486 research outputs found
Policy implications of warming permafrost
Permafrost is perennially frozen ground occurring in about 24% of the exposed land surface in the Northern Hemisphere. The distribution of permafrost is controlled by air temperature and, to a lesser extent, by snow depth, vegetation, orientation to the sun and soil properties. Any location with annual average air temperatures below freezing can potentially form permafrost.
Snow is an effective insulator and modulates the effect of air temperature, resulting in permafrost temperatures up to 6°C higher than the local mean annual air temperature. Most of the current permafrost formed during or since the last ice age and can extend down to depths of more than 700 meters in parts of northern Siberia and Canada. Permafrost includes the contents of the ground before it was frozen, such as bedrock, gravel, silt and organic material. Permafrost often contains large lenses, layers and wedges of pure ice that grow over many years as a result of annual freezing and thawing of the surface soil laye
Evaluation of Climatic and Anthropogenic Impacts on Dust Erodibility: A Case Study in Xilingol Grassland, China
Aeolian dust is dependent on erosivity (i.e., wind speed) and erodibility (i.e., land surface conditions). The effect of erodibility on dust occurrence remains poorly understood. In this study, we proposed a composite erodibility index (dust occurrence ratio, DOR) and examined its interannual variation at a typical steppe site (Abaga-Qi) in Xilingol Grassland, China, during spring of 1974–2018. Variation in DOR is mainly responsible for dust occurrence (R2 = 0.80, p-value < 0.001). During 2001–2018, DOR values were notably higher than those during 1974–2000. There was also a general declining trend with fluctuations. This indicates that the land surface conditions became vulnerable to wind erosion but was gradually reversed with the implementation of projects to combat desertification in recent years. To understand the relative climatic and anthropogenic impacts on erodibility, multiple regression was conducted between DOR and influencing factors for the period of 2001–2018. Precipitation (spring, summer, and winter) and temperature (summer, autumn, and winter), together with livestock population (June) explained 82% of the variation in DOR. Sheep and goat population made the greatest contribution. Therefore, reducing the number of sheep and goat could be an effective measure to prevent dust occurrence in Xilingol Grassland
Interacting effects of growing season and winter climate change on nitrogen and carbon cycling in northern hardwood forests
Human activities such as fossil fuel combustion and deforestation have increased atmospheric concentrations of carbon dioxide, reactive nitrogen, and other greenhouse gases. As a result, Earth's surface has warmed by 0.85 °C since the pre-industrial era and will continue to warm. Many northern latitude temperate forest ecosystems mitigate the effects of both elevated carbon dioxide and atmospheric nitrogen deposition through retention of carbon and nitrogen in plants and soils. However, the continued ability of these ecosystems to store carbon and nitrogen will be altered with continued climate change. Warmer winters will lead to reduced depth and duration of snowpack, which insulates soils from cold winter air. Climate change over the next century will therefore affect soil temperatures in northern temperate forests in opposing directions across seasons, with warmer soils in