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Large influence of soil moisture on long-term terrestrial carbon uptake
Although the terrestrial biosphere absorbs about 25 per cent of anthropogenic carbon dioxide (CO
2
) emissions, the rate of land carbon uptake remains highly uncertain, leading to uncertainties in climate projections
1
,
2
. Understanding the factors that limit or drive land carbon storage is therefore important for improving climate predictions. One potential limiting factor for land carbon uptake is soil moisture, which can reduce gross primary production through ecosystem water stress
3
,
4
, cause vegetation mortality
5
and further exacerbate climate extremes due to land–atmosphere feedbacks
6
. Previous work has explored the impact of soil-moisture availability on past carbon-flux variability
3
,
7
,
8
. However, the influence of soil-moisture variability and trends on the long-term carbon sink and the mechanisms responsible for associated carbon losses remain uncertain. Here we use the data output from four Earth system models
9
from a series of experiments to analyse the responses of terrestrial net biome productivity to soil-moisture changes, and find that soil-moisture variability and trends induce large CO
2
fluxes (about two to three gigatons of carbon per year; comparable with the land carbon sink itself
1
) throughout the twenty-first century. Subseasonal and interannual soil-moisture variability generate CO
2
as a result of the nonlinear response of photosynthesis and net ecosystem exchange to soil-water availability and of the increased temperature and vapour pressure deficit caused by land–atmosphere interactions. Soil-moisture variability reduces the present land carbon sink, and its increase and drying trends in several regions are expected to reduce it further. Our results emphasize that the capacity of continents to act as a future carbon sink critically depends on the nonlinear response of carbon fluxes to soil moisture and on land–atmosphere interactions. This suggests that the increasing trend in carbon uptake rate may not be sustained past the middle of the century and could result in accelerated atmospheric CO
2
growth.
Earth system models suggest that soil-moisture variability and trends will induce large carbon releases throughout the twenty-first century.
Journal Article
Carbon capture and storage : technologies, policies, economics, and implementation strategies
This book focuses on issues related to a suite of technologies known as \"Carbon Capture and Storage (CCS),\" which can be used to capture and store underground large amounts of industrial CO2 emissions. It addresses how CCS should work, as well as where, why, and how these technologies should be deployed, emphasizing the gaps to be filled in terms of research and development, technology, regulations, economics, and public acceptance.
Book
The fate of carbon in a mature forest under carbon dioxide enrichment
Atmospheric carbon dioxide enrichment (eCO2) can enhance plant carbon uptake and growth1 5, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration6. Although evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth3 5, it is unclear whether mature forests respond to eCO2 in a similar way. In mature trees and forest stands7 10, photosynthetic uptake has been found to increase under eCO2 without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO2 unclear4,5,7 11. Here using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO2 exposure. We show that, although the eCO2 treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO2, and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO2 fertilization as a driver of increased carbon sinks in global forests. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.
Journal Article
Three cheers for trees! : a book about our carbon footprint
\"Simple text and color photographs provide an introduction to carbon footprints\"-- Provided by publisher.
Book
Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions
Carbon dioxide (CO
2
) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO
2
concentrations. Using a global compilation of high-frequency CO
2
measurements, we demonstrate that nocturnal CO
2
emissions are on average 27% (0.9 gC m
−2
d
−1
) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO
2
by photosynthesis. Because current global estimates of CO
2
emissions to the atmosphere from running waters (0.65–1.8 PgC yr
−1
) rely primarily on discrete measurements of dissolved CO
2
obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO
2
emissions may elevate global estimates from running waters to the atmosphere by 0.20–0.55 PgC yr
−1
.
Failing to account for emission differences between day and night will lead to an underestimate of global CO
2
emissions from rivers by up to 0.55 PgC yr
–1
, according to analyses of high-frequency CO
2
measurements.
Journal Article
Carbon dioxide capture : an effective way to combat global warming
This topical brief summarizes the various options available for carbon capture and presents the current strategies involved in CO₂ reduction. The authors focus on current CO₂ capture technologies that facilitate the reduction of greenhouse gas (CO₂) emissions and reduce global warming. This short study will interest environmental researchers, teachers and students who have an interest in global warming.
