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Abstract Increased warming due to climate change can induce heat stress in humans and adversely affect labour productivity due to heat-related morbidity. Here, we use a simulation model to examine the effects of heat stress, through declined labour capacity under +1.5 °C and 3.5 °C warming scenarios on agriculture and welfare across the three agroecological zones (Sudanian, Sudano-Sahelian, and Sahelian) in Burkina Faso. In the two scenarios, domestic production declines, with outdoor labour-intensive sectors such as cropping and mining being the most affected, reducing gross domestic product by 9% and 20%, respectively. All households lose welfare in all scenarios except non-poor households in the +1.5 °C scenario. Across zones, crop production declines strongest in the crop-producing Sudanian and Sudano-Sahelian zones. In contrast, relative welfare losses are strongest for households in the Sahelian zone. The study highlights the most vulnerable sectors, household groups, and zones requiring urgent attention in heat stress adaptation and mitigation policies. 

Included are 100 years of monthly mean ocean model output from CESM1.2 integrations for the Eocene carried out by Adam Aleksinski and Matthew Huber, with critical assistance from Alexandra Jahn, and with assistance and support from Jiang Zhu (NCAR). These simulations were carried out at NCAR. These simulations incorporate results using the standard Eocene Deepmip 1 boundary conditions (Lunt et al, 2017), including the boundary condition datasets (Herold et al., 2014), and were branched off originally from simulations carried out at NCAR by Jiang Zhu (Zhu et al., 2020). The three simulations included here incorporate neodymium in them for the first time and span a range of CO2 and gateway configurations that make it appropriate for the Middle Eocene to late Eocene. The continuation (“SF_SU_55Ma_init-hycont”) experiment run continued from the end of Zhu et al. (2020)’s 3x preindustrial pCO2 (854.1 ppm) experiment, which used DeepMIP compliant geography and bathymetry for simulating the early Eocene. This simulation was run for a total of 4,800 years. Two runs each branched from this SF_SU_55Ma_init-hycont after 1,200 years of runtime, and each ran for 3,600 years after that point. In the Open Drake Passage experimental run (SF_SU_55Ma_open-hycont), the atmospheric pCO2 concentration from the continuation simulation was retained, and the bathymetry of the Drake Passage and Tasman Seaway were both lowered to a depth of 1973 mbsl. In the Halved pCO2 experiment SF_SU_55Ma_cool), the Herold et al original bathymetry was retained, but atmospheric pCO2 was reduced by a factor of half, to 427.05 ppm. The model output is global in extent and is netcdf format, which has been tarred and gzipped, and follows standard conventions for ocean GCMs. The data are on an irregular 'POP' grid. All the necessary information to read and process these data are included in the netcdf metadata. 

Abstract The Miocene (∼23–5 Ma) is a past warm epoch when global surface temperatures varied between ∼5 and 8°C warmer than today, and CO₂concentration was ∼400–800 ppm. The narrowing/closing of the tropical ocean gateways and widening of high‐latitude gateways throughout the Miocene is likely responsible for the evolution of the ocean's overturning circulation to its modern structure, though the mechanisms remain unclear. Here, we investigate early and middle Miocene ocean circulation in an opportunistic climate model intercomparison (MioMIP1), using 14 simulations with different paleogeography, CO₂, and vegetation. The strength of the Southern Ocean‐driven Meridional Overturning Circulation (SOMOC) bottom cell is similar in the Miocene and Pre‐Industrial (PI) but dominates the Miocene global MOC due to weaker Northern Hemisphere overturning. The Miocene Atlantic MOC (AMOC) is weaker than PI in all the simulations (by 2–21 Sv), possibly due to its connection with an Arctic that is considerably fresher than today. Deep overturning in the North Pacific (PMOC) is present in three simulations (∼5–10 Sv), of which two have a weaker AMOC, and one has a stronger AMOC (compared to its PMOC). Surface freshwater fluxes control northern overturning such that the basin with the least freshwater gain has stronger overturning. While the orography, which impacts runoff direction (Pacific vs. Atlantic), has an inconsistent impact on northern overturning across simulations, overall, features associated with the early Miocene—such as a lower Tibetan Plateau, the Rocky Mountains, and a deeper Panama Seaway—seem to favor PMOC over AMOC. 

