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Geoenergy and geoengineering applications usually involve fluid injection into and production from fractured media. Accounting for fractures is important because of the strong poromechanical coupling that ties pore pressure changes and deformation. A possible approach to the problem uses equivalent porous media to reduce the computational cost and model complexity instead of explicitly including fractures in the models. We investigate the validity of this simplification by comparing these two approaches. Simulation results show that pore pressure distribution significantly differs between the two approaches even when both are calibrated to predict identical values at the injection and production wells. Additionally, changes in fracture stability are not well captured with the equivalent porous medium. We conclude that explicitly accounting for fractures in numerical models may be necessary under some circumstances to perform reliable coupled thermohydromechanical simulations, which could be used in conjunction with other tools for induced seismicity forecasting., A.Z. acknowledges the financial support received from the “Iran's Ministry of Science, Research and Technology” (PhD students' sabbatical grants) for visiting IDAEA‐CSIC. The contribution of F.P. is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—project number PA 3451/1‐1. R.M. is thankful for the support from US DOE through Carbon SAFE Macon County Project DE‐FE0029381. V.V. acknowledges funding from the Spanish National Research Council (CSIC) through the Intramural project 201730I100 and from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (Grant agreement No. 801809). IDAEA‐CSIC is a Center of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018‐000794‐S). The authors declare no conflict of interest.

The North Atlantic warming hole (NAWH) is referred to as a reduced warming, or even cooling, of the North Atlantic during an anthropogenic‐driven global warming. A NAWH is predicted by climate models during the 21st century, and its pattern is already emerging in observations. Despite the known key role of the North Atlantic surface temperatures in setting the Northern Hemisphere climate, the mechanisms behind the NAWH are still not fully understood. Using state‐of‐the‐art climate models, we show that anthropogenic aerosol forcing opposes the formation of the NAWH (by leading to a local warming) and delays its emergence by about 30 years. In agreement with previous studies, we also demonstrate that the relative warming of the North Atlantic under aerosol forcing is due to changes in ocean heat fluxes, rather than air‐sea fluxes. These results suggest that the predicted reduction in aerosol forcing during the 21st century may accelerate the formation of the NAWH., Key Points Using CMIP6 and CESM‐LE simulations, we show that aerosol forcing generates a global cooling trend with a warming in the North AtlanticThis trend opposes the North Atlantic warming hole trend due to greenhouse gasesAerosol forcing delays the formation of the North Atlantic warming hole by about 30 years

Quantifying the efficacy of different climate forcings is important for understanding the real‐world climate sensitivity. This study presents a systematic multimodel analysis of different climate driver efficacies using simulations from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP). Efficacies calculated from instantaneous radiative forcing deviate considerably from unity across forcing agents and models. Effective radiative forcing (ERF) is a better predictor of global mean near‐surface air temperature (GSAT) change. Efficacies are closest to one when ERF is computed using fixed sea surface temperature experiments and adjusted for land surface temperature changes using radiative kernels. Multimodel mean efficacies based on ERF are close to one for global perturbations of methane, sulfate, black carbon, and insolation, but there is notable intermodel spread. We do not find robust evidence that the geographic location of sulfate aerosol affects its efficacy. GSAT is found to respond more slowly to aerosol forcing than CO2 in the early stages of simulations. Despite these differences, we find that there is no evidence for an efficacy effect on historical GSAT trend estimates based on simulations with an impulse response model, nor on the resulting estimates of climate sensitivity derived from the historical period. However, the considerable intermodel spread in the computed efficacies means that we cannot rule out an efficacy‐induced bias of ±0.4 K in equilibrium climate sensitivity to CO2 doubling when estimated using the historical GSAT trend., Key Points Multimodel mean efficacies computed using effective radiative forcing are close to one for major anthropogenic drivers, but there is notable intermodel spreadSurface temperature‐driven radiative feedbacks are generally not constant through time across forcing experimentsPDRMIP results suggest that the efficacy impact on equilibrium climate sensitivity derived from the historical period is limited to ±0.4 °C or better

