Extreme Precipitation Across the North Atlantic: Model-Data Comparisons from the PETM

Abstract:

Climate model simulations of the PETM warming have mainly focused on replicating the global thermal response through greenhouse forcing, i.e. CO₂, at levels compatible with observations. Comparatively less effort has gone into assessing the skill of models in replicating the response of the hydrologic cycle to the warming, particularly on regional scales. Here we have assembled proxy records of regional precipitation, focusing on the Mid-Atlantic Coasts of North America (New Jersey) and Europe (Spain), which we compare against new simulations of a high-resolution climate model (CAM v5.3). Given the added possibility of the PETM initiating during a maxima in eccentricity, we have employed a two by two experimental design to test the response of the hydrologic system to both greenhouse gas and orbital forcing in order to deconvolve the signals. Key analyses included monthly median/quartile values to determine shifts in seasonality and exceedance frequency of individual events to analyze changes in the tail of the distribution. Modeled results show excellent agreement with observations in Northern Spain, with a significant increase in both overall and extreme precipitation events resulting from increased CO₂ levels, while changing the orbital parameters to maximize solar insolation during boreal summer results in a suppression of this effect. The development of sustained atmospheric rivers appears to be a contributing factor. The North American Coast also shows increases in both overall and extreme precipitation with comparatively less influence from changing orbital parameters. Observed changes in this region may be linked to increased extratropical cyclone activity. These varying responses may contribute to the observed variation in the timing of hydrologic changes relative to the carbon isotope excursion on either side of the Atlantic (Duller et al., 2019).

References:

Duller, Robert A., et al. Delayed sedimentary response to abrupt climate change at the Paleocene-Eocene boundary, northern Spain. Geology 47.2 (2019). https://doi.org/10.1130/G45631.1.