Carbon budget

The IPCC Sixth Assessment Reports defines carbon budget as the following two concepts: • "An assessment of carbon cycle sources and sinks on a global level, through the synthesis of evidence for fossil fuel and cement emissions, emissions and removals associated with land use and land-use change, ocean and natural land sources and sinks of carbon dioxide (CO2), and the resulting change in atmospheric CO2 concentration. This is referred to as the global carbon budget."; or • "The maximum amount of cumulative net global anthropogenic CO2 emissions that would result in limiting global warming to a given level with a given probability, taking into account the effect of other anthropogenic climate forcers. This is referred to as the total carbon budget when expressed starting from the pre-industrial period, and as the remaining carbon budget when expressed from a recent specified date." Global carbon budgets can be further divided into national emissions budgets, so that countries can set specific climate mitigation goals. An emissions budget may be distinguished from an emissions target, as an emissions target may be internationally or nationally set in accordance with objectives other than a specific global temperature and are commonly applied to the annual emissions in a single year as well. == Estimations ==

Recent and currently remaining carbon budget Several organisations provide annual updates to the remaining carbon budget, including the Global Carbon Project, the Mercator Research Institute on Global Commons and Climate Change (MCC) and the CONSTRAIN project. In March 2022, before formal publication of the "Global Carbon Budget 2021" preprint, scientists reported, based on Carbon Monitor (CM) data, that after COVID-19-pandemic-caused record-level declines in 2020, global emissions rebounded sharply by 4.8% in 2021, indicating that at the current trajectory, the carbon budget for a likelihood for limiting warming to 1.5 °C would be used up within 9.5 years. In April 2022, the now reviewed and officially published The Global Carbon Budget 2021 concluded that fossil emissions rebounded from pandemic levels by around +4.8% relative to 2020 emissions – returning to 2019 levels. It identifies three major issues for improving reliable accuracy of monitoring, shows that China and India surpassed 2019 levels (by 5.7% and 3.2%) while the EU and the US stayed beneath 2019 levels (by 5.3% and 4.5%), quantifies various changes and trends, for the first time provides models' estimates that are linked to the official country GHG inventories reporting, and suggests that the remaining carbon budget at 1. Jan 2022 for a 50% likelihood to limit global warming to 1.5 °C (albeit a temporary exceedence is to be expected) is 120 GtC (420 Gt) – or 11 years of 2021 emissions levels. They found we can emit 250 GtCO2 or 6 years of emissions at current level starting from January 2023, for having a 50% chance to stay below 1.5 degrees. For reaching this target humanity will need to zero CO2 emissions by the year 2034. To have a 50% chance of staying below 2 degrees humanity can emit 1220 Gt or 30 years of emissions at current level. Carbon budget in gigatonnes and factors The finding of an almost linear relationship between global temperature rise and cumulative carbon dioxide emissions has encouraged the estimation of global emissions budgets in order to remain below dangerous levels of warming. Since the pre-industrial period (year 1750) to 2019, approximately 2390 Gigatonnes of (Gt ) has already been emitted globally. Estimations might not include all amplifying climate change feedbacks, although the most authoritative carbon budget assessments as summarised by the IPCC do account explicitly for these.), and • the impact of Earth system feedbacks that would otherwise not be covered. The estimates vary according to the global temperature target that is chosen, the probability of staying below that target, and the emission of other non- greenhouse gases (GHGs). This approach was first applied in the 2018 Special report on Global Warming of 1.5 °C by the IPCC, and was also used in its 2021 Working Group I Contribution to the Sixth Assessment Report. Carbon budget estimates depend on the likelihood or probability of avoiding a temperature limit, and the assumed warming that is projected to be caused by non- emissions. These estimates assume non- emissions are also reduced in line with deep decarbonisation scenarios that reach global net zero emissions. Carbon budget estimates thus depend on how successful society is in reducing non- emissions together with carbon dioxide emissions. Scientists estimated that remaining carbon budgets can be 220 Gt higher or lower depending on how successful non- emissions are reduced. ==Pathways to stay within carbon budget==

National emissions budgets Carbon budgets are applicable to the global level. To translate these global carbon budgets to the country level, a set of value judgments have to be made on how to distribute the total and remaining carbon budget. In light of the many differences between nations, including but not limited to population, level of industrialisation, national emissions histories, and mitigation capabilities, scientists have made attempts to allocate global carbon budgets among countries using methods that follow various principles of equity. Allocating national emissions budgets is comparable to sharing the effort to reduce global emissions, underlined by some assumptions of state-level responsibility of climate change. Many authors have conducted quantitative analyses which allocate emissions budgets, often simultaneously addressing disparities in historical GHG emissions between nations. One guiding principle that is used to allocate global emissions budgets to nations is the principle of "common but differentiated responsibilities and respective capabilities" that is included in the United Nations Framework Convention on Climate Change (UNFCCC). and has been part of the key international agreements on climate change (UNFCCC, the Kyoto Protocol and the Paris Agreement). Consequently, those countries with the highest cumulative historical emissions have the most responsibility to take the strongest actions and help developing countries to mitigate their emissions and adapt to climate change. This principle is recognized in international treaties and has been part of the diplomatic strategies by developing countries, that argue that they need larger emissions budgets to reduce inequity and achieve sustainable development. Another common equity principle for calculating national emissions budgets is the "egalitarian" principle. This principle stipulates individuals should have equal rights, and therefore emissions budgets should be distributed proportionally according to state populations. This principle may be favoured by nations with larger or rapidly growing populations, A third equity principle that has been employed in national budget calculations considers national sovereignty. and the early phase of the European Union Emissions Trading Scheme (EU ETS) This principle is often favoured by developed countries, as it allocates larger emissions budgets to them. is not a 'standard of equity'". Other scholars have highlighted that "to treat states as the owners of emission rights has morally problematic consequences". ==See also==