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It would be ‘convenient’ to have a climate solution, where technological innovations fix the problem without any change to current institutions, structures, and lifestyles. However, even though we have some interesting options at lab scale, innovation must be scaled up to make a difference, and it is impossible between now and 2050 for the ‘convenient’ solution to be built at the necessary scale. In addition, there can be no physically meaningful offsets because trees take too long to grow and there are no realistic emissions-negating technologies. This book’s journey to zero emissions reduces technological risk to a minimum by assuming that only technologies that already exist at scale can help, and that they will be deployed only at rates comparable with recent history. This is not ‘convenient’ in that it involves some societal change and therefore we must find the courage to act. However, we can still have a high quality of life, and expand many of the activities we most value.
Amorphous materials transition from solid-like to liquid-like behaviour (yield) under large stresses. Their constituent elements are caged in metastable configurations due to their neighbours. Microscale interactions between these elements lead to a large energy barrier to break the cages and trigger a plastic rearrangement. Thermal fluctuations can alter the yielding point as the elements hop to new configurations in anticipation. This work bridges the gap between molecular-scale physics and bulk rheology in thermal amorphous materials by connecting a classical density functional theory to a thermally activated elastoplastic model (EPM). We use a model system of solvent-free polymer-grafted nanoparticles which show rheological characteristics similar to those of soft glassy materials. We formulate the evolution of the free energy in a deforming array of polymer-grafted nanoparticles to obtain the energy landscape as an input to our EPM. We examine how the apparent yield stress depends on the shape of the energy landscape, thermal fluctuations and the rate of deformation. Our general scaling analyses reveal different regimes of structural relaxation governed by the applied shear rate and the inherent time scale for thermal hops. The complex interplay between mechanical loading and thermal fluctuations is further characterized by performing a variety of shear tests with different deformation history. The proposed framework provides an understanding of the yielding transition by integrating across a vast range of length and time scales.
In this chapter, we consider hope as the supremely political virtue, which is to say one that helps us to venture great things in the business of building a shared life. We also consider questions of scale, and the idea that we should be happy to ‘start small’ and attend, first of all, and even mainly, to the challenges and opportunities that lie closest to hand, in our homes, localities and places of work.
This paper investigates the nonlinear dynamics of horizontal shear instability in an incompressible, stratified and rotating fluid in the non-traditional $f$-plane, i.e. with the full Coriolis acceleration, using direct numerical simulations. The study is restricted to two-dimensional horizontal perturbations. It is therefore independent of the vertical (traditional) Coriolis parameter. However, the flow has three velocity components due to the horizontal (non-traditional) Coriolis parameter. Three different scenarios of nonlinear evolution of the shear instability are identified, depending on the non-dimensional Brunt–Väisälä frequency $N$ and the non-dimensional non-traditional Coriolis parameter $\tilde {f}$ (non-dimensionalised by the maximum shear), in the range $\tilde {f}\lt N$ for fixed Reynolds and Schmidt numbers $ \textit{Re}=2000$, $ \textit{Sc}=1$. When the stratification is strong $N\gg 1$, the shear instability generates stable Kelvin–Helmholtz billows like in the traditional limit $\tilde {f}=0$. Furthermore, when $N\gg 1$, the governing equations for any $\tilde {f}$ can be transformed into those for $\tilde {f}=0$. This enables us to directly predict the characteristics of the flow depending on $\tilde {f}$ and $N$. When $N$ is around unity and $\tilde {f}$ is above a threshold, the primary Kelvin–Helmholtz vortex is destabilised by secondary instabilities but it remains coherent. For weaker stratification, $N\leqslant 0.5$ and $\tilde {f}$ large enough, secondary instabilities develop vigorously and destroy the primary vortex into small-scales turbulence. Concomitantly, the enstrophy rises to high values by stretching/tilting as in fully three-dimensional flows. A local analysis of the flow prior to the onset of secondary instabilities reveals that the Fjørtoft necessary condition for instability is satisfied, suggesting that they correspond to shear instabilities.
The proponents of the ‘convenient solution’ discussed in Chapter 3 see the cost of climate action as one of government investment in new infrastructure. However, as there is not time for this to scale sufficiently, we must think differently about cost. Voluntarily restraining ourselves from emitting activities may save us money, but in most cases at present, purchasing equipment compatible with zero emissions costs more than the emitting alternative. Eventually, governments will legislate to ban emissions, by which time we will only compare the costs of different emissions-free alternatives. On the journey to that point, governments can aim to help us change by subsidising zero-emissions projects or taxing emitting activities. Carbon pricing has proved to be politically impossible, due to competition in trade and the high costs it would place on householders. Instead, we can all re-think the timescale of our purchasing decisions and recognise that paying for the higher costs of emissions-free options today is in reality an investment in the future, like a pension or savings account, aiming to avoid the far worse costs of a global war over food.
