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Significance

Research blending climate models with physiological data has projected that large geographical areas may soon experience heat stress exceeding limits for human thermoregulation. Modeled thermoregulatory limits were derived from laboratory research using thermal-step protocols. Despite the growing popularity of this technique, its principal assumption—that core temperature inflection during stepped increases in heat or humidity demarcates thermoregulatory upper limits—has not been validated. By exposing participants for 9 h to conditions just above or below the core temperature inflection point, we found that thermal-step protocols effectively identify the conditions above which thermoregulation is impossible. Our findings provide critical support for heat stress projections incorporating empirical tolerance limits. We also provide data characterizing physiological strain during prolonged, uncompensable heat exposure.

Abstract

Recent projections suggest that large geographical areas will soon experience heat and humidity exceeding limits for human thermoregulation. The survivability limits modeled in that research were based on laboratory studies suggesting that humans cannot effectively thermoregulate in wet bulb temperatures (Twb) above 26 to 31 °C, values considerably lower than the widely publicized theoretical threshold of 35 °C. The newly proposed empirical limits were derived from the Twb corresponding to the core temperature inflection point in participants exposed to stepped increases in air temperature or relative humidity in a climate-controlled chamber. Despite the increasing use of these thermal-step protocols, their validity has not been established. We used a humidity-step protocol to estimate the Twb threshold for core temperature inflection in 12 volunteers. To determine whether this threshold truly demarcates the Twb above which thermoregulation is impossible, each participant was subsequently exposed to Twb above (~33.7 °C, Tabove) and below (~30.9 °C, Tbelow) their respective inflection point (~32.3 °C, Twb) for up to 9 h (in random order). Core temperature rose continuously in Tabove. It was projected that core temperatures associated with heat stroke (40.2 °C) would occur within 10 h. While Tbelow was also uncompensable, the core temperature rate of rise was considerably lower than in Tabove such that it would take >24 h to reach 40.2 °C. Our study supports thermal-step protocols as an effective technique for evaluating survivability limits for heat exposure and provides a direct assessment of the limits of human thermoregulation.

Bend down on a coastal beach or a riverbank and you will inevitably spot them. A quick look into a gutter and there they are. Drag a plankton net into a lake, river, or ocean, and you will easily collect them. Plastic debris is everywhere. It knows no borders, transferring the thousands of chemicals that compose it—or attach themselves to its surface—from one ecosystem to another, along with the microorganisms (including pathogens) that colonize it.

By dedicating this special issue of Environmental Science and Pollution Research (ESPR) to the source, fate, and effects of plastic litters in the European land-sea continuum, we aimed to bring together scientists from different fields of expertise to improve our understanding of plastic pollution across ecosystem boundaries. Most of them took part in the Mission Tara Microplastics conducted over 7 months to investigate plastic pollution across nine major European rivers. They discovered that the median concentration of large microplastics (LMPs, 500 µm–5 mm)—the most studied size fraction to date—was lower in European rivers than in other global regions, while small microplastics (SMPs, 25–500 µm) were found to dominate in mass, with SMP/LMP ratios reaching up to 1000:1 in some rivers. Results were also coming from other field campaigns, including a comparison between the two most plastic-polluted zones of the world ocean (Tara Mediterranean and Tara Pacific). The use of a 3D Lagrangian simulation of the dispersion of riverine microplastics into the Mediterranean Sea indicated that 65% of river inputs consist of floating microplastics drifting in the surface layer and 35% of dense MPs sinking to deeper layers, with further dispersion at sea driven by mesoscale and sub-mesoscale structures.

