Paleodust Insights into Dust Impacts on Climate

2019 ◽  
Vol 32 (22) ◽  
pp. 7897-7913 ◽  
Author(s):  
Samuel Albani ◽  
Natalie M. Mahowald
Keyword(s):  
Climate Change ◽  
Land Use Changes ◽  
West African Monsoon ◽  
Informed Choice ◽  
West African ◽  
The Arctic ◽  
Model Parameters ◽  
Size Distributions ◽  
The Past ◽  
Dust Load

Abstract Mineral dust acts both as a tracer and a forcing agent of climate change. Past dust variability, imprinted in paleodust records from natural archives, offers the unique opportunity to reconstruct the global dust cycle within a range of possibilities that plausibly encompass future variations in response to climate change and land-cover and land-use changes. Dust itself has direct and indirect feedbacks on the climate system, through impacts on the atmosphere radiative budget and the carbon cycle. Starting from well-constrained reconstructions of the present and past dust cycle, we focus on quantifying dust direct impacts on the atmospheric radiation. We discuss the intrinsic effects of dust onto climate, and how changes in the global dust budget and surface conditions modulate the effective impacts on surface temperatures and precipitation. Most notably, the presence of dust tends to enhance the West African monsoon and warm the Arctic. We also highlight how different choices in terms of dust optical properties and size distributions may yield opposite results, and what are the observational constraints we can use to make an informed choice of model parameters. Finally, we discuss how dust variability might have influenced ongoing climate transitions in the past. In particular we found that a reduction in dust load, along with a reduced cryosphere cover, acted to offset Arctic warming during the deglaciation, potentially playing a role in shaping the Northern Hemisphere deglacial dynamics.

scholarly journals Combined effects of predicted climate and land use changes on future hydrological droughts in the Luanhe River basin, China

2021 ◽  
Author(s):  
Xu Chen ◽  
Ruiguang Han ◽  
Yongjie Wang
Keyword(s):  
Climate Change ◽  
Land Use ◽  
Land Use Change ◽  
River Basin ◽  
Emission Scenario ◽  
Land Use Changes ◽  
Model Parameters ◽  
Baseline Scenario ◽  
Luanhe River Basin ◽  
Hydrological Droughts

Abstract Drought can be impacted by both climate change and land use change in different ways. Thus, in order to predict future drought conditions, hydrological simulations as an ideal means, can be used to account for both projected climate change and projected land use change. In this study, projected climate and land use changes were integrated with the SWAT (Soil and Water Assessment Tool) model to estimate the combined impact of climate and land use projections on hydrological droughts in the Luanhe River basin. We presented that the measured runoff and the remote sensing inversion of soil water content were simultaneously used to validate the model to ensure the reliability of model parameters. Following the calibration and validation, the SWAT model was forced with downscaled precipitation and temperature outputs from a suite of nine Global Climate Models (GCMs) based on the CMIP5, corresponding to three different representative concentration pathways (RCP 2.6, RCP 4.5 and 8.5) for three distinct time periods: 2011–2040, 2041–2070 and 2071–2100, referred to as early-century, mid-century and late-century, respectively, and the land use predicted by CA-Markov model in the same future periods. Hydrological droughts were quantified using the Standardized Runoff Index (SRI). Compared to the baseline scenario (1961–1990), mild drought occurred more frequently during the next three periods (except the 2080s under the RCP2.6 emission scenario). Under the RCP8.5 emission scenario, the probability of severe drought or above occurring in the 2080s increased, the duration prolonged and the severity increased. Under the RCP2.6 scenario, the upper central region of the Luanhe river in the 2020s and upper reaches of the Luanhe river in the 2080s, were more likely to suffer extreme drought events. And under the RCP8.5 scenario, the middle and lower Luanhe river in the 2080s, were more likely to suffer these conditions.

scholarly journals Spatiotemporal patterns of tundra fires: late-Quaternary charcoal records from Alaska

2015 ◽  
Vol 12 (3) ◽  
pp. 3177-3209 ◽  
Author(s):  
M. L. Chipman ◽  
V. Hudspith ◽  
P. E. Higuera ◽  
P. A. Duffy ◽  
R. Kelly ◽  
...  
Keyword(s):  
Climate Change ◽  
Late Quaternary ◽  
Rotation Period ◽  
Arctic Tundra ◽  
Ecosystem Processes ◽  
Anthropogenic Climate Change ◽  
The Arctic ◽  
Spatial And Temporal Patterns ◽  
The Past ◽  
Tundra Ecosystem

