Global warming in the pipeline

Abstract

Improved knowledge of glacial-to-interglacial global temperature change yields Charney (fast-feedback) equilibrium climate sensitivity 1.2 ± 0.3°C (2σ) per W/m2, which is 4.8°C ± 1.2°C for doubled CO2. Consistent analysis of temperature over the full Cenozoic era—including ‘slow’ feedbacks by ice sheets and trace gases—supports this sensitivity and implies that CO2 was 300–350 ppm in the Pliocene and about 450 ppm at transition to a nearly ice-free planet, exposing unrealistic lethargy of ice sheet models. Equilibrium global warming for today’s GHG amount is 10°C, which is reduced to 8°C by today’s human-made aerosols. Equilibrium warming is not ‘committed’ warming; rapid phaseout of GHG emissions would prevent most equilibrium warming from occurring. However, decline of aerosol emissions since 2010 should increase the 1970–2010 global warming rate of 0.18°C per decade to a post-2010 rate of at least 0.27°C per decade. Thus, under the present geopolitical approach to GHG emissions, global warming will exceed 1.5°C in the 2020s and 2°C before 2050. Impacts on people and nature will accelerate as global warming increases hydrologic (weather) extremes. The enormity of consequences demands a return to Holocene-level global temperature. Required actions include: (1) a global increasing price on GHG emissions accompanied by development of abundant, affordable, dispatchable clean energy, (2) East-West cooperation in a way that accommodates developing world needs, and (3) intervention with Earth’s radiation imbalance to phase down today’s massive human-made ‘geo-transformation’ of Earth’s climate. Current political crises present an opportunity for reset, especially if young people can grasp their situation.

Global polycrisis: the causal mechanisms of crisis entanglement

“…Human resource consumption and pollution output are pushing Earth's physical and ecological systems far from their previous equilibria, imperiling the stability of many other global systems critical to human wellbeing, from food production to international security. For instance, our emissions of greenhouse gases have created an energy imbalance at the planet's surface (more heat coming in from space than going out) of about 1.36 Watts per square meter (Hansen et al, 2023). This extra energy – now equivalent to nearly one million Hiroshima-sized atomic bombs exploded in the atmosphere every day – is producing increasingly extreme storms, floods, heat waves, and droughts, affecting billions of people and worsening population displacement, social instability, and conflict (Adelphi & PIK, 2020; Ide et al, 2020; Schleussner et al, 2016).…”

“…For example, since HIV first appeared four decades ago, outbreaks of zoonotic viral disease have become increasingly severe and frequent, from the SARS outbreak of 2002 to H1N1 in 2009, MERS in 2012, Ebola in 2014, Zika in 2015, Ebola again in 2018, Covid-19 in 2019, and most recently mpox and Marburg (Araf et al, 2023; CFR, 2023; Smith et al, 2014). Meanwhile, climate heating is also accelerating: between 1970 and 2010, Earth's tropospheric temperature increased about 0.18 °C per decade; between 2010 and 2040, warming is predicted to increase to 0.27 °C per decade, a rise in rate of 50% (Hansen et al, 2023, p. 21). And because this warming makes zoonotic disease outbreaks more likely, two seemingly discrete crises – pandemics and calamitous weather – are becoming increasingly entwined (Carlson et al, 2022).…”

Last Glacial Maximum pattern effects reduce climate sensitivity estimates

“…Our results suggest that the LGM feedback is more positive than the 2xCO 2 feedback because of the LGM ice-sheet forcing and resulting SST pattern. Failing to account for this difference in feedbacks would lead to the inference of higher values of modern-day ECS from the LGM, e.g., ( 54 ). Some past studies using fully coupled models have considered these feedback differences indirectly by applying an “efficacy” adjustment ( 55 ) to the LGM forcings.…”

Final call: Climate change and us

“…Finally, reduced burning of fossil fuels used in shipping (as must happen) has reduced (reflective) aerosol release and has dramatically accelerated heating as a consequence. 16…”