A citizen science initiative with schoolchildren Plastique à la loupe was also introduced, which compared for the first time the distribution of different litter sizes (macrolitter and meso- and microplastics) over a large set of riverbanks and coastal beaches sampled in France. Special emphasis was also given to the mismanaged litters in French urban areas, with articles depicting their composition, spatiotemporal variations, sources, and transport dynamics in cities of all sizes. An example of the physiological impact of microplastics was given by exposing beached plastic pellets to mussels, key intertidal bioengineers, and filter-feeders that are particularly susceptible to both plastic ingestion and release of potentially toxic mixtures of intrinsic and extrinsic chemical compounds. Finally, a pan-European study of the bacterial plastisphere revealed for the first time the presence of a virulent human pathogenic bacterium (Shewanella putrefaciens) detected on microplastics in a river. A clear distinction between plastisphere metabolomes and diversity from freshwater and marine water was found in most of the river-to-sea continuum, helping to mitigate the risk of pathogens transfer between freshwater and marine systems. With the United Nations global plastic treaty on the horizon, this special issue emphasizes the need to unite interdisciplinary expertise to deepen our understanding of plastic pollution and to conduct reliable ecological risk assessments across ecosystem boundaries.

Abstract

Inland waters are an important resource, a highly diverse habitat, and a key component of global biogeochemical cycles. Oxygen plays a major role in inland-water ecosystem functioning, but long-term changes in its cycling remain unknown. Here, we quantify global inland-water oxygen production, consumption, and exchange with the atmosphere during 1900–2010 using a spatially explicit, mass-balanced, mechanistic model that takes into account changes in climate, hydrology, human activities, and the coupled biogeochemical (oxygen-nutrient-organic matter) dynamics. The model results show that global inland-water oxygen turnover increased during 1900–2010: production from 0.16 to 0.94 Pg year−1 and consumption from 0.44 to 1.47 Pg year−1. Inland waters overall remained heterotrophic and a sink of atmospheric oxygen. Direct human perturbations (changes in hydrology and nutrient supply) were more important in increasing oxygen turnover than indirect effects via warming.

Abstract

Bitcoin mines—massive computing clusters generating cryptocurrency tokens—consume vast amounts of electricity. The amount of fine particle (PM2.5) air pollution created because of their electricity consumption and its effect on environmental health is pending. In this study, we located the 34 largest mines in the United States in 2022, identified the electricity-generating plants that responded to them, and pinpointed communities most harmed by Bitcoin mine-attributable air pollution. From mid-2022 to mid-2023, the 34 mines consumed 32.3 terawatt-hours of electricity—33% more than Los Angeles—85% of which came from fossil fuels. We estimated that 1.9 million Americans were exposed to ≥0.1 μg/m3 of additional PM2.5 pollution from Bitcoin mines, often hundreds of miles away from the communities they affected. Americans living in four regions—including New York City and near Houston—were exposed to the highest Bitcoin mine-attributable PM2.5 concentrations (≥0.5 μg/m3) with the greatest health risks.

Abstract

Homo sapiens has evolved to reproduce exponentially, expand geographically, and consume all available resources. For most of humanity’s evolutionary history, such expansionist tendencies have been countered by negative feedback. However, the scientific revolution and the use of fossil fuels reduced many forms of negative feedback, enabling us to realize our full potential for exponential growth. This natural capacity is being reinforced by growth-oriented neoliberal economics—nurture complements nature. Problem: the human enterprise is a ‘dissipative structure’ and sub-system of the ecosphere—it can grow and maintain itself only by consuming and dissipating available energy and resources extracted from its host system, the ecosphere, and discharging waste back into its host. The population increase from one to eight billion, and >100-fold expansion of real GWP in just two centuries on a finite planet, has thus propelled modern techno-industrial society into a state of advanced overshoot. We are consuming and polluting the biophysical basis of our own existence. Climate change is the best-known symptom of overshoot, but mainstream ‘solutions’ will actually accelerate climate disruption and worsen overshoot. Humanity is exhibiting the characteristic dynamics of a one-off population boom–bust cycle. The global economy will inevitably contract and humanity will suffer a major population ‘correction’ in this century.

Keywords: overshoot; exceptionalism; human nature; cognitive obsolescence; exponential growth; ‘K’ strategist; over population; over consumption; climate change; energy transition; dissipative structure; civilizational collapse; population correction