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At least 433 records · Page 24Linked to original sources

USGS2016

Teleconnected ocean forcing of Western North American droughts and pluvials during the last millennium

Western North America (WNA) is rich in hydroclimate reconstructions, yet questions remain about the causes of decadal-to-multidecadal hydroclimate variability. Teleconnection patterns preserved in annually-resolved tree-ring reconstructed drought maps, and anomalies in a global network of proxy sea surface temperature (SST) reconstructions, were used to reassess the evidence linking ocean forcing to WNA hydroclimate variability over the past millennium. Potential forcing mechanisms of the Medieval Climate Anomaly (MCA) and individual drought and pluvial events—including two multidecadal-length MCA pluvials—were evaluated. We show strong teleconnection patterns occurred during the driest (wettest) years within persistent droughts (pluvials), implicating SSTs as a potent hydroclimate forcing mechanism. The role of the SSTs on longer timescales is more complex. Pacific teleconnection patterns show little long-term change, whereas low-resolution SST reconstructions vary over decades to centuries. While weaker than the tropical Pacific teleconnections, North Atlantic teleconnection patterns and SST reconstructions also show links to WNA droughts and pluvials, and may in part account for longer-term WNA hydroclimate changes. Nonetheless, evidence linking WNA hydroclimate to SSTs still remains sparse and nuanced—especially over long-timescales with a broader range of hydroclimatic variability than characterized during the 20th century.

Quaternary Science Reviews↗

USGS2006

Shrinking ponds in subarctic Alaska based on 1950-2002 remotely sensed images

Over the past 50 years, Alaska has experienced a warming climate with longer growing seasons, increased potential evapotranspiration, and permafrost warming. Research from the Seward Peninsula and Kenai Peninsula has demonstrated a substantial landscape-level trend in the reduction of surface water and number of closed-basin ponds. We investigated whether this drying trend occurred at nine other regions throughout Alaska. One study region was from the Arctic Coastal Plain where depp permafrost occurs continuously across the landscape. The other eight study regions were from the boreal forest regions where discontinuous permafrost occurs. Mean annual precipitation across the study regions ranged from 100 to over 700 min yr-1. We used remotely sensed imagery from the 1950s to 2002 to inventory over 10,000 closed-basin ponds from at least three periods from this time span. We found a reduction in the area and number of shallow, closed-basin ponds for all boreal regions. In contrast, the Arctic Coastal Plain region had negligible change in the area of closed-basin ponds. Since the 1950s, surface water area of closed-basin ponds included in this analysis decreased by 31 to 4 percent, and the total number of closed-basin ponds surveyed within each study region decreased from 54 to 5 percent. There was a significant increasing trend in annual mean temperature and potential evapotranspiration since the 1950s for all study regions. There was no significant trend in annual precipitation during the same period. The regional trend of shrinking ponds may be due to increased drainage as permafrost warms, or increased evapotranspiration during a warmer and extended growing season. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗

USGS2008

Titan's inventory of organic surface materials

Cassini RADAR observations now permit an initial assessment of the inventory of two classes, presumed to be organic, of Titan surface materials: polar lake liquids and equatorial dune sands. Several hundred lakes or seas have been observed, of which dozens are each estimated to contain more hydrocarbon liquid than the entire known oil and gas reserves on Earth. Dark dunes cover some 20% of Titan's surface, and comprise a volume of material several hundred times larger than Earth's coal reserves. Overall, however, the identified surface inventories (>3 × 10 4 km 3 of liquid, and >2 × 10 5 km 3 of dune sands) are small compared with estimated photochemical production on Titan over the age of the solar system. The sand volume is too large to be accounted for simply by erosion in observed river channels or ejecta from observed impact craters. The lakes are adequate in extent to buffer atmospheric methane against photolysis in the short term, but do not contain enough methane to sustain the atmosphere over geologic time. Unless frequent resupply from the interior buffers this greenhouse gas at exactly the right rate, dramatic climate change on Titan is likely in its past, present and future.