Making a safe climate for the generations that follow us requires that we reduce our emissions to zero, at least at a steady rate, and by 2050. We can take five steps to deliver this change: understand our emissions; anticipate the moments when we take important decisions about big purchases; gather good information about the way we cause emissions in daily life; reflect on how our emissions trade off with other priorities; and re-think the main priorities and goals of our life. Living with zero emissions does not require misery, but requires restraint that can be life-enhancing, and the seed for new creativity and fulfilment.
The real threat of climate change is not about temperature, sea levels, wind or fire. It is about food. Due to global warming, the world’s total food supply will reduce to be less than total demand. This will eventually lead to a world war over food and there is a serious possibility that this could occur in this century. By 2010, we were halfway to accumulating in the atmosphere half the greenhouse gas emissions that are likely to tip us into a food war. If global annual emissions continue to increase at current rates, the atmosphere will be ‘full’ by around 2045, and starvation and war will follow. To date, our response has involved more talking than serious action, and while we have begun to make some good changes, they are at far smaller scale than required. However, we can choose to live well and soon with zero emissions, and we can prosper while we do so. This book is a hopeful one, but our hope is based on the reality of what is possible in the time available, not on dreaming that inaction now will lead to an easier option later.
For three decades, politicians have promised that new technologies will solve climate change, but they haven’t emerged at meaningful scale. So, instead we must act with technologies we already have, which will involve some restraint. However, knowing this fact does not of itself motivate change. Instead, we present a new framing of our response to climate change as an expression of our values. The restraint, perhaps lasting for two or three decades, that is required to deal with climate change is not only a sacrifice. Embracing it can also help us to find a different good life, as responsible and joyful custodians of creation. The seven virtues inspire us to lift up our heads, be honest about the options and motivate our action, and encourage us to find a safe climate, in good faith.
With this chapter we move from the ‘cardinal’ virtues of courage, prudence, temperance and justice to the ‘theological’ virtues of faith, hope and love. In particular, we ask what faith – belief in God, and in the wider Christian creed – means for what we have already considered. We see that, far from encouraging us to disregard justice and responsibility in this life for the sake of the next, it teaches us to see the world as God’s creation and other human beings as bearing God’s image, spurring us to action with all the more energy.
Recent theoretical and experimental investigations have revealed that flapping compliant membrane wings can significantly enhance propulsive performance (e.g. Tzezana & Breuer J. Fluid Mech., 2019, vol. 862, pp. 871–888) and energy harvesting efficiency (e.g. Mathai et al. J. Fluid Mech., 2022, vol. 942, p. R4) compared with rigid foils. Here, we numerically investigate the effects of the in-plane stretching stiffness (or aeroelastic number), $K_{\!S}$, the flapping frequency, ${\textit{St}}_c$, and the pitching amplitude, $\theta _0$, on the propulsive performance of a compliant membrane undergoing combined heaving and pitching in uniform flow. Distinct optimal values of $K_{\!S}$ are identified that respectively maximise thrust and efficiency: thrust can be increased by 200 %, and efficiency by 100 %, compared with the rigid case. Interestingly, these optima do not occur at resonance but at frequency ratios (flapping to natural) below unity, and this ratio increases with flapping frequency. Using a force decomposition based on the second invariant of the velocity gradient tensor $Q$, which measures the relative strength between the rotation and deformation of fluid elements, we show that thrust primarily arises from $Q$-induced and body-acceleration forces. The concave membrane surface can trap the leading-edge vortex (LEV) generated during the previous half-stroke, generating detrimental $Q$-induced drag. However, moderate concave membrane deformation weakens this LEV and enhances body-acceleration-induced thrust. Thus, the optimal $K_{\!S}$ for maximum thrust occurs below resonance, balancing beneficial deformation against excessive drag. Furthermore, by introducing the membrane’s deformation into a tangential angle at the leading edge and substituting it into an existing scaling law developed for rigid plates, we obtain predictive estimates for the thrust and power coefficients of the membrane. The good agreement confirms the validity of this approach and offers insights for performance prediction.
