Low-carbon energy transitions aim to stay within a carbon budget limiting potential climate change to 2 ºC-or well below-through substantial growth in renewable energy sources alongside improved energy efficiency and carbon capture and storage. Current scenarios tend to overlook their low net energy returns compared to existing fossil fuel infrastructure. Correcting from gross to net energy, we show that a low-carbon transition would likely lead to a 24 to 31% decline in net energy per capita by 2050, implying a strong reversal of recent rising trends of 0.5% per annum. Unless vast end use efficiency savings can be achieved in the coming decades, current lifestyles might be impaired. To maintain present net energy returns, solar and wind renewable power sources should grow two to three times faster than in other proposals. We suggest a new indicator, 'energy return on carbon' (EROC), to assist in maximizing net energy from the remaining carbon budget. Gross Energy 550 EJ Net Energy 523 EJ 27 EJ reinvested End use energy services 219 EJ Energy losses 304 EJ Consumption on necessities 100 EJ Non-essentials 119 EJ Gross Energy 550 EJ Net Energy 367 EJ 183 EJ Reinvested End use energy services 154 EJ Energy losses 213 EJ Consumption on necessities 100 EJ Non-essentials 54 EJ High EROI Economy (EROI = 20:1) Low EROI Economy (EROI = 3:1)

The Paris Agreement takes a bottom-up approach to tackling climate change with parties submitting pledges in the form of nationally determined contributions (NDCs). Studies show that the sum of these national pledges falls short of meeting the agreement's 2°C target. To explore this discrepancy, we analyse individual pledges and classify them into four categories. By doing so, a lack of consistency and transparency is highlighted, which we correct for by performing a normalisation that makes pledges directly comparable. This involves calculating changes in emissions by 2030, using data for the most recent base year of 2015. We find that pledges framed in terms of absolute emission reductions against historical base years generally produce the greatest ambition, with average emission reductions of 16% by 2030. Pledges defined as GDP intensity targets perform the worst with average emission increases of 61% by 2030. We propose that a normalisation procedure of the type as we develop becomes part of the NDC process. It will allow to not only increase the transparency of pledges for policymakers and wider society, but also promote more effective NDCs upon revision as is foreseen to happen every 5 years under the 'ratcheting mechanism' of the agreement.

Carbon leakage is the effect of emissions transferring to certain countries due to others having a stricter climate policy. This phenomenon is shown to have undercut the effectiveness of the Kyoto Protocol. Considering the increasingly globalised nature of the world economy, carbon leakage may have an even greater potential under the Paris Agreement some fifteen years later. Although a more global approach to combatting climate change, the Paris Agreement is susceptible to leakage because of its lack of policy harmonization and enforcement mechanisms.Here we perform the first quantitative analysis of the potential for carbon leakage under Paris, using the GTAP-E general equilibrium model of the world economy with energy and carbon emissions to analyse leakage effects under six scenarios. Two of these scenarios analyse regions implementing climate policy in isolation, two greater participation, but still not harmonized, global Paris Agreement policy, and a further two analyse the effect of a US withdrawal from the agreement. Both cases are considered with and without the US withdrawal. Our analysis demonstrates that there is potential for significant carbon leakage effects, in line with the rates produced from studies on the Kyoto Protocol. Depending on model elasticities, we find medium carbon leakage in the range of 1-9% (with a central estimate of 3-4%) under co-ordinated Paris Agreement policy across countries, compared to high leakage of 8-31% when countries operate in isolation. However, scenarios where the US withdraws from the agreement result in roughly doubling of leakage rates, in the range of 3-16% (central estimate 7%), which demonstrates the vulnerability of the Paris Agreement in its current form. To limit leakage effects greater policy co-ordination to achieve consistent implicit carbon prices is needed across countries.

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