1,721,188 research outputs found
Multiple Climate Tipping Points Metrics for Improved Sustainability Assessment of Products and Services
Get PDFMounting evidence indicates that climate tipping points can have large, potentially irreversible, impacts on the earth system and human societies. Yet, climate change metrics applied in current sustainability assessment methods generally do not consider these tipping points, with the use of arbitrarily determined time horizons and assumptions that the climate impact of a product or service is independent of emission timing. Here, we propose a new method for calculating climate tipping characterization factors for greenhouse gases (carbon dioxide, methane, and nitrous oxide) at midpoint. It covers 13 projected tipping points, incorporates the effect that the crossing of a given tipping point has on accelerating the crossing of other tipping points, and addresses uncertainties in the temperature thresholds that trigger the tipping points. To demonstrate the added value of the new metric, we apply it to emissions stemming from end-of-life of plastic polymers and compare them with commonly used metrics. This highlights the need to consider climate tipping in sustainability assessment of products and services
Climate change mitigation: trade-offs between delay and strength of action required
No full textClimate change mitigation via a reduction in the anthropogenic emissions of carbon dioxide (CO2) is the principle requirement for reducing global warming, its impacts, and the degree of adaptation required. We present a simple conceptual model of anthropogenic CO2 emissions to highlight the trade off between delay in commencing mitigation, and the strength of mitigation then required to meet specific atmospheric CO2 stabilization targets. We calculate the effects of alternative emission profiles on atmospheric CO2 and global temperature change over a millennial timescale using a simple coupled carbon cycle-climate model. For example, if it takes 50 years to transform the energy sector and the maximum rate at which emissions can be reduced is ?2.5% , delaying action until 2020 would lead to stabilization at 540 ppm. A further 20 year delay would result in a stabilization level of 730 ppm, and a delay until 2060 would mean stabilising at over 1,000 ppm. If stabilization targets are met through delayed action, combined with strong rates of mitigation, the emissions profiles result in transient peaks of atmospheric CO2 (and potentially temperature) that exceed the stabilization targets. Stabilization at 450 ppm requires maximum mitigation rates of ?3% to ?5% , and when delay exceeds 2020, transient peaks in excess of 550 ppm occur. Consequently tipping points for certain Earth system components may be transgressed. Avoiding dangerous climate change is more easily achievable if global mitigation action commences as soon as possible. Starting mitigation earlier is also more effective than acting more aggressively once mitigation has begun. <br/
Quantifying the feedback between ocean heating and CO2 solubility as an equivalent carbon emission
No full textThere are inherent difficulties in quantifying carbon cycle-climate feedbacks over the 21st century because the system is in a transient state. The conventional approach of deriving gain factors only strictly applies at equilibrium, and they differ with scenario and with respect to different climate variables (e.g., CO2, radiative forcing, and temperature) which have different time lags. Here we show that the positive feedback whereby ocean heating reduces the solubility of CO2 can be quantified in a. scenario-independent way, directly from ocean heat content changes, by expressing it as an 'equivalent carbon emission'. On annual to centennial timescales, the feedback has the same impact on atmospheric CO2 as an equivalent emission flux of fossil fuel carbon. From ocean heat-content data we quantify the ocean heating-CO2 solubility positive feedback, which increased in average strength from an equivalent emission of ~0.08 PgC yr-I oyer 1961-2003 to ~0.19 PgC yr-1 during 1993-2003
Reduced carbon cycle resilience across the Palaeocene-Eocene Thermal Maximum
Get PDFThis is the final version. Available on open access from EGU via the DOI in this recordSeveral past episodes of rapid carbon cycle and climate change are hypothesised to be the result of the Earth system reaching a tipping point beyond which an abrupt transition to a new state occurs. At the Palaeocene-Eocene Thermal Maximum (PETM) at ∼ 56 Ma and at subsequent hyperthermal events, hypothesised tipping points involve the abrupt transfer of carbon from surface reservoirs to the atmosphere. Theory suggests that tipping points in complex dynamical systems should be preceded by critical slowing down of their dynamics, including increasing temporal autocorrelation and variability. However, reliably detecting these indicators in palaeorecords is challenging, with issues of data quality, false positives, and parameter selection potentially affecting reliability. Here we show that in a sufficiently long, high-resolution palaeorecord there is consistent evidence of destabilisation of the carbon cycle in the ∼ 1.5 Myr prior to the PETM, elevated carbon cycle and climate instability following both the PETM and Eocene Thermal Maximum 2 (ETM2), and different drivers of carbon cycle dynamics preceding the PETM and ETM2 events. Our results indicate a loss of "resilience" (weakened stabilising negative feedbacks and greater sensitivity to small shocks) in the carbon cycle before the PETM and in the carbon-climate system following it. This pre-PETM carbon cycle destabilisation may reflect gradual forcing by the contemporaneous North Atlantic Volcanic Province eruptions, with volcanism-driven warming potentially weakening the organic carbon burial feedback. Our results are consistent with but cannot prove the existence of a tipping point for abrupt carbon release, e.g. from methane hydrate or terrestrial organic carbon reservoirs, whereas we find no support for a tipping point in deep ocean temperature.This work was supported by an EPSRC/ReCoVER
