Simulated CO2 level, starting at 421.08 ppmv in 2023, and zero emissions,
per Dr. Roy Spencer's 2023 version Simple Model. Reference:
Spencer, RW (2023). ENSO Impact on the Declining CO2 Sink Rate. J Mari Scie
Res Ocean, 6(4), 163-170, https://doi.org/10.33140/jmsro.06.04.03

Equilibrium CO2 level is 293.60, half-way down to that is 357.34 ppmv.
Half-life is 34.31 years, e-folding lifetime (adjustment time) is 49.50 years.
YEAR  CO2
2023  421.1
2024  418.5
2025  416.0
2026  413.5
2027  411.1
2028  408.7
2029  406.4
2030  404.1
2031  401.9
2032  399.7
2033  397.5
2034  395.4
2035  393.4
2036  391.4
2037  389.4
2038  387.5
2039  385.6
2040  383.7
2041  381.9
2042  380.1
2043  378.4
2044  376.6
2045  375.0
2046  373.3
2047  371.7
2048  370.1
2049  368.6
2050  367.1
2051  365.6
2052  364.1
2053  362.7
2054  361.3
2055  359.9
2056  358.6
2057  357.3
** 357.3 ppmv: half of the 127.5 ppmv CO2 above equilibrium is gone **
** date 2057.3: One half-life (34.3 years) reached **
2058  356.0
2059  354.7
2060  353.5
2061  352.3
2062  351.1
2063  350.0
2064  348.8
2065  347.7
2066  346.6
2067  345.5
2068  344.5
2069  343.5
2070  342.5
2071  341.5
2072  340.5
** date 2072.5: e-folding life (49.5 years) and level (340.50 ppmv) reached **
2073  339.6
2074  338.6
2075  337.7
2076  336.8
2077  336.0
2078  335.1
2079  334.3
2080  333.4
2081  332.6
2082  331.8
2083  331.1
2084  330.3