How can computer models help test hypotheses?


Another major component of our work centers around how we can use climate model simulations to better understand phenomena underpinning the environmental and climatic signals imprinted in the natural archives. In collaboration with various climate modeling groups, we routinely conduct earth system ‘sensitivity experiments’ under varying boundary conditions and climate forcings. Results from this work have thus far demonstrated that tropical rainfall variability across Australasia is particularly sensitive to an array of forcings and feedbacks that operate on varying time scales, including Indian and Pacific Ocean temperature variability (Griffiths et al., 2016), glacial meltwater pulses in the North Atlantic (Zhang et al., 2018), and vegetation and dust aerosol emissions across Africa (Griffiths et al., 2020).

In other modeling work with colleagues from NASA Goddard Institute for Space Studies, we are working to better constrain cloud and convective processes—one of the major sources of uncertainty in climate model projections—in the GISS ModelE2.1 climate model using paleoclimate proxy data. Recently, we demonstrated that paleoclimates have the potential to constrain these cloud parameterizations in a perturbed parameter ensemble (PPE) of the atmosphere-only version of ModelE2.1 (Ramos et al., submitted to JAMES). The next phases of this work are threefold: (1) conduct a suite of fully coupled, isotope-enabled simulations for select time periods [e.g., Last Glacial Maximum (LGM), mid-Holocene (MH), and Pre-industrial (PI)] using a wide ensemble of cloud and convective parameter sets; (2) perform paleoclimate data assimilation on this PPE using sea surface temperature (SST) and water isotope proxies; and (3) use the posteriors from these time period assimilations to identify which cloud and convection parameters provide the best match to the proxy data, then conduct present-day and doubled CO2 experiments with these parameter sets to calculate a narrowed estimate of equilibrium climate sensitivity (ECS). The hope is that, ultimately, these results will help to better constrain ECS and improve simulations of past and future climates.

Representative Publications

On the Remote Impacts of Mid-Holocene Saharan Vegetation on South American Hydroclimate: A Modeling Intercomparison.
Tiwari, S., Ramos, R. D., Pausata, F. S. R., LeGrande, A. N., Griffiths, M. L., Beltrami, H., Wainer, I., de Vernal, A., Litchmore, D. T., Chandan, D., Peltier, W. R., and Tabor, C. R., 2023. Geophysical Research Letters.

Constraining cloud and convective parameterizations in a climate model using paleoclimate data.
Ramos, R.D., LeGrande, A.N., Griffiths, M.L., Elsaesser, G., Litchmore, D.T., Tierney, J.E., Pausata, F.S.R., and Nusbaumer. J., 2022. Journal of Advances in Modeling Systems.

Asian monsoon evolution linked to Pacific temperature gradients since the late Miocene.
Lu, J., Yang, H., Griffiths, M.L., Burls, N.J., Xiao, G., Yang, J., Wang, J., Johnson, K.R., Xie, S., 2021. Earth and Planetary Science Letters, 563: 116882.

End of Green Sahara amplified mid-to late Holocene megadroughts in mainland Southeast Asia.
Griffiths, M.L., Johnson, K.R., Pausata, F.S., White, J.C., Henderson, G.M., Wood, C.T., Yang, H., Ersek, V., Conrad, C. and Sekhon, N., 2020. Nature communications 11(1), 1-12.

​​East Asian hydroclimate modulated by the position of the westerlies during Termination I.
Zhang, H., Griffiths, M.L., Chiang, J.C.H., Kong, W., Wu, S., Atwood, A., Huang, J., Cheng, H., Ning, Y., Xie, S., 2018. Science 362, 580-583. Associated Perspective.

Western Pacific hydroclimate linked to global climate variability over the past two millennia.
Griffiths, M.L., Kimbrough, A.K., Gagan, M.K., Drysdale, R.N., Cole, J., Johnson, K., Zhao, J.-x., Cook, B., Hellstrom, J.C., Hantoro, W.S., 2016. Nature Communications, 7:11719.


Collaborative Research: Constraining cloud and convective parameterizations using paleoclimate data assimilation. [PI: M.L. Griffiths; co-PIs: J. Tierney (U. Arizona), G. Elsaesser (Columbia/NASA GISS)]. National Science Foundation, Paleo Perspectives on Climate Change (P2C2), AGS-GEO/ATM-2202999, $876,154 ($359,865 to Griffiths). 07/01/22 – 06/30/25.

Dry or Wet in East Asia During Heinrich Events? New Perspectives from Multiproxy Cave Records and Coupled Model Simulations [PI: M.L. Griffiths]. National Science Foundation, Paleo Perspectives on Climate Change (P2C2), AGS-GEO/ATM-1805544, $298,939. 02/01/19 – 01/31/22.


Riovie Ramos, William Paterson University
Allegra LeGrande, NASA Goddard Institute for Space Studies
Francesco S.R. Pausata, University of Quebec
Natalie Burls, George Mason University
John Chiang, University of California, Berkeley
Clay Tabor, University of Connecticut
Jessica Tierney, University of Arizona
Greg Elsaesser, NASA Goddard Institute for Space Studies