Northern Galápagos corals reveal twentieth century warming in the eastern tropical Pacific

Models and observations disagree regarding sea surface temperature (SST) trends in the eastern tropical Pacific. We present a new Sr/Ca‐SST record that spans 1940–2010 from two Wolf Island corals (northern Galápagos). Trend analysis of the Wolf record shows significant warming on multiple timescales, which is also present in several other records and gridded instrumental products. Together, these data sets suggest that most of the eastern tropical Pacific has warmed over the twentieth century. In contrast, recent decades have been characterized by warming during boreal spring and summer (especially north of the equator), and subtropical cooling during boreal fall and winter (especially south of the equator). These SST trends are consistent with the effects of radiative forcing, mitigated by cooling due to wind forcing during boreal winter, as well as intensified upwelling and a strengthened Equatorial Undercurrent.Key PointsA new coral Sr/Ca record from Wolf Island, Galápagos, indicates SST warming on decadal to multidecadal timescalesTrend analysis of multiple data sets confirms long‐term warming throughout the eastern tropical Pacific, consistent with radiative forcingEastern Pacific warming since 1982 is overprinted by seasonally variable cooling from wind forcing and the ocean dynamical thermostatPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142987/1/grl56975_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142987/2/grl56975-sup-0001-2017GL075323-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142987/3/grl56975.pd

Separating Decadal Global Water Cycle Variability from Sea Level Rise

Under a warming climate, amplification of the water cycle and changes in precipitation patterns over land are expected to occur, subsequently impacting the terrestrial water balance. On global scales, such changes in terrestrial water storage (TWS) will be reflected in the water contained in the ocean and can manifest as global sea level variations. Naturally occurring climate-driven TWS variability can temporarily obscure the long-term trend in sea level rise, in addition to modulating the impacts of sea level rise through natural periodic undulation in regional and global sea level. The internal variability of the global water cycle, therefore, confounds both the detection and attribution of sea level rise. Here, we use a suite of observations to quantify and map the contribution of TWS variability to sea level variability on decadal timescales. In particular, we find that decadal sea level variability centered in the Pacific Ocean is closely tied to low frequency variability of TWS in key areas across the globe. The unambiguous identification and clean separation of this component of variability is the missing step in uncovering the anthropogenic trend in sea level and understanding the potential for low-frequency modulation of future TWS impacts including flooding and drought

Bifurcation and upwelling of the equatorial undercurrent west of the Galapagos Archipelago

Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(4), (2020): 887-905, doi:10.1175/JPO-D-19-0110.1.The Equatorial Undercurrent (EUC) encounters the Galápagos Archipelago on the equator as it flows eastward across the Pacific. The impact of the Galápagos Archipelago on the EUC in the eastern equatorial Pacific remains largely unknown. In this study, the path of the EUC as it reaches the Galápagos Archipelago is measured directly using high-resolution observations obtained by autonomous underwater gliders. Gliders were deployed along three lines that define a closed region with the Galápagos Archipelago as the eastern boundary and 93°W from 2°S to 2°N as the western boundary. Twelve transects were simultaneously occupied along the three lines during 52 days in April–May 2016. Analysis of individual glider transects and average sections along each line show that the EUC splits around the Galápagos Archipelago. Velocity normal to the transects is used to estimate net horizontal volume transport into the volume. Downward integration of the net horizontal transport profile provides an estimate of the time- and areal-averaged vertical velocity profile over the 52-day time period. Local maxima in vertical velocity occur at depths of 25 and 280 m with magnitudes of (1.7 ± 0.6) × 10−5 m s−1 and (8.0 ± 1.6) × 10−5 m s−1, respectively. Volume transport as a function of salinity indicates that water crossing 93°W south (north) of 0.4°S tends to flow around the south (north) side of the Galápagos Archipelago. Comparisons are made between previous observational and modeling studies with differences attributed to effects of the strong 2015/16 El Niño event, the annual cycle of local winds, and varying longitudes between studies of the equatorial Pacific.This work was supported by National Science Foundation (Grants OCE-1232971 and OCE-1233282) and the NASA Earth and Space Science Fellowship Program (Grant 80NSSC17K0443)

The equatorial current system west of the Galapagos Islands during the 2014-16 El Niño as observed by underwater gliders

Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(1),(2021): 3-17, https://doi.org/10.1175/JPO-D-20-0064.1.The strong El Niño of 2014–16 was observed west of the Galápagos Islands through sustained deployment of underwater gliders. Three years of observations began in October 2013 and ended in October 2016, with observations at longitudes 93° and 95°W between latitudes 2°N and 2°S. In total, there were over 3000 glider-days of data, covering over 50 000 km with over 12 000 profiles. Coverage was superior closer to the Galápagos on 93°W, where gliders were equipped with sensors to measure velocity as well as temperature, salinity, and pressure. The repeated glider transects are analyzed to produce highly resolved mean sections and maps of observed variables as functions of time, latitude, and depth. The mean sections reveal the structure of the Equatorial Undercurrent (EUC), the South Equatorial Current, and the equatorial front. The mean fields are used to calculate potential vorticity Q and Richardson number Ri. Gradients in the mean are strong enough to make the sign of Q opposite to that of planetary vorticity and to have Ri near unity, suggestive of mixing. Temporal variability is dominated by the 2014–16 El Niño, with the arrival of depressed isopycnals documented in 2014 and 2015. Increases in eastward velocity advect anomalously salty water and are uncorrelated with warm temperatures and deep isopycnals. Thus, vertical advection is important to changes in heat, and horizontal advection is relevant to changes in salt. Implications of this work include possibilities for future research, model assessment and improvement, and sustained observations across the equatorial Pacific.We gratefully acknowledge the support of the National Science Foundation (OCE-1232971, OCE-1233282) and the Ocean Observing and Monitoring Division of the National Oceanographic and Atmospheric Administration (NA13OAR4830216)

The Pacific Equatorial Undercurrent in three generations of global climate models and glider observations

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125, (2020): e2020JC016609, doi:10.1029/2020JC016609.The Equatorial Undercurrent (EUC) is a vital component of the coupled ocean‐atmosphere system in the tropical Pacific. The details of its termination near the Galápagos Islands in the eastern Pacific have an outsized importance to regional circulation and ecosystems. Subject to diverse physical processes, the EUC is also a rigorous benchmark for global climate models (GCMs). Simulations of the EUC in three generations of GCMs are evaluated relative to recent underwater glider observations along 93°W. Simulations of the EUC have improved, but a slow bias of ~36% remains in the eastern Pacific, along with a dependence on resolution. Additionally, the westward surface current is too slow, and stratification is too strong (weak) by ~50% above (within) the EUC. These biases have implications for mixing in the equatorial cold tongue. Downstream lies the Galápagos, now resolved to varying degrees by GCMs. Properly representing the Galápagos is necessary to avoid new biases as the EUC improves.We gratefully acknowledge support from the National Science Foundation (OCE‐1232971 and OCE‐1233282) and the Global Ocean Monitoring and Observing program (formerly the Ocean Observing and Monitoring Division) of the National Oceanographic and Atmospheric Administration (NA13OAR4830216).2021-04-2

Equatorial Pacific coral geochemical records show recent weakening of the Walker Circulation

Equatorial Pacific ocean-atmosphere interactions affect climate globally, and a key component of the coupled system is the Walker Circulation, which is driven by sea surface temperature (SST) gradients across the equatorial Pacific. There is conflicting evidence as to whether the SST gradient and Walker Circulation have strengthened or weakened over the late twentieth century. We present new records of SST and sea surface salinity (SSS) spanning 1959-2010 based on paired measurements of Sr/Ca and δ18O in a massive Porites coral from Butaritari atoll in the Gilbert Islands, Republic of Kiribati, in the central western equatorial Pacific. The records show 2-7 year variability correlated with the El Niño-Southern Oscillation (ENSO) and corresponding shifts in the extent of the Indo-Pacific Warm Pool, and decadal-scale signals related to the Pacific Decadal Oscillation and the Pacific Warm Pool Index. In addition, the Butaritari coral records reveal a small but significant increase in SST (0.39°C) from 1959 to 2010 with no accompanying change in SSS, a trend that persists even when ENSO variability is removed. In contrast, larger increases in SST and SSS are evident in coral records from the equatorial Pacific Line Islands, located east of Butaritari. Taken together, the equatorial Pacific coral records suggest an overall reduction in the east-west SST and SSS gradient over the last several decades, and a recent weakening of the Walker Circulation

Coordinated hydrological regimes in the Indo-Pacific region during the past two millennia

Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 25 (2010): PA1102, doi:10.1029/2009PA001871.Instrumental data suggest that major shifts in tropical Pacific atmospheric dynamics and hydrology have occurred within the past century, potentially in response to anthropogenic warming. To better understand these trends, we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes (δDwax) in marine sediments from southwest Sulawesi, Indonesia, to compile a detailed reconstruction of central Indo-Pacific Warm Pool (IPWP) hydrologic variability spanning most of the last two millennia. Our paleodata are highly correlated with a monsoon reconstruction from Southeast Asia, indicating that intervals of strong East Asian summer monsoon (EASM) activity are associated with a weaker Indonesian monsoon (IM). Furthermore, the centennial-scale oscillations in our data follow known changes in Northern Hemisphere climate (e.g., the Little Ice Age and Medieval Warm Period) implying a dynamic link between Northern Hemisphere temperatures and IPWP hydrology. The inverse relationship between the EASM and IM suggests that migrations of the Intertropical Convergence Zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the IPWP throughout most of the past two millennia.This research was supported by the U.S. NSF, the Ocean and Climate Change Institute at WHOI, and a National Defense Science and Engineering Graduate Fellowship to J. Tierney

International Research Institute for Climate and Society

This report documents the process and results of the index insurance design effort leading to the index insurance contracts for Adi Ha in 2009. This report represents deliverables 1 and 2 in the terms of reference with Oxfam America, it outlines and compares analysis and design methodologies including the performance of rainfall simulators for index-based contract design. It also details contracts, methodologies, associated issues, and important lessons learned. A separate project report details the Experimental Games, deliverable 3 in the terms of reference. IRI has delivered contracts and methodology with a significant portion of the effort provided without cost to Oxfam America. This includes contributions from several external researchers who have contributed time at no cost. Substantial funders who have provided additional sponsorship include NOAA, NSF, (through its CRED DMUU center at Columbia), the Columbia Earth Institute postdoctoral program, the Columbia University Lamont postdoctoral program, and an Earth Institute CGSD seed grant. The insurance effort is one component of the Oxfam HARITA project, with the insurance designed to target key gaps left in the HARITA holistic climate risk management portfolio. Because this report focuses on the insurance contract design, it does not provide a comprehensive overview of the full climate risk management strategy, although it does refer to particular components in discussion of design issues. For a complete overview of the risk management and adaptation portfolio, the reader should refer to Oxfam HARITA project documentation. Many partners have participated substantially in the contract design effort. Major partners in this project include the Relief Society of Tigray (REST), Dedebit Credit and Savings Institution (DECSI), Nyala Insurance Company, the Ethiopian Productive Safety Net Program (PSNP), the Government of Ethiopian National Meteorological Agency (ENMA), Swiss Re, Mekele University, Oxfam Horn of Africa Regional Office, and Oxfam America (project coordinator). Any successes of this project depend strongly on the outstanding effort, skill, active engagement, and level of insights from the partners. Crop modeling parameters were obtained from LEAP and Mekele University. This project benefits strongly from groundwork and ongoing index insurance projects in Ethiopia and elsewhere by WFP and the World Bank CRMG

Increased light, moderate, and severe clear-air turbulence in response to climate change

Anthropogenic climate change is expected to strengthen the vertical wind shears at aircraft cruising altitudes within the atmospheric jet streams. Such a strengthening would increase the prevalence of shear instabilities, which generate clear-air turbulence. Climate modelling studies have indicated that the amount of moderate-or-greater clear-air turbulence on transatlantic flight routes in winter will increase significantly in future as the climate changes. However, the individual responses of light, moderate, and severe clear-air turbulence have not previously been studied, despite their importance for aircraft operations. Here we use climate model simulations to analyse the transatlantic wintertime clear-air turbulence response to climate change in five aviation-relevant turbulence strength categories. We find that the probability distributions for an ensemble of 21 clear-air turbulence diagnostics generally gain probability in their right-hand tails when the atmospheric carbon dioxide concentration is doubled. By converting the diagnostics into equivalent eddy dissipation rates, we find that the ensemble-average airspace volume containing light clear-air turbulence increases by 59% (with an intra-ensemble range of 43–68%), light-to-moderate by 75% (39–96%), moderate by 94% (37–118%), moderate-to-severe by 127% (30–170%), and severe by 149% (36–188%). These results suggest that the prevalence of transatlantic wintertime clear-air turbulence will increase significantly in all aviation-relevant strength categories as the climate changes