Geophysical Research Letters↗

USGS2004

Mars: Water, water everywhere

Mars is a very watery planet, but all the water seems to be frozen. Divining the amount and distribution of this water, past and present, is essential for understanding martian climates, and more.

Nature↗

USGS2018

Global sea-level contribution from Arctic land ice: 1971 to 2017

The Arctic Monitoring and Assessment Program (AMAP) (AMAP, 2017) identifies the Arctic as the largest regional source of land ice to global sea-level rise in the 2003 to 2014 period. Yet, this contextualization ignores the longer perspective from in-situ records of glacier mass balance. Here, using 18 (> 55 °N latitude) glacier and ice cap mass balance series in the 1971 to 2017 period, we develop a semi-empirical estimate of annual sealevel contribution from seven Arctic regions by scaling the in-situ records to GRACE averages. We contend that our estimate represents the most accurate mass balance assessment so far available before the 1992 start of satellite altimetry. We estimate the 1971 to 2017 eustatic sea-level contribution from land ice north of ~55° N to be 23.0±12.3 mm sea-level equivalent (SLE). In all regions, the cumulative sealevel rise curves exhibit an acceleration, especially after 1988. Greenland is the source of 46% of the Arctic sea-level rise contribution (10.6±7.3 mm), followed by Alaska (5.7±2.2 mm), Arctic Canada (3.2±0.7 mm) and the Russian High Arctic (1.5±0.4 mm). Our annual results exhibit co-variability over a 43 year overlap (1971 to 2013) with the alternative dataset of Marzeion et al (2015) (M15). However, we find a 1.36x lower sea-level contribution, in agreement with satellite gravimetry. The IPCC Fifth Assessment report identified constraining the pre-satellite era sealevel budget as a topic of low scientific understanding that we address and specify sealevel contributions coinciding with IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) “present day” (2005-2015) and “recent past” (1986-2005) reference periods. We assess an Arctic land ice loss of 8.3 mm SLE during the recent past and 12.4 mm SLE during the present day.

Environmental Research Letters↗

USGS2008

Paleoclimatic significance of chemical weathering in loess-derived paleosols of subarctic central Alaska

Chemical weathering in soils has not been studied extensively in high-latitude regions. Loess sequences with modern soils and paleosols are present in much of subarctic Alaska, and allow an assessment of present and past chemical weathering. Five sections were studied in detail in the Fairbanks, Alaska, area. Paleosols likely date to mid-Pleistocene interglacials, the last interglacial, and early-to-mid-Wisconsin interstadiale. Ratios of mobile (Na, Ca, Mg, Si) to immobile (Ti or Zr) elements indicate that modern soils and most interstadial and interglacial paleosols are characterized by significant chemical weathering. Na2O/TiO2 is lower in modern soils and most paleosols compared to parent loess, indicating depletion of plagioclase. In the clay fraction, smectite is present in Tanana and Yukon River source sediments, but is absent or poorly expressed in modern soils and paleosols, indicating depletion of this mineral also. Loss of both plagioclase and smectite is well expressed in soils and paleosols as lower SiO 2/TiO2. Carbonates are present in the river source sediments, but based on CaO/TiO2, they are depleted in soils and most paleosols (with one exception in the early-to-mid-Wisconsin period). Thus, most soil-forming intervals during past interglacial and interstadial periods in Alaska had climatic regimes that were at least as favorable to mineral weathering as today, and suggest boreal forest or acidic tundra vegetation. ?? 2008 Regents of the University of Colorado.