Abstract. Anthropogenic climate change has altered many ecosystem processes in the Arctic tundra and may have resulted in unprecedented fire activity. Evaluating the significance of recent fires requires knowledge from the paleo-fire record because observational data in the Arctic span only several decades, much shorter than the natural fire rotation in Arctic tundra regions. Here we report results of charcoal analysis on lake sediments from four Alaskan lakes to infer the broad spatial and temporal patterns of tundra fire occurrence over the past 35 000 years. Background charcoal accumulation rates are low in all records (range = 0–0.05 pieces cm-2 year-1), suggesting minimal biomass burning across our study areas. Charcoal peak analysis reveals that the mean fire return interval (FRI; years between consecutive fire events) ranged from 1648 to 6045 years at our sites, and that the most recent fire events occurred from 882 to 7031 years ago, except for the CE 2007 Anaktuvuk River Fire. These mean FRI estimates are longer than the fire rotation periods estimated for the past 63 years in the areas surrounding three of the four study lakes. This result suggests that the frequency of tundra burning was higher over the recent past compared to the late Quaternary in some tundra regions. However, the ranges of FRI estimates from our paleo-fire records overlap with the expected values based on fire-rotation-period estimates from the observational fire data, and thus quantitative differences are not significant. Together with previous tundra-fire reconstructions, these data suggest that the rate of tundra burning was spatially variable and that fires were extremely rare in our study areas throughout the late Quaternary. Given the rarity of tundra burning over multiple millennia in our study areas and the pronounced effects of fire on tundra ecosystem processes such as carbon cycling, dramatic tundra ecosystem changes are expected if anthropogenic climate change leads to more frequent tundra fires.

scholarly journals Early Holocene cold snaps and their expression in the moraine record of the Eastern European Alps

2021 ◽  
Author(s):  
Sandra M. Braumann ◽  
Joerg M. Schaefer ◽  
Stephanie M. Neuhuber ◽  
Christopher Lüthgens ◽  
Alan J. Hidy ◽  
...  
Keyword(s):  
Climate Change ◽  
Arctic Region ◽  
Climate System ◽  
Early Holocene ◽  
Ice Age ◽  
The Arctic ◽  
European Alps ◽  
Eastern European ◽  
Exposure Dating ◽  
The Past

Abstract. Glaciers preserve climate variations in their geological and geomorphological records, which makes them prime candidates for climate reconstructions. Investigating the glacier-climate system over the past millennia is particularly relevant because, first, the amplitude and frequency of natural climate variability during the Holocene provides the climatic context against which modern, human-induced climate change must be assessed. Second, the transition from the last glacial to the current interglacial promises important insights into the climate system during warming, which is of particular interest with respect to ongoing climate change. Evidence of stable ice margin positions that record cooling during the past 12 ka are preserved in two glaciated valleys of the Silvretta Massif in the Eastern European Alps, the Jamtal (JAM) and the Laraintal (LAR). We mapped and dated moraines in these catchments including historical ridges using Beryllium-10 Surface Exposure Dating (10Be SED) techniques, and correlate resulting moraine formation intervals with climate proxy records to evaluate the spatial and temporal scale of these cold phases. The new geochronologies indicate two moraine formation intervals (MFI) during the Early Holocene (EH): 10.8 ± 0.7 ka (n = 9) and 11.2 ± 0.8 ka (n = 12). Boulder ages along historical moraines (n = 6) imply at least two glacier advances during the Little Ice Age (LIA; c. 1250–1850 CE), around 1300 CE and in the second half of the 18th century. An earlier advance to the same position may have occurred around 500 CE. The Jamtal and Laraintal moraine chronologies provide evidence that millennial scale EH warming was superimposed by centennial scale cooling. The timing of EH moraine formation is contemporaneous with brief temperature drops identified in local and regional paleoproxy records, most prominently with the Preboreal Oscillation (PBO), and is consistent with moraine deposition in other catchments in the European Alps, and in the Arctic region. This consistency points to cooling beyond the local scale and therefore a regional or even hemispheric climate driver. Freshwater input sourced from the Laurentide Ice Sheet (LIS), which changed circulation patterns in the North Atlantic, is a plausible explanation for EH cooling and moraine formation in the Nordic region and in Europe.

scholarly journals The effect of explicit convection on climate change in the West African monsoon and central West African Sahel rainfall

2021 ◽  
pp. 1-42
Keyword(s):  
Climate Change ◽  
West African Monsoon ◽  
West African ◽  
Annual Rainfall ◽  
Moist Convection ◽  
The West ◽  
African Monsoon ◽  
Dominant Feature ◽  
West African Sahel ◽  
African Sahel