Book
Mineral protection regulates long-term global preservation of natural organic carbon
The balance between photosynthetic organic carbon production and respiration controls atmospheric composition and climate
1
,
2
. The majority of organic carbon is respired back to carbon dioxide in the biosphere, but a small fraction escapes remineralization and is preserved over geological timescales
3
. By removing reduced carbon from Earth’s surface, this sequestration process promotes atmospheric oxygen accumulation
2
and carbon dioxide removal
1
. Two major mechanisms have been proposed to explain organic carbon preservation: selective preservation of biochemically unreactive compounds
4
,
5
and protection resulting from interactions with a mineral matrix
6
,
7
. Although both mechanisms can operate across a range of environments and timescales, their global relative importance on 1,000-year to 100,000-year timescales remains uncertain
4
. Here we present a global dataset of the distributions of organic carbon activation energy and corresponding radiocarbon ages in soils, sediments and dissolved organic carbon. We find that activation energy distributions broaden over time in all mineral-containing samples. This result requires increasing bond-strength diversity, consistent with the formation of organo-mineral bonds
8
but inconsistent with selective preservation. Radiocarbon ages further reveal that high-energy, mineral-bound organic carbon persists for millennia relative to low-energy, unbound organic carbon. Our results provide globally coherent evidence for the proposed
7
importance of mineral protection in promoting organic carbon preservation. We suggest that similar studies of bond-strength diversity in ancient sediments may reveal how and why organic carbon preservation—and thus atmospheric composition and climate—has varied over geological time.
Broadening activation energy distributions and increasing radiocarbon ages reveal the global importance of mineral protection in promoting organic carbon preservation.
Journal Article
Carbon capture
The burning of fossil fuels releases carbon dioxide (CO2), and these CO2 emissions are a major driver of climate change. Carbon capture offers a path to climate change mitigation that has received relatively little attention. In this volume in the MIT Press Essential Knowledge series, Howard Herzog offers a concise guide to carbon capture, covering basic information as well as the larger context of climate technology and policy. Carbon capture, or carbon dioxide capture and storage (CCS), refers to a suite of technologies that reduce CO2 emissions by \"capturing\" CO2 before it is released into the atmosphere and then transporting it to where it will be stored or used. It is the only climate change mitigation technique that deals directly with fossil fuels rather than providing alternatives to them. Herzog, a pioneer in carbon capture research, begins by discussing the fundamentals of climate change and how carbon capture can be one of the solutions. He explains capture and storage technologies, including chemical scrubbing and the injection of CO2 deep underground. He reports on current efforts to deploy CCS at factories and power plants and attempts to capture CO2 from the air itself. Finally, he explores the policies and politics in play around CCS and argues for elevating carbon capture in the policy agenda.
Book
Soil moisture-atmosphere feedback dominates land carbon uptake variability
Year-to-year changes in carbon uptake by terrestrial ecosystems have an essential role in determining atmospheric carbon dioxide concentrations
. It remains uncertain to what extent temperature and water availability can explain these variations at the global scale
. Here we use factorial climate model simulations
and show that variability in soil moisture drives 90 per cent of the inter-annual variability in global land carbon uptake, mainly through its impact on photosynthesis. We find that most of this ecosystem response occurs indirectly as soil moisture-atmosphere feedback amplifies temperature and humidity anomalies and enhances the direct effects of soil water stress. The strength of this feedback mechanism explains why coupled climate models indicate that soil moisture has a dominant role
, which is not readily apparent from land surface model simulations and observational analyses
. These findings highlight the need to account for feedback between soil and atmospheric dryness when estimating the response of the carbon cycle to climatic change globally
, as well as when conducting field-scale investigations of the response of the ecosystem to droughts
. Our results show that most of the global variability in modelled land carbon uptake is driven by temperature and vapour pressure deficit effects that are controlled by soil moisture.
Journal Article