Arctic, Antarctic, and Alpine Research↗

USGS2007

Digital outlines and topography of the glaciers of the American West

Alpine glaciers have generally receded during the past century (post-“Little Ice Age”) because of climate warming (Oerlemans and others, 1998; Mann and others, 1999; Dyurgerov and Meier, 2000; Grove, 2001). This general retreat has accelerated since the mid 1970s, when a shift in atmospheric circulation occurred (McCabe and Fountain, 1995; Dyurgerov and Meier, 2000). The loss in glacier cover has had several profound effects. First, the shrinkage of glaciers results in a net increase in stream flow, typically in late summer when water supplies are at the lowest levels (Fountain and Tangborn, 1985). This additional water is important to ecosystems (Hall and Fagre, 2003) and to human water needs (Tangborn, 1980). However, if shrinkage continues, the net contribution to stream flow will diminish, and the effect upon these benefactors will be adverse. Glacier shrinkage is also a significant factor in current sea level rise (Meier, 1984; Dyurgerov and Meier, 2000). Second, many of the glaciers in the West Coast States are located on stratovolcanoes, and continued recession will leave oversteepened river valleys. These valleys, once buttressed by ice are now subject to failure, creating conditions for lahars (Walder and Driedger, 1994; O’Connor and others, 2001). Finally, reduction or loss of glaciers reduce or eliminate glacial activity as an important geomorphic process on landscape evolution and alters erosion rates in high alpine areas (Hallet and others, 1996). Because of the importance of glaciers to studies of climate change, hazards, and landscape modification, glacier inventories have been published for Alaska (Manley, in press), China (http://wdcdgg.westgis.ac.cn/DATABASE/Glacier/Glacier.asp), Nepal (Mool and others, 2001), Switzerland (Paul and others, 2002), and the Tyrolian Alps of Austria (Paul, 2002), among other locales. To provide the necessary data for assessing the magnitude and rate of glacier change in the American West, exclusive of Alaska (fig. 1), we are constructing a geographic information system (GIS) database. The data on glacier location and change will be derived from maps, ground-based photographs, and aerial and satellite images. Our first step, reported here, is the compilation of a glacier inventory of the American West. The inventory is compiled from the 1:100,000 (100K) and 1:24,000 (24K)-scale topographic maps published by the U.S. Geological Survey (USGS) and U.S. Forest Service (USFS). The 24K-scale maps provide the most detailed mapping of perennial snow and ice features. This report informs users of the data about the challenges we faced in compiling the data and discusses its errors and uncertainties. We rely on the expertise of the original cartographers in distinguishing “permanent snow and ice” from seasonal snow, although we know, through personal experience, of cartographic misjudgments. Whether “permanent” means indefinite or resident for several years is impossible to determine within the scope of this study. We do not discriminate between “glacier,” defined as permanent snow or ice that moves (Paterson, 1994), and stagnant snow and ice features. Therefore, we leave to future users the final determination of seasonal versus permanent snow features and the discrimination between true glaciers and stagnant snow and ice bodies. We believe that future studies of more regional focus and knowledge can most accurately refine our initial inventory. For simplicity we refer to all snow and ice bodies in this report as glaciers, although we recognize that most probably do not strictly meet the requirements; many may be snow patches.

Open-File Report↗

USGS2020

Assessment of water quality and fecal contamination sources at Hook Pond, East Hampton, New York

Summary The U.S. Geological Survey, in cooperation with the Village of East Hampton, New York, conducted a 1-year study from August 2017 to August 2018 to provide data necessary to improve understanding of the sources of nutrients and pathogens to Hook Pond watershed to allow for possible mitigation or reduction of loads. Chronic eutrophication and recent concern over harmful cyanobacteria in Hook Pond are the result of past and present land uses and a changing climate that have prompted the Village of East Hampton and local businesses to study and remediate factors contributing to the persistent loading of nutrients, organic contaminants, and pathogens. This assessment of Hook Pond, Hook Pond Dreen, and shallow groundwater provides the most comprehensive set of water-quality data to date. Interpretations presented in this study and the data on which they are based can be used to support management decisions, inform and contribute to modeling, and serve as a baseline for future assessments. Results from continuous monitoring of water temperature, specific conductance, and elevation at Hook Pond site 10 (Maidstone Club golf cart bridge), as well as ancillary weather and tidal data from nearby stations, were used to help explain seasonal and storm-related concentration variation of nitrogen, phosphorus, wastewater-indicator compounds, and pathogens. Data collected were also compared to existing historical data. Physicochemical constituents measured on a routine basis throughout the pond and along the tributary showed the spatial variability in water temperature, specific conductance, dissolved oxygen, pH, turbidity, and chlorophyll a and phycocyanin fluorescence. A lakebed survey was compiled based on the year-round sampling throughout the pond for future comparisons. Water-quality data from shallow groundwater at points around Hook Pond and adjacent to Hook Pond Dreen were interpreted and quantified to estimate relative contributions and species of nutrients, wastewater-indicator compounds, and microbial source tracking (MST) markers to base flow. To supplement the continuous water-surface elevation data, a single set of discharge measurements was collected under normal (nonstorm) conditions to better understand the relative contributions and dilution of surface waters by contaminated groundwater. The nutrient and physicochemical data from this study can be used in conjunction with current and future models and decision support tools to guide planned and ongoing restoration efforts, such as dredging to reduce sediment accumulation, opening a pathway to the ocean (which would change the salinity and flow dynamics of the pond and adjacent groundwater), and addressing growing concerns over cyanobacterial blooms, while serving as a baseline for measuring changes resulting from sea-level rise, climate change, and changes in nutrient loading. The microbial source tracking and indicator bacteria results can help direct efforts to reduce runoff and direct contributions of fecal contamination from dogs and waterfowl along Hook Pond Dreen. The results can also be used to assess the current state of wastewater infrastructure surrounding and contributing to Hook Pond Dreen, based on detection of human markers throughout the year and with both Bacteroides and coliphage methods.

