Climate sensitivity, sea level and atmospheric carbon dioxide

Area of Science:

• Paleoclimatology
• Climate modeling
• Earth system science

Background:

• Cenozoic climate data reveal covariations between temperature, sea level, and CO2.
• Understanding climate sensitivity is crucial for predicting future climate change.
• Previous estimates of climate sensitivity have uncertainties related to data and model assumptions.

Purpose of the Study:

• To infer climate sensitivity from Cenozoic temperature, sea level, and CO2 data.
• To investigate the state-dependence of climate sensitivity using a simplified global model.
• To assess the implications of high carbon dioxide emissions for Earth's habitability.

Main Methods:

• Analysis of Pleistocene and Eemian climate oscillations for climate sensitivity estimates.
• Development and application of a simplified global climate model focusing on essential processes.
• Investigation of slow feedbacks, including ice sheet dynamics and atmospheric CO2 changes.

Main Results:

• Fast-feedback climate sensitivity is estimated at 3±1°C for a 4 W/m² CO2 forcing, with less ambiguity from glacial-interglacial cycles (3-4°C).
• Climate sensitivity increases towards warmer initial states due to reduced low cloud cover and increased water vapor.
• Slow feedbacks, like ice sheet changes, amplify Earth system sensitivity over longer timescales, but models may exaggerate response times.

Conclusions:

• Burning all fossil fuels would lead to extreme warming, making most of the planet uninhabitable.
• Current adaptation strategies may be insufficient given the potential for extreme climate change.
• Accurate paleoclimate data are essential for refining climate sensitivity estimates and improving future climate projections.