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.

On the essentials of drought in a changing climate.

Droughts of the future are likely to be more frequent, severe, and longer lasting than they have been in recent decades, but drought risks will be lower if greenhouse gas emissions are cut aggressively. This review presents a synopsis of the tools required for understanding the statistics, physics, and dynamics of drought and its causes in a historical context. Although these tools have been applied most extensively in the United States, Europe, and the Amazon region, they have not been as widely used in other drought-prone regions throughout the rest of the world, presenting opportunities for future research.

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.

Testing Hopkins' Bioclimatic Law with PhenoCam data.

Premise Of The Study: We investigated the spatial and temporal patterns of vegetation phenology with phenometrics derived from PhenoCam imagery. Specifically, we evaluated the Bioclimatic Law proposed by Hopkins, which relates phenological transitions to latitude, longitude, and elevation.

Methods: "Green-up" and "green-down" dates-representing the start and end of the annual cycles of vegetation activity-were estimated from measures of canopy greenness calculated from digital repeat photography.

Mid-latitude net precipitation decreased with Arctic warming during the Holocene.

The latitudinal temperature gradient between the Equator and the poles influences atmospheric stability, the strength of the jet stream and extratropical cyclones. Recent global warming is weakening the annual surface gradient in the Northern Hemisphere by preferentially warming the high latitudes; however, the implications of these changes for mid-latitude climate remain uncertain. Here we show that a weaker latitudinal temperature gradient-that is, warming of the Arctic with respect to the Equator-during the early to middle part of the Holocene coincided with substantial decreases in mid-latitude net precipitation (precipitation minus evapotranspiration, at 30° N to 50° N).

Exacerbation of the 2013-2016 Pan-Caribbean Drought by Anthropogenic Warming.

The Caribbean islands are expected to see more frequent and severe droughts from reduced precipitation and increased evaporative demand due to anthropogenic climate change. Between 2013 and 2016, the Caribbean experienced a widespread drought due in part to El Niño in 2015-2016, but it is unknown whether its severity was exacerbated by anthropogenic warming. This work examines the role of recent warming on this drought, using a recently developed high-resolution self-calibrating Palmer Drought Severity Index data set.

Relative impacts of mitigation, temperature, and precipitation on 21st-century megadrought risk in the American Southwest.

Megadroughts are comparable in severity to the worst droughts of the 20th century but are of much longer duration. A megadrought in the American Southwest would impose unprecedented stress on the limited water resources of the area, making it critical to evaluate future risks not only under different climate change mitigation scenarios but also for different aspects of regional hydroclimate. We find that changes in the mean hydroclimate state, rather than its variability, determine megadrought risk in the American Southwest.

Unprecedented 21st century drought risk in the American Southwest and Central Plains.

In the Southwest and Central Plains of Western North America, climate change is expected to increase drought severity in the coming decades. These regions nevertheless experienced extended Medieval-era droughts that were more persistent than any historical event, providing crucial targets in the paleoclimate record for benchmarking the severity of future drought risks. We use an empirical drought reconstruction and three soil moisture metrics from 17 state-of-the-art general circulation models to show that these models project significantly drier conditions in the later half of the 21st century compared to the 20th century and earlier paleoclimatic intervals.