Abstract. Simple climate models play an integral role in the policy and scientific communities. They are used for climate mitigation scenarios within integrated assessment models, complex climate model emulation, and uncertainty analyses. Here we describe Hector v1.0, an open source, objectoriented, simple global climate carbon-cycle model. This model runs essentially instantaneously while still representing the most critical global-scale earth system processes. Hector has a three-part main carbon cycle: a one-pool atmosphere, land, and ocean. The model's terrestrial carbon cycle includes primary production and respiration fluxes, accommodating arbitrary geographic divisions into, e.g., ecological biomes or political units. Hector actively solves the inorganic carbon system in the surface ocean, directly calculating airsea fluxes of carbon and ocean pH. Hector reproduces the global historical trends of atmospheric [CO 2 ], radiative forcing, and surface temperatures. The model simulates all four Representative Concentration Pathways (RCPs) with equivalent rates of change of key variables over time compared to current observations, MAGICC (a well-known simple climate model), and models from the 5th Coupled Model Intercomparison Project. Hector's flexibility, open-source nature, and modular design will facilitate a broad range of research in various areas.

Abstract. Simple climate models (SCMs) are numerical representations of the Earth's gas cycles and climate system. SCMs are easy to use and computationally inexpensive, making them an ideal tool in both scientific and decision-making contexts (e.g., complex climate model emulation, parameter estimation experiments, climate metric calculations, and probabilistic analyses). Despite their prolific use, the fundamental responses of SCMs are often not directly characterized. In this study, we use fundamental impulse tests of three chemical species (CO2, CH4, and black carbon – BC) to understand the fundamental gas cycle and climate system responses of several comprehensive (Hector v2.0, MAGICC 5.3, MAGICC 6.0) and idealized (FAIR v1.0, AR5-IR) SCMs. We find that while idealized SCMs are widely used, they fail to capture the magnitude and timescales of global mean climate responses under emissions perturbations, which can produce biased temperature results. Comprehensive SCMs, which have physically based nonlinear forcing and carbon cycle representations, show improved responses compared to idealized SCMs. Even the comprehensive SCMs, however, fail to capture the response timescales to BC emission perturbations seen recently in two general circulation models. Some comprehensive SCMs also generally respond faster than more complex models to a 4×CO2 concentration perturbation, although this was not evident for lower perturbation levels. These results suggest where improvements should be made to SCMs. Further, we demonstrate here a set of fundamental tests that we recommend as a standard evaluation suite for any SCM. Fundamental impulse tests allow users to understand differences in model responses and the impact of model selection on results.

Abstract. Simple climate models play an integral role in policy and scientific communities. They are used for climate mitigation scenarios within integrated assessment models, complex climate model emulation, and uncertainty analyses. Here we describe Hector v0.1, an open source, object-oriented, simple global climate carbon-cycle model. This model runs essentially instantaneously while still representing the most critical global scale earth system processes. Hector has three main carbon pools: an atmosphere, land, and ocean. The model's terrestrial carbon cycle includes respiration and primary production, accommodating arbitrary geographic divisions into, e.g., ecological biomes or political units. Hector's actively solves the inorganic carbon system in the surface ocean, directly calculating air–sea fluxes of carbon and ocean pH. Hector reproduces the global historical trends of atmospheric [CO2] and surface temperatures. The model simulates all four Representative Concentration Pathways with high correlations (R>0.7) with current observations, MAGICC (a well-known simple climate model), and the Coupled Model Intercomparison Project version 5. Hector is freely available under an open source license, and its modular design will facilitate a broad range of research in various areas.

Abstract. Simple climate models (SCMs) are numerical representations of the Earth’s gas cycles and climate system. SCMs are easy to use and computationally inexpensive, making them an ideal tool in both scientific and decision-making contexts (e.g., complex climate model emulation; parameter estimation experiments; climate metric calculations; and probabilistic analyses). Despite their prolific use, the fundamental responses of SCMs are often not directly characterized. In this study, we use unit tests of three chemical species (CO2, CH4, and BC) to understand the fundamental gas cycle and climate system responses of several SCMs (Hector v2.0, MAGICC 5.3, MAGICC 6.0, FAIR v1.0, and AR5-IR). We find that while idealized SCMs are widely used, they fail to capture important global mean climate response features, which can produce biased temperature results. Comprehensive SCMs, which have non-linear forcing and physically-based carbon cycle representations, show improved responses compared to idealized SCMs. Even some comprehensive SCMs fail to capture response timescales of more complex models under BC or CO2 forcing perturbations. These results suggest where improvements should be made to SCMs. Further, we provide a set of fundamental tests that we recommend as a standard validation suite for any SCM. Unit tests allow users to understand differences in model responses and the impact of model selection on results.

The U.S. Global Change Research Program (USGCRP or “the Program”) is at a pivotal moment in its evolution as it works to develop its next decadal strategy. Constrained by an outdated mandate and facing an increasing demand for actional and usable climate information, the Program has an opportunity to re-envision its already robust participatory mechanisms to improve engagement with historically marginalized communities. The disability community is acutely sensitive to Earth’s changing climate, facing threats from extreme weather, in addition to enhanced risks due to systematic ableism in our policy and planning spaces. However, the disability community can also be a critical source of innovative ideas and inclusive practices that can ensure the climate documents guiding future policy development are just and equitable. By adopting a disability lens in its strategy update plans, the Program can ensure that the climate information it provides to local and regional decision-makers through the National Climate Assessment process supports future U.S. climate policy with the tenets of justice and equity at the core. In particular, the Program should revise its community engagement framework guided by 1) the social model of disability, 2) narratives from within the disability community, and 3) ideas of universal design.