North Atlantic sea-surface temperatures (SSTs) exhibit variability on seasonal to decadal timescales, providing a potential source of predictability for the atmospheric circulation and regional climate on these timescales. Recent work has shown that initialized climate models have skill in predicting the decadal evolution of North Atlantic SSTs [1], but this will only help to predict regional climate in the surrounding continents if models can correctly simulate the atmospheric response to these SST anomalies. There is growing evidence that models systematically underestimate the atmospheric response to extratropical SST anomalies [2], and that this may be rectified by increasing the atmospheric resolution to resolve mesoscale processes over ocean frontal zones [3]. Here, we investigate the large-scale atmospheric circulation response to idealized Gulf Stream SST anomalies in two configurations of the Community Atmospheric Model (CAM6), one with 1-degree resolution globally and one with regional grid refinement of 1/8-degree over the North Atlantic. The variable resolution configuration, which resolves mesoscale atmospheric processes, shows a large negative response of the wintertime North Atlantic Oscillation (NAO) to a strengthening of the SST gradient across the Gulf Stream (a 2-standard-deviation NAO anomaly for SST anomalies that vary between ±2°C). The response is substantially weaker and has a different spatial structure in the lower resolution simulations. The large-scale atmospheric circulation response in the variable resolution simulations results from mesoscale processes that enhance convection over the Gulf Stream and lead to latent-heating and divergence anomalies in the upper troposphere. These results suggest that the atmospheric circulation response to extratropical SST anomalies may be fundamentally different at higher resolution. Regional refinement in key regions offers a potential pathway towards improving simulation of the atmospheric response to extratropical SST anomalies and thus improving multi-year regional climate predictions. [1] Yeager, S.G., et al., 2018, https://doi.org/10.1175/BAMS-D-17-0098.1. [2] Simpson, I.R., et al., 2018, https://doi.org/10.1175/JCLI-D-18-0168.1. [3] Czaja, A., et al., 2019, https://doi.org/10.1007/s40641-019-00148-5.

Heat has historically resulted in more mortality than any other severe weather-related phenomenon in the United States, with the U.S. Centers for Disease Control attributing more than six hundred deaths to extreme heat each year. Agricultural workers are particularly vulnerable to environmental heat exposure: mortality rates due to heat amongst crop workers are twenty times higher than in the general worker population. The vulnerability of this group of workers to heat is exacerbated by factors such as economic vulnerability, immigration status, language barriers, access to health care, and the absence of worker heat standards in all but three of the fifty United States. Climate change threatens to increase the risk of heat-related illness in agricultural workers, but so far there has been no nation-wide evaluation of the expected change in heat exposure in a warmer climate for this group of workers. Here, we estimate baseline and future exposure of agricultural workers in the main growing regions of the continental U.S. to extreme heat. Given the diverse health impacts of different types of heat events, we compare metrics for both single day extremes and multi-day heat waves, and calculate how these statistics will change at the county level with 2 and 4 degrees Celsius of global warming. Our findings serve as a guideline for determining regionally appropriate heat standards, and underscore the need for agencies in all agricultural states to make preparations for a warmer climate.