Browsing by Author "Parsons, LA"

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Open Access
Do Multi-Model Ensembles Improve Reconstruction Skill in Paleoclimate Data Assimilation?
(Earth and Space Science, 2021-04-01) Parsons, LA; Amrhein, DE; Sanchez, SC; Tardif, R; Brennan, MK; Hakim, GJ
Reconstructing past climates remains a difficult task because pre-instrumental observational networks are composed of geographically sparse and noisy paleoclimate proxy records that require statistical techniques to inform complete climate fields. Traditionally, instrumental or climate model statistical relationships are used to spread information from proxy measurements to other locations and to other climate variables. Here ensembles drawn from single climate models and from combinations of multiple climate models are used to reconstruct temperature variability over the last millennium in idealized experiments. We find that reconstructions derived from multi-model ensembles produce lower error than reconstructions from single-model ensembles when reconstructing independent model and instrumental data. Specifically, we find the largest decreases in error over regions far from proxy locations that are often associated with large uncertainties in model physics, such as mid- and high-latitude ocean and sea-ice regions. Furthermore, we find that multi-model ensemble reconstructions outperform single-model reconstructions that use covariance localization. We propose that multi-model ensembles could be used to improve paleoclimate reconstructions in time periods beyond the last millennium and for climate variables other than air temperature, such as drought metrics or sea ice variables.
Open Access
Global labor loss due to humid heat exposure underestimated for outdoor workers
(Environmental Research Letters, 2022-01-01) Parsons, LA; Masuda, YJ; Kroeger, T; Shindell, D; Wolff, NH; Spector, JT
Humid heat impacts a large portion of the world's population that works outdoors. Previous studies have quantified humid heat impacts on labor productivity by relying on exposure response functions that are based on uncontrolled experiments under a limited range of heat and humidity. Here we use the latest empirical model, based on a wider range of temperatures and humidity, for studying the impact of humid heat and recent climate change on labor productivity. We show that globally, humid heat may currently be associated with over 650 billion hours of annual lost labor (148 million full time equivalent jobs lost), 400 billion hours more than previous estimates. These differences in labor loss estimates are comparable to losses caused by the COVID-19 pandemic. Globally, annual heat-induced labor productivity losses are estimated at 2.1 trillion in 2017 PPP$, and in several countries are equivalent to more than 10% of gross domestic product. Over the last four decades, global heat-related labor losses increased by at least 9% (>60 billion hours annually using the new empirical model) highlighting that relatively small changes in climate (<0.5 C) can have large impacts on global labor and the economy.
Open Access
Impacts of warming on outdoor worker well-being in the tropics and adaptation options
(One Earth, 2024-03-15) Masuda, YJ; Parsons, LA; Spector, JT; Battisti, DS; Castro, B; Erbaugh, JT; Game, ET; Garg, T; Kalmus, P; Kroeger, T; Mishra, V; Shindell, D; Tigchelaar, M; Wolff, NH; Vargas Zeppetello, LR
Over a billion outdoor workers live in the tropics, where nearly a fifth of all hours in the year are hot and humid enough to exceed recommended safety thresholds for workers conducting heavy labor. Reviews have focused on heat impacts on worker health, well-being, and productivity, but synthesis on how to increase resilience to heat for outdoor workers is lacking. Here we assess current and future heat exposure in the tropics and review four bodies of literature on heat impacts on workers. We also synthesize knowledge about mitigation and adaptation uncertainties as well as the actions that can be taken to strengthen worker resilience. We show that under an additional 1°C of warming, ∼800 million people in the tropics will live in areas where heavy work should be limited for over half of the hours in the year. Our review provides primary, secondary, and tertiary solutions that will inform policies and practices as well as research that is needed to bolster worker resilience and well-being.
