Climate models can correctly simulate the continuum of global-average temperature variability.

Climate records exhibit scaling behavior with large exponents, resulting in larger fluctuations at longer timescales. It is unclear whether climate models are capable of simulating these fluctuations, which draws into question their ability to simulate such variability in the coming decades and centuries. Using the latest simulations and data syntheses, we find agreement for spectra derived from observations and models on timescales ranging from interannual to multimillennial. Our results confirm the existence of a scaling break between orbital and annual peaks, occurring around millennial periodicities. That both simple and comprehensive ocean-atmosphere models can reproduce these features suggests that long-range persistence is a consequence of the oceanic integration of both gradual and abrupt climate forcings. This result implies that Holocene low-frequency variability is partly a consequence of the climate system's integrated memory of orbital forcing. We conclude that climate models appear to contain the essential physics to correctly simulate the spectral continuum of global-mean temperature; however, regional discrepancies remain unresolved. A critical element of successfully simulating suborbital climate variability involves, we hypothesize, initial conditions of the deep ocean state that are consistent with observations of the recent past.

Beaks promote rapid morphological diversification along distinct evolutionary trajectories in labrid fishes (Eupercaria: Labridae).

The upper and lower jaws of some wrasses (Eupercaria: Labridae) possess teeth that have been coalesced into a strong durable beak that they use to graze on hard coral skeletons, hard-shelled prey, and algae, allowing many of these species to function as important ecosystem engineers in their respective marine habitats. While the ecological impact of the beak is well understood, questions remain about its evolutionary history and the effects of this innovation on the downstream patterns of morphological evolution. Here we analyze 3D cranial shape data in a phylogenetic comparative framework and use paleoclimate modeling to reconstruct the evolution of the labrid beak across 205 species. We find that wrasses evolved beaks three times independently, once within odacines and twice within parrotfishes in the Pacific and Atlantic Oceans. We find an increase in the rate of shape evolution in the Scarus+Chlorurus+Hipposcarus (SCH) clade of parrotfishes likely driven by the evolution of the intramandibular joint. Paleoclimate modeling shows that the SCH clade of parrotfishes rapidly morphologically diversified during the middle Miocene. We hypothesize that possession of a beak in the SCH clade coupled with favorable environmental conditions allowed these species to rapidly morphologically diversify.

A Pliocene Precipitation Isotope Proxy-Model Comparison Assessing the Hydrological Fingerprints of Sea Surface Temperature Gradients.

The Pliocene offers insights into future climate, with near-modern atmospheric pCO2 and global mean surface temperature estimated to be 3-4°C above pre-industrial. However, the hydrological response differs between future global warming and early Pliocene climate model simulations. This discrepancy results from the use of reduced meridional and zonal sea surface temperature (SST) gradients, based on foraminiferal Mg/Ca and Alkenone proxy evidence, to force the early Pliocene simulation. Subsequent, SST reconstructions based on the organic proxy TEX86, have found warmer temperatures in the warm pool, bringing the magnitude of the gradient reductions into dispute. We design an independent test of Pliocene SST scenarios and their hydrological cycle "fingerprints." We use an isotope-enabled General Circulation Model, iCAM5, to model the distribution of water isotopes in precipitation in response to four climatological SST and sea-ice fields representing modern, abrupt 4 × CO2, late Pliocene and early Pliocene climates. We conduct a proxy-model comparison with all the available precipitation isotope proxy data, and we identify target regions that carry precipitation isotopic fingerprints of SST gradients as priorities for additional proxy reconstructions. We identify two regions with distinct precipitation isotope (D/H) fingerprints resulting from reduced SST gradients: the Maritime Continent (D-enriched due to reduced convective rainfall) and the Sahel (wetter, more deep convection, D-depleted). The proxy-model comparison using available plant wax reconstructions, mostly from Africa, is promising but inconclusive. Additional proxy reconstructions are needed in both target regions and in much of the world for significant tests of SST scenarios and dynamical linkages to the hydrological cycle.

Unraveling forced responses of extreme El Niño variability over the Holocene.

Uncertainty surrounding the future response of El Niño-Southern Oscillation (ENSO) variability to anthropogenic warming necessitates the study of past ENSO sensitivity to substantial climate forcings over geological history. Here, we focus on the Holocene epoch and show that ENSO amplitude and frequency intensified over this period, driven by an increase in extreme El Niño events. Our study combines new climate model simulations, advances in coral proxy system modeling, and coral proxy data from the central tropical Pacific. Although the model diverges from the observed coral data regarding the exact magnitude of change, both indicate that modern ENSO variance eclipsed paleo-estimates over the Holocene, albeit against the backdrop of wide-ranging natural variability. Toward further constraining paleo-ENSO, our work underscores the need for multimodel investigations of additional Holocene intervals alongside more coral data from periods with larger climate forcing. Our findings implicate extreme El Niño events as an important rectifier of mean ENSO intensity.

Race and ethnic minority, local pollution, and COVID-19 deaths in Texas.

The costs of COVID-19 are extensive, and, like the fallout of most health and environmental crises in the US, there is growing evidence that these costs weigh disproportionately on communities of color. We investigated whether county-level racial composition and fine particulate pollution (PM2.5) are indicators for COVID-19 incidence and death rates in the state of Texas. Using county-level data, we ran linear regressions of percent minority as well as historic 2000-2016 PM2.5 levels against COVID-19 cases and deaths per capita. We found that a county's percent minority racial composition, defined as the percentage of population that identifies as Black or Hispanic, highly correlates with COVID-19 case and death rates. Using Value-of-Statistical-Life calculations, we found that economic costs from COVID-19 deaths fall more heavily on Black and Hispanic residents in Harris County, the most populous county in Texas. We found no consistent evidence or significant correlations between historic county-average PM2.5 concentration and COVID-19 incidence or death. Our findings suggest that public health and economic aid policy should consider the racially-segregated burden of disease to better mitigate costs and support equity for the duration and aftermath of health crises.

