Part Two / How our Planet is Changing

Tamsin Edwards

All online sources accessed on 4 March 2022

122. The kind of heat that was expected only once a decade Intergovernmental Panel on Climate Change, ‘Summary for policymakers’, in Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, ed. V. Masson-Delmotte et al. (Cambridge: Cambridge University Press, in press), Fig. SPM.6: ‘Hot temperature extremes over land’, https://www.ipcc.ch/report/ar6/wg1/. Hot temperature extremes are defined as daily maximum temperatures over land that were exceeded on average once per decade between 1850 and 1900.

     Extreme heavy rain is now 30 per cent more likely Ibid., Fig. SPM.6: ‘Heavy precipitation over land’. Extreme precipitation events are defined as the daily precipitation amount over land that was exceeded on average once per decade between 1850 and 1900.

     Droughts … are 70 per cent more likely Ibid., Fig. SPM.6: ‘Agricultural and ecological droughts in drying regions’. Drought events are defined as the annual average of total column soil moisture below the tenth percentile of the 1850–1900 period. Results are shown for drying regions only.

     some of which we have made three … times more likely Otto, F. E. L., et al., ‘Likelihood of Cape Town water crisis tripled by climate change’, World Weather Attribution, 13 July 2018, https://www.worldweatherattribution.org/the-role-of-climate-change-in-the-2015-2017-drought-in-the-western-cape-of-south-africa.

     doubling them by the end of the century CO₂ emissions from all sectors increase from around 40 gigatonnes to 80 gigatonnes between 2015 to 2100, i.e. an average of just under 0.5 gigatonnes per year (of which the vast majority are from fossil fuels, not deforestation). This is similar to the average increase of fossil fuel CO₂ emissions, from around 26 gigatonnes per year to around 36 gigatonnes per year during the twenty-year period 2000–2019, estimated in the global carbon budget for 2021: Global Carbon Project, ‘Infographics: Global carbon budget 2021’, https://www.globalcarbonproject.org/carbonbudget/21/infographics.htm.

     When our ancestors were beginning to craft stone tools Harmand, S., ‘3.3-million-year-old stone tools from Lomekwi 3, West Turkana, Kenya’, Nature, 521 (7552), 2015: 310–15, https://doi.org/10.1038/nature14464; Brahic, C., ‘Human ancestors got a grip on tools 3 million years ago’, New Scientist, 22 January 2015, https://www.newscientist.com/article/dn26844-human-ancestors-got-a-grip-on-tools-3-million-years-ago; Skinner, M. M., et al., ‘Human-like hand use in Australopithecus africanus’, Science, 347 (6220), 2015: 395–9, https://doi.org/10.1126/science.1261735.

     hundreds of millions more people exposed to deadly heatwaves Hoegh-Guldberg, O., et al., ‘Impacts of 1.5ºC global warming on natural and human systems’, in Intergovernmental Panel on Climate Change, Global Warming of 1.5°C: An IPCC Special Report on the Impacts of Global Warming of 1.5°C above Pre-industrial Levels and Related Global Greenhouse Gas Emission Pathways, in the Context of Strengthening the Global Response to the Threat of Climate Change, Sustainable Development, and Efforts to Eradicate Poverty, ed. V. Masson-Delmotte (Cambridge: Cambridge University Press, 2018), https://www.ipcc.ch/sr15/chapter/chapter-3/.

124. even at 1.5°C of warming, sea ice … will almost disappear Intergovernmental Panel on Climate Change, ‘Summary for policymakers’, in Climate Change 2021: The Physical Science Basis, paragraph B.2.5: ‘The Arctic is likely to be practically sea ice-free in September at least once before 2050 under the five illustrative scenarios considered in this report.’ Under the lowest of these emissions scenarios (SSP1-1.9), the global surface temperature relative to 1950–2000 is predicted to increase by 1.5°C in 2021–40, 1.6°C in 2041–60 and 1.4°C in 2081–2100, i.e. 1.5°C with limited overshoot: ibid., Table SPM.1.

     At 3–4°C of warming it will disappear entirely Fox-Kemper, B., et al., ‘Ocean, cryosphere and sea level change’, in Intergovernmental Panel on Climate Change, Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, ed. V. Masson-Delmotte et al. (Cambridge: Cambridge University Press, in press), https://www.ipcc.ch/report/ar6/wg1/, ‘Executive summary’ : ‘The practically ice-free state is projected to occur more often with higher greenhouse gas concentrations, and it will become the new normal for high-emissions scenarios by the end of this century (high confidence) … At sustained warming levels between 1.5°C and 2°C, the Arctic Ocean will become practically sea ice-free in September in some years (medium confidence) … At sustained warming levels between 2°C and 3°C, the Arctic Ocean will be practically sea ice-free throughout September in most years (medium confidence) … At sustained warming levels between 3°C and 5°C, the Arctic Ocean will become practically sea ice-free throughout several months in most years (high confidence).’

     Even at these temperatures Lee, J.-Y., et al., ‘Future global climate: scenario-based projections and near-term information’, in Intergovernmental Panel on Climate Change, Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, ed. V. Masson-Delmotte et al. (Cambridge: Cambridge University Press, in press), doi: 10.1017/9781009157896.006.

     10°C hotter by the year 2300 Ibid., Table 4.9. Under the highest illustrative emissions scenario (SSP5-8), the best estimate (mean) for the increased in global air surface temperature by 2300 relative to 1950–2000 is 9.6°C, with a very likely (90 per cent) possibility of anywhere between 6.6 and 14.1°C.

125. ‘unless there are immediate, rapid, and large-scale reductions’ Intergovernmental Panel on Climate Change, ‘Climate change widespread, rapid, and intensifying’ (press release for the completion of the IPCC Working Group I report Climate Change 2021: The Physical Science Basis), 9 August 2021, https://www.ipcc.ch/2021/08/09/ar6-wg1-20210809-pr.

     if those policies are successfully enforced Carbon Brief, ‘Analysis: do COP26 promises keep global warming below 2°C?’, 10 November 2021, https://www.carbonbrief.org/analysis-do-cop26-promises-keep-global-warming-below-2c.