Editing IPCC:AR6/WGI/TS (section)

=== Selected Updates and/or New Results Since AR5 and SR1.5 ===

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* '''Timing of crossing 1.5°C global warming:''' Slightly different approaches are used in SR1.5 and in this Report. SR1.5 assessed a ''likely'' range of 2030 to 2052 for reaching a global warming level of 1.5°C (for a 30-year period), assuming a continued, constant rate of warming. In AR6, combining the larger estimate of global warming to date and the assessed climate response to all considered scenarios, the central estimate of crossing 1.5°C of global warming (for a 20-year period) occurs in the early 2030s, in the early part of the ''likely'' range assessed in SR1.5, assuming no major volcanic eruption. (Section TS.1.3, Cross-Section Box TS.1)
* '''Remaining carbon budgets:''' The AR5 had assessed the transient climate response to cumulative emissions of CO <sub>2</sub> to be ''likely'' in the range of 0.8°C to 2.5°C per 1000 GtC (1 Gigatonne of carbon, GtC, = 1 Petagram of carbon, PgC, = 3.664 Gigatonnes of carbon dioxide, GtCO <sub>2</sub> ), and this was also used in SR1.5. The assessment in AR6, based on multiple lines of evidence, leads to a narrower ''likely'' range of 1.0°C–2.3°C per 1000 GtC. This has been incorporated in updated estimates of remaining carbon budgets (see Section TS.3.3.1), together with methodological improvements and recent observations. (Sections TS.1.3 and TS.3.3)
* '''Effect of short-lived climate forcers on global warming in coming decades:''' The SR1.5 stated that reductions in emissions of cooling aerosols partially offset greenhouse gas mitigation effects for two to three decades in pathways limiting global warming to 1.5°C. The AR6 assessment updates the AR5 assessment of the net cooling effect of aerosols and confirms that changes in short-lived climate forcers will ''very likely'' cause further warming in the next two decades across all scenarios. (Section TS.1.3, Box TS.7)
* '''COVID-19:''' Temporary emissions reductions in 2020 associated with COVID-19 containment led to small and positive net radiative effect (warming influence). However, global and regional climate responses to this forcing are undetectable above internal climate variability due to the temporary nature of emissions reductions. (Section TS.3.3)

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