National Center for Atmospheric Research, Boulder, 80305, United States of America
Abstract. Differences in the Atlantic meridional overturning circulation (AMOC) from the Younger Dryas (YD) to the Holocene can be explained by, but not limited to, factors relating to atmospheric greenhouse gas concentrations, discharge of freshwater into the surface ocean, and changes in Earth's orbital parameters. Utilizing the Community Earth System Model (CESM1.0.5) with moderate resolution, this study evaluates how Younger Dryas seasonal and annual radiative forcing affect the climate change and variability. The Younger Dryas to Holocene changes in radiative forcing are mostly attributed to change in orbital parameters and to lesser extent to the relatively small rise in atmosphere pCO2, which is supported by a comparison of model simulations with proxy reconstructions of sea surface temperature and oceanic δ18O. These factors led to increased precipitation and reduced transport of water masses in the North Atlantic Ocean. Atmospheric pCO2 and orbital parameter changes are not substantial enough to explain the transition to the Younger Dryas northern hemispheric cooling. Younger Dryas to Holocene changes in the Monsoonal circulation over the African continent appears to be more affected by changes in orbital parameters than in atmospheric pCO2 but underestimated compared to observed reconstructions from ice and sediment cores. Thus, additional mechanisms such as fresh water hosed-cooling and/or ice sheet-albedo effect need to be considered to explain the Younger Dryas to Holocene climate change and variability.
How to cite. Hughlett, T. M., Winguth, A. M. E., and Rosenbloom, N.: The Effects of
Younger Dryas Orbital Parameter
Changes on Radiative Forcing and
Circulation, Clim. Past Discuss. [preprint], https://doi.org/10.5194/cp-2018-23, in review, 2018.
Received: 05 Mar 2018 – Discussion started: 01 Jun 2018
This study used the Community Earth System Model version 1.2 to isolate and compare changes in radiative forcing due to orbital and atmospheric pCO2 concentrations for the Younger Dryas cooling event. It was determined that while neither parameter alone could induce a cooling comparative to the Younger Dryas, the changes in orbital parameters and the resultant changing of radiative forcing imparts a more pronounced effect on the climate than radiative changes due to pCO2.
This study used the Community Earth System Model version 1.2 to isolate and compare changes in...