1,720,995 research outputs found
Global methane pledge versus carbon dioxide emission reduction
Full text linkMethane (CH _4 ) is a potent greenhouse gas whose contribution to anthropogenic radiative forcing of the climate system is second only to carbon dioxide (CO _2 ). CH _4 emission reduction has become critical to global climate mitigation policy, resulting most notably in the global methane pledge (GMP), pledging a 30% reduction of CH _4 emissions by 2030. Methane is, however, much shorter-lived in the atmosphere than CO _2 , so emissions reductions may have different impacts on global warming over time. We quantify the difference over time in global annual mean surface temperature of the GMP versus the equivalent amount of CO _2 emission reduction. The avoidance of CH _4 emissions in the 2020s due to the GMP initially results in greater relative cooling than the avoidance of the equivalent amount of CO _2 emissions over the same period, but less relative cooling after ∼2060, when almost all CH _4 emitted during the 2020s has been removed from the atmosphere but much of the CO _2 emitted during the 2020s remains. However, if the GMP places the world on a lower CH _4 emissions trajectory after 2030, this results in a persistently and substantially greater reduction to global warming than the equivalent change in the CO _2 emissions trajectory, with a maximum difference of 0.22 ± 0.06 ^∘ C in 2055 and relative cooling for well over a century. This equates to a large difference in avoided climate change damages if momentum in CH _4 emission reduction from the GMP can be sustained after the 2020s. While the greatest reduction in warming is obtained by reducing both CH _4 and CO _2 emissions, our results underscore the striking global societal benefits of sustained reduction in CH _4 emissions
Climate feedbacks derived from spatial gradients in recent climatology
No full textClimate feedbacks, including Planck, surface albedo, water vapor-lapse rate (WVLR) and cloud feedbacks, determine how much surface temperatures will eventually warm to balance anthropogenic radiative forcing. Climate feedbacks remain difficult to constrain directly from temporal variation in observed surface warming and radiation budgets due to the pattern effect and low signal-to-noise ratio, with only order 1°C historic rise in surface temperatures and high uncertainty in aerosol radiative forcing. This study presents a new method to analyze climate feedbacks from observations by empirically fitting simplified reduced-physics relations for outgoing radiation at the top of the atmosphere (TOA) to observed spatial variation in climate properties and radiation budgets. Spatial variations in TOA outgoing radiation are dominated by the dependence on surface temperature: around 91% of the spatial variation in clear sky albedo, and 77% of spatial variation in clear sky TOA outgoing longwave radiation, is functionally explained by variation in surface temperatures. These simplified and observationally constrained relations are then differentiated with respect to spatial contrasts in surface temperature to reveal the Planck, fixed-cloud albedo (λ_albedo) and WVLR (λ_WVLR) climate feedbacks spatially for both clear sky and all sky conditions. The resulting global all sky climate feedback values are λ_WVLR=1.28 (1.13 to 1.45 at 66%) Wm-2K-1, and λ_albedo=0.64 (0.53 to 0.74) Wm-2 for the 2003-2023 period reducing to 0.35 (0.29 to 0.41) Wm-2K-1 under 4°C warming after cryosphere retreat. Our findings agree well with complex Earth system model evaluations based on temporal climate perturbations, and our approach is complementary
Ice sheet‐albedo feedback estimated from most recent deglaciation
Full text linkIce sheet feedbacks are underrepresented in model assessments of climate sensitivity and their magnitudes are still poorly constrained. We combine a recently published record of Earth's Energy Imbalance (EEI) with existing reconstructions of temperature, atmospheric composition, and sea level to estimate both the magnitude and timescale of the ice sheet-albedo feedback since the Last Glacial Maximum. This facilitates the first opportunity to quantify this feedback over the most recent deglaciation using a proxy data-driven approach. We find the ice sheet-albedo feedback to be amplifying, increasing the total climate feedback parameter by 42% and reaching an equilibrium magnitude of 0.55 Wm−2K−1, with a 66% confidence interval of 0.45–0.63 Wm−2K−1. The timescale to equilibrium is estimated as 3.6 ka (66% confidence: 1.9–5.5 ka). These results provide new evidence for the timescale and magnitude of the amplifying ice sheet-albedo feedback that will drive anthropogenic warming for millennia to come
Recommended from our members
Climate nonlinearities: selection, uncertainty, projections, and damages
Full text linkClimate projections are uncertain; this uncertainty is costly and impedes progress on climate policy. This uncertainty is primarily parametric (what numbers do we plug into our equations?), structural (what equations do we use in the first place?), and due to internal variability (natural variability intrinsic to the climate system). The former and latter are straightforward to characterise in principle, though may be computationally intensive for complex climate models. The second is more challenging to characterise and is therefore often ignored. We developed a Bayesian approach to quantify structural uncertainty in climate projections, using the idealised energy-balance model representations of climate physics that underpin many economists' integrated assessment models (IAMs) (and therefore their policy recommendations). We define a model selection parameter, which switches on one of a suite of proposed climate nonlinearities and multidecadal climate feedbacks. We find that a model with a temperature-dependent climate feedback is most consistent with global mean surface temperature observations, but that the sign of the temperature-dependence is opposite of what Earth system models suggest. This difference of sign is likely due to the assumption tha the recent pattern effect can be represented as a temperature dependence. Moreover, models other than the most likely one contain a majority of the posterior probability, indicating that structural uncertainty is important for climate projections. Indeed, in projections using shared socioeconomic pathways similar to current emissions reductions targets, structural uncertainty dwarfs parametric uncertainty in temperature. Consequently, structural uncertainty dominates overall non-socioeconomic uncertainty in economic projections of climate change damages, as estimated from a simple temperature-to-damages calculation. These results indicate that considering structural uncertainty is crucial for IAMs in particular, and for climate projections in general
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“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
How does lake primary production scale with lake size?
Full text linkKleiber’s 3/4-scaling law for metabolism with mass is one of the most striking regularities in biological sciences. Kleiber’s law has been shown to apply not only to individual organisms but also to communities and even the whole-ecosystem properties such as the productivity of estuaries. Might Kleiber’s law also then apply to lake ecosystems? Here, we show that for a collection of whole-lake primary production measurements, production scales to the 3/4 power of lake volume, consistent with Kleiber’s law. However, this relationship is not explicable by analogy to theories developed for individual organisms. Instead, we argue that dimensional analysis offers a simple explanation. After accounting for latitudinal gradients in temperature and insolation, whole-lake primary production scales isometrically with lake area. Because Earth’s topography is self-affine, meaning there are global-scale differences between vertical and horizontal scaling of topography, lake volume scales super-linearly with lake surface area. 3/4 scaling for primary production by volume then results from these other two scaling relationships. The identified relationship between the primary production and temperature- and insolation-adjusted area may be useful for constraining lakes’ global annual productivity and photosynthetic efficiency. More generally, this suggests that there are multiple paths to realizing the 3/4 scaling of metabolism rather than a single unifying law, at least when comparing across levels of biological organization
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Bias in the shoreline development index: Ecological implications illustrated with an analysis of littoral-pelagic habitat coupling
Full text linkWe reexamined the relationship between the shoreline development index and metrics of habitat coupling using a bias-corrected variant of the shoreline development index. Our findings suggest that previously reported correlations may be artifacts of scale-dependent bias in shoreline development index measurements. The results highlight the need for careful measurement when seeking to understand links between lake morphology and ecological processes
- …