The El Niño–Southern Oscillation (ENSO) in the tropical Pacific Ocean is of key importance to global climate and weather. However, state‐of‐the‐art climate models still disagree on the ENSO's response under climate change. The potential role of atmospheric ozone changes in this context has not been explored before. Here we show that differences between typical model representations of ozone can have a first‐order impact on ENSO amplitude projections in climate sensitivity simulations. The vertical temperature gradient of the tropical middle‐to‐upper troposphere adjusts to ozone changes in the upper troposphere and lower stratosphere, modifying the Walker circulation and consequently tropical Pacific surface temperature gradients. We show that neglecting ozone changes thus results in a significant increase in the number of extreme ENSO events in our model. Climate modeling studies of the ENSO often neglect changes in ozone. We therefore highlight the need to understand better the coupling between ozone, the tropospheric circulation, and climate variability., Key Points The representation of ozone in climate change simulations can lead to major differences in projected ENSO amplitudesMechanistically, this effect is directly related to an ozone‐induced damping of the Walker circulation response to CO2 forcingENSO modeling studies with climatologically inconsistent ozone might be missing an important mechanism

It has been suggested that the Sun may evolve into a period of lower activity over the 21st century. This study examines the potential climate impacts of the onset of an extreme “Maunder Minimum‐like” grand solar minimum using a comprehensive global climate model. Over the second half of the 21st century, the scenario assumes a decrease in total solar irradiance of 0.12% compared to a reference Representative Concentration Pathway 8.5 experiment. The decrease in solar irradiance cools the stratopause (∼1 hPa) in the annual and global mean by 1.2 K. The impact on global mean near‐surface temperature is small (∼−0.1 K), but larger changes in regional climate occur during the stratospheric dynamically active seasons. In Northern Hemisphere wintertime, there is a weakening of the stratospheric westerly jet by up to ∼3–4 m s−1, with the largest changes occurring in January–February. This is accompanied by a deepening of the Aleutian Low at the surface and an increase in blocking over Northern Europe and the North Pacific. There is also an equatorward shift in the Southern Hemisphere midlatitude eddy‐driven jet in austral spring. The occurrence of an amplified regional response during winter and spring suggests a contribution from a top‐down pathway for solar‐climate coupling; this is tested using an experiment in which ultraviolet (200–320 nm) radiation is decreased in isolation of other changes. The results show that a large decline in solar activity over the 21st century could have important impacts on the stratosphere and regional surface climate., Key Points A future decline in solar activity would not offset projected global warmingA future decline in solar activity could have larger regional effects in winterTop‐down mechanism contributes to Northern Hemisphere regional response

[1] In the Indian Ocean, in situ data are sparse both in time and space. Therefore, numerical models are one of the major tools for further understanding of the ocean circulation. We have implemented, validated, and done a 40 year simulation experiment forced by synoptic atmospheric data by using the Miami Isopycnic Coordinate Ocean Model (MICOM) not previously used for the Indian Ocean. The simulation results compare well to available observations including an extensive altimeter data set from ERS and TOPEX/Poseidon. The model simulation discovered an anticyclonic gyre in the southern Bay of Bengal, confirmed by altimeter data and previously unknown. This gyre is clearly influenced by the strength of the Indian Monsoon Current. From the 40 year interannual investigation, abnormal cooling as high as 4°C was simulated off Indonesia, in the eastern part of the Indian Ocean, and warming in the west, off Somalia, during years which coincide with negative Southern Oscillation Index (SOI). These years also coincide with Pacific Ocean El Nino years, except for 1961. The cooling off Indonesia is normally followed by a warming the following year. We also observed a reduction in upwelling off the southwest coast of India, which is one of the major fishing areas along the continental shelf, which also coincide with El Nino–Southern Oscillation (ENSO) years. We conclude that El Nino events occur very clearly in the Indian Ocean.