Progress in Physical Geography: Earth and Environment

We analyse the ‘three flaws’ to potentially defining a formal Anthropocene geological time unit as advanced by Ruddiman (2018). (1) We recognize a long record of pre-industrial human impacts, but note that these increased in relative magnitude slowly and were strongly time-transgressive by comparison with the extraordinarily rapid, novel and near-globally synchronous changes of post-industrial time. (2) The rules of stratigraphic nomenclature do not ‘reject’ pre-industrial anthropogenic signals – these have long been a key characteristic and distinguishing feature of the Holocene. (3) In contrast to the contention that classical chronostratigraphy is now widely ignored by scientists, it remains vital and widely used in unambiguously defining geological time units and is an indispensable part of the Earth sciences. A mounting body of evidence indicates that the Anthropocene, considered as a precisely defined geological time unit that begins in the mid-20th century, is sharply distinct from the Holocene.

This paper responds to and supports the earlier ‘Three Flaws’ paper by William Ruddiman (this journal, 2018). It builds upon his critique of the method used by the Anthropocene Working Group in determining the start date of the Anthropocene. While chronostratigraphy is acknowledged as the best means of establishing a framework for the division of deep time – on geological timescales of millions of years – it is argued that the method is unsuitable for use on archaeological and historical timescales. Close proximity in time between the chronostratigraphic observer and the stratigraphic boundary in question renders the placement of a precisely defined, globally synchronous timeline onto highly time-transgressive evidence inappropriate on these scales of analysis. Application of the method hinders rather than helps understanding of the role of human impact on Earth System change; it leads to a loss of the bigger picture and to relative neglect of the crucial evidence provided by humanly modified ground – the missing strata in most chronostratigraphic accounts of the Anthropocene start. A more ground-up approach is called for. Recognition of humans as geological agents needs to be accompanied by recognition of the distinctive traces of human agency in the ground, which are unprecedented in the stratigraphic records of earlier geological time periods.

In 2015, the journal Science invited me to comment on the start of anthropogenic change. That request was likely related to the fact that the Anthropocene Working Group (AWG) of the International Commission of Stratigraphy was thinking of choosing a formal start date for the Anthropocene at or after 1950. Joined by three co-authors (Ruddiman et al., 2015), we emphasized the many near-global anthropogenic changes that preceded 1950 by centuries to millennia. Early in 2018, Progress in Physical Geography (PiPG) published a more extended critique of mine regarding this possible AWG action. I noted three flaws in choosing 1950 as the formal start date. In response to this challenge, the AWG recently submitted two draft papers to PiPG, one rebutting my 2018 paper (Zalasiewicz et al.), and one supporting and extending it (Edgeworth et al.). The first part of this reply elaborates on the flaws cited in my 2018 PiPG paper, incorporating comments from Edgeworth et al. The second part addresses the criticisms in Zalasiewicz et al.

The impact of land cover on lightning and convective precipitation in the summertime over Europe was analysed using five-year data. Lightning data were obtained with the Optical Transient Detector (OTD) at a 0.5° × 0.5° spatial resolution and the convective precipitation data were calculated by the NCEP/DOE AMIP-II Reanalysis at a ∼1.9° × 1.9° spatial resolution. Data concerning land cover were obtained from the Global Land Cover Facility, although the original 14 categories were grouped into seven categories (water, forest, shrubland, grassland, cropland, bare ground and urban). For all latitude ranges, forested areas tend to increase convective activity during the warm period of the year, and the general effect of shrubland areas is to suppress convective activity. The behaviour of convection in relation to grasslands and croplands depends on latitude. At low latitudes both vegetation types tend to increase convection during the summer. At high latitudes, grassland and cropland areas appear to be associated with the opposite effect in relation to convection: grass suppresses and crops enhance it. Finally, bare soil tends to decrease convective activity. These results seem to be related to the impact of vegetation on soil moisture and roughness. In general, vegetation areas associated with high soil moisture contents and high values in roughness length tend to enhance convective activity.

This review and analysis illustrates that the spatial distribution and temporal clustering of tornadoes in the United States are changing. Tornado activity is increasing throughout the Southeast and in the southern portion of the Midwest and is decreasing throughout the southern and northwestern portions of the Great Plains and in the northern Midwest. This eastward shift is seen in tornado density maps, regional and gridded trends, and in an eastward shift of the mean center of tornadoes at the annual scale and in summer. The mean centers of tornado activity in other seasons are rather insensitive to these changes. Tornadoes are also clustering on fewer days in the year, and days with few tornadoes are becoming less common whereas days with many tornadoes are becoming more common. These concurrent and opposing trends are subsequently altering the frequency distribution of tornado days. The seasonality of these big tornado days also appears to be changing, as their increase in frequency is greatest in the fall and winter. Lastly, the increasing frequency of these big tornado days, which are most common in the Southeast and southern Midwest, contributes to the documented eastward shift in tornado activity.