Abstract The evolution of the spatial pattern of ocean surface warming affects global radiative feedback, yet different climate models provide varying estimates of future patterns. Paleoclimate data, especially from past warm periods, can help constrain future equilibrium warming patterns. By analyzing marine temperature records spanning the past 10 million years with a regression‐based technique that removes temporal dimensions, we extract long‐term ocean warming patterns and quantify relative sea surface temperature changes across the global ocean. This analysis revealed a distinct pattern of amplified warming that aligns with equilibrated model simulations under high CO₂conditions, yet differs from the transient warming pattern observed over the past 160 years. This paleodata‐model comparison allows us to identify models that better capture fundamental aspects of Earth's warming response, while suggesting how ocean heat uptake and circulation changes modify the development of warming patterns over time. By combining this paleo‐ocean warming pattern with equilibrated model simulations, we characterized the likely evolution of global ocean warming as the climate system approaches equilibrium. 

Abstract During the early‐to‐middle Miocene, global mean surface temperature (GMST) was approximately 8°C warmer than preindustrial, with a greater temperature increase in polar regions than the tropics. However, existing Miocene simulations underestimate this warmth, particularly in northern high latitudes. To address this discrepancy, we investigate the potential role of cloud phase. Using the Community Earth System Model, we conduct a paleoclimate sensitivity study focused on modifying ice nucleation and cloud phase partitioning schemes. These modifications increase the GMST, with a strong temperature rise in high latitudes and a muted increase in the tropics. These increases are driven by enhanced longwave cloud forcing, resulting from increased ice cloud amounts and cloud water content, and are amplified by water vapor and lapse rate feedbacks in the Arctic. Our study highlights that the improved parameterizations of cloud phase processes enhance models' capability to simulate Miocene high‐latitude warmth and potentially other warm climates. 

As heatwaves become more frequent, intense, and longer-lasting due to climate change, the question of breaching thermal limits becomes pressing. A wet-bulb temperature (T_w) of 35 °C has been proposed as a theoretical upper limit on human abilities to biologically thermoregulate. But, recent—empirical—research using human subjects found a significantly lower maximum T_wat which thermoregulation is possible even with minimal metabolic activity. Projecting future exposure to this empirical critical environmental limit has not been done. Here, using this more accurate threshold and the latest coupled climate model results, we quantify exposure to dangerous, potentially lethal heat for future climates at various global warming levels. We find that humanity is more vulnerable to moist heat stress than previously proposed because of these lower thermal limits. Still, limiting warming to under 2 °C nearly eliminates exposure and risk of widespread uncompensable moist heatwaves as a sharp rise in exposure occurs at 3 °C of warming. Parts of the Middle East and the Indus River Valley experience brief exceedances with only 1.5 °C warming. More widespread, but brief, dangerous heat stress occurs in a +2 °C climate, including in eastern China and sub-Saharan Africa, while the US Midwest emerges as a moist heat stress hotspot in a +3 °C climate. In the future, moist heat extremes will lie outside the bounds of past human experience and beyond current heat mitigation strategies for billions of people. While some physiological adaptation from the thresholds described here is possible, additional behavioral, cultural, and technical adaptation will be required to maintain healthy lifestyles. 

Abstract. The Oligocene (33.9–23.03 Ma) had warm climates with flattened meridional temperature gradients, while Antarctica retained a significant cryosphere. These may pose imperfect analogues to distant future climate states with unipolar icehouse conditions. Although local and regional climate and environmental reconstructions of Oligocene conditions are available, the community lacks synthesis of regional reconstructions. To provide a comprehensive overview of marine and terrestrial climate and environmental conditions in the Oligocene, and a reconstruction of trends through time, we review marine and terrestrial proxy records and compare these to numerical climate model simulations of the Oligocene. Results, based on the present relatively sparse data, suggest temperatures around the Equator that are similar to modern temperatures. Sea surface temperatures (SSTs) show patterns similar to land temperatures, with warm conditions at mid- and high latitudes (∼60–90°), especially in the Southern Hemisphere (SH). Vegetation-based precipitation reconstructions of the Oligocene suggest regionally drier conditions compared to modern times around the Equator. When compared to proxy data, climate model simulations overestimate Oligocene precipitation in most areas, particularly the tropics. Temperatures around the mid- to high latitudes are generally underestimated in models compared to proxy data and tend to overestimate the warming in the tropics. In line with previous proxy-to-model comparisons, we find that models underestimate polar amplification and overestimate the Equator-to-pole temperature gradient suggested from the available proxy data. This further stresses the urgency of solving this widely recorded problem for past warm climates, such as the Oligocene. 

