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It is always possible to find arguments to make 1.5°C forever possible, but they increasingly diverge from reality. It is time to admit that the world will cross 1.5°C and the likelihood of returning below 1.5°C via overshoot is slim. But, failing on 1.5°C does not mean the world has failed. The Paris Agreement is about balancing risks in a ‘well below 2°C’ world, and that level of ambition remains achievable despite a less certain climate outcome. We no longer need scenarios with impossibly steep emission declines to 1.5°C, but more nuanced country-level scenarios integrating national circumstances and feasible ambitions. This is harder for researchers, but more confronting for policy makers. Crossing 1.5°C is not a time to give up but a time to acknowledge our failures and find a new hope moving forward.

Carbon dioxide removal (CDR) policy is evolving rapidly but remains fragmented. Upcoming initiatives by the G7 members, which face expectations to be frontrunners in CDR deployment, should follow five principles for robust policies. This will be critical to prepare for distributional conflicts associated with achieving net-zero and net-negative emissions, both domestically and internationally.

Commitments to net-zero carbon dioxide (CO2) or greenhouse gas (GHG) emissions targets now cover 88% of countries’ emissions. Underlying the accounting behind net-zero frameworks is the assumption that emissions can be balanced with removals such that their net climate effect is zero. However, when considering the full climate impacts of CO2emissions and removals, there are reasons to expect that the two are not equivalent in terms of their climate outcomes. We identify potential contributors to non-equivalence, including impermanence, biogeophysical and non-CO2GHG effects, and argue that these non-equivalencies need to be accounted for to achieve climate goals. Given key uncertainties about the full climate impact of CO2removal, it is prudent to prioritize emission reductions over removals.

The COP26 Glasgow process resulted in many countries strengthening their 2030 emissions reduction targets and announcing net-zero pledges for 2050–2070 but it is not clear how this would impact future warming. Here, we use four diverse integrated assessment models (IAMs) to assess CO2emission trajectories in the near- and long-term on the basis of national policies and pledges, combined with a non-CO2infilling model and a simple climate model to assess the temperature implications. We also consider the feasibility of national long-term pledges towards net-zero. While near-term pledges alone lead to warming above 2 °C, the addition of long-term pledges leads to emissions trajectories compatible with a future well below 2 °C, across all four IAMs. However, while IAM heterogeneity translates to diverse decarbonization pathways towards long-term targets, all modelled pathways indicate several feasibility concerns, relating to the cost of mitigation and the rates and scales of deployed technologies and measures.

Day-to-day changes in CO2emissions from human activities, in particular fossil-fuel combustion and cement production, reflect a complex balance of influences from seasonality, working days, weather and, most recently, the COVID-19 pandemic. Here, we provide a daily CO2emissions dataset for the whole year of 2020, calculated from inventory and near-real-time activity data. We find a global reduction of 6.3% (2,232 MtCO2) in CO2emissions compared with 2019. The drop in daily emissions during the first part of the year resulted from reduced global economic activity due to the pandemic lockdowns, including a large decrease in emissions from the transportation sector. However, daily CO2emissions gradually recovered towards 2019 levels from late April with the partial reopening of economic activity. Subsequent waves of lockdowns in late 2020 continued to cause smaller CO2reductions, primarily in western countries. The extraordinary fall in emissions during 2020 is similar in magnitude to the sustained annual emissions reductions necessary to limit global warming at 1.5 °C. This underscores the magnitude and speed at which the energy transition needs to advance.

Most of the integrated assessment modelling literature focuses on cost-effective pathways towards given temperature goals. Conversely, using seven diverse integrated assessment models, we project global energy CO2emissions trajectories on the basis of near-term mitigation efforts and two assumptions on how these efforts continue post-2030. Despite finding a wide range of emissions by 2050, nearly all the scenarios have median warming of less than 3 °C in 2100. However, the most optimistic scenario is still insufficient to limit global warming to 2 °C. We furthermore highlight key modelling choices inherent to projecting where emissions are headed. First, emissions are more sensitive to the choice of integrated assessment model than to the assumed mitigation effort, highlighting the importance of heterogeneous model intercomparisons. Differences across models reflect diversity in baseline assumptions and impacts of near-term mitigation efforts. Second, the common practice of using economy-wide carbon prices to represent policy exaggerates carbon capture and storage use compared with explicitly modelling policies.

