The more greenhouse gas (like CO2) we release the more temperatures will rise . As the planet warms melting ice, thawing permafrost and other responses from the Earth itself (see the feedbacks chapter) will make temperatures rise even more [2,3].
How much greenhouse gas we release depends mainly on how much energy we use, and how it is produced [4,5]. These factors are dictated by politics, economics, innovation [6,7], population growth and energy use per person .
Climate modellers use several different well-considered scenarios of human behaviour to predict different possible future changes in temperature [9,10]. These predictions, along with a range of possible results, are shown in the graph posted .
The green line in this graph represents a future where there is no change or addition to current climate policies [12,13,14]. It’s estimated that this would cause 4.5°C of global warming by 2100 [15,16].
If we implement climate policies such that CO2 emissions peak at roughly 40Gt per year around 2040 [17,18] and become roughly constant at 15Gt per year after 2080 , the light blue line is more likely. This corresponds with 2.5°C of warming by 2100 [12,16].
The dark purple line represents a future where extremely rigorous and strict climate policies  are put into place during 2020 . This would still cause 1.6°C of global warming by 2100 [15,16]!
 https://earthobservatory.nasa.gov/features/GlobalWarming/page2.php (Final Paragraph)
 https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_TS_FINAL.pdf (Page 58 Paragraph 2)
 https://www.pnas.org/content/pnas/105/6/1786.full.pdf (Arctic Sea Ice)
 https://feu-us.org/behind-the-climate-pledges/ (Key Conclusions Page ii Bullet points)
 https://ane4bf-datap1.s3-eu-west-1.amazonaws.com/wmocms/s3fs-public/ckeditor/files/United_in_Science_ReportFINAL_0.pdf?XqiG0yszsU_sx2vOehOWpCOkm9RdC_gN(Ambitious Policy Measures page 24)
 https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions#global-inequalities-in-co2-emissions (para 1 – but rest of the sections are interesting and relevant!)
 https://link.springer.com/article/10.1007/s10584-011-0148-z (Introduction paragraph 1)
 https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter12_FINAL.pdf (Figure 12.5)
 https://link.springer.com/article/10.1007/s10584-011-0148-z (3.3.1 paragraph 2)
 https://link.springer.com/article/10.1007/s00382-012-1636-1(Summary and Conclusion Paragraph 4)
 https://report.ipcc.ch/srocc/pdf/SROCC_SPM_Approved.pdf (Table SPM.1)
 https://link.springer.com/article/10.1007%2Fs10584-011-0151-4 (RCP4.5 stabilization Scenarios Paragraph 3 and Figure 3a)
 https://link.springer.com/article/10.1007/s10584-011-0148-z (Figure 6)
 https://link.springer.com/article/10.1007%2Fs10584-011-0151-4 (RCP4.5 stabilization Scenario Paragraph 1 and Figure 3a)
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