Year: 2023
Type: book-chapter
Abstract: Net GHG emissions in this report refer to releases of greenhouse gases from anthropogenic sources minus removals by anthropogenic sinks, for those species of gases that are reported under the common reporting format of the United Nations Framework Convention on Climate Change (UNFCCC): CO 2 from fossil fuel combustion and industrial processes (CO 2 -FFI); net CO 2 emissions from land use, land-use change and forestry (CO 2 -LULUCF); methane (CH 4 ); nitrous oxide (N 2 O); and fluorinated gases (F-gases) comprising hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF 6 ), as well as nitrogen trifluoride (NF 3 ).Different datasets for GHG emissions exist, with varying time horizons and coverage of sectors and gases, including some that go back to 1850.In this report, GHG emissions are assessed from 1990, and CO 2 sometimes also from 1850.Reasons for this include data availability and robustness, scope of the assessed literature, and the differing warming impacts of non-CO 2 gases over time.7 GHG emission metrics are used to express emissions of different greenhouse gases in a common unit.Aggregated GHG emissions in this report are stated in CO 2 -equivalent (CO 2 -eq) using the Global Warming Potential with a time horizon of 100 years (GWP100) with values based on the contribution of Working Group I to the AR6.The choice of metric depends on the purpose of the analysis, and all GHG emission metrics have limitations and uncertainties, given that they simplify the complexity of the physical climate system and its response to past and future GHG emissions.{Cross-Chapter Box 2 in Chapter 2, Supplementary Material 2.SM.3,Box TS.2; AR6 WGI Chapter 7 Supplementary Material} 8In this SPM, uncertainty in historic GHG emissions is reported using 90% uncertainty intervals unless stated otherwise.GHG emission levels are rounded to two significant digits; as a consequence, small differences in sums due to rounding may occur.9 Global databases make different choices about which emissions and removals occurring on land are considered anthropogenic.Currently, net CO 2 fluxes from land reported by global bookkeeping models used here are estimated to be about 5.5 GtCO 2 yr -1 higher than the aggregate global net emissions based on national GHG inventories.This difference, which has been considered in the literature, mainly reflects differences in how anthropogenic forest sinks and areas of managed land are defined.Other reasons for this difference, which are more difficult to quantify, can arise from the limited representation of land management in global models and varying levels of accuracy and completeness of estimated LULUCF fluxes in national GHG inventories.Neither method is inherently preferable.Even when the same methodological approach is applied, the large uncertainty of CO 2 -LULUCF emissions can lead to substantial revisions to estimated emissions.{Cross-Chapter Box 3 in Chapter 3, 7.2, SRCCL SPM A.3.3} 10 For consistency with WGI, historical cumulative CO 2 emissions from 1850 to 2019 are reported using 68% confidence intervals.
Language: English
Subfield: Economics and Econometrics
Domain: Social Sciences
SDG: Climate action
Open Access status: bronze
OpenAlex ID: W4385168292