Abstract Humid heat extremes, characterized by high wet bulb temperature (Tw), pose significant health risks. While strong El Niño events are known to affect the frequency of extreme Tw days, the distinct impacts of Central Pacific (CP) and Eastern Pacific (EP) El Niño events remain understudied. Using a 12‐member CMIP6 ensemble at discrete global warming targets (+1.5, 2, 3, 4°C), this study shows progressively enhanced humid heat extent during EP events primarily in Mainland Southeast Asia, while South Asia experiences regionally opposing effects from EP and CP events. EP and CP events drive distinctly different, regionally varying patterns of dangerous Tw, yet both significantly increase the affected population and area impacted by humid heat extremes at all global warming levels. This amplification surpasses the impact of an additional degree of global warming, highlighting El Niño's compounding effect on heat stress threats across warmer climates. 

Abstract. Climate variability is typically amplified towards polar regions. The underlying causes, notably albedo and humidity changes, are challenging to accurately quantify with observations or models, thus hampering projections of future polar amplification. Polar amplification reconstructions from the ice-free early Eocene (∼56–48 Ma) can exclude ice albedo effects, but the required tropical temperature records for resolving timescales shorter than multi-million years are lacking. Here, we reconstruct early Eocene tropical sea surface temperature variability by presenting an up to ∼4 kyr resolution biomarker-based temperature record from Ocean Drilling Program (ODP) Site 959, located in the tropical Atlantic Ocean. This record shows warming across multiple orbitally paced carbon cycle perturbations, coeval with high-latitude-derived deep-ocean bottom waters, showing that these events represent transient global warming events (hyperthermals). This implies that orbital forcing caused global temperature variability through carbon cycle feedbacks. Importantly, deep-ocean temperature variability was amplified by a factor of 1.7–2.3 compared to the tropical surface ocean, corroborating available long-term estimates. This implies that fast atmospheric feedback processes controlled meridional temperature gradients on multi-million year, as well as orbital, timescales during the early Eocene. Our combined records have several other implications. First, our amplification factor is somewhat larger than the same metric in fully coupled simulations of the early Eocene (1.1–1.3), suggesting that models slightly underestimate the non-ice-related – notably hydrological – feedbacks that cause polar amplification of climate change. Second, even outside the hyperthermals, we find synchronous eccentricity-forced temperature variability in the tropics and deep ocean that represent global mean sea surface temperature variability of up to 0.7 °C, which requires significant variability in atmospheric pCO2. We hypothesize that the responsible carbon cycle feedbacks that are independent of ice, snow, and frost-related processes might play an important role in Phanerozoic orbital-scale climate variability throughout geological time, including Pleistocene glacial–interglacial climate variability. 

Abstract The Miocene (∼23–5 Ma) experienced substantial paleogeographic changes, including the shoaling of the Panama Seaway and closure of the Tethys Seaway, which altered exchange pathways between the Pacific and Atlantic Oceans. Changes in continental configuration and topography likely also influenced global wind patterns. Here, we investigate how these changes affected surface wind‐driven gyre circulation and interbasin volume transport using 14 fully coupled climate model simulations of the early and middle Miocene. The North and South Atlantic gyres, along with the South Pacific gyre, are weaker in the Miocene simulations compared to pre‐industrial (PI), while the North Pacific gyres are stronger. These changes largely follow the wind stress curl and basin width changes. Westward flow through the Panama Seaway occurs only in early Miocene simulations when the Tethys Seaway is open and transports are strongly westward. As the Tethys transport declines, flow across the Panama Seaway gradually reverses from westward (into the Pacific) to eastward (into the Atlantic). In simulations with a closed Tethys Seaway, the Panama transport is consistently eastward. The Southern Hemisphere westerlies are weaker than PI in all simulations, contributing to a reduced Antarctic Circumpolar Current (ACC) in 11 of the 14 cases. In the remaining three, a stronger ACC is simulated, likely due to a combination of enhanced meridional density gradients and model‐dependent sensitivities. These findings highlight how changes in Miocene seaways and wind patterns reshaped ocean circulation, influencing interbasin exchange, thermohaline properties, and global climate.