Increasing Health Risks During Outdoor Sports Due To Climate Change in Texas: Projections Versus Attitudes.

Extreme heat is a recognized threat to human health. This study examines projected future trends of multiple measures of extreme heat across Texas throughout the next century, and evaluates the expected climate changes alongside Texas athletic staff (coach and athletic trainer) attitudes toward heat and climate change. Numerical climate simulations from the recently published Community Earth System Model version 2 and the Climate Model Intercomparison Project were used to predict changes in summer temperatures, heat indices, and wet bulb temperatures across Texas and also within specific metropolitan areas. A survey examining attitudes toward the effects of climate change on athletic programs and student athlete health was also distributed to high-school and university athletic staff. Heat indices are projected to increase beyond what is considered healthy/safe limits for outdoor sports activity by the mid-to-late 21st century. Survey results reveal a general understanding and acceptance of climate change and a need for adjustments in accordance with more dangerous heat-related events. However, a portion of athletic staff still do not acknowledge the changing climate and its implications for student athlete health and their athletic programs. Enhancing climate change and health communication across the state may initiate important changes to athletic programs (e.g., timing, duration, intensity, and location of practices), which should be made in accordance with increasingly dangerous temperatures and weather conditions. This work employs a novel interdisciplinary approach to evaluate future heat projections alongside attitudes from athletic communities toward climate change.

Response to Comment on "No consistent ENSO response to volcanic forcing over the last millennium".

Robock claims that our analysis fails to acknowledge that pan-tropical surface cooling caused by large volcanic eruptions may mask El Niño warming at our central Pacific site, potentially obscuring a volcano-El Niño connection suggested in previous studies. Although observational support for a dynamical response linking volcanic cooling to El Niño remains ambiguous, Robock raises some important questions about our study that we address here.

No consistent ENSO response to volcanic forcing over the last millennium.

The El Niño-Southern Oscillation (ENSO) shapes global climate patterns yet its sensitivity to external climate forcing remains uncertain. Modeling studies suggest that ENSO is sensitive to sulfate aerosol forcing associated with explosive volcanism but observational support for this effect remains ambiguous. Here, we used absolutely dated fossil corals from the central tropical Pacific to gauge ENSO's response to large volcanic eruptions of the last millennium. Superposed epoch analysis reveals a weak tendency for an El Niño-like response in the year after an eruption, but this response is not statistically significant, nor does it appear after the outsized 1257 Samalas eruption. Our results suggest that those models showing a strong ENSO response to volcanic forcing may overestimate the size of the forced response relative to natural ENSO variability.

Tracking the Strength of the Walker Circulation with Stable Isotopes in Water Vapor.

General circulation models (GCMs) predict that the global hydrological cycle will change in response to anthropogenic warming. However, these predictions remain uncertain, in particular for precipitation [IPCC, 2013]. Held and Soden [2006] suggest that as lower-tropospheric water vapor concentration increases in a warming climate, the atmospheric circulation and convective mass fluxes will weaken. Unfortunately, this process is difficult to constrain, as convective mass fluxes are poorly observed and incompletely simulated in GCMs. Here, we demonstrate that stable hydrogen isotope ratios in tropical atmospheric water vapor can trace changes in temperature, atmospheric circulation and convective mass flux in a warming world. We evaluate changes in temperature, the distribution of water vapor, vertical velocity (ω) and advection, and water isotopes in vapor (δD V ) in water isotopeenabled GCM experiments for modern vs. high CO 2 atmospheres to identify spatial patterns of circulation change over the tropical Pacific. We find that slowing circulation in the tropical Pacific moistens the lower troposphere and weakens convective mass flux, both of which impact the δD of water vapor in the mid-troposphere. Our findings constitute a critical demonstration of how water isotope ratios in the tropical Pacific respond to changes in radiative forcing and atmospheric warming. Moreover, as changes in δD V can be observed by satellites, our results develop new metrics for the detection of global warming impacts to the hydrological cycle and, specifically, the strength of the Walker Circulation.

El Niño increases the risk of lower Mississippi River flooding.

Mississippi River floods rank among the costliest climate-related disasters in the world. Improving flood predictability, preparedness, and response at seasonal to decadal time-scales requires an understanding of the climatic controls that govern flood occurrence. Linking flood occurrence to persistent modes of climate variability like the El Niño-Southern Oscillation (ENSO) has proven challenging, due in part to the limited number of high-magnitude floods available for study in the instrumental record. To augment the relatively short instrumental record, we use output from the Community Earth System Model (CESM) Last Millennium Ensemble (LME) to investigate the dynamical controls on discharge extremes of the lower Mississippi River. We show that through its regional influence on surface water storage, the warm phase of ENSO preconditions the lower Mississippi River to be vulnerable to flooding. In the 6-12 months preceding a flood, El Niño generates a positive precipitation anomaly over the lower Mississippi basin that gradually builds up soil moisture and reduces the basin's infiltration capacity, thereby elevating the risk of a major flood during subsequent rainstorms. Our study demonstrates how natural climate variability mediates the formation of extreme floods on one of the world's principal commercial waterways, adding significant predictive ability to near- and long-term forecasts of flood risk.