Tropical mountain ice core δ18O: A Goldilocks indicator for global temperature change.

Very high tropical alpine ice cores provide a distinct paleoclimate record for climate changes in the middle and upper troposphere. However, the climatic interpretation of a key proxy, the stable water oxygen isotopic ratio in ice cores (δ18Oice), remains an outstanding problem. Here, combining proxy records with climate models, modern satellite measurements, and radiative-convective equilibrium theory, we show that the tropical δ18Oice is an indicator of the temperature of the middle and upper troposphere, with a glacial cooling of -7.35° ± 1.1°C (66% CI). Moreover, it severs as a "Goldilocks-type" indicator of global mean surface temperature change, providing the first estimate of glacial stage cooling that is independent of marine proxies as -5.9° ± 1.2°C. Combined with all estimations available gives the maximum likelihood estimate of glacial cooling as -5.85° ± 0.51°C.

Contrasting influences of biogeophysical and biogeochemical impacts of historical land use on global economic inequality.

Climate change has significant implications for macro-economic growth. The impacts of greenhouse gases and anthropogenic aerosols on economies via altered annual mean temperature (AMT) have been studied. However, the economic impact of land-use and land-cover change (LULCC) is still unknown because it has both biogeochemical and biogeophysical impacts on temperature and the latter differs in latitudes and disturbed land surface types. In this work, based on multi-model simulations from the Coupled Model Intercomparison Project Phase 6, contrasting influences of biogeochemical and biogeophysical impacts of historical (1850-2014) LULCC on economies are found. Their combined effects on AMT result in warming in most countries, which harms developing economies in warm climates but benefits developed economies in cold climates. Thus, global economic inequality is increased. Besides the increased AMT by the combined effects, day-to-day temperature variability is enhanced in developing economies but reduced in developed economies, which further deteriorates global economic inequality.

Trends in surface equivalent potential temperature: A more comprehensive metric for global warming and weather extremes.

Trends in surface air temperature (SAT) are a common metric for global warming. Using observations and observationally driven models, we show that a more comprehensive metric for global warming and weather extremes is the trend in surface equivalent potential temperature (Thetae_sfc) since it also accounts for the increase in atmospheric humidity and latent energy. From 1980 to 2019, while SAT increased by 0.79[Formula: see text], Thetae_sfc increased by 1.48[Formula: see text] globally and as much as 4[Formula: see text] in the tropics. The increase in water vapor is responsible for the factor of 2 difference between SAT and Thetae_sfc trends. Thetae_sfc increased more uniformly (than SAT) between the midlatitudes of the southern hemisphere and the northern hemisphere, revealing the global nature of the heating added by greenhouse gases (GHGs). Trends in heat extremes and extreme precipitation are correlated strongly with the global/tropical trends in Thetae_sfc. The tropical amplification of Thetae_sfc is as large as the arctic amplification of SAT, accounting for the observed global positive trends in deep convection and a 20% increase in heat extremes. With unchecked GHG emissions, while SAT warming can reach 4.8[Formula: see text] by 2100, the global mean Thetae_sfc can increase by as much as 12[Formula: see text], with corresponding increases of 12[Formula: see text] (median) to 24[Formula: see text] (5% of grid points) in land surface temperature extremes, a 14- to 30-fold increase in frequency of heat extremes, a 40% increase in the energy available for tropical deep convection, and an up to 60% increase in extreme precipitation.

Double Trouble of Air Pollution by Anthropogenic Dust.

With urbanization worldwide in recent decades, anthropogenic dust (AD) emissions due to heavy urban construction and off-road vehicle use have been increasing. Its perturbations on urban air pollution at the global scale are still unclear. Based on observations, we found that a high urban AD optical depth is often accompanied by severe non-dust aerosol optical depth in the planetary boundary layer (PBL), both magnitudes even comparable. To investigate the causes, an AD emission inventory constrained by satellite retrievals is implemented in a global climate model. The results show that AD-induced surface radiative cooling of up to -15.9 ± 4.0 W m-2 regionally leads to reduced PBL height, which deteriorates non-dust pollution, especially over India and northern China, in addition to the tremendous direct AD contribution to pollutants. The estimated global total premature mortality due to AD is 0.8 million deaths per year and is more severe in populous regions.

Analysis of Cloud-Resolving Model Simulations for Scale Dependence of Convective Momentum Transport.

We use 3-D cloud-resolving model (CRM) simulations of two mesoscale convective systems at mid-latitudes and a simple statistical ensemble method to diagnose the scale dependency of convective momentum transport (CMT) and CMT-related properties, and evaluate a parameterization scheme for convection-induced pressure gradient (CIPG) developed by Gregory et al. (GKI97). GKI97 relates CIPG to a constant coefficient multiplied by mass flux and vertical mean wind shear. CRM results show that mass fluxes and CMT exhibit strong scale dependency in temporal evolution and vertical structure. The prevalent understandings of CMT characteristics in terms of upgradient/downgradient transport are applicable to updrafts but not downdrafts across a wide range of grid spacings (4-512 km). For the small-to-median grid spacings (4~64 km), GKI97 reproduces some aspects of CIPG scale dependency except for underestimating the variations of CIPG as grid spacing decreases. However, for large grid spacings (128~512 km), GKI97 might even less adequately parameterize CIPG because it omits the contribution from either the nonlinear shear or buoyancy forcings. Further diagnosis of CRM results suggests that inclusion of nonlinear shear forcing in GKI97 is needed for the large grid spacings, and use of the three-updraft and one downdraft approach proposed in an earlier study may help a modified GKI97 capture more variations of CIPG as grid spacing decreases for the small-to-median grid spacings. Further, the optimal coefficients used in GKI97 seems insensitive to grid spacings, but they might be different for updrafts and downdrafts, for different MCS types, and for zonal and meridional components.