Early Career Research Project Award (number:
RFFECR 002) and an NERC Studentship to DIAM (number:
NE/J500112/1) hosted at Ocean and Earth Science at the University
of Southampton, with revised analyses performed at Stockholm
Resilience Centre. TML was supported by a Royal Society
Wolfson Research Merit Award and the NERC “JET” large grant
(NE/N018508/1)
Effect of AMOC collapse on ENSO in a high resolution general circulation model
No full textWe look at changes in the El Niño Southern Oscillation (ENSO) in a high-resolution eddy-permitting climate model experiment in which the Atlantic Meridional Circulation (AMOC) is switched off using freshwater hosing. The ENSO mode is shifted eastward and its period becomes longer and more regular when the AMOC is off. The eastward shift can be attributed to an anomalous eastern Ekman transport in the mean equatorial Pacific ocean state. Convergence of this transport deepens the thermocline in the eastern tropical Pacific and increases the temperature anomaly relaxation time, causing increased ENSO period. The anomalous Ekman transport is caused by a surface northerly wind anomaly in response to the meridional sea surface temperature dipole that results from switching the AMOC off. In contrast to a previous study with an earlier version of the model, which showed an increase in ENSO amplitude in an AMOC off experiment, here the amplitude remains the same as in the AMOC on control state. We attribute this difference to variations in the response of decreased stochastic forcing in the different models, which competes with the reduced damping of temperature anomalies. In the new high-resolution model, these effects approximately cancel resulting in no change in amplitude
Observational constraints on the causes of Holocene CO2 change
No full textThe mechanisms that controlled past atmospheric CO2 levels are not directly measurable, hence many proxy data sources are combined when reconstructing past carbon cycling. The accuracy of Holocene modeling reconstructions is checked by seeking consistency between data-based observables and their numerically simulated counterparts. A new framework is presented to evaluate which combinations of observables can best constrain carbon cycle mechanisms with the minimum of uncertainty. We show that when previous studies have combined ocean temperatures, ocean [CO32?], and the ?13C of atmospheric CO2 as observables, uncertainties in the data sources are amplified by over 2 orders of magnitude when reconstructing the mechanisms responsible for CO2 increase. However, incorporating mean ?13C of ocean DIC since 8000 years ago as an additional data source reduces the uncertainties by more than a factor of 5, making this observable a priority for future research. Our analysis indicates that the 20 ppm increase in CO2 between 8000 years BP and preindustrial was caused by significant CaCO3 precipitation and a reduction in the ocean soft tissue pump. Meanwhile, an increase in terrestrial carbon storage opposed the CO2 increase. The methods presented here are useful for investigating a range of paleoclimate events
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Closing loops to rebalance the global carbon cycle: Biomass flows modelling of global agricultural carbon fluxes
No full textSince the beginning of farming, and even before, humans have been actively modifying our environment in order to harvest biomass. With the ‘Great Acceleration’ of the industrial age, the global system of biomass harvest for food production has become a major driver of Earth system processes, and caused multi-dimensional sustainability issues which must be addressed in order to meet continued increases in demand for food and other biomass. In addition, bioenergy generation, with the subsequent storage of some or all of the carbon content of the feedstock (known as bioenergy with carbon storage or BECS), is now seen as an important tool for rebalancing the carbon cycle. This thesis has used a biomass flows modelling approach to examine possible trajectories for the socio-ecological metabolism of humanity, with a focus on fluxes of carbon contained in biomass. This approach connects social and economic drivers of biomass harvest with physical Earth systems processes such as the global carbon cycle. Meeting growing food demand in the years 2000-2050 is likely to be a significant challenge in its own right, necessitating the harvest of over 30% of terrestrial biomass. This can only be done without significant damage to natural ecosystems if large increases in efficiency and intensity of food production are achieved, or diets are altered. The production of livestock products is shown to be a major cause of inefficiency in biomass harvest, and changes to livestock demand or production are particularly powerful in ensuring a less damaging relationship with Earth system processes. If increases in efficiency are achieved, it may be possible to grow dedicated bioenergy crops, which, combined with the biomass available in waste and residue streams can be used to generate significant carbon dioxide removal (CDR) fluxes via BECS. Following this strategy it is possible to have a non-trivial effect on atmospheric CO2 concentration by 2050. Increasing the intensity of biomass harvest, particularly when low intensity pasture is replaced with intense bioenergy cropping, also has significant implications for ecological energy flows, and the potential trade-off between protecting biodiversity and growing bioenergy crops to mitigate climate change is also discussed. This body of work presents several interesting areas of potential conflict in different drivers of biomass harvest, and suggestions are made for ways in which to develop the approach in order to explore them
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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