Recent demands by developing countries, like India, that developed countries need to reach net-negative emissions, must be negotiated seriously under the UNFCCC. Failure to acknowledge that limiting global average temperature rise to 1.5°C leaves very little carbon budget for equitable redistribution risks further ambiguity on how to achieve the Paris Agreement’s goals.

If rapid and just transformations to low-carbon societies are to take place, citizens need to obtain the necessary knowledge and skills to critically examine and choose adequate climate policy options. An emphasis on critical climate education research and implementation is therefore required.

Nitrous oxide (N2O), like carbon dioxide, is a long-lived greenhouse gas that accumulates in the atmosphere. Over the past 150 years, increasing atmospheric N2O concentrations have contributed to stratospheric ozone depletion1and climate change2, with the current rate of increase estimated at 2 per cent per decade. Existing national inventories do not provide a full picture of N2O emissions, owing to their omission of natural sources and limitations in methodology for attributing anthropogenic sources. Here we present a global N2O inventory that incorporates both natural and anthropogenic sources and accounts for the interaction between nitrogen additions and the biochemical processes that control N2O emissions. We use bottom-up (inventory, statistical extrapolation of flux measurements, process-based land and ocean modelling) and top-down (atmospheric inversion) approaches to provide a comprehensive quantification of global N2O sources and sinks resulting from 21 natural and human sectors between 1980 and 2016. Global N2O emissions were 17.0 (minimum–maximum estimates: 12.2–23.5) teragrams of nitrogen per year (bottom-up) and 16.9 (15.9–17.7) teragrams of nitrogen per year (top-down) between 2007 and 2016. Global human-induced emissions, which are dominated by nitrogen additions to croplands, increased by 30% over the past four decades to 7.3 (4.2–11.4) teragrams of nitrogen per year. This increase was mainly responsible for the growth in the atmospheric burden. Our findings point to growing N2O emissions in emerging economies—particularly Brazil, China and India. Analysis of process-based model estimates reveals an emerging N2O–climate feedback resulting from interactions between nitrogen additions and climate change. The recent growth in N2O emissions exceeds some of the highest projected emission scenarios3,4, underscoring the urgency to mitigate N2O emissions.

Government policies during the COVID-19 pandemic have drastically altered patterns of energy demand around the world. Many international borders were closed and populations were confined to their homes, which reduced transport and changed consumption patterns. Here we compile government policies and activity data to estimate the decrease in CO2emissions during forced confinements. Daily global CO2emissions decreased by –17% (–11 to –25% for ±1σ) by early April 2020 compared with the mean 2019 levels, just under half from changes in surface transport. At their peak, emissions in individual countries decreased by –26% on average. The impact on 2020 annual emissions depends on the duration of the confinement, with a low estimate of –4% (–2 to –7%) if prepandemic conditions return by mid-June, and a high estimate of –7% (–3 to –13%) if some restrictions remain worldwide until the end of 2020. Government actions and economic incentives postcrisis will likely influence the global CO2emissions path for decades.

New synthesis shows what a wasted decade means for the climate pact made in Paris.

Global emissions of carbon dioxide (CO2) from fossil fuels and industry increased by 2.2% per year on average between 2005 and 20151. Global emissions need to peak and decline rapidly to limit climate change to well below 2 °C of warming2,3, which is one of the goals of the Paris Agreement4. Untangling the reasons underlying recent changes in emissions trajectories is critical to guide efforts to attain those goals. Here we analyse the drivers of decreasing CO2emissions in a group of 18 developed economies that have decarbonized over the period 2005–2015. We show that within this group, the displacement of fossil fuels by renewable energy and decreases in energy use explain decreasing CO2emissions. However, the decrease in energy use can be explained at least in part by a lower growth in gross domestic product. Correlation analysis suggests that policies on renewable energy are supporting emissions reductions and displacing fossil fuels in these 18 countries, but not elsewhere, and that policies on energy efficiency are supporting lower energy use in these 18 countries, as well as more widely. Overall, the evidence shows that efforts to reduce emissions are underway in many countries, but these efforts need to be maintained and enhanced by more stringent policy actions to support a global peak in emissions followed by global emissions reductions in line with the goals of the Paris Agreement3.

