Improved knowledge of glacial-to-interglacial global temperature change implies that fast-
feedback equilibrium climate sensitivity is at least ~4°C for doubled CO2 (2×CO2), with likely
range 3.5-5.5°C. Greenhouse gas (GHG) climate forcing is 4.1 W/m2
larger in 2021 than in
1750, equivalent to 2×CO2 forcing. Global warming in the pipeline is greater than prior
estimates. Eventual global warming due to today’s GHG forcing alone – after slow feedbacks
operate – is about 10°C. Human-made aerosols are a major climate forcing, mainly via their
effect on clouds. We infer from paleoclimate data that aerosol cooling offset GHG warming for
several millennia as civilization developed. A hinge-point in global warming occurred in 1970
as increased GHG warming outpaced aerosol cooling, leading to global warming of 0.18°C per
decade. Aerosol cooling is larger than estimated in the current IPCC report, but it has declined
since 2010 because of aerosol reductions in China and shipping. Without unprecedented global
actions to reduce GHG growth, 2010 could be another hinge point, with global warming in
following decades 50-100% greater than in the prior 40 years. The enormity of consequences of
warming in the pipeline demands a new approach addressing legacy and future emissions. The
essential requirement to “save” young people and future generations is return to Holocene-level
global temperature. Three urgently required actions are: 1) a global increasing price on GHG
emissions, 2) purposeful intervention to rapidly phase down present massive geoengineering of
Earth’s climate, and 3) renewed East-West cooperation in a way that accommodates developing
world needs.