Open Access
Implications of CMIP6 Projected Drying Trends for 21st Century Amazonian Drought Risk
(Earth's Future, 2020-10-01) Parsons, LA
Recent exceptionally hot droughts in Amazonia have highlighted the potential role of global warming in driving changes in rainfall and temperatures in the region. The previous generation of global climate models projected that eastern Amazonia would receive less future precipitation while western Amazonia would receive more precipitation, but many of these models disagreed on future precipitation trends in the region. Here Coupled Modeling Intercomparison Project, Phase 6 (CMIP6) models are used to examine the shifting risk of eastern Amazonian droughts under high and low future greenhouse gas emissions scenarios. This new generation of models shows better agreement that most of the Amazonian basin will receive less future rainfall, with particularly strong agreement that eastern and southern Amazonia will dry in the 21st century. These models suggest that global warming may be increasing the likelihood of exceptionally hot drought in the region. With unabated global warming, recent particularly warm and severe droughts will become more common by midcentury, but reducing the rate of greenhouse gas emissions can make extremely hot and dry years less common in the future. Simulated future rainfall changes in Amazonia under high greenhouse gas emissions are associated with changes in the tropical Pacific, but many climate models struggle to reproduce observed trends in the tropical Pacific. These shortcomings highlight the need to improve confidence in global climate models' ability to simulate observed trends in the tropics, even if more CMIP6 models agree on the sign of future rainfall trends.
Open Access
Local Regions Associated With Interdecadal Global Temperature Variability in the Last Millennium Reanalysis and CMIP5 Models
(Journal of Geophysical Research: Atmospheres, 2019-09-01) Parsons, LA; Hakim, GJ
Despite the importance of interdecadal climate variability, we have a limited understanding of which geographic regions are associated with global temperature variability at these timescales. The instrumental record tends to be too short to develop sample statistics to study interdecadal climate variability, and Coupled Model Intercomparison Project, Phase 5 (CMIP5) climate models tend to disagree about which locations most strongly influence global mean interdecadal temperature variability. Here we use a new paleoclimate data assimilation product, the Last Millennium Reanalysis (LMR), to examine where local variability is associated with global mean temperature variability at interdecadal timescales. The LMR framework uses an ensemble Kalman filter data assimilation approach to combine the latest paleoclimate data and state-of-the-art model data to generate annually resolved field reconstructions of surface temperature, which allow us to explore the timing and dynamics of preinstrumental climate variability in new ways. The LMR consistently shows that the middle- to high-latitude north Pacific and the high-latitude North Atlantic tend to lead global temperature variability on interdecadal timescales. These findings have important implications for understanding the dynamics of low-frequency climate variability in the preindustrial era.
Open Access
Magnitudes and Spatial Patterns of Interdecadal Temperature Variability in CMIP6
(Geophysical Research Letters, 2020-04-16) Parsons, LA; Brennan, MK; Wills, RCJ; Proistosescu, C
Attribution and prediction of global and regional warming requires a better understanding of the magnitude and spatial characteristics of internal global mean surface air temperature (GMST) variability. We examine interdecadal GMST variability in Coupled Modeling Intercomparison Projects, Phases 3, 5, and 6 (CMIP3, CMIP5, and CMIP6) preindustrial control (piControl), last millennium, and historical simulations and in observational data. We find that several CMIP6 simulations show more GMST interdecadal variability than the previous generations of model simulations. Nonetheless, we find that 100-year trends in CMIP6 piControl simulations never exceed the maximum observed warming trend. Furthermore, interdecadal GMST variability in the unforced piControl simulations is associated with regional variability in the high latitudes and the east Pacific, whereas interdecadal GMST variability in instrumental data and in historical simulations with external forcing is more globally coherent and is associated with variability in tropical deep convective regions.
