The role of enhanced rock weathering deployment with agriculture in limiting future warming and protecting coral reefs

Abstract: Meeting the net-zero carbon emissions commitments of major economies by mid-century requires large-scale deployment of negative emission technologies (NETs). Terrestrial enhanced rock weathering on croplands (ERW) is a NET with co-benefits for agriculture, soils and ocean acidification that creates opportunities for generating income unaffected by diminishing carbon taxes as emissions approach net-zero. Here we show that ERW deployment with croplands to deliver net 2 Gt CO2 yr−1 removal approximately doubles the probability of meeting the Paris 1.5 °C target at 2100 from 23% to 42% in a high mitigation Representative Concentration Pathway 2.6 baseline climate. Carbon removal via carbon capture and storage (CCS) at the same rate had an equivalent effect. Co-deployment of ERW and CCS tripled the chances of meeting a 1.5 °C target (from 23% to 67%), and may be sufficient to reverse about one third of the surface ocean acidification effect caused by increases in atmospheric CO2 over the past 200 years. ERW increased the percentage of coral reefs above an aragonite saturation threshold of 3.5 from 16% to 39% at 2100, higher than CCS, highlighting a co-benefit for marine calcifying ecosystems. However, the degree of ocean state recovery in our simulations is highly uncertain and ERW deployment cannot substitute for near-term rapid CO2 emissions reductions

Impact of negative and positive CO₂ emissions on global warming metrics using an ensemble of Earth system model simulations

The benefits of implementing negative emission technologies in the global warming response to cumulative carbon emissions until the year 2420 are assessed following the shared socioeconomic pathway (SSP) 1-2.6, the sustainable development scenario, with a comprehensive set of intermediate-complexity Earth system model integrations. Model integrations include 86 different model realisations covering a wide range of plausible climate states. The global warming response is assessed in terms of two key climate metrics: the effective transient climate response to cumulative CO2 emissions (eTCRE), measuring the surface warming response to cumulative carbon emissions and associated non-CO2 forcing, and the effective zero emissions commitment (eZEC), measuring the extent of any continued warming after net-zero CO2 emissions are reached. The transient climate response to cumulative CO2 emissions (TCRE) is estimated as 2.2 K EgC−1 (median value) with a 10 %–90 % range of 1.75 to 3.13 K EgC−1 in 2100, approximated from the eTCRE by removing the contribution of non-CO2 forcing. During the positive emission phase, the eTCRE decreases from 2.71 (2.0 to 3.65) to 2.61 (1.91 to 3.62) K EgC−1 due to a weakening in the dependence of radiative forcing on atmospheric carbon, which is partly opposed by an increasing fraction of the radiative forcing warming the surface as the ocean stratifies. During the net negative and zero emission phases, a progressive reduction in the eTCRE to 2.0 (1.39 to 2.96) K EgC−1 is driven by the reducing airborne fraction as atmospheric CO2 is drawn down mainly by the ocean. The model uncertainty in the slopes of warming versus cumulative CO2 emissions varies from being controlled by the radiative feedback parameter during positive emissions to being affected by carbon-cycle parameters during net negative emissions, consistent with the drivers of uncertainty diagnosed from the coefficient of variation of the contributions in the eTCRE framework. The continued warming after CO2 emissions cease and remain at zero gives a model mean eZEC of −0.03 K after 25 years, which decreases in time to −0.21 K at 90 years after emissions cease. However, there is a spread in the ensemble with a temperature overshoot occurring in 20 % of the ensemble members at 25 years after cessation of emissions. If net negative emissions are included, there is a reduction in atmospheric CO2 and there is a decrease in temperature overshoot so that the eZEC is positive in only 5 % of the ensemble members. Hence, incorporating negative emissions enhances the ability to meet climate targets and avoid risk of continued warming after net zero is reached

Development of an optimisation framework for integrated planning of the renewable energy and water supply