Five years after the adoption of the Paris Climate Agreement, growth in global CO2emissions has begun to falter. The pervasive disruptions from the COVID-19 pandemic have radically altered the trajectory of global CO2emissions. Contradictory effects of the post-COVID-19 investments in fossil fuel-based infrastructure and the recent strengthening of climate targets must be addressed with new policy choices to sustain a decline in global emissions in the post-COVID-19 era.

With sources of renewable energy spreading fast, all sectors can do more to decarbonize the world, argue Christiana Figueres and colleagues.

Chinese provinces ultimately implement China’s national climate policies. In the 2000s, there were unbalanced emission transfers (emissions produced in one region but consumed in other regions) between China’s well- and less-developed regions, mainly related to demand in the well-developed eastern provinces. In the past decade, the plateau in China’s exported emissions and changes in its industrial structure suggest that the features of the provincial emission transfers could have changed. We construct a Chinese provincial multiyear, multisector model (multi-regional input–output model) to investigate the structural changes in China’s provincial emission transfers from 2002 to 2012. We find that from 2007 to 2012, the international-export-associated emission transfers driven by eastern provinces decreased by 17% after the 262% increase in 2002–07, while investment dominated 99% of the increase in emission transfers. At the sector level, emissions caused by construction in the east and west, and technology-intensive manufacturing in the center that largely related to investment were the major components of the increasing emission transfers in 2007–12, accounting for 23%, 21%, and 10% of the increase, respectively. Our findings indicate that attention should be given to committed emissions from investment and the interaction between non-uniform provincial climate policies and economic relationships between provinces.

Achieving the long-term temperature goal of the Paris Agreement requires forest-based mitigation. Collective progress towards this goal will be assessed by the Paris Agreement’s Global stocktake. At present, there is a discrepancy of about 4 GtCO2yr−1in global anthropogenic net land-use emissions between global models (reflected in IPCC assessment reports) and aggregated national GHG inventories (under the UNFCCC). We show that a substantial part of this discrepancy (about 3.2 GtCO2yr−1) can be explained by conceptual differences in anthropogenic forest sink estimation, related to the representation of environmental change impacts and the areas considered as managed. For a more credible tracking of collective progress under the Global stocktake, these conceptual differences between models and inventories need to be reconciled. We implement a new method of disaggregation of global land model results that allows greater comparability with GHG inventories. This provides a deeper understanding of model–inventory differences, allowing more transparent analysis of forest-based mitigation and facilitating a more accurate Global stocktake.

Current emission pledges to the Paris Agreement appear insufficient to hold the global average temperature increase to well below 2 °C above pre-industrial levels. Yet, details are missing on how to track progress towards the ‘Paris goal’, inform the five-yearly ‘global stocktake’, and increase the ambition of Nationally Determined Contributions (NDCs). We develop a nested structure of key indicators to track progress through time. Global emissions track aggregated progress, country-level decompositions track emerging trends that link directly to NDCs, and technology diffusion indicates future reductions. We find the recent slowdown in global emissions growth is due to reduced growth in coal use since 2011, primarily in China and secondarily in the United States. The slowdown is projected to continue in 2016, with global CO2emissions from fossil fuels and industry similar to the 2015 level of 36 GtCO2. Explosive and policy-driven growth in wind and solar has contributed to the global emissions slowdown, but has been less important than economic factors and energy efficiency. We show that many key indicators are currently broadly consistent with emission scenarios that keep temperatures below 2 °C, but the continued lack of large-scale carbon capture and storage threatens 2030 targets and the longer-term Paris ambition of net-zero emissions.

Stop using the worst-case scenario for climate warming as the most likely outcome — more-realistic baselines make for better policy.

