ABSTRACT
Non-technical summary We summarize some of the past year's most important findings within climate change-related research. New research has improved our understanding of Earth's sensitivity to carbon dioxide, finds that permafrost thaw could release more carbon emissions than expected and that the uptake of carbon in tropical ecosystems is weakening. Adverse impacts on human society include increasing water shortages and impacts on mental health. Options for solutions emerge from rethinking economic models, rights-based litigation, strengthened governance systems and a new social contract. The disruption caused by COVID-19 could be seized as an opportunity for positive change, directing economic stimulus towards sustainable investments. Technical summary A synthesis is made of ten fields within climate science where there have been significant advances since mid-2019, through an expert elicitation process with broad disciplinary scope. Findings include: (1) a better understanding of equilibrium climate sensitivity;(2) abrupt thaw as an accelerator of carbon release from permafrost;(3) changes to global and regional land carbon sinks;(4) impacts of climate change on water crises, including equity perspectives;(5) adverse effects on mental health from climate change;(6) immediate effects on climate of the COVID-19 pandemic and requirements for recovery packages to deliver on the Paris Agreement;(7) suggested long-term changes to governance and a social contract to address climate change, learning from the current pandemic, (8) updated positive cost-benefit ratio and new perspectives on the potential for green growth in the short- A nd long-term perspective;(9) urban electrification as a strategy to move towards low-carbon energy systems and (10) rights-based litigation as an increasingly important method to address climate change, with recent clarifications on the legal standing and representation of future generations. Social media summary Stronger permafrost thaw, COVID-19 effects and growing mental health impacts among highlights of latest climate science. Copyright © The Author(s), 2021. Published by Cambridge University Press.
ABSTRACT
Limiting warming to well below 2 degrees C requires rapid and complete decarbonisation of energy systems. We compare economy-wide modelling of 1.5 degrees C and 2 degrees C scenarios with sector-focused analyses of four critical sectors that are difficult to decarbonise: aviation, shipping, road freight transport, and industry. We develop and apply a novel framework to analyse and track mitigation progress in these sectors. We find that emission reductions in the 1.5 degrees C and 2 degrees C scenarios of the IMAGE model come from deep cuts in CO2 intensities and lower energy intensities, with minimal demand reductions in these sectors' activity. We identify a range of additional measures and policy levers that are not explicitly captured in modelled scenarios but could contribute significant emission reductions. These are demand reduction options, and include less air travel (aviation), reduced transportation of fossil fuels (shipping), more locally produced goods combined with high load factors (road freight), and a shift to a circular economy (industry). We discuss the challenges of reducing demand both for economy-wide modelling and for policy. Based on our sectoral analysis framework, we suggest modelling improvements and policy recommendations, calling on the relevant UN agencies to start tracking mitigation progress through monitoring key elements of the framework (CO2 intensity, energy efficiency, and demand for sectoral activity, as well as the underlying drivers), as a matter of urgency. Key policy insights Four critical sectors (aviation, shipping, road freight, and industry) cannot cut their CO2 emissions to zero rapidly with technological supply-side options alone. Without large-scale negative emissions, significant demand reductions for those sectors' activities are needed to meet the 1.5-2 degrees C goal. Policy priorities include affordable alternatives to frequent air travel;smooth connectivity between low-carbon travel modes;speed reductions in shipping and reduced demand for transporting fossil fuels;distributed manufacturing and local storage;and tightening standards for material use and product longevity. The COVID-19 crisis presents a unique opportunity to enact lasting CO2 emissions reductions, through switching from frequent air travel to other transport modes and online interactions. Policies driving significant demand reductions for the critical sectors' activities would reduce reliance on carbon removal technologies that are unavailable at scale.