Urbanisation, population growth, and economic development have turned cities into largest water resources consumers. The adverse effect of climate change adds even more pressure on the existing water resources and makes it inevitable to consider drought-proof technologies such as desalination to supply the increasing urban water demand. However, the energy intensity of these technologies questions the sustainability of their long-term application and highlights the necessity of considering renewable energy sources to meet their energy demand. In land-restricted urban areas, electricity from residential rooftop grid-connected photovoltaics (PVs) is a promising clean energy source, which can contribute to the urban energy mix. Although, the intermittency of the surplus output from PV systems is a barrier for a higher potential capacity of their installation. This surplus energy is a result of the mismatch between energy generation and demand occurring during the day in the residential sector. This study aims to address both issues of sustainable water supply and surplus PV output intermittency in the context of the integrated water and energy management. Different water supply system components are considered as deferrable loads exhausting surplus PV output at the time of its generation. Accordingly, the optimal decisions for a desalination-based water supply system driven by grid electricity and surplus PV output (hybrid energy sources) are achieved using mathematical optimisation modelling supported by three tools: geographical information system (GIS), system advisor model (SAM), and Excel. The linear programming model is first developed for the optimal scheduling of the integrated system and then extended as a mixed integer linear programming (MILP) model to also include the optimal strategic decisions. The model considers temporal and spatial water and energy demands, supply systems configuration, resources capacities and associated costs as well as electricity pricing tariffs. It, then, gives the optimal solution such that it leads to the greatest compatibility of the water supply system operation with available renewable energy and the least system costs over the defined planning horizon. The model is tested for current and future water supply in an urban area located in the north-western corridor of Perth, Western Australia (WA). However, it can be applied to any urban area located in arid and semi-arid regions. The initial results for optimal operation of the system showed that considering surplus PV output as a part of water-related energy mix leads to higher PV installation capacity and significant savings in operational and maintenance (O&M) costs. Compared to fixed (yearly basis) and semi-flexible (seasonal basis) operation of the water supply system, flexible (hourly basis) mode of operation resulted in the most compatibility with available surplus PV output; and therefore, a higher share of renewable energy in water-related energy mix. It also showed higher economic benefits over other operational scenarios in terms of the total system costs. In all cases, however, the availability of surplus PV output is a detrimental factor to the economic performance of the system. The optimal long-term planning for the water supply system operated compatibly with available renewable energy resulted in a multistage construction and expansion of water supply components for sustainable demand supply. In addition, it was shown that decentralised water supply systems operated in flexible mode, leads to less discounted total cost of the system and higher level of potential PV uptake capacities, compared to centralised water supply systems operated in fixed mode; even though the surplus PV output is considered as a part of their energy mix. In this regard, the effect of the householders’ free will for up taking PV systems and probable imposed O&M costs of the flexible mode of operation needs to be taken into account if the decentralised scenario is chosen to be implemented in practice. It was also indicated that considering the effect of the indirect environmental impact of purchasing grid electricity for water supply affects the optimal results in terms of system components capacity as well as the timing of the construction and expansion of the water supply system. It also results in less indirect greenhouse gas emission and higher discounted total cost of the system over the planning horizon. In this respect, the generation source of purchased electricity plays a significant role. Finally, the achieved insight into the different aspects of the desalination-based water supply system driven by hybrid energy sources led to the series of recommendations for future studies in the context of the integrated water and energy management

Water Security and Clean Energy, Co-benefits of an Integrated Water and Energy Management

Considering daily surplus output from grid-connected rooftop photovoltaics (PVs) as part of an urban water-related energy mix, this can incentivise the connection of higher number of PVs to the existing grid networks. It has also the benefit of delivering sustainability to energy-intensive water supply technologies such as desalination in cities located in dry climate regions. In this paper, we describe an optimal operation of a desalination-based urban water supply system driven by both grid electricity and surplus PV output. Three tools of geographical information system, system advisor model and Excel are integrated to support a linear programming model. The model is solved through a two-step optimisation approach taking into account water and energy demand and supply systems as well as time of use electricity tariffs. The optimum solution for the north-western corridor of Perth, Australia, shows 12.1 % total cost reduction per day for water supplier and 123 % increase in PV installation capacity; resulting in great benefits for both water and energy sectors