Minute hybodont shark teeth from uppermost Albian–lower Cenomanian (mid-Cretaceous) continental deposits of Djebel Amour (Saharan Atlas, Algeria) are described. They are assigned to a new genus and species of Lonchidiidae, Lonchidionoides trifurcatum. Similar teeth recently reported from the Early Cretaceous of Brazil are here referred to as Lonchidionoides sp. The heterodont dentition of Lonchidionoides is characterized by clutching anterior teeth with a tricuspid crown and larger crushing posterior teeth with less individualized cusps. Lateral teeth show an intermediate morphology. The two occurrences of this non-marine hybodontiform genus may reflect the existence of a large ancestral distribution area that was divided during the opening of the South Atlantic, as previously suggested for several groups of cartilaginous and bony fishes.
If we are realistic about deployment rates, we can anticipate that by 2050, we will be able to access about half the energy we would like, all of which will be emissions-free electricity. We will have very little carbon storage and cannot draw on any more biomass. This means that delivering a safe climate requires electrifying everything, halving our demand for energy and phasing out the seven non-energy activities that lead to emissions: deforestation, fugitive emissions, sheep and cows, most fertilisers, aeroplane contrails, and conventional cement and rice. Eventually these limits will be imposed on us as constraints through health and safety regulation, but for now they require voluntary restraint that we must embrace by choice if we are concerned about climate safety. However, we can live great lives within this reduced budget.
Seductive messaging about ‘convenient’ technological solutions have prevented us recognising and acting on the need for restraint as a core component of climate action, yet restraint has in the past led to faster change than technological innovation. The actions that allow us to deliver a safe climate are specified in the chapter and are highly specific. At home, we should aim to switch from gas boilers to electric heat pumps, from petrol to electric cars, to phase out our use of fossil aeroplanes and certain key foods, and we can also reduce our total requirement for energy. In teams, at work or in other contexts, we can pursue the same goals, while also aiming to reduce the construction of new large objects (buildings, vehicles, infrastructure or large equipment) and to support suppliers and customers on the same journey. As lobbyists, individually or in groups, we can influence politicians and business leaders to make it easier for us to follow the key actions that lead to zero emissions.
The Pliocene marine mammal fauna is the best sampled and most intensely studied in the world, preserving many modern genera of cetaceans. Today, harbor porpoises (Phocoena phocoena Linnaeus, 1758) as well as other extant genera of odontocetes (Tursiops, Stenella, Lagenorhynchus, Physeter, Pseudorca, Globicephala) inhabit the western North Atlantic. Many similar forms were reported from the early Pliocene Yorktown Formation—except for porpoises (Phocoenidae), which are key members of modern marine ecosystems, but surprisingly absent from the fossil record in this region. Hence, there are unresolved questions concerning the dispersal and biogeography of this group. In this study, we report the first fossil Phocoenidae from the western North Atlantic, a series of four isolated periotics of Phocoena sp. from Pliocene strata near Charleston, South Carolina, USA, and describe the bony labyrinth of one of these. The periotics show several external anatomical characters diagnostic for phocoenids, and we used μCT scanning to reconstruct a three-dimensional model of the bony labyrinth to further test this interpretation. We performed 13 measurements on the model surface and compared those with a sampling of other phocoenid specimens. By assessing the taxonomic affinity of the fossils, we gain a better understanding of marine ecosystems through a dynamic interval of the Neogene and shed light on the origins and dispersal of a major odontocete clade.
Biodegradable microplastics (BMPs) are reported to have a priming effect on soil organic matter (SOM) decomposition. However, their impact on the turnover of specific SOM components, especially nitrogen (N)-containing ones, remains unclear. Given the wide use of poly(butylene adipate-co-terephthalate) (PBAT) in agricultural films and the crucial role of amino sugar N-acetylglucosamine (NAG) in microbial necromass, the effects of PBAT BMPs on NAG decomposition in soil were investigated. We found that PBAT accelerated the decomposition of NAG, with specific effects varying considerably in the two soils examined (Yingtan soil and Nanjing soil). Microbial biomass and metagenomic sequencing analyses revealed that, in Yingtan soil with low available N (6 mg kg-1), PBAT promoted the incorporation of NAG into living microbial biomass, and increased the abundance of NAG phosphorylation and isomerization genes (amgK and glmM). In Nanjing soil with high available N (127 mg kg-1), chitin synthase gene (CHS1) abundance decreased and there was no significant change in microbial biomass, indicating the extra NAG decomposed in PBAT-treated soils might mainly enter the glycolysis pathway to generate energy rather than synthesizing new cells. Potential PBAT degraders enriched were also NAG degraders, suggesting carbon-rich PBAT selected for microbes that could obtain N from amino sugars.