New York↗

USGS2002

Simulation of a proposed emergency outlet from Devils Lake, North Dakota

From 1993 to 2001, Devils Lake rose more than 25 feet, flooding farmland, roads, and structures around the lake and causing more than $400 million in damages in the Devils Lake Basin. In July 2001, the level of Devils Lake was at 1,448.0 feet above sea level 1 , which was the highest lake level in more than 160 years. The lake could continue to rise to several feet above its natural spill elevation to the Sheyenne River (1,459 feet above sea level) in future years, causing extensive additional flooding in the basin and, in the event of an uncontrolled natural spill, downstream in the Red River of the North Basin as well. The outlet simulation model described in this report was developed to determine the potential effects of various outlet alternatives on the future lake levels and water quality of Devils Lake. Lake levels of Devils Lake are controlled largely by precipitation on the lake surface, evaporation from the lake surface, and surface inflow. For this study, a monthly water-balance model was developed to compute the change in total volume of Devils Lake, and a regression model was used to estimate monthly water-balance data on the basis of limited recorded data. Estimated coefficients for the regression model indicated fitted precipitation on the lake surface was greater than measured precipitation in most months, fitted evaporation from the lake surface was less than estimated evaporation in most months, and ungaged inflow was about 2 percent of gaged inflow in most months. Dissolved sulfate was considered to be the key water-quality constituent for evaluating the effects of a proposed outlet on downstream water quality. Because large differences in sulfate concentrations existed among the various bays of Devils Lake, monthly water-balance data were used to develop detailed water and sulfate mass-balance models to compute changes in sulfate load for each of six major storage compartments in response to precipitation, evaporation, inflow, and outflow from each compartment. The storage compartments--five for Devils Lake and one for Stump Lake--were connected by bridge openings, culverts, or natural channels that restricted mixing between compartments. A numerical algorithm was developed to calculate inflow and outflow from each compartment. Sulfate loads for the storage compartments first were calculated using the assumptions that no interaction occurred between the bottom sediments and the water column and no wind- or buoyancy-induced mixing occurred between compartments. However, because the fitted sulfate loads did not agree with the estimated sulfate loads, which were obtained from recorded sulfate concentrations, components were added to the sulfate mass-balance model to account for the flux of sulfate between bottom sediments and the lake and for mixing between storage compartments. Mixing between compartments can occur during periods of open water because of wind and during periods of ice cover because of water-density differences between compartments. Sulfate loads calculated using the sulfate mass-balance model with sediment interaction and mixing between compartments closely matched sulfate loads computed from historical concentrations. The water and sulfate mass-balance models were used to calculate potential future lake levels and sulfate concentrations for Devils Lake and Stump Lake given potential future values of monthly precipitation, evaporation, and inflow. Potential future inputs were generated using a scenario approach and a stochastic approach. In the scenario approach, historical values of precipitation, evaporation, and inflow were repeated in the future for a particular sequence of historical years. In the stochastic approach, a statistical time-series model was developed to randomly generate potential future inputs. The scenario approach was used to evaluate the effectiveness of various outlet alternatives, and the stochastic approach was used to evaluate the hydrologic and water-quality effects of the potential outlet alternatives that were selected on the basis of the scenario analysis. Given potential future lake levels and sulfate concentrations