Chinese coal consumption dropped 2.9% in 2014 according to preliminary official statistics released in 2015. This was hailed as historic after China’s meteoric growth in the 2000s. The International Energy Agency used it to estimate ∼1.5% reduction in Chinese fossil CO2emissions for 2014, and an unprecedented 0.2% reduction in global emissions. Similar preliminary coal consumption statistics are announced every year, and will be watched closely after China’s recent slowdown in emissions growth and pledge to peak emissions in 2030 or earlier. However, Chinese energy statistics are frequently revised and often contain large anomalies, implying high uncertainty. For example, BP used different Chinese data to estimate a 0.9% increase in 2014 CO2emissions. Here, we analyse these preliminary announcements, with an approach that can be used to assess the robustness of similar future announcements. We show that the preliminary 2.9% reduction in coal consumption is inappropriate for estimating CO2emissions, that coal-derived energy consumption stayed flat but is likely to have decreased in 2015, and that Chinese fossil CO2emissions probably increased ∼0.8% in 2014. We also analyse recent revisions of official energy statistics, and find that they imply 925 MtCO2(11.2%) higher emissions for 2013, and 7.6 GtCO2(9.2%) higher total emissions for 2000–2013.

The remaining carbon budget consistent with limiting warming to 1.5 °C allows 20 more years of current emissions according to one study, but is already exhausted according to another. Both are defensible. We need to move on from a unique carbon budget, and face the nuances.

How confident are we that CO2emissions must reach net zero or below to halt CO2‐induced warming? The IPCC's sixth assessment report concluded that “limiting human‐induced global warming to a specific level requires … reaching at least net zero CO2emissions.” This is much stronger language than the special report on the global warming of 1.5°C, which concluded that reaching net zero CO2emissions would be sufficient. Here we show that “approximately net zero” is better supported than “at least net zero.” We estimate the rate of adjustment to zero emissions (RAZE) parameter (−0.24 to +0.17%/yr), defined as the fractional change in CO2‐induced warming after CO2emissions cease. The RAZE determines the CO2emissions compatible with halting warming over multiple decades: in 1.5°C‐consistent scenarios, CO2emissions consistent with halting anthropogenic warming are +2.2 GtCO2/yr (5–95th percentile range spans −7.3 to +6.2 GtCO2/yr), similar to the expected emissions from unmodelled Earth system feedbacks. How confident are we that CO2emissions will need to reach net zero (where human‐made CO2emissions into the atmosphere are approximately balanced with CO2removals through carbon capture and storage, nature‐based solutions, etc.) or below to halt human‐induced warming? Here we show that “approximately net zero” is the best‐estimate requirement to stabilize warming. To do this we show that the behavior of the climate system's temperature response following net zero can be defined using a new parameter (the rate of adjustment to zero emissions, RAZE), which spans −0.24 to +0.17%/yr. The RAZE determines the ongoing rate of CO2emissions or removals compatible with halting warming. In scenarios which reach approximately 1.5°C warming, CO2emissions consistent with halting human‐made warming over multi‐decadal timescales span −7.3 to +6.2 GtCO2/yr with a best‐estimate of +2.2 GtCO2/yr. Planning for net negative global CO2emissions remains important, given the chance of global temperatures overshooting 1.5°C, along with research to better understand the emissions consistent with warming stabilization. The conditions for stabilization of global temperature at any level depend on the multi‐century carbon and thermal cycle responseThis is described by the rate of adjustment to zero emissions parameter, spanning −0.24 to +0.17%/yr (−0.036 to 0.025°C/decade at 1.5°C)In 1.5°C scenarios, CO2emissions consistent with halting anthropogenic warming over multi‐decadal timescales span −7.3 to +6.2 GtCO2/yr The conditions for stabilization of global temperature at any level depend on the multi‐century carbon and thermal cycle response This is described by the rate of adjustment to zero emissions parameter, spanning −0.24 to +0.17%/yr (−0.036 to 0.025°C/decade at 1.5°C) In 1.5°C scenarios, CO2emissions consistent with halting anthropogenic warming over multi‐decadal timescales span −7.3 to +6.2 GtCO2/yr

To have a >50% chance of limiting warming below 2 °C, most recent scenarios from integrated assessment models (IAMs) require large-scale deployment of negative emissions technologies (NETs). These are technologies that result in the net removal of greenhouse gases from the atmosphere. We quantify potential global impacts of the different NETs on various factors (such as land, greenhouse gas emissions, water, albedo, nutrients and energy) to determine the biophysical limits to, and economic costs of, their widespread application. Resource implications vary between technologies and need to be satisfactorily addressed if NETs are to have a significant role in achieving climate goals.

