positively to CO2 much more strongly than to temperature (both tropical sea surface temperatures and estimates of global mean surface temperature). The weaker sensitivity to temperature may be due to reduced variance in long-term climate relative to in higher latitudes, or to the occurrence of lethal or sub-lethal temperatures during the warmest times of the Eocene. Physiological models predict that productivity should be the most sensitive to CO2 within the angiosperms, a prediction supported by our analyses if productivity is linked to species richness; however, evaluations of non-angiosperm assemblages are needed to more completely test this idea.

Proceedings of the National Academy of Sciences, 2010

Proceedings of the National Academy of Sciences, 2008

PLoS ONE, 2012

The degree of leaf dissection and the presence of leaf teeth, along with tooth size and abundance... more The degree of leaf dissection and the presence of leaf teeth, along with tooth size and abundance, inversely correlate with mean annual temperature (MAT) across many plant communities. These relationships form the core of several methods for reconstructing MAT from fossils, yet the direct selection of temperature on tooth morphology has not been demonstrated experimentally. It is also not known if atmospheric CO 2 concentration affects leaf shape, limiting confidence in ancient climate reconstructions because CO 2 has varied widely on geologic timescales. Here I report the results of growing Acer rubrum (red maple) in growth cabinets at contrasting temperature and CO 2 conditions. The CO 2 treatment imparted no significant differences in leaf size and shape, while plants grown at cooler temperatures tended to have more teeth and more highly dissected leaves. These results provide direct evidence for the selection of temperature on leaf shape in one species, and support a key link in many leaf-climate methods. More broadly, these results increase confidence for using leaf shape in fossils to reconstruct paleoclimate.

Nature, 2012

Many palaeoclimate studies have quantified pre-anthropogenic climate change to calculate climate ... more Many palaeoclimate studies have quantified pre-anthropogenic climate change to calculate climate sensitivity (equilibrium temperature change in response to radiative forcing change), but a lack of consistent methodologies produces a wide range of estimates and hinders comparability of results. Here we present a stricter approach, to improve intercomparison of palaeoclimate sensitivity estimates in a manner compatible with equilibrium projections for future climate change. Over the past 65 million years, this reveals a climate sensitivity (in K W 21 m 2 ) of 0.3-1.9 or 0.6-1.3 at 95% or 68% probability, respectively. The latter implies a warming of 2.2-4.8 K per doubling of atmospheric CO 2 , which agrees with IPCC estimates.

The New phytologist, 2011

Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. Ho... more Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. However, most models incorporate a single variable or use traits that are not physiologically or functionally linked to climate, limiting their predictive power. Further, they often underestimate paleotemperature relative to other proxies.