generated using either the scenario or stochastic approach and potential future ambient flows and sulfate concentrations for the Sheyenne River receiving waters, daily outlet discharges could be calculated for virtually any outlet alternative. For the scenario approach, future ambient flows and sulfate concentrations for the Sheyenne River were generated using the same sequence of years used for generating water-balance data for Devils Lake. For the stochastic approach, a procedure was developed for generating daily Sheyenne River flows and sulfate concentrations that were "in-phase" with the generated water-balance data for Devils Lake. Simulation results for the scenario approach indicated that neither of the West Bay outlet alternatives provided effective flood-damage reduction without exceeding downstream water-quality constraints. However, both Pelican Lake outlet alternatives provided significant flood-damage reduction with only minor downstream water-quality changes. The most effective alternative for controlling rising lake levels was a Pelican Lake outlet with a 480-cubic-foot-per-second pump capacity and a 250-milligram-per-liter downstream sulfate constraint. However, this plan is costly because of the high pump capacity and the requirement of a control structure on Highway 19 to control the level of Pelican Lake. A less costly, though less effective for flood-damage reduction, plan is a Pelican Lake outlet with a 300-cubic-foot-per-second pump capacity and a 250-milligram-per-liter downstream sulfate constraint. The plan is less costly because the pump capacity is smaller and because the control structure on Highway 19 is not required. The less costly Pelican Lake alternative with a 450-milligramper- liter downstream sulfate constraint rather than a 250-milligram-per-liter downstream sulfate constraint was identified by the U.S. Army Corps of Engineers as the preferred alternative for detailed design and engineering analysis. Simulation results for the stochastic approach indicated that the geologic history of lake-level fluctuations of Devils Lake for the past 2,500 years was consistent with a climatic history that consisted of two climate states--a wet state, similar to conditions during 1980-99, and a normal state, similar to conditions during 1950-78. The transition times between the wet and normal climatic periods occurred randomly. The average duration of the wet climatic periods was 20 years, and the average duration of the normal climatic periods was 120 years. The stochastic approach was used to generate 10,000 independent sequences of lake levels and sulfate concentrations for Devils Lake for water years 2001-50. Each trace began with the same starting conditions, and the duration of the current wet cycle was generated randomly for each trace. Each trace was generated for the baseline (natural) condition and for the Pelican Lake outlet with a 300-cubic-foot-per-second pump capacity and a 450-milligram-per-liter downstream sulfate constraint. The outlet significantly lowered the probabilities of future lake-level increases within the next 50 years and did not substantially increase the probabilities of reaching low lake levels or poor water-quality conditions during the same period.

Water-Resources Investigations Report↗

USGS2024

What the cliffs near America’s earliest settlements tell us about climate change

Climate change is a big problem for natural habitats, people, and the systems that support society, including roads, water supply, electrical grids, and phone and internet connections. It’s an important theme in politics, economics, and culture. Scientists make computer models to show what the climate might be like in the future, and it looks very different from what we are used to. Scientists can also learn about the future climate by looking at geological records from the past. About 3 million years ago, most of the US east coast was under water. Sediments that collected on the ocean floor show what the ocean environment was like back then. Some of these sediments are now exposed above water as bluffs along the James River near colonial Jamestown in southeastern Virginia, and they hold many clues as to what Earth may look like in the future.