Abstract The West African monsoon (WAM) is the dominant feature of West African climate providing the majority of annual rainfall. Projections of future rainfall over the West African Sahel are deeply uncertain with a key reason likely to be moist convection, which is typically parameterized in global climate models. Here, we use a pan-Africa convection permitting simulation (CP4), alongside a parameterized convection simulation (P25), to determine the key processes that underpin the effect of explicit convection on the climate change of the central West African Sahel (8°W-2°E, 12-17°N). In current climate, CP4 affects WAM processes on multiple scales compared to P25. There are differences in the diurnal cycles of rainfall, moisture convergence, and atmospheric humidity. There are upscale impacts: the WAM penetrates farther north, there is greater humidity over the north Sahel and the Saharan heat low regions, the sub-tropical subsidence rate over the Sahara is weaker, and ascent within the tropical rain belt is deeper. Under climate change, the WAM shifts northwards and Hadley circulation weakens in P25 and CP4. The differences between P25 and CP4 persist, however, underpinned by process differences at the diurnal and large-scales. Mean rainfall increases 17.1% in CP4 compared to 6.7% in P25 and there is greater weakening in tropical ascent and sub-tropical subsidence in CP4. These findings show the limitations of parameterized convection and demonstrate the value that explicit convection simulations can provide to climate modellers and climate policy decision makers.

scholarly journals Temporal and spatial variations of aerosol physical and chemical properties over West Africa: AMMA aircraft campaign in summer 2006

2010 ◽  
Vol 10 (2) ◽  
pp. 4463-4500 ◽  
Author(s):  
A. Matsuki ◽  
B. Quennehen ◽  
A. Schwarzenboeck ◽  
S. Crumeyrolle ◽  
H. Venzac ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Chemical Properties ◽  
West African Monsoon ◽  
West African ◽  
Size Distributions ◽  
Physical And Chemical Properties ◽  
African Monsoon ◽  
Physical And Chemical ◽  
Aitken Mode ◽  
And Chemical Properties

Abstract. While West Africa is recognized as being one of the global hot-spots of atmospheric aerosols, the presence of West African Monsoon is expected to create significant spatial and temporal variations in the regional aerosol properties through mixing particles from various sources (mineral dust, biomass burning, sulfates, sea salt). To improve our understanding of the complexity of the aerosol-cloud system in that region, the African Monsoon Multidisciplinary Analysis (AMMA) project has been launched, providing valuable data sets of in-situ and remote sensing measurements including satellites for extended modeling. The French ATR-42 research aircraft was deployed in Niamey, Niger (13°30' N, 02°05' E) in summer 2006, during the three special observation periods (SOPs) of AMMA. These three SOPs covered both dry and wet periods before and after the onset of the Western African Monsoon. State of the art physico-chemical aerosol measurements on the ATR-42 showed a notable seasonal transition in averaged number size distributions where (i) the Aitken mode is dominating over the accumulation mode during the dry season preceding the monsoon arrival and (ii) the accumulation mode increasingly gained importance after the onset of the West African monsoon and even dominated the Aitken mode after the monsoon had fully developed. An extended analysis of the vertical dependence of size spectra, comparing the three observation periods, revealed that the decreasing concentration of the Aitken mode particles, as we move from SOP1 (June) to SOP2a1 (July), and SOP2a2 (August), was less pronounced in the monsoon layer as compared to the overlying Saharan dust layer and free troposphere. In order to facilitate to all partners within the AMMA community radiative transfer calculations, validation of satellite remote sensors, and detailed transport modeling, the parameters describing the mean log-normally fitted number size distributions as a function of altitude and special observation periods were summarized and subsequently related to simultaneously performed measurements of major aerosol particle chemical composition. Extended TEM-EDX analysis of the chemical composition of single aerosol particles revealed dominance of mineral dust (aluminosilicate) even in the submicron particle size range during the dry period, gradually replaced by prevailing biomass burning and sulfate particles, after the onset the monsoon period. The spatial and temporal evolution from SOP1 to SOP2a1 and SOP2a2 of the particle physical and chemical properties and associated aerosol hygroscopic properties are remarkably consistent.

scholarly journals Atmospheric Sb in the Arctic during the past 16,000 years: Responses to climate change and human impacts

2008 ◽  
Vol 22 (1) ◽  
pp. n/a-n/a ◽  
Author(s):  
Michael Krachler ◽  
Jiancheng Zheng ◽  
David Fisher ◽  
William Shotyk
Keyword(s):  
Climate Change ◽  
Human Impacts ◽  
The Arctic ◽  
The Past

scholarly journals Regional impacts of climate change in the Arctic and Antarctic

