Summary for policymakers

The Working Group I contribution to the IPCC.s Fifth Assessment Report (AR5) considers new evidence of climate change based on many independent scientific analyses from observations of the climate system, paleoclimate archives, theoretical studies of climate processes and simulations using climate models. It builds upon the Working Group I contribution to the IPCC's Fourth Assessment Report (AR4), and incorporates subsequent new findings of research. As a component of the fifth assessment cycle, the IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) is an important basis for information on changing weather and climate extremes. This Summary for Policymakers (SPM) follows the structure of the Working Group I report. The narrative is supported by a series of overarching highlighted conclusions which, taken together, provide a concise summary. Main sections are introduced with a brief paragraph in italics which outlines the methodological basis of the assessment. The degree of certainty in key findings in this assessment is based on the author teams. evaluations of underlying scientific understanding and is expressed as a qualitative level of confidence (from very low to very high) and, when possible, probabilistically with a quantified likelihood (from exceptionally unlikely to virtually certain). Confidence in the validity of a finding is based on the type, amount, quality, and consistency of evidence (e.g., data, mechanistic understanding, theory, models, expert judgment) and the degree of agreement. Probabilistic estimates of quantified measures of uncertainty in a finding are based on statistical analysis of observations or model results, or both, and expert judgment. Where appropriate, findings are also formulated as statements of fact without using uncertainty qualifiers. (See Chapter 1 and Box TS.1 for more details about the specific language the IPCC uses to communicate uncertainty). The basis for substantive paragraphs in this Summary for Policymakers can be found in the chapter sections of the underlying report and in the Technical Summary. These references are given in curly brackets

Belgium’s national emission pathway in the context of the global remaining carbon budget

This Science Brief assesses the implications of the scientific evidence on carbon budgets presented in the latest assessment of the Intergovernmental Panel on Climate Change for national carbon budgets and emissions reductions in Belgium. Based on the best available science, the global remaining carbon budget for limiting global warming to 1.5°C amounts to 400 billion tons of carbon dioxide emissions (GtCO2). The implications of this global remaining carbon budget for Belgium can be explored by using equity and fairness principles to determine a fair national carbon budget share. A variety of principles was applied ranging from approaches that are considered inherently unfair (a grandfathering approach) to approaches that have been proposed by developing country experts. Based on this wide range of distribution keys, the minimum emissions reduction for Belgium that puts their national trajectory in line with limiting global warming to 1.5°C and on track to reach net zero greenhouse gas emissions by mid‐century is ‐69% in 2030 relative to 1990 levels. If Belgium’s net zero greenhouse gas target would be advanced from 2050 to 2042, the corresponding emissions reductions in 2030 would amount to ‐61% relative to 1990 level

Carbon price variations in 2°C scenarios explored

AIM AND SCOPE Clarify the variations in carbon prices found in mitigation scenarios that limit global mean surface temperature increase to below 2°C relative to preindustrial levels. CONTEXT Integrated assessment models1 (IAM) are dominant tools for the development of long-term emissions scenarios in line with climate objectives. There is a large variety of IAMs and, together with variations in socioeconomic and technological assumptions, this variety results in important differences in model behavior. For the achievement of low emissions scenarios, models typically assume or produce an implicit shadow price for carbon or represent policy instruments, including carbon pricing. This briefing aims at exploring and understanding the variation in these carbon price estimates for stringent climate change mitigation scenarios. The focus of this exercise will be on scenarios that limit global mean temperature surface increase (henceforth, warming) to below 2°C relative to preindustrial levels with a greater than 66% probability. This choice is driven by data availability for this particular temperature objective, and does not represent an official or scientific interpretation of the Paris Agreement long-term temperature goal. The assumption is that the qualitative insights would also to

Turn Down the Heat: Climate Extremes, Regional Impacts and the Case for Resilience

This report focuses on the risks of climate change to development in Sub-Saharan Africa, South East Asia and South Asia. Building on the 2012 report, Turn Down the Heat: Why a 4 degrees C Warmer World Must be Avoided, this new scientific analysis examines the likely impacts of present day, 2 degrees C and 4 degrees C warming on agricultural production, water resources, and coastal vulnerability for affected populations. The report show that significant significant climate and development impacts are already being felt in some regions, and in some cases multiple threats of increasing extreme heat waves, sea level rise, more severe storms, droughts and floods are expected to have further severe negative implications for the poorest. These impacts are likely to push many vulnerable households below the poverty trap threshold with high temperature extreme's negative impact on the yields of food crops. Promoting economic growth, the eradication of poverty and inequality will likely be a tougher challenge than the one it already is, and immediate steps must be taken to help countries adapt to these risks. The report shows that with the substantive reduction of greenhouse gas emissions, many of the worst projected climate impacts could still be avoided by holding warming below 2 degrees C

The cumulative carbon budget and its implications

The cumulative impact of carbon dioxide (CO2) emissions on climate has potentially profound economic and policy implications. It implies that the long-term climate change mitigation challenge should be reframed as a stock problem, while the overwhelming majority of climate policies continue to focus on the flow of CO2 into the atmosphere in 2030 or 2050. An obstacle, however, to the use of a cumulative carbon budget in policy is uncertainty in the size of this budget consistent with any specific temperature-based goal such as limiting warming to 2°C. This arises from uncertainty in the climate response to CO2 emissions, which is relatively tractable, and uncertainty in future warming due to non-CO2 drivers, which is less so. We argue these uncertainties are best addressed through policies that recognize the need to reduce net global CO2 emissions to zero to stabilize global temperatures but adapt automatically to evolving climate change. Adaptive policies would fit well within the Paris Agreement under the UN Framework Convention on Climate Change

Understand and reduce uncertainties to keep temperature targets on track

IIASA research has found explanations for variations in estimates of global greenhouse gas emissions by 2030. According to the researchers, actions set out in countries’ nationally determined contributions are described ambiguously, introducing uncertainty into the stocktaking process. This poses a danger that action plans will not be strengthened sufficiently to avoid dangerous levels of climate change

Net zero targets in science and policy

Since the adoption of the 2015 Paris Agreement and the publication of the 2018 Special Report on Global Warming of 1.5°C of the Intergovernmental Panel on Climate Change, net zero targets have become a central feature in climate policy. This Perspective looks back at the scientific foundations of this recent policy development, the current state of play, and next frontiers for research on this topic

Analysis of the Copenhagen Accord pledges and its global climatic impacts‚ a snapshot of dissonant ambitions

This analysis of the Copenhagen Accord evaluates emission reduction pledges by individual countries against the Accord's climate-related objectives. Probabilistic estimates of the climatic consequences for a set of resulting multi-gas scenarios over the 21st century are calculated with a reduced complexity climate model, yielding global temperature increase and atmospheric CO2 and CO2-equivalent concentrations. Provisions for banked surplus emission allowances and credits from land use, land-use change and forestry are assessed and are shown to have the potential to lead to significant deterioration of the ambition levels implied by the pledges in 2020. This analysis demonstrates that the Copenhagen Accord and the pledges made under it represent a set of dissonant ambitions. The ambition level of the current pledges for 2020 and the lack of commonly agreed goals for 2050 place in peril the Accord's own ambition: to limit global warming to below 2 °C, and even more so for 1.5 °C, which is referenced in the Accord in association with potentially strengthening the long-term temperature goal in 2015. Due to the limited level of ambition by 2020, the ability to limit emissions afterwards to pathways consistent with either the 2 or 1.5 °C goal is likely to become less feasibl