Virginia↗

USGS2010

Spatial distribution of pingos in Northern Asia

Pingos are prominent periglacial landforms in vast regions of the Arctic and Subarctic. They are indicators of modern and past conditions of permafrost, surface geology, hydrology and climate. A first version of a detailed spatial geodatabase of more than 6000 pingo locations in a 3.5 ?? 106 km2 region of Northern Asia was assembled from topographic maps. A first order analysis was carried out with respect to permafrost, landscape characteristics, surface geology, hydrology, climate, and elevation datasets using a Geographic Information System (GIS). Pingo heights in the dataset vary between 2 and 37 m, with a mean height of 4.8 m. About 64% of the pingos occur in continuous permafrost with high ice content and thick sediments; another 19% in continuous permafrost with moderate ice content and thick sediments. The majority of these pingos likely formed through closed system freezing, typical of those located in drained thermokarst lake basins of northern lowlands with continuous permafrost. About 82% of the pingos are located in the tundra bioclimatic zone. Most pingos in the dataset are located in regions with mean annual ground temperatures between -3 and -11 ??C and mean annual air temperatures between -7 and -18 ??C. The dataset confirms that surface geology and hydrology are key factors for pingo formation and occurrence. Based on model predictions for near-future permafrost distribution, hundreds of pingos along the southern margins of permafrost will be located in regions with thawing permafrost by 2100, which ultimately may lead to increased occurrence of pingo collapse. Based on our dataset and previously published estimates of pingo numbers from other regions, we conclude that there are more than 11 000 pingos on Earth. ?? 2010 Author(s).

Cryosphere Discussions↗

USGS2008

Prehistoric Packrats Piled Up Clues to Climate Change

Scientists from the U.S. Geological Survey and Northern Arizona University studying climate change in the Southwestern United States are getting a helping hand?or would that be paw??from prehistoric packrats. By hoarding parts of animals and plants, including seeds and leaves, in garbage piles or ?middens,? these bushy-tailed rodents preserved crucial ecological and environmental information about the past. From these middens, scientists are able to reconstruct plant communities and natural systems from as long ago as 50,000 years. The contents of middens allow scientists to understand how ecosystems responded to rapid, large-scale climate changes of the past. The insights gained from midden research could offer clues to future changes driven by rapid climate shifts.

Fact Sheet↗

USGS2013

Fragmentation and thermal risks from climate change interact to affect persistence of native trout in the Colorado River basin

Impending changes in climate will interact with other stressors to threaten aquatic ecosystems and their biota. Native Colorado River cutthroat trout (CRCT; Oncorhynchus clarkii pleuriticus ) are now relegated to 309 isolated high-elevation ( > 1700 m) headwater stream fragments in the Upper Colorado River Basin, owing to past nonnative trout invasions and habitat loss. Predicted changes in climate (i.e., temperature and precipitation) and resulting changes in stochastic physical disturbances (i.e., wildfire, debris flow, and channel drying and freezing) could further threaten the remaining CRCT populations. We developed an empirical model to predict stream temperatures at the fragment scale from downscaled climate projections along with geomorphic and landscape variables. We coupled these spatially explicit predictions of stream temperature with a Bayesian Network (BN) model that integrates stochastic risks from fragmentation to project persistence of CRCT populations across the upper Colorado River basin to 2040 and 2080. Overall, none of the populations are at risk from acute mortality resulting from high temperatures during the warmest summer period. In contrast, only 37% of populations have a greater than or equal to 90% chance of persistence for 70 years (similar to the typical benchmark for conservation), primarily owing to fragmentation. Populations in short stream fragments < 7 km long, and those at the lowest elevations, are at the highest risk of extirpation. Therefore, interactions of stochastic disturbances with fragmentation are projected to be greater threats than warming for CRCT populations. The reason for this paradox is that past nonnative trout invasions and habitat loss have restricted most CRCT populations to high-elevation stream fragments that are buffered from the potential consequences of warming, but at risk of extirpation from stochastic events. The greatest conservation need is for management to increase fragment lengths to forestall these risks.