Support practices (SPs) influence the magnitude of soil loss and can be readily influenced by human interventions to mitigate soil loss. The SPs factor is expressed as the P-factor in the widely used soil erosion model – the universal soil loss equation (USLE) – and its revised version. Although the effects of SPs on soil erosion are well recognized, the quantification of the P-factor for soil loss modeling remains challenging. This limitation of the P-factor particularly restricts the applicability of USLE-based models at large scales. Here, we analyzed the P-factor values in USLE-based models from 196 published articles. The results were as follows: (a) an increasing trend in the number of studies has been observed in recent years, especially at large scales; (b) the P-factor values for paddy fields, orchards, and croplands were 0.16 ± 0.15, 0.47 ± 0.12, and 0.49 ± 0.21, respectively, and in terms of different types of SPs, the P-factor values for terracing, contouring, and strip-cropping were 0.28 ± 0.18, 0.52 ± 0.24, and 0.49 ± 0.28, respectively; (c) various methods have been developed for P-factor qualification, although the methods that consider SP conditions were most frequently used in studies with relatively smaller areas (< 100 km²), suggesting that USLE-based models are in need of improvement via the quantification of the P-factor, particularly with respect to the regional and global scale; and (d) further improvements of the P-factor for soil erosion modeling should concentrate on building P-factor datasets at the regional level according to data on the effectiveness of SPs on soil loss control based on field experiments in published articles, using advanced image processing techniques based on higher-resolution satellite imagery and developing proxy indicators for P-factors at large scales.

Urban climate risks have a wide range of impacts on the health of more than 50% of the world’s population, which is a critical issue relating to climate change. To support urban climate study and categorise different urban environments and their atmospheric impacts in a consistent way, the Local Climate Zone (LCZ) classification scheme has been developed. The World Urban Database and Access Portal Tools project aims to map the LCZ of cities across the globe. However, previous classification approaches based on satellite images have limitations regarding the characterisation of three-dimensional features such as building heights. This study aims to apply convolutional neural networks to classify LCZ types based on ground-level images, which can provide more detail of the urban environments. Validation results have shown an overall accuracy of 69.6%. The new method outperformed previous satellite-based studies for classifying the LCZ types Compact Mid-rise, Sparsely Built, Heavy Industry, and Bare Rock or Paved.

Barrier islands are dynamic ecosystems that change gradually from coastal processes, including currents and tides, and rapidly from episodic events, such as storms. These islands provide many important ecosystem services, including storm protection and erosion control to the mainland, habitat for fish and wildlife, and tourism. Habitat maps, developed by scientists, provide a critical tool for monitoring changes to these dynamic ecosystems. Barrier island monitoring often requires custom habitat maps due to several factors, including island size and the classification of unique geomorphology-based habitats, such as beach, dune, and barrier flats. In this study, we reviewed barrier-island-specific habitat mapping efforts and highlighted common habitat class types, source data, and mapping approaches. We also developed a framework for mapping geomorphology-based barrier island habitats using a rule-based, geographic object-based image analysis approach, which included the use of field data, tide data, high-resolution orthophotography, and lidar data. This framework integrates several barrier island mapping advancements with regard to the use of landscape position information for automated dune extraction and the use of Monte Carlo analyses for the treatment of elevation uncertainty for elevation-dependent habitats. Specifically, we used the uncertainty analyses to refine automated dune delineation based on elevation relative to extreme storm water levels and to increase the accuracy of intertidal and supratidal/upland habitat delineation. We found that dune extraction results were enhanced when elevation relative to storm water levels and visual interpretation were also applied. This framework could also be applied to beach–dune systems found along a mainland.

“The Anthropocene” currently serves as a framework to acknowledge global human influences on the earth systems. Different prominent authors call for geographers and especially physical geographers to intensify their involvement in the discussions on the theme. A bibliometric analysis shows that geographers are already one of the leading contributors to the keyword Anthropocene in journal articles. While we generally support the standpoint of increased engagement with the topic, we want to emphasize that we need to do more than only attaching the “Anthropocene” label to our daily research practice. A critical engagement with and reflection of the research questions and contexts is needed to play a vital role as discussant in the debate. We should take advantage of the diverse themes, topics and viewpoints of our subject by actively following a more critical approach to our research practices in order to find those geographic ties that join us and our discipline and that enable us to contribute more substantially to the Anthropocene debate.

Although one of the most studied organisms in other disciplines, the role of birds as zoogeomorphic agents has been somewhat overlooked in geography literature. Bird nests serve as a manifestation of the reciprocal relationships that birds have with their environment. Dr Nicholas E. Collias’s “The evolution of nests and nest-building in birds”, published in American Zoologist (1964), was one of the first to hypothesize the intimate connection between bird nests and their landscapes. Researchers interested in understanding the role birds have as zoogeomorphic agents should view Collias (1964) as an essential resource for information and inspiration for further exploration.