Open Access
Ocean-Atmosphere Trajectories of Extended Drought in Southwestern North America
(Journal of Geophysical Research: Atmospheres, 2019-08-27) Parsons, LA; Coats, S
Multiyear droughts are a common occurrence in southwestern North America (SWNA), but it is unclear what causes these persistent dry periods. The ocean-atmosphere conditions coinciding with droughts have traditionally been studied using correlation and composite methods, which suggest that cool conditions in the tropical Pacific are associated with SWNA droughts and warm conditions are associated with wet periods in SWNA. Nevertheless, the extent to which multiyear droughts are truly consistent with this paradigm remains unknown. This is, in part, because the temporal trajectory of ocean-atmosphere conditions during these dry periods have not been sufficiently characterized. Here we examine the continuum of ocean-atmosphere trajectories before, during, and after multiyear droughts in SWNA using observation-based data and an ensemble of climate model simulations from the Community Earth System Model. An examination of sea surface temperature patterns at the beginning, middle, and end of SWNA droughts shows that an El Niño event tends to precede SWNA droughts, a cool tropical Pacific occurs during droughts, and central Pacific El Niño events end droughts. However, moderate El Niño events can occur in the middle of persistent droughts, so a warm tropical Pacific does not always end these dry periods. These findings are important for drought predictability and emphasize the need to improve simulations of the magnitude, life cycle, and frequency of occurrence of El Niño events.
Open Access
Quantifying Structural Uncertainty in Paleoclimate Data Assimilation With an Application to the Last Millennium
(Geophysical Research Letters, 2020-11-28) Amrhein, DE; Hakim, GJ; Parsons, LA
Paleoclimate reconstruction relies on estimates of spatiotemporal relationships among climate quantities to interpolate between proxy data. This work quantifies how structural uncertainties in those relationships translate to uncertainties in reconstructions of past climate. We develop and apply a data assimilation uncertainty quantification approach to paleoclimate networks and observational uncertainties representative of data for the last millennium. We find that structural uncertainties arising from uncertain spatial covariance relationships typically contribute 10% of the total uncertainty in reconstructed temperature variability at small (∼200 km), continental, and hemispheric length scales, with larger errors (50% or larger) in regions where long-range climate covariances are least certain. These structural uncertainties contribute far more to errors in uncertainty quantification, sometimes by a factor of 5 or higher. Accounting for and reducing uncertainties in climate model dynamics and resulting covariance relationships will improve paleoclimate reconstruction accuracy.
Open Access
The Threat of Multi-Year Drought in Western Amazonia
(Water Resources Research, 2018-09-01) Parsons, LA; LeRoy, S; Overpeck, JT; Bush, M; Cárdenes-Sandí, GM; Saleska, S
Recent “once-in-a-century” Amazonian droughts highlight the impacts of drought and climate change on this region's vegetation, carbon storage, water cycling, biodiversity, land use, and economy. The latest climate model simulations suggest this region will experience worsening future drought. However, the instrumental record is too short to quantify the range of background drought variability, or to evaluate extended drought risk in climate models. To overcome these limitations, we generated a new, highly resolved lake record of hydroclimatic variability within the western Amazon Basin. We find that Amazonia has regularly experienced multi-year droughts over the last millennium. Our results indicate that current climate model simulations likely underestimate the background risk of multi-year Amazonian drought. These findings illustrate that the future sustainability of the Amazonian forest and its many services may require management strategies that consider the likelihood of multi-year droughts superimposed on a continued warming trend.
Open Access
Tropical deforestation accelerates local warming and loss of safe outdoor working hours
(One Earth, 2021-12-17) Parsons, LA; Jung, J; Masuda, YJ; Vargas Zeppetello, LR; Wolff, NH; Kroeger, T; Battisti, DS; Spector, JT
Climate change has increased heat exposure in many parts of the tropics, negatively impacting outdoor worker productivity and health. Although it is known that tropical deforestation is associated with local warming, the extent to which this additional heat exposure affects people across the tropics is unknown. In this modeling study, we combine worker health guidelines with satellite, reanalysis, and population data to investigate how warming associated with recent deforestation (2003–2018) affects outdoor working conditions across low-latitude countries, and how future global climate change will magnify heat exposure for people in deforested areas. We find that the local warming from 15 years of deforestation was associated with losses in safe thermal working conditions for 2.8 million outdoor workers. We also show recent large-scale forest loss was associated with particularly large impacts on populations in locations such as the Brazilian states of Mato Grosso and Pará. Future global warming and additional forest loss will magnify these impacts.