Upper Colorado River Basin↗

USGS2014

Climate Change 2014: Technical Summary

Human interference with the climate system is occurring (WGI AR5 SPM Section D.3; WGI AR5 Sections 2.2, 6.3, 10.3 to 10.6, 10.9). Climate change poses risks for human and natural systems. The assessment of impacts, adaptation, and vulnerability in the Working Group II contribution to the IPCC’s Fifth Assessment Report (WGII AR5) evaluates how patterns of risks and potential benefits are shifting due to climate change. It considers how impacts and risks related to climate change can be reduced and managed through adaptation and mitigation. The report assesses needs, options, opportunities, constraints, resilience, limits, and other aspects associated with adaptation. It recognizes that risks of climate change will vary across regions and populations, through space and time, dependent on myriad factors including the extent of adaptation and mitigation. For the past 2 decades, IPCC’s Working Group II has developed assessments of climate change impacts, adaptation, and vulnerability. The WGII AR5 builds from the WGII contribution to the IPCC’s Fourth Assessment Report (WGII AR4), published in 2007, and the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX), published in 2012. It follows the Working Group I contribution to the AR5. The WGII AR5 is presented in two parts (Part A: Global and Sectoral Aspects, and Part B: Regional Aspects), reflecting the expanded literature basis and multidisciplinary approach, increased focus on societal impacts and responses, and continued regionally comprehensive coverage. [1.1 to 1.3] The number of scientific publications available for assessing climate change impacts, adaptation, and vulnerability more than doubled between 2005 and 2010, with especially rapid increases in publications related to adaptation, allowing for a more robust assessment that supports policymaking (high confidence). The diversity of the topics and regions covered has similarly expanded, as has the geographic distribution of authors contributing to the knowledge base for climate change assessments. Authorship of climate change publications from developing countries has increased, although it still represents a small fraction of the total. The unequal distribution of publications presents a challenge to the production of a comprehensive and balanced global assessment.

Book chapter↗

USGS2016

Predicting tree biomass growth in the temperate-boreal ecotone: is tree size, age, competition or climate response most important?

As global temperatures rise, variation in annual climate is also changing, with unknown consequences for forest biomes. Growing forests have the ability to capture atmospheric CO 2 and thereby slow rising CO 2 concentrations. Forests’ ongoing ability to sequester C depends on how tree communities respond to changes in climate variation. Much of what we know about tree and forest response to climate variation comes from tree-ring records. Yet typical tree-ring datasets and models do not capture the diversity of climate responses that exist within and among trees and species. We address this issue using a model that estimates individual tree response to climate variables while accounting for variation in individuals’ size, age, competitive status, and spatially structured latent covariates. Our model allows for inference about variance within and among species. We quantify how variables influence aboveground biomass growth of individual trees from a representative sample of 15 northern or southern tree species growing in a transition zone between boreal and temperate biomes. Individual trees varied in their growth response to fluctuating mean annual temperature and summer moisture stress. The variation among individuals within a species was wider than mean differences among species. The effects of mean temperature and summer moisture stress interacted, such that warm years produced positive responses to summer moisture availability and cool years produced negative responses. As climate models project significant increases in annual temperatures, growth of species like Acer saccharum , Quercus rubra , and Picea glauca will vary more in response to summer moisture stress than in the past. The magnitude of biomass growth variation in response to annual climate was 92–95% smaller than responses to tree size and age. This means that measuring or predicting the physical structure of current and future forests could tell us more about future C dynamics than growth responses related to climate change alone.

Minnesota↗

USGS2009

Historical fire and multidecadal drought as context for piñon - Juniper woodland restoration in western Colorado

