966 research outputs found
Global and regional importance of the direct dust-climate feedback.
Feedbacks between the global dust cycle and the climate system might have amplified past climate changes. Yet, it remains unclear what role the dust-climate feedback will play in future anthropogenic climate change. Here, we estimate the direct dust-climate feedback, arising from changes in the dust direct radiative effect (DRE), using a simple theoretical framework that combines constraints on the dust DRE with a series of climate model results. We find that the direct dust-climate feedback is likely in the range of -0.04 to +0.02 Wm -2 K-1, such that it could account for a substantial fraction of the total aerosol feedbacks in the climate system. On a regional scale, the direct dust-climate feedback is enhanced by approximately an order of magnitude close to major source regions. This suggests that it could play an important role in shaping the future climates of Northern Africa, the Sahel, the Mediterranean region, the Middle East, and Central Asia
Potential climate forcing of land use and land cover change
Pressure on land resources is expected to increase as global population continues to climb and the world becomes more affluent, swelling the demand for food. Changing climate may exert additional pressures on natural lands as present-day productive regions may shift, or soil quality may degrade, and the recent rise in demand for biofuels increases competition with edible crops for arable land. Given these projected trends there is a need to understand the global climate impacts of land use and land cover change (LULCC). Here we quantify the climate impacts of global LULCC in terms of modifications to the balance between incoming and outgoing radiation at the top of the atmosphere (radiative forcing, RF) that are caused by changes in long-lived and short-lived greenhouse gas concentrations, aerosol effects, and land surface albedo. We attribute historical changes in terrestrial carbon storage, global fire emissions, secondary organic aerosol emissions, and surface albedo to LULCC using simulations with the Community Land Model version 3.5. These LULCC emissions are combined with estimates of agricultural emissions of important trace gases and mineral dust in two sets of Community Atmosphere Model simulations to calculate the RF of changes in atmospheric chemistry and aerosol concentrations attributed to LULCC. With all forcing agents considered together, we show that 40% (+/- 16 %) of the present-day anthropogenic RF can be attributed to LULCC. Changes in the emission of non-CO2 greenhouse gases and aerosols from LULCC enhance the total LULCC RF by a factor of 2 to 3 with respect to the LULCC RF from CO2 alone. This enhancement factor also applies to projected LULCC RF, which we compute for four future scenarios associated with the Representative Concentration Pathways. We attribute total RFs between 0.9 and 1.9 W m(-2) to LULCC for the year 2100 (relative to a preindustrial state). To place an upper bound on the potential of LULCC to alter the global radiation budget, we include a fifth scenario in which all arable land is cultivated by 2100. This theoretical extreme case leads to a LULCC RF of 3.9 W m(-2) (+/- 0.9 W m(-2)), suggesting that not only energy policy but also land policy is necessary to minimize future increases in RF and associated climate changes
Counterfactually Probing Language Identity in Multilingual Models
Techniques in causal analysis of language models illuminate how linguistic
information is organized in LLMs. We use one such technique, AlterRep, a method
of counterfactual probing, to explore the internal structure of multilingual
models (mBERT and XLM-R). We train a linear classifier on a binary language
identity task, to classify tokens between Language X and Language Y. Applying a
counterfactual probing procedure, we use the classifier weights to project the
embeddings into the null space and push the resulting embeddings either in the
direction of Language X or Language Y. Then we evaluate on a masked language
modeling task. We find that, given a template in Language X, pushing towards
Language Y systematically increases the probability of Language Y words, above
and beyond a third-party control language. But it does not specifically push
the model towards translation-equivalent words in Language Y. Pushing towards
Language X (the same direction as the template) has a minimal effect, but
somewhat degrades these models. Overall, we take these results as further
evidence of the rich structure of massive multilingual language models, which
include both a language-specific and language-general component. And we show
that counterfactual probing can be fruitfully applied to multilingual models.Comment: 12 pages, 5 figures, MRL Workshop @ EMNLP 202
The KO*-rings of BT^m, the Davis-Januszkiewicz Spaces and certain toric manifolds
This paper contains an explicit computation of the KO*-ring structure of an
m-fold product of CP^{\infty}, the Davis-Januszkiewicz spaces and toric
manifolds which have trivial Sq^2-homology.Comment: 34 page
Links between topography, wind, deflation, lakes and dust: The case of the Bodélé Depression, Chad
The Bodélé Depression, Chad is the planet's largest single source of dust. Deflation from the Bodélé could be seen as a simple coincidence of two key prerequisites: strong surface winds and a large source of suitable sediment. But here we hypothesise that long term links between topography, winds, deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land-atmosphere processes with topography acting as the overall controlling agent. We use a variety of observational and numerical techniques, including a regional climate model, to show that: 1) contemporary deflation from the Bodélé is delineated by topography and a surface wind stress maximum; 2) the Tibesti and Ennedi mountains play a key role in the generation of the erosive winds in the form of the Bodélé Low Level Jet (LLJ); 3) enhanced deflation from a stronger Bodélé LLJ during drier phases, for example, the Last Glacial Maximum, was probably sufficient to create the shallow lake in which diatoms lived during wetter phases, such as the Holocene pluvial. Winds may therefore have helped to create the depression in which erodible diatom material accumulated. Instead of a simple coincidence of nature, dust from the world's largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world's largest dust source. Similar processes plausibly operate in other dust hotspots in topographic depressions
