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ABSTRACT We combine parallax distances to nearby O stars with parsec-scale resolution three-dimensional dust maps of the local region of the Milky Way (within 1.25 kpc of the Sun) to simulate the transfer of Lyman continuum photons through the interstellar medium (ISM). Assuming a fixed gas-to-dust ratio, we determine the density of ionized gas, electron temperature, and H$$\alpha$$ emissivity throughout the local Milky Way. There is good morphological agreement between the predicted and observed H$$\alpha$$ all-sky map of the Wisconsin H$$\alpha$$ Mapper. We find that our simulation underproduces the observed H$$\alpha$$ emission while overestimating the sizes of H ii regions, and we discuss ways in which agreement between simulations and observations may be improved. Of the total ionizing luminosity of $$5.84 \times 10^{50}~{\rm photons \, s^{-1}}$$, 15 per cent is absorbed by dust, 64 per cent ionizes ‘classical’ H ii regions, 11 per cent ionizes the diffuse warm ionized medium, and 10 per cent escapes the simulation volume. We find that 18 per cent of the high-altitude ($$|b| > 30{}^{\circ }$$) H$$\alpha$$ arises from dust scattered rather than direct emission. These initial results provide an impressive validation of the three-dimensional dust maps and O-star parallaxes, opening a new frontier for studying the ionized ISM’s structure and energetics in three dimensions. 

Given the existential threat of climate change, we urge the heliophysics scientific community to consider ways in which we might further contribute to global efforts to address climate change. Whole atmosphere studies reveal that climate change processes impact even the uppermost regions of the atmosphere. The heliophysics research community now has models spanning the surface through the upper thermosphere and a diversity of observational datasets of the middle and upper atmosphere that span multiple decades. These studies indicate that the middle and upper atmosphere provide multiple vertical footprints for climate change and thus can contribute to an understanding of whole atmosphere climate change processes in the complex atmosphereland- ocean system. This white paper outlines recommendations for expansion of long-term data sets; simulations of climate with whole atmosphere models; engagement in collaborations with the tropospheric research community; and exploration of the possibility of heliophysics contributions to climate assessment efforts. Additionally, we recommend education and outreach efforts to help members of the wider community become more knowledgeable about climate change; support for efforts to increase the diversity of the heliophysics science community; support for international collaborations, and climate mitigation measures that our science community can implement to reduce greenhouse gas emissions from our research, education, and outreach activities.