Fire is known to structure tree populations, but the role of broad-scale climate variability is less clear. For example, the influence of climatic “teleconnections” (the relationship between oceanic–atmospheric fluctuations and anomalous weather patterns across broad scales) on forest age structure is relatively unexplored. We sampled semiarid piñon–juniper ( Pinus edulis – Juniperus osteosperma ) woodlands in western Colorado, USA, to test the hypothesis that woodland age structures are shaped by climate, including links to oceanic–atmospheric fluctuations, and by past fires and livestock grazing. Low-severity surface fire was lacking, as fire scars were absent, and did not influence woodland densities, but stand-replacing fires served as long-rotation (>400–600 years), stand-initiating events. Old-growth stands (>300 years old) were found in 75% of plots, consistent with a long fire rotation. Juniper and piñon age structures suggest contrasting responses during the past several centuries to dry and wet episodes linked to the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO). Juniper density increased slightly during periods of drought, positive (warm) AMO (after &sim;10-year lag), and negative (cool) PDO. In contrast, piñon populations may still be recovering from a long, drought-filled period (AD 1620–1820), with pulses of recovery favored during cool AMO, warm PDO, and above-average moisture periods. Analysis of 20th-century tree establishment and instrumental climate data corroborate the long-term relationships between age structure and climate. After Euro–American settlement (AD 1881), livestock grazing reduced understory grasses and forbs, reducing competition with tree seedlings and facilitating climate-induced increases in piñons. Thus tree populations in these woodlands are in flux, affected by drought and wet periods linked to oceanic–atmospheric variability, Euro–American livestock grazing, and long-rotation, high-severity fires. Reductions in livestock grazing levels may aid ecological restoration efforts. However, given long-term fluctuations in tree density and composition, and expected further drought, thinning or burning to reduce tree populations may be misdirected.

Colorado↗

USGS2012

Holocene diatom flora and climate history of Medicine Lake, Northern California, USA

A 226-cm-long sediment core spanning the past ~ 11,400 years was recovered from Medicine Lake, on the Modoc Plateau in northeastern California. Diatom assemblages provide a record of lake level that is driven by local and regional climate changes and changes in basin morphology due to the activity of Medicine Lake volcano. The diatom record indicates that throughout its history, Medicine Lake was an oligotrophic lake, dominated by Cyclotella stelligera and C. pseudostelligera . Variations in lake level are suggested by changes in the structure of the diatom assemblages. The lowest part of the core (11,400 to 10,300 cal yr B.P.) contains the transition from glacial to interglacial conditions. From about 11,000 to 5500 cal yr B.P., the lake filled two small, steep-sided basins or one basin with two steep-sided sub-basins connected by a shallow shelf. During this time, the diatom evidence (Cyclotella/Navicula ratio) indicates that effective moisture increased, leading to a deeper lake. Over the past 5500 years the diatom record indicates fluctuations in lake level. The change in lake level pattern from one of increasing depth prior to about 5500 cal yr B.P. to one of variable depths may be related to changes in the morphology of the Medicine Lake basin in addition to shifts in local and regional climate. During this latter period the Cyclotella/Navicula ratio varies, suggesting that the level of the lake fluctuated, resulting in changes in colonizable shelf area.

California↗

USGS2026

Cyanobacteria and aquatic ecosystem dynamics across 28,000 years of environmental changes in subtropical North America

Ecological pressures on aquatic ecosystems have increased over recent centuries due to human activities and climate change. However, contextualizing ecosystem deterioration is often challenging due to limited knowledge of environmental changes over millennial timescales. Subtropical Carolina bays in North Carolina, USA, have remained unglaciated, preserving paleolimnological records that extend back to the last glacial period. Here, we analyzed a sediment core from the ecologically rich Lake Waccamaw spanning more than 28,000 years for aquatic proxies of nutrients, photosynthetic pigments, cyanotoxins, carbon isotopes, and terrestrial proxies of pollen and charcoal. The study explored paleolimnological changes in the aquatic environment connected to land changes and climate during the late Quaternary in the southeastern Atlantic Coastal Plain. Results reveal that while current levels of colonial cyanobacteria are high, past levels of cyanobacteria, other primary producers, and cyanotoxins were higher under natural climate variability. Abrupt ecosystem responses to increasing trophic conditions during Interstadial 3 (27.8–26.4 cal ka BP) and the early Holocene (11.4–7 cal ka BP) were marked by increases in primary producer abundance, deciduous vegetation expansion, and fire activity. Cyanobacteria remained dominant throughout the record, with colonial forms prevailing during the Holocene. Increases in pigment concentrations aligned with Quercus and were primarily driven by hydroclimatic variability and nutrient stoichiometry. Transitions between Pinus and Quercus pollen matched stadials and interstadials in the δ 18 Ο record from the North Greenland Ice Core Project (NGRIP). This study highlights the value of multi-proxy millennial-scale paleolimnological records for understanding aquatic ecosystem responses to climate conditions during the late Pleistocene.

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