CCR People

Gerald A. Meehl, Senior Scientist

Short Bio

Gerald A. Meehl is a Senior Scientist at the National Center for Atmospheric Research (NCAR) and heads the Climate Change Research Section. His research interests include studying the interactions between El Niño/Southern Oscillation (ENSO) and the monsoons of Asia; identifying possible effects on global climate of changing anthropogenic forcings, such as carbon dioxide and aerosols, as well as natural forcings, such as solar variability; quantifying possible future changes of weather and climate extremes in a warmer climate; and understanding the interplay between internally generated climate variability and the response to external forcings, particularly in the context of understanding and predicting decadal climate variability. He has been involved with all five Intergovernmental Panel on Climate Change (IPCC) climate change assessment reports, serving as contributing author (1990), lead author (1995), coordinating lead author (2001, 2007), and most recently lead author on the near-term climate change chapter for the IPCC AR5 that was completed in 2013. He received his Ph.D. in climate dynamics from the University of Colorado, and was a recipient of the Jule G. Charney Award of the American Meteorological Society in 2009. Dr. Meehl is an Associate Editor for the Journal of Climate, a Fellow of both the American Meteorological Society and the American Geophysical Union, and a Visiting Senior Fellow at the University of Hawaii Joint Institute for Marine and Atmospheric Research. He serves as co-chair of the Community Earth System Model Climate Variability and Change Working Group. Additionally, he has been a member and co-chair of the World Climate Research Programme (WCRP) Working Group on Coupled Models (WGCM), the group that coordinates the international global climate model experiments addressing anthropogenic climate change through the Coupled Model Intercomparison Project (CMIP). He also is a member of the WGCM CMIP Panel that is tasked with formulating the current CMIP6 international model intercomparison activity.

Notable Research Highlights

Discovered, defined, and named the Tropospheric Biennial Oscillation (TBO) that connects interannual variability of the Asian-Australian monsoon system with tropical Pacific sea surface temperature on biennial timescales, and subsequently showed how processes involved with decadal climate variability of the Interdecadal Pacific Oscillation (IPO) in the Indo-Pacific region could modulate the TBO so that in some decades the system is more biennial than others (Meehl, 1987, Mon. Wea. Rev.; Meehl, 1993, J. Climate; Meehl, 1994, Science; Meehl, 1997, J. Climate; Meehl and Arblaster, 2001, Geophys. Res. Lett.; Meehl and Arblaster, 2002a,b, J. Climate; Meehl et al., 2003, J. Climate; Meehl and Arblaster, 2011, J. Climate; Meehl and Arblaster, 2012, Geophys. Res. Lett.)

Led the first effort to address science questions involved with possible changes in future weather and climate extremes in the physical climate system (Meehl et al., 2000a,b, Bulletin Amer. Meteorol. Soc.)

Published the first study documenting future changes of heat waves in a warmer climate and the associated physical processes that are responsible (Meehl and Tebaldi, 2004, Science)

First to quantify processes and changes associated with weather and climate extremes in a warmer climate due to increasing greenhouse gases for frost days (Meehl et al., 2004, Clim. Dyn.) and precipitation extremes (Meehl et al., 2005, Geophys. Res. Lett.); connected patterns of extremes over North America to El Niño anomalies; and showed how those patterns could change in the future with changes in the tropical Pacific base state (Meehl et al., 2007a,b, Geophys. Res. Lett.)

Identified for the first time that the ratio of daily record high temperatures to record low minimum temperatures over the U.S. has been increasing to values greater than one in the presence of mean surface warming, and will continue to increase in the future (Meehl et al., 2009, Geophys. Res. Lett.); and generalized the future changes in the ratio over the U.S. based on mean temperature increase (Meehl and Tebaldi, 2016, Proc. Nat. Acad. Sci.)

Published the first study using analyses of two global coupled climate models to quantify climate change commitment due to human-caused warming (Meehl et al., 2005, Science), and confirmed that result with additional analyses in a single model (Meehl et al., 2006, J. Climate)

Discovered and defined a new mechanism connecting solar variability to tropical Pacific climate whereby small solar forcing changes are amplified by dynamically coupled interactions and cloud feedbacks in the Pacific to produce a La Niña-like response coincident with peaks in solar forcing followed a couple years later by an El Niño-like response (referred to as the “bottom-up” mechanism) (Meehl et al., 2003, J. Climate; Meehl et al., 2008, J. Climate; Meehl and Arblaster, 2009, J. Climate; Meehl et al., 2009, Science; Meehl et al., 2013, Geophys. Res. Lett.)

Documented observed and modeled processes for, and defined future changes to, the Asian-Australian monsoon system, El Niño, and El Niño teleconnections (Meehl, 1990, J. Climate; Meehl et al., 1993, J. Climate; Meehl and Washington, 1993, Science; Meehl et al., 2006, Clim. Dyn.; Meehl and Teng, 2007, Clim. Dyn.)

Discovered and defined a new mechanism that produces decadal timescale variability associated with the Interdecadal Pacific Oscillation (IPO) (Meehl and Hu, 2006, J. Climate) and identified its importance for decadal climate prediction (Meehl et al., 2010, J. Climate)

Led the effort to address the science questions involved with the new field of decadal climate prediction (Meehl et al., 2009, 2014, Bull. Amer. Meteorol. Soc.)

First to address the early-2000s slowdown of global warming (sometimes called the “hiatus”) by identifying where heat goes during hiatus decades (defined as decades with little global mean surface temperature trend, when heat goes into the subsurface ocean), defined mechanisms for producing hiatus and accelerated warming decades, and put these naturally-occurring processes in the context of the response to increasing GHGs and global temperature trends (Meehl et al., 2011, Nature Clim. Change; Meehl et al., 2013, J. Climate; Meehl et al., 2016, Nature Clim. Change)

First to quantify the role of internal decadal variability associated with the negative phase of the IPO to expansions of Antarctic sea ice from 2000 to 2014 (Meehl et al., 2016, Nature Geoscience)

First to publish an initialized decadal climate prediction based on a physical process--connecting interannual ENSO variability with decadal timescale transitions of the Interdecadal Pacific Oscillation--to predict a transition of the IPO to positive in the 2015-2019 time frame, with larger rates of global warming from 2013 to 2022 (Meehl et al., 2016, Nature Communications)

Documented processes and mechanisms associated with the seasonal cycle and interannual variability in the Southern Hemisphere (Meehl, 1987, Mon. Wea. Rev.; Meehl, 1991, J. Climate; Meehl et al., 1998, Tellus; Meehl and van Loon, 2017, Geophys. Res. Lett.)

Documented processes and mechanisms associated with decadal climate variability globally (Meehl et al., 1998, Geophys. Res. Lett.; Meehl et al., 2000, J. Climate), in the Pacific (Meehl et al., 2009, J. Climate), and over North America (Meehl et al., 2012, J. Climate; Meehl et al., 2015, Geophys. Res. Lett.)

Documented skill of initialized decadal hindcasts in simulating large climate shifts associated with the IPO (Meehl and Teng, 2012, 2014a,b, Geophys. Res. Lett.; Meehl et al., 2014, Nature Clim. Change; Meehl et al., 2015, Geophys. Res. Lett.)

Performed multiple pioneering studies to quantify possible future climate changes due to increases of greenhouse gases, with a particular focus on the Asia-Pacific and North American regions (Meehl and Washington, 1986, Mon. Wea. Rev.; Meehl and Washington, 1990, Clim. Change; Meehl and Washington, 1996, Nature; Meehl et al., 2000, J. Climate; Meehl and Arblaster, 2003, Clim. Dyn.; Meehl et al., 2004, J. Climate; Meehl et al., 2012, J. Climate; Meehl et al., 2013, J. Climate)

Starting in 1995, under the auspices of the World Climate Research Programme, initiated and led the Coupled Model Intercomparison Project (CMIP) as part of the WCRP/CLIVAR Working Group on Coupled Models; this led to the first coordinated comparison of a set of climate change experiments performed by modeling groups from around the world for CMIP3 and assessed in the IPCC AR4, subsequently leading to CMIP5 simulations assessed in the IPCC AR5, and CMIP6 simulations assessed in the IPCC AR6. CMIP has transformed the field of climate science by making state-of-the-art climate change experiments openly available to researchers and students around the world (Meehl et al., 1997, EOS; Meehl et al., 2000, Bull. Amer. Meteorol. Soc.; Meehl et al., 2005, Bull. Amer. Meteorol. Soc.; Meehl et al., 2007, Bull. Amer. Meteorol. Soc.; Meehl et al., 2014, EOS)

Participated as an author in all five of the Intergovernmental Panel on Climate Change (IPCC) assessments (contributing author in the First, lead author in the Second, coordinating lead author in the Third and Fourth, all for the climate change projections chapters; and lead author in the Fifth for the near-term climate change chapter)

CGD People

Gerald A. Meehl, Senior Scientist