efore the pandemic, many academics were frequent flyers. We travelled to conferences and board meetings, to conduct fieldwork, to visit collaborators and to give seminars and lectures. Many of us took multiple long-haul flights per year and have accrued thousands of air miles.Yet we are also acutely aware of the negative impacts of travel. Before the outbreak of COVID-19, the transport sector as a whole accounted for 24% of annual global emissions of carbon dioxide. Aviation was responsible for about 3%, road transport 18% and rail less than 1% (ref. 1).The vast majority of flights were taken by a small minority of frequent flyers. In the United Kingdom, 15% of the population was responsible for 70% of the flights 2 . There are clear inequalities in who travels by air 3 .Academics are part of this hypermobile lifestyle. The sum total of travel associated with attendance at one large academic conference can release as much CO 2 as an entire city in a Emissions associated with large academic meetings could be slashed by boosting virtual attendance and regional hubs, new calculations suggest. Some 28,000 people travelled to the American Geophysical Union's 2019 Fall Meeting, resulting in 80,000 tonnes of carbon emissions.

Growth in aviation contributes more to global warming than is generally appreciated because of the mix of climate pollutants it generates. Here, we model the CO2 and non-CO2 effects like nitrogen oxide emissions and contrail formation to analyse aviation’s total warming footprint. Aviation contributed approximately 4% to observed human-induced global warming to date, despite being responsible for only 2.4% of global annual emissions of CO2. Aviation is projected to cause a total of about 0.1 °C of warming by 2050, half of it to date and the other half over the next three decades, should aviation’s pre-COVID growth resume. The industry would then contribute a 6%–17% share to the remaining 0.3 °C–0.8 °C to not exceed 1.5 °C–2 °C of global warming. Under this scenario, the reduction due to COVID-19 to date is small and is projected to only delay aviation’s warming contribution by about five years. But the leveraging impact of growth also represents an opportunity: aviation’s contribution to further warming would be immediately halted by either a sustained annual 2.5% decrease in air traffic under the existing fuel mix, or a transition to a 90% carbon-neutral fuel mix by 2050.

The need for high-precision calculations with 64-bit or 32-bit floating-point arithmetic for weather and climate models is questioned. Lower-precision numbers can accelerate simulations and are increasingly supported by modern computing hardware. This paper investigates the potential of 16-bit arithmetic when applied within a shallow water model that serves as a medium complexity weather or climate application. There are several 16-bit number formats that can potentially be used (IEEE half precision, BFloat16, posits, integer, and fixed-point). It is evident that a simple change to 16-bit arithmetic will not be possible for complex weather and climate applications as it will degrade model results by intolerable rounding errors that cause a stalling of model dynamics or model instabilities. However, if the posit number format is used as an alternative to the standard floating-point numbers, the model degradation can be significantly reduced. Furthermore, mitigation methods, such as rescaling, reordering, and mixed precision, are available to make model simulations resilient against a precision reduction. If mitigation methods are applied, 16-bit floating-point arithmetic can be used successfully within the shallow water model. The results show the potential of 16-bit formats for at least parts of complex weather and climate models where rounding errors would be entirely masked by initial condition, model, or discretization error. Plain Language Summary 64-bit floating-point numbers are the standard number format for scientific computing in fluid dynamics, which allows for very precise calculations with negligible rounding errors. The need for calculations at this precision level has been questioned for weather and climate models, as errors are caused primarily by insufficient observations or deficiencies of the models themselves. Reducing numerical precision can accelerate simulations and low-precision number formats are increasingly supported by modern computers. This paper investigates the potential of low numerical precision with numbers that only use 16 bit of information, when applied within simulations of weather and climate. The different number formats are applied in a two-dimensional oceanic or atmospheric circulation model. There are several 16-bit number formats that can potentially be used, all of which have considerably larger rounding errors than the standard 64-bit numbers. A simple change to 16 bits for all calculations will not be possible as it will degrade simulation results. However, if mitigation methods are applied, 16-bit calculations can be used successfully within the applications of this paper. The results show the potential of 16-bit number formats for at least parts of complex weather and climate models.

Energy budget-based backscatter in a shallow water model of a double gyre basin, Ocean Modelling (2018), doi: https://doi.Highlights • Generalization of the energy budget backscatter for a sub-grid eddy parameterization • Rossby number-dependent dissipation scaling controls the forward energycascade • Parameterization is tested successfully in a double gyre basin shallow water model • The energy cycle of the model is considerably improved at low computational cost AbstractThe parameterization of sub-grid scale processes is one of the key challenges towards improved numerical simulations of the atmospheric and oceanic circulation. Numerical weather prediction models as well as climate models would benefit from more sophisticated turbulence closures that allow for less spurious dissipation at the grid-scale and consequently higher and more realistic levels of eddy kinetic energy (EKE). Recent studies propose to use a hyperviscous closure in combination with an additional deterministic forcing term as a negative viscosity to represent backscatter of energy from unresolved scales. The sub-grid EKE is introduced as an additional prognostic variable that is fed by dissipation at the grid scale, and enables recycling of EKE via the backscatter term at larger scales. This parameterization was previously shown to work well in zonally re-entrant channel configurations. Here, a generalization in the form of a Rossby number-dependent scaling for the strength of the backscatter is introduced to represent the emergence of a forward energy-cascade in unbalanced flows near the boundaries. We apply the parameterization to a shallow water model of a double gyre basin and provide evidence for its general applicability.In terms of mean state and variability, a low resolution model is considerably ⇤ Corresponding author improved towards a high resolution control run at low additional computational cost.