Contributions of past and present human generations to committed warming caused by carbon dioxide

We developed a highly simplified approach to estimate the contributions of the past and present human generations to the increase of atmospheric CO ₂ and associated global average temperature increases. For each human generation of adopted 25-year length, we use simplified emission test cases to estimate the committed warming passed to successive children, grandchildren, and later generations. We estimate that the last and the current generation contributed approximately two thirds of the presentday CO₂-induced warming. Because of the long time scale required for removal of CO₂ from the atmosphere as well as the time delays characteristic of physical responses of the climate system, global mean temperatures are expected to increase by several tenths of a degree for at least the next 20 years even if CO₂ emissions were immediately cut to zero; that is, there is a commitment to additional CO₂-induced warming even in the absence of emissions. If the rate of increase of CO₂ emissions were to continue up to 2025 and then were cut to zero, a temperature increase of ≈1.3°C compared to preindustrial conditions would still occur in 2100, whereas a constant-CO₂-emissions scenario after 2025 would more than double the 2100 warming. These calculations illustrate the manner in which each generation inherits substantial climate change caused by CO₂ emissions that occurred previously, particularly those of their parents, and shows that current CO₂ emissions will contribute significantly to the climate change of future generations.