Search

Meeting the Paris Agreement temperature goal necessitates limiting methane (CH 4 )-induced warming, in addition to achieving net-zero or (net-negative) carbon dioxide (CO 2 ) emissions. In our model, for the median 1.5°C scenario between 2020 and 2050, CH 4 mitigation lowers temperatures by 0.1°C; CO 2 increases it by 0.2°C. CO 2 emissions continue increasing global mean temperature until net-zero emissions are reached, with potential for lowering temperatures with net-negative emissions. By contrast, reducing CH 4 emissions starts to reverse CH 4 -induced warming within a few decades. These differences are hidden when framing climate mitigation using annual ‘CO 2 -equivalent’ emissions, including targets based on aggregated annual emission rates. We show how the different warming responses to CO 2 and CH 4 emissions can be accurately aggregated to estimate warming by using ‘warming-equivalent emissions', which provide a transparent and convenient method to inform policies and measures for mitigation, or demonstrate progress towards a temperature goal. The method presented (GWP*) uses well-established climate science concepts to relate GWP100 to temperature, as a simple proxy for a climate model. The use of warming-equivalent emissions for nationally determined contributions and long-term strategies would enhance the transparency of stocktakes of progress towards a long-term temperature goal, compared to the use of standard equivalence methods. This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 2)’.

This paper provides an outline of a new interdisciplinary project called FixOurFood, funded through UKRI’s ‘Transforming UK food systems’ programme. FixOurFood aims to transform the Yorkshire food system to a regenerative food system and will work to answer two main questions: (1) What do regenerative food systems look like? (2) How can transformations be enabled so that we can achieve a regenerative food system? To answer these questions, FixOurFood will work with diverse stakeholders to change the Yorkshire food system and use the learning to inform change efforts in other parts of the UK and beyond. Our work will focus on shifting trajectories towards regenerative dynamics in three inter-related systems of: healthy eating for young children, hybrid food economies and regenerative farming. We do this by a set of action-orientated interventions in schools and the food economy, metrics, policies and deliverables that can be applied in Yorkshire and across the UK. This article introduces the FixOurFood project and concludes by assessing the potential impact of these interventions and the importance we attach to working with stakeholders in government, business, third sector and civil society. Biotechnology and Biological Sciences Research Council. Grant Number: BB/V004581/1

A box plot showing the 0, 25, 50, 75, and 100 percentiles for the net-zero GHG emissions year, as defined using GWP100, for different classifications of scenarios in the IPCC Special Report on Global Warming of 1.5C (SR15). The scenario classifications are as described in SR15. The scenarios end in 2100, and the box plots that are cut off in 2100 mean that the remainder of the distribution occurs after 2100. The ‘marker’ scenarios are the four illustrative pathways used in SR15, noting that one does not reach net zero GHG emissions by 2100 (The ‘Low Energy Demand’ scenario). Both the ‘1.5C low overshoot’, and the combined group of ‘1.5C no and low overshoot’ have over 25% of scenarios which do not reach net-zero GHG emissions, defined using GWP100, by 2100.

Unless there is immediate, unprecedented, reduction in global demand for carbon-intensive energy and products, then capture and permanent storage of billions of tonnes of carbon dioxide (CO2) annually will be needed before mid-century to meet Paris Agreement goals. Yet competition from cheaper, temporary, carbon storage means that permanent disposal remains starved of investment, currently representing about 0.1% of Energy and Industrial Process (EIP) emissions. This stored fraction must reach 100% to stop EIPs causing global warming. Here we show that a cost-effective transition can occur by mandating an increasing stored fraction through a progressive Carbon Takeback Obligation (CTO) on fossil fuel producers and importers. Projected costs of storage to the consumer are lower than pricing carbon emissions in conventional 1.5{\deg}C scenarios until the 2040s, and comparable or lower thereafter. A CTO combined with measures to reduce CO2 production would deliver the lowest-risk pathway to achieving net zero.

Empirical evidence suggests that variations in climate affect economic growth across countries over time. However, little is known about the relative impacts of climate change on economic outcomes when global mean surface temperature (GMST) is stabilized at 1.5°C or 2°C warming relative to pre-industrial levels. Here we use a new set of climate simulations under 1.5°C and 2°C warming from the ‘Half a degree Additional warming, Prognosis and Projected Impacts' (HAPPI) project to assess changes in economic growth using empirical estimates of climate impacts in a global panel dataset. Panel estimation results that are robust to outliers and breaks suggest that within-year variability of monthly temperatures and precipitation has little effect on economic growth beyond global nonlinear temperature effects. While expected temperature changes under a GMST increase of 1.5°C lead to proportionally higher warming in the Northern Hemisphere, the projected impact on economic growth is larger in the Tropics and Southern Hemisphere. Accounting for econometric estimation and climate uncertainty, the projected impacts on economic growth of 1.5°C warming are close to indistinguishable from current climate conditions, while 2°C warming suggests statistically lower economic growth for a large set of countries (median projected annual growth up to 2% lower). Level projections of gross domestic product (GDP) per capita exhibit high uncertainties with median projected global average GDP per capita approximately 5% lower at the end of the century under 2°C warming relative to 1.5°C. The correlation between climate-induced reductions in per capita GDP growth and national income levels is significant at the p

We argue that it would be desirable to use Jeffreys' priors in the construction of numerical model based probabilistic climate forecasts, in order that those forecasts could be argued to be objective. Hitherto, this has been considered computationally unfeasible. We propose an approximation that we believe makes it feasible, and derive closed-form expressions for various simple cases.

4 páginas