The Paris Agreement has increased the incentive to verify reported anthropogenic carbon dioxide emissions with independent Earth system observations. Reliable verification requires a step change in our understanding of carbon cycle variability.

Any limit on future global warming is associated with a quota on cumulative global CO2emissions. We translate this global carbon quota to regional and national scales, on a spectrum of sharing principles that extends from continuation of the present distribution of emissions to an equal per-capita distribution of cumulative emissions. A blend of these endpoints emerges as the most viable option. For a carbon quota consistent with a 2 °C warming limit (relative to pre-industrial levels), the necessary long-term mitigation rates are very challenging (typically over 5% per year), both because of strong limits on future emissions from the global carbon quota and also the likely short-term persistence in emissions growth in many regions.

It has long been assumed that human development depends on economic growth, that national economic expansion in turn requires greater energy use and, therefore, increased greenhouse-gas emissions. These interdependences are the topic of current research. Scarcely explored, however, is the impact of international trade: although some nations develop socio-economically and import high-embodied-carbon products, it is likely that carbon-exporting countries gain significantly fewer benefits. Here, we use new consumption-based measures of national carbon emissions to explore how the relationship between human development and carbon changes when we adjust national emission rates for trade. Without such adjustment of emissions, some nations seem to be getting far better development ‘bang’ for the carbon ‘buck’ than others, who are showing scant gains for disproportionate shares of global emissions. Adjusting for the transfer of emissions through trade explains many of these outliers, but shows that further socio-economic benefits are accruing to carbon-importing rather than carbon-exporting countries. We also find that high life expectancies are compatible with low carbon emissions but high incomes are not. Finally, we see that, despite strong international trends, there is no deterministic industrial development trajectory: there is great diversity in pathways, and national histories do not necessarily follow the global trends.

The large number of acquisitions taking place in the chemical industry has increased the need to efficiently assess the process safety risks at such facilities so that they meet the requirements of the acquiring company. This can be difficult if the technology issues are not fully disclosed during the “Due Diligence” phase of an acquisition.

Solute transport through a porous medium is typically modelled assuming the porous medium is rigid. However, many applications exist where the porous medium is deforming, including, municipal landfill liners, mine tailings dams, and land subsidence. In this paper, mass balance laws are used to derive the flow and transport equations for a deforming porous medium. The equations are derived in both spatial and material co‐ordinate systems. Solute transport through an engineered landfill liner is used as an illustrative example to show the differences between the theory for a rigid porous medium, and small and large deformation analysis of a deforming porous medium. It is found that the large deformation model produces shorter solute breakthrough times, followed by the small deformation model, and then the rigid porous medium model. It is also found that it is important to include spatial and temporal void ratio variations in the large deformation analysis. It is shown that a non‐linear large deformation model may greatly reduce the solute breakthrough time, compared to a standard transport analysis typically employed by environmental engineers. Copyright © 2002 John Wiley & Sons, Ltd.

A transition regionmay be defined as a region of rapid change in medium properties about the interfacebetween two porous media or at the interfacebetween a porous medium and a reservoir. Modelling the transition region between different porous media can assist in the selection of the most appropriate boundary conditions for the standard advection–dispersion equation (ADE). An advantage of modelling the transition region is that it removes the need for explicitly defining boundary conditions, though boundary conditions may be recovered as limiting cases. As the width of a transition region is reduced, the solution of the transition region model (TR model) becomes equivalent to the solution of the standard ADE model with correct boundary conditions. In this paper numerical simulations using the TR model are employed to select the most appropriate boundary conditions for the standard ADE under a variety of configurations and conditions. It is shown that at the inlet boundary between a reservoir and porous medium, continuity of solute mass flux should be used as the boundary condition. At the boundary interface between two porous media both continuity of solute concentration and solute mass flux should be used. Finally, in a finite porous medium where the solute is allowed to advect freely from the exit point, both continuity of solute concentration and solute mass flux should be used as the outlet boundary condition. The findings made here are discussed with reference to a detailed review of previous relevant theoretical and experimental observations. Copyright © 2001 John Wiley & Sons, Ltd.