Today we review an analysis of various scenarios for CO2 emission reduction, based on the voluntary pledges made by 190 countries attending the Paris conference COP 21. On the assumption that these pledges are implemented, beginning in 2020 and ending in 2030, the longer term implications to limit further warming depend on either a continuation of the level of decarbonization pledged (“Paris continued” which is around 2% per year)or an increase in the reductions (“Paris increased” which is around 5% per year). The probability of limiting warming to 2 deg C is only 8% under Paris continued while limiting it to 4 deg C is 75%. Under Paris increased, the probability of limiting warming to 2 deg C increases to 30%. Under any scenario, the need to bring carbon emissions to net zero before 2100 is required to avoid 2 deg C warming.
Key Quotes:
“The Paris–Continued ambition scenario assumes that countries continue to decarbonize their economies beyond 2030 with the same annual decarbonization rate that was required to achieve their INDCs between 2020 and 2030. If their decarbonization rate is below a specified minimum (2% per year), they instead follow a path defined by that 2% minimum rate”
“The Paris–Continued ambition scenario reduces the probability of temperature change exceeding 4°C in 2100 by 75% compared with the Reference-Low policy scenario and by 80% compared with the Reference–No policy scenario.“
“In the Paris-Continued ambition scenario, the probability of limiting warming to 2°C increases to 8% as opposed to virtually no chance in the two Reference scenarios.” “the Paris–Increased ambition scenario assumes a higher minimum decarbonization rate (5% per year) beyond 2030. This minimum rate is consistent with the average decarbonization rate required by the European Union and the United States to achieve their INDCs from 2020 to 2030“
“If ambition is scaled up after 2030—as in the Paris–Increased ambition scenario—the probability of limiting warming to 2°C increases to about 30%. If we assume even greater post-2030 emissions reductions, the probability of limiting warming to less than 2°C could be 50% or more.”
“to limit warming to any level, CO2 emissions at the global level must ultimately be brought to zero”
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