Tropical nighttime warming as a dominant driver of variability in the terrestrial carbon sink

The terrestrial biosphere is currently a strong carbon (C) sink but may switch to a source in the 21st century as climate-driven losses exceed CO2-driven C gains, thereby accelerating global warming. Although it has long been recognized that tropical climate plays a critical role in regulating interannual climate variability, the causal link between changes in temperature and precipitation and terrestrial processes remains uncertain. Here, we combine atmospheric mass balance, remote sensing-modeled datasets of vegetation C uptake, and climate datasets to characterize the temporal variability of the terrestrial C sink and determine the dominant climate drivers of this variability. We show that the interannual variability of global land C sink has grown by 50–100% over the past 50 y. We further find that interannual land C sink variability is most strongly linked to tropical nighttime warming, likely through respiration. This apparent sensitivity of respiration to nighttime temperatures, which are projected to increase faster than global average temperatures, suggests that C stored in tropical forests may be vulnerable to future warming

Trends in the sources and sinks of carbon dioxide

Efforts to control climate change require the stabilization of atmospheric CO2 concentrations. This can only be achieved through a drastic reduction of global CO2 emissions. Yet fossil fuel emissions increased by 29% between 2000 and 2008, in conjunction with increased contributions from emerging economies, from the production and international trade of goods and services, and from the use of coal as a fuel source. In contrast, emissions from land-use changes were nearly constant. Between 1959 and 2008, 43% of each year's CO2 emissions remained in the atmosphere on average; the rest was absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO2 emissions that remains in the atmosphere each year has likely increased, from about 40% to 45%, and models suggest that this trend was caused by a decrease in the uptake of CO2 by the carbon sinks in response to climate change and variability. Changes in the CO2 sinks are highly uncertain, but they could have a significant influence on future atmospheric CO2 levels. It is therefore crucial to reduce the uncertainties

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018.

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field

Variability and Trends in the Carbon Cycle

This thesis examines the mechanisms that control the removal of anthropogenic CO2 from the atmosphere on timescales of decades to centuries. I focus on applying Bayesian statistical methods to constrain models of CO2 uptake, detect trends from observations and provide uncertainty analysis for integrated assessment models for climate change. I first apply a data assimilation technique to a newly-released database of sur- face ocean carbon measurements. This application uses model-based information to compensate for data sparsity in a novel way and globally maps trends in the partial pressure of surface ocean pCO2. The results provide a new estimate of the growth in the total air-sea flux of CO2 and regional trend estimates. In particular, the result in the Southern Ocean provides new insights into the physical and chemical controls on CO2 uptake in that region of the ocean. I then review model and data-based estimates of the Southern Ocean CO2 uptake and how it may change under climate change. I use an observational system observing experiment to show that the standing uncertainty in Southern Ocean CO2 uptake could be resolved with a float-based sampling network with between 150-200 members. I also show that changes to Southern Ocean CO2 fluxes predicted by models as a result of climate change will take decades to detect directly. The last chapter focuses on the implications of uncertainty in the present and future carbon cycle for models that are used to price CO2 emissions as an externality of economic growth. The scientific contribution quantifies the implications of the large uncertainty in estimates of historical land use emissions of CO2 to future projections. This study novelly highlights the critical role that uncertainty in the response of the natural carbon sinks plays in evaluating the economic impacts of climate change and quantifies how reductions in that uncertainty can be used to improve the efficiency of climate policy design

A growing oceanic carbon uptake: Results from an inversion study of surface pCO(2) data

Concerted community efforts have been devoted to producing an authoritative climatology of air-sea CO2 fluxes, but identifying decadal trends in CO2 fluxes has proven to be more challenging. The available surface pCO(2) estimates are too sparse to separate long-term trends from decadal and seasonal variability using simple linear models. We introduce Markov Chain Monte Carlo sampling as a novel technique for estimating the historical pCO(2) at the ocean surface. The result is a plausible history of surface pCO(2) based on available measurements and variability inferred from model simulations. Applying the method to a modern database of pCO(2) data, we find that two thirds of the ocean surface is trending toward increasing uptake of CO2, with a mean (year 2000) uptake of 2.3 0.5 PgC yr(-1) of anthropogenic carbon and an increase in the global annual uptake over the 30 year time period of 0.4 0.1 PgC yr(-1) decade(-1). The results are particularly interesting in the Southern Ocean, where we find increasing uptake of carbon over this time period, in contrast to previous studies. We find evidence for increased ventilation of deep ocean carbon, in response to increased winds, which is more than offset by an associated surface cooling

An observing system simulation for Southern Ocean carbon dioxide uptake

The Southern Ocean is critically important to the oceanic uptake of anthropogenic CO2. Up to half of the excess CO2 currently in the ocean entered through the Southern Ocean. That uptake helps to maintain the global carbon balance and buffers transient climate change from fossil fuel emissions. However, the future evolution of the uptake is uncertain, because our understanding of the dynamics that govern the Southern Ocean CO2 uptake is incomplete. Sparse observations and incomplete model formulations limit our ability to constrain the monthly and annual uptake, interannual variability and long-term trends. Float-based sampling of ocean biogeochemistry provides an opportunity for transforming our understanding of the Southern Ocean CO2 flux. In this work, we review current estimates of the CO2 uptake in the Southern Ocean and projections of its response to climate change. We then show, via an observational system simulation experiment, that float-based sampling provides a significant opportunity for measuring the mean fluxes and monitoring the mean uptake over decadal scales

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