1998 ◽  
Vol 27 ◽  
pp. 543-552 ◽  
Author(s):  
Gunter Weller
Keyword(s):  
Climate Change ◽  
Sea Ice ◽  
Climate Impacts ◽  
Indigenous Populations ◽  
The Arctic ◽  
Future Climate Change ◽  
Greenhouse Warming ◽  
Polar Regions ◽  
Sea Ice Extent ◽  
The Past

Regional assessments of impacts due to global climate change are a high priority in the international programs on global-change research. in the polar regions, climate models indicate an amplification of global greenhouse warming, but there are large differences between the results of various models, and uncertainties about the magnitude and timing of the expected changes. Also, the observed high-latitude climate trends over the past few decades are much more regional and patchy than predicted by the models. As a first step in assessing possible climate impacts, model results are compared with observations of changes in temperature, precipitation, sea-ice extent, the permafrost regime and other cryospheric parameters. While considerable uncertainties remain in the long-term prediction of change, there is some agreement between model results and observed trends by season on shorter time-scales, The warming observed over the land masses of the Arctic over the past few decades is matched by corresponding observed decreases in snow cover the glacier mass, balances, by thawing of the permafrost, and to a lesser degree by reductions in sea-ice extent. in Antarctica, warming in the Antarctic Peninsula and Ross Sea regions is associated with large decreases in ice-shelf areas and reduced ice thicknesses on the lakes in the McMurdo Dry Valleys. Major future impacts due to global greenhouse warming are likely to include permafrost thawing on and and its consequences for ecosystems and humans; changes in the productivity of marine ecosystems in the Arctic and Southern Ocean: economic impacts on fisheries, petroleum and other human activities; and social impacts on northern indigenous populations. Some of these impacts will have positive ramifications, but most are likely to be detrimental. While uncertainties exist about the future, climate change in the polar regions during the past few decades can be shown to have had major impacts already which will become much mole pronounced if present trends continue.

scholarly journals Early Holocene cold snaps and their expression in the moraine record of the eastern European Alps

2021 ◽  
Vol 17 (6) ◽  
pp. 2451-2479
Author(s):  
Sandra M. Braumann ◽  
Joerg M. Schaefer ◽  
Stephanie M. Neuhuber ◽  
Christopher Lüthgens ◽  
Alan J. Hidy ◽  
...  
Keyword(s):  
Climate Change ◽  
Arctic Region ◽  
Climate System ◽  
Early Holocene ◽  
Ice Age ◽  
The Arctic ◽  
European Alps ◽  
Eastern European ◽  
Exposure Dating ◽  
The Past

Abstract. Glaciers preserve climate variations in their geological and geomorphological records, which makes them prime candidates for climate reconstructions. Investigating the glacier–climate system over the past millennia is particularly relevant first because the amplitude and frequency of natural climate variability during the Holocene provides the climatic context against which modern, human-induced climate change must be assessed. Second, the transition from the last glacial to the current interglacial promises important insights into the climate system during warming, which is of particular interest with respect to ongoing climate change. Evidence of stable ice margin positions that record cooling during the past 12 kyr are preserved in two glaciated valleys of the Silvretta Massif in the eastern European Alps, the Jamtal (JAM) and the Laraintal (LAR). We mapped and dated moraines in these catchments including historical ridges using beryllium-10 surface exposure dating (10Be SED) techniques and correlate resulting moraine formation intervals with climate proxy records to evaluate the spatial and temporal scale of these cold phases. The new geochronologies indicate the formation of moraines during the early Holocene (EH), ca. 11.0 ± 0.7 ka (n = 19). Boulder ages along historical moraines (n = 6) suggest at least two glacier advances during the Little Ice Age (LIA; ca. 1250–1850 CE) around 1300 CE and in the second half of the 18th century. An earlier advance to the same position may have occurred around 500 CE. The Jamtal and Laraintal moraine chronologies provide evidence that millennial-scale EH warming was superimposed by centennial-scale cooling. The timing of EH moraine formation coincides with brief temperature drops identified in local and regional paleoproxy records, most prominently with the Preboreal Oscillation (PBO) and is consistent with moraine deposition in other catchments in the European Alps and in the Arctic region. This consistency points to cooling beyond the local scale and therefore a regional or even hemispheric climate driver. Freshwater input sourced from the Laurentide Ice Sheet (LIS), which changed circulation patterns in the North Atlantic, is a plausible explanation for EH cooling and moraine formation in the Nordic region and in Europe.

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