Lil-Bevo: Explorations of Strategies for Training Language Models in More Humanlike Ways
We present Lil-Bevo, our submission to the BabyLM Challenge. We pretrained
our masked language models with three ingredients: an initial pretraining with
music data, training on shorter sequences before training on longer ones, and
masking specific tokens to target some of the BLiMP subtasks. Overall, our
baseline models performed above chance, but far below the performance levels of
larger LLMs trained on more data. We found that training on short sequences
performed better than training on longer sequences.Pretraining on music may
help performance marginally, but, if so, the effect seems small. Our targeted
Masked Language Modeling augmentation did not seem to improve model performance
in general, but did seem to help on some of the specific BLiMP tasks that we
were targeting (e.g., Negative Polarity Items). Training performant LLMs on
small amounts of data is a difficult but potentially informative task. While
some of our techniques showed some promise, more work is needed to explore
whether they can improve performance more than the modest gains here. Our code
is available at https://github.com/venkatasg/Lil-Bevo and out models at
https://huggingface.co/collections/venkatasg/babylm-653591cdb66f4bf68922873aComment: Proceedings of the BabyLM Challeng
Counterfactual Probing for the Influence of Affect and Specificity on Intergroup Bias
While existing work on studying bias in NLP focues on negative or pejorative
language use, Govindarajan et al. (2023) offer a revised framing of bias in
terms of intergroup social context, and its effects on language behavior. In
this paper, we investigate if two pragmatic features (specificity and affect)
systematically vary in different intergroup contexts -- thus connecting this
new framing of bias to language output. Preliminary analysis finds modest
correlations between specificity and affect of tweets with supervised
intergroup relationship (IGR) labels. Counterfactual probing further reveals
that while neural models finetuned for predicting IGR labels reliably use
affect in classification, the model's usage of specificity is inconclusive.
Code and data can be found at: https://github.com/venkatasg/intergroup-probingComment: To appear in Findings of ACL 202
Are the impacts of land use on warming underestimated in climate policy?
© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Environmental Research Letters 12 (2017): 094016, doi:10.1088/1748-9326/aa836d.While carbon dioxide emissions from energy use must be the primary target of climate change
mitigation efforts, land use and land cover change (LULCC) also represent an important source of
climate forcing. In this study we compute time series of global surface temperature change separately
for LULCC and non-LULCC sources (primarily fossil fuel burning), and show that because of the
extra warming associated with the co-emission of methane and nitrous oxide with LULCC carbon
dioxide emissions, and a co-emission of cooling aerosols with non-LULCC emissions of carbon
dioxide, the linear relationship between cumulative carbon dioxide emissions and temperature has a
two-fold higher slope for LULCC than for non-LULCC activities. Moreover, projections used in the
Intergovernmental Panel on Climate Change (IPCC) for the rate of tropical land conversion in the
future are relatively low compared to contemporary observations, suggesting that the future
projections of land conversion used in the IPCC may underestimate potential impacts of LULCC. By
including a ‘business as usual’ future LULCC scenario for tropical deforestation, we find that even if
all non-LULCC emissions are switched off in 2015, it is likely that 1.5 â—¦C of warming relative to the
preindustrial era will occur by 2100. Thus, policies to reduce LULCC emissions must remain a high
priority if we are to achieve the low to medium temperature change targets proposed as a part of the
Paris Agreement. Future studies using integrated assessment models and other climate simulations
should include more realistic deforestation rates and the integration of policy that would reduce
LULCC emissions.We would like to acknowledge the support from
grants NSF-ATM1049033, NSF-CCF-1522054, NSFAGS-
1048827 and DOE-SC0016362, DOE Office
of Science Biogeochemical Cycles Feedbacks and
ACME Science Focus Areas as well as assistance
from the Atkinson Center for a Sustainable Futur
Short-Term Impacts of 2017 Western North American Wildfires On Meteorology, the Atmosphere\u27s Energy Budget, and Premature Mortality
Western North American fires have been increasing in magnitude and severity over the last few decades. The complex coupling of fires with the atmospheric energy budget and meteorology creates short-term feedbacks on regional weather altering the amount of pollution to which Americans are exposed. Using a combination of model simulations and observations, this study shows that the severe fires in the summer of 2017 increased atmospheric aerosol concentrations leading to a cooling of the air at the surface, reductions in sensible heat fluxes, and a lowering of the planetary boundary layer height over land. This combination of lower-boundary layer height and increased aerosol pollution from the fires reduces air quality. We estimate that from start of August to end of October 2017, ~400 premature deaths occurred within the western US as a result of short-term exposure to elevated PM2.5 from fire smoke. As North America confronts a warming climate with more fires the short-term climate and pollution impacts of increased fire activity should be assessed within policy aimed to minimize impacts of climate change on society
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