Explore the vast range of titles available.

This paper presents interrelated indicators for tracking progress towards the Paris Agreement. Findings show broad consistency with keeping warming below 2 °C, but technological advances are needed to achieve net-zero emissions. 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 1 . 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 2 , 3 track aggregated progress 1 , country-level decompositions track emerging trends 4 , 5 , 6 that link directly to NDCs 7 , and technology diffusion 8 , 9 , 10 indicates future reductions. We find the recent slowdown in global emissions growth 11 is due to reduced growth in coal use since 2011, primarily in China and secondarily in the United States 12 . The slowdown is projected to continue in 2016, with global CO 2 emissions from fossil fuels and industry similar to the 2015 level of 36 GtCO 2 . 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 13 threatens 2030 targets and the longer-term Paris ambition of net-zero emissions.

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 CO2 emissions 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 CO2 emissions. 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.Between 2005 and 2015, several developed economies experienced decreases in CO2 emissions. In this study, emissions in 18 countries are broken down and the potential effects of energy and climate policies on emission declines are explored.

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.

An analysis of preliminary official statistics shows that, rather than falling as claimed, coal-derived energy consumption in China stayed flat in 2014, while fossil CO 2 emissions probably increased slightly, with a decrease expected for 2015. Chinese coal consumption dropped 2.9% in 2014 according to preliminary official statistics 1 released in 2015. This was hailed as historic after China’s meteoric growth in the 2000s 2 . The International Energy Agency used it to estimate ∼1.5% reduction in Chinese fossil CO 2 emissions for 2014 3 , and an unprecedented 0.2% reduction in global emissions 4 . 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 5 , 6 , implying high uncertainty. For example, BP used different Chinese data to estimate a 0.9% increase in 2014 CO 2 emissions 7 , 8 . 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 CO 2 emissions, that coal-derived energy consumption stayed flat but is likely to have decreased in 2015, and that Chinese fossil CO 2 emissions probably increased ∼0.8% in 2014. We also analyse recent revisions of official energy statistics, and find that they imply 925 MtCO 2 (11.2%) higher emissions for 2013, and 7.6 GtCO 2 (9.2%) higher total emissions for 2000–2013.

Rapid growth in global CO 2 emissions from fossil fuels and industry ceased in the past two years, despite continued economic growth. Decreased coal use in China was largely responsible, coupled with slower global growth in petroleum and faster growth in renewables.

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 CO sub(2) emissions 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 CO sub(2) emissions. 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 CO sub(2) emissions, that coal-derived energy consumption stayed flat but is likely to have decreased in 2015, and that Chinese fossil CO sub(2) emissions probably increased 0.8% in 2014. We also analyse recent revisions of official energy statistics, and find that they imply 925 MtCO sub(2) (11.2%) higher emissions for 2013, and 7.6 GtCO sub(2) (9.2%) higher total emissions for 2000-2013.

In the 2000s, the rapid growth of CO2 emitted in the production of exports from developing to developed countries, in which China accounted for the dominant share, led to concerns that climate polices had been undermined by international trade. Arguments on “carbon leakage” and “competitiveness”—which led to the refusal of the U.S. to ratify the Kyoto Protocol—put pressure on developing countries, especially China, to limit their emissions with Border Carbon Adjustments used as one threat. After strong growth in the early 2000s, emissions exported from developing to developed countries plateaued and could have even decreased since 2007. These changes were mainly due to China: In 2002–2007, China's exported emissions grew by 827 MtCO2, amounting to almost all the 892 MtCO2 total increase in emissions exported from developing to developed countries, while in 2007–2012, emissions exported from China decreased by 229 MtCO2, contributing to the total decrease of 172 MtCO2 exported from developing to developed countries. We apply Structural Decomposition Analysis to find that, in addition to the diminishing effects of the global financial crisis, the slowdown and eventual plateau was largely explained by several potentially permanent changes in China: Decline in export volume growth, improvements in CO2 intensity, and changes in production structure and the mix of exported products. We argue that growth in China's exported emissions will not return to the high levels during the 2000s, therefore the arguments for climate polices focused on embodied emissions such as Border Carbon Adjustments are now weakened. Plain Language Summary In the 2000s, CO2 emissions from production in developed countries flattened while emissions from their consumption grew. The rapid growth of exported emissions from developing countries to developed countries, with the largest contribution from China, played a significant role. This led to concerns that climate polices had been undermined by rapid growth in international trade. Since around 2007, growth in these exported emissions has plateaued, predominantly due to changes in China. Our study investigates China's changes, demonstrating that in addition to the effects of global financial crisis, China implemented potentially permanent structural changes. We argue that China's exported emissions are unlikely to return to the growth levels from the 2000s, and therefore trade‐related climate polices will be much less relevant. Key Points CO2 exported from developing to developed countries has plateaued since 2007 due to a plateau in China's exported CO2 The slowdown in China's exported CO2 was largely explained by improvements in the CO2 intensity and structural change Arguments for Border Carbon Adjustments may become less relevant due to the plateau in Chinese exported emissions

This dissertation discusses how to find suitable ways to measure the effective \"size\" of a quantum superposition state (aka a Schrödinger cat state), and analyzes the microscopic dynamics of flux/current superposition states in superconducting loops containing Josephson junctions. These states have been claimed to be examples of macroscopic or at least mesoscopic cat states. In Part I, I define one class of measures based on how many microscopic degrees of freedom would need to be measured to distinguish the two branches of a superposition from each other, as well as one simpler measure based on differences in mode occupation numbers in systems of indistinguishable particles. Along the way, I review and extend many results related to quantum state estimation and quantum state discrimination. I pay special attention to the crucial distinction between systems of distinguishable and indistinguishable particles, something which has not always been done in earlier literature on the subject. In Part II, I develop a method based on functional integrals to calculate correlation functions for the microscopic electronic degrees of freedom in a superconductor. I use this approach to estimate the effective size of superposed current states. This appears to be the first time that these states have been carefully analyzed at the microscopic level rather than in terms of macroscopic observables. The conclusion is that the superposition states produced in the two most celebrated experiments of this kind to date are not macroscopic according to the measures used in this dissertation, and will likely not be according to any other measure that is based on whether or not a large number of microscopic degrees of freedom are in different states in the two branches of a superposition state. The vast majority of electrons do not effectively participate in the superposition behavior in any significant way. Finally, I find that although larger superpositions of flux/current states in superconducting loops can in principle be realized, it is almost certainly not possible to push them anywhere close to the macroscopic scale.

We study the generalized Unruh effect for accelerated reference frames that include rotation in addition to acceleration. We focus particularly on the case where the motion is planar, with presence of a static limit in addition to the event horizon. Possible definitions of an accelerated vacuum state are examined and the interpretation of the Minkowski vacuum state as a thermodynamic state is discussed. Such athermodynamic state is shown to depend on two parameters, the acceleration temperature and a drift velocity, which are determined by the acceleration and angular velocity of the accelerated frame. We relate the properties of Minkowski vacuum in the accelerated frame to the excitation spectrum of a detector that is stationary in this frame. The detector can be excited both by absorbing positive energy quanta in the \"hot\" vacuum state and by emitting negative energy quanta into the \"ergosphere\" between the horizon and the static limit. The effects are related to similar effects in the gravitational field of a rotating black hole.