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Sensitivity of the Palaeocene-Eocene Thermal Maximum climate to cloud properties
Jeffrey T Kiehl1, Christine A Shields
1National Center for Atmospheric Research, , 1850 Table Mesa Drive, Boulder, CO 80305, USA.
Summary
Investigating past greenhouse events like the Palaeocene-Eocene Thermal Maximum (PETM) is crucial. Lowering cloud condensation nuclei (CCN) in climate models significantly warms simulations, suggesting cloud properties influence past climate reconstructions.
Area of Science:
- Paleoclimatology
- Climate Modeling
- Earth Science
Background:
- The Palaeocene-Eocene Thermal Maximum (PETM) around 55 million years ago was a period of rapid global warming.
- This event is linked to increased greenhouse gases, particularly carbon dioxide and methane.
- Studying past high-carbon dioxide climates is vital for understanding future climate change and validating climate models.
Purpose of the Study:
- To investigate the sensitivity of pre-PETM and PETM climate simulations to changes in cloud properties.
- To assess the role of cloud condensation nuclei (CCN) and cloud microphysics in simulating past warm climates.
- To determine if altered cloud properties can reconcile model simulations with proxy data for Eocene temperatures.
Main Methods:
- Utilized climate modeling to simulate pre-PETM and PETM conditions.
- Varied cloud condensation nuclei (CCN) concentrations and liquid water cloud microphysical properties in simulations.
- Compared simulated surface temperatures with paleoclimate proxy data.
Main Results:
- Lowering CCN levels in simulations resulted in significant warming, particularly at high latitudes.
- The study highlights the potential impact of past cloud property variations on climate sensitivity.
- Simulated warming due to altered cloud properties suggests lower atmospheric CO2 concentrations may be needed to match proxy data.
Conclusions:
- Cloud properties, specifically CCN levels and cloud microphysics, are critical factors for accurately simulating past warm climates like the PETM.
- Variations in cloud characteristics could explain discrepancies between climate models and paleoclimate evidence.
- This research implies that changes in cloud radiative effects may have played a substantial role in regulating Eocene temperatures and potentially reducing the required CO2 forcing.
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