Desert dust exerts twice the longwave radiative heating estimated by climate models

This code obtains the DustCOMM data set, including a calculation of the longwave direct radiative effect of desert dust. The main function to run DustCOMM is main_constrain_modern_dust_cycle.m. This function takes the following inputs: • The number of desired bootstrap iterations (e.g., ~50 for quick results; 1000 iterations are normally used for results used in a publication) • The model # to use (this should almost always be zero) • A spare variable that can be used for various purposes (this should almost always be zero) • The year for which to run the code. This should be 0 to run the code for the standard 2004-2008 climatology obtained in Kok et al. (2021a, b). The main_constrain_modern_dust_cycle.m code performs the following actions: - It initializes variables and settings. Some of this is done in the sub-scripts load_data_and_pars_modern_dust_cycle.m and initialize_variables.m - It loops over the number of desired bootstrap iterations (the variable nBoots). For each bootstrap iteration, it randomly draws a globally averaged atmospheric dust size distribution (from Adebiyi and Kok, 2020), size-resolved mass extinction efficiency (based on Kok et al., 2017), and a set of global model simulations (see pick_model.m) of how 1 Tg of dust loading of each particle size from each of the 9 dust source regions is distributed across the world (from the CESM, IMPACT, GISS ModelE2.1, GEOS/GOCART, MONARCH, or INCA models). - It then draws the dust AOD at the 15 regions defined in Ridley et al. (2016) (see obtain_Ridley_DAOD.m) - Then it figures out how many Tg of dust are needed from each of the 9 source regions to produce a 2D map of dust AOD that minimizes the disagreement against the dust AOD in the 15 regions. - It then calculates the various attributes of the global dust cycle, including the LW direct radiative effect (in the function calc_LW_rad_forcing.m, which is called by the script calc_results_modern_dust_cycle.m) - The processing of the results of each bootstrap iteration occurs in process_results_modern_dust_cycle The abstract of the corresponding article, titled "**Desert dust exerts twice the longwave radiative heating estimated by climate models**", is as follows: Although desert dust is the most abundant atmospheric aerosol by mass, its longwave radiative effects remain unclear, obscuring the impacts of dust on weather and climate. Using a data-driven analytical model constrained by observations, we show that scattering and absorption of longwave radiation by dust heats the planet by +0.25 ± 0.06 W m⁻² (90% confidence). This is nearly twice the value simulated by current climate models, which omit longwave scattering and underrepresent super coarse dust (diameter > 10 μm). These omissions bias modeled surface energy fluxes, cloud responses, precipitation, and atmospheric circulation. At the global scale, the sign and magnitude of the net dust direct radiative effect remain uncertain, with additional work needed to constrain shortwave cooling effects. These findings show that improving the representation of dust interactions with longwave radiation can improve weather forecasting and is essential to resolve the role of dust in climate change.