Climate Modeling at GFDL: The Scientific Challenges V. Ramaswamy NOAA/ Geophysical Fluid Dynamics Laboratory November 12, 2008

Be a world leader for the production of timely and reliable knowledge and assessments on natural climate variability and anthropogenic changes and in the development of the required earth system models. Work cooperatively in NOAA to advance its expert assessments of changes in national and global climate through research, improved models, and products. GFDL Mission Directly supports the DOC And NOAA Strategic Goals One of 2 Climate Modeling Centers called for in the US Climate Change Science Program [CCSP]

Atmospheric, Ocean, Land, Coupled, Earth System Model Developments Matrix Managed

AM2, LM2, SIS, OM3 (MOM4) AM3, LM3, SIS, OM3 (MOM4, GOLD) CM2.0 CM AR4, WMO/UNEP GFDL’s Recent Major Climate Model Developments CCSPs, NARCCAP B-gridFV core FV, CS cores Hi-res AM2 CM 2.4 ESM 2.1 w/ OM3 {M,G} CM3

Anthro. RF > 0 (v. high conf.) 20 th Cent. continental warming likely due to human activity Projected global warming Projected pattern of rainfall changes in 21 st Cent. Projected warming pattern in early and late 21 st Cent. NOAA/ GFDL model simulations contributed to IPCC AR4 AR4 conclusions

Global decreases in sulfate aerosol  warmer U.S. summers in 2100 CCSP 1.1 CCSP 3.2  (sfc - tropos): Models vs. Obs. CCSP 2.4 CCSP 3.3 NOAA/ GFDL contribution to CCSP reports

OUTLINE Understanding present climate; quantifying the causal factors and attribution of past climate change; and projections of future climate changes. Challenges and progress in modeling the Atmosphere, Ocean, Coupled Atmosphere-Ocean, and Biosphere to address the key issues.

Schwarzkopf and Ramaswamy (2008)

The World Has Warmed Globally averaged, the planet is about 0.75°C warmer than it was in 1860, based upon dozens of high-quality long records using thermometers worldwide, including land and ocean. Eleven of the last 12 years are among 12 warmest since 1850 in the global average. Globally averaged, the planet is ~0.75°C warmer than it was in 1860, based upon dozens of high-quality long records, including land and ocean. Eleven of the last 12 years are among 12 warmest since 1850 in the global average. IPCC AR4

Nat = Natural Forcing Anth = Anthropogenic Forcing AllForc = (Nat + Anth) Forcings CRU = Observations GFDL Climate Model CM IPCC AR4 simulation

Human and Natural Drivers of Climate Change IPCC (2007)

GFDL CM 2.1 Anthropogenic forcings and response [ ]

Uncertainties Aerosol microphysics Aerosol-Cloud interaction

Sulfate AOD overestimated (Europe) AOD overestimated (East coast) Biomass emissions underestimated (S Africa) Biomass emissions underestimated (S America) AOD GFDL CM2.1 ( ) Aerosol Optical Depths from GFDL Coupled Model 2.1 (CM2.1), AVHRR, and MODIS

The Future What will be the impacts of changes in Greenhouse Gases and Aerosols?

How might future changes in aerosols affect climate? HISTORICAL and FUTURE SCENARIOS CO 2 concentrations ppmv Emissions of Short-lived Gases and Aerosols (A1B) NO x (Tg N yr -1 ) SO 2 (Tg SO 2 yr -1 ) BC (Tg C yr -1 ) Horowitz, JGR, 2006 Large uncertainty in future emission trajectories for short-lived species Pollution controls A1B IPCC, 2001

Up to 40% of U.S. warming in summer (2090s-2000s) from short-lived species From changing well-mixed greenhouse gases +short-lived species From changing only short-lived species Warming from increases in BC + decreases in sulfate; depends critically on highly uncertain future emission trajectories Results from GFDL Climate Model [Levy et al., 2008] Change in Summer Temperature 2090s-2000s (°C)

New Science Questions for Next- Generation Model What are the roles of aerosol-cloud interactions in climate and climate change? How will land and ocean carbon cycles interact with climate change? To what extent is decadal prediction possible? What are the dominant chemistry-climate feedbacks?

Atmospheric Model Developments to Address the New Questions Interactive chemistry to link emissions to aerosol composition Aerosol activation requires super-saturation at cloud scale => Sub-grid PDFs of vertical velocity for convective and stratiform clouds Sufficiently realistic tropical land precipitation for land carbon model Stratospheric model for chemistry and links to troposphere, including those on multi-year scales relevant to decadal prediction

Model – satellite difference spectrum Unit: W m -2 OLRWindow band Total skyClear skyTotal skyClear sky CERES GCM GCM- CERES Overestimation Underestimation H2O vib-rotWindow [Huang et al GRL] Total-sky MODEL-AIRS radiance difference Water vapor band radiance error budget

Clean/Maritime Polluted/Continental Aerosol Indirect Effects (1 st and 2 nd ) Ramanathan et al. (2001) Aerosol vs. Dynamics

T = 288 K p = 850 hPa Aerosol mass = { 0.5, 0.5, 0.5 } x kg CCN activation is a non-linear function of vertical velocity from Ming et al. (2006, JAS)

updraft: activation downdraft: evaporation ~ 12.9 km Large Eddy Simulation shows small-scale activation. simulation by Chris Golaz

Large-scale CCN activation Layer-averaged activation: Because N* is non-linear However,

To use satellites to evaluate GCMs, the GCM must be sampled like the satellites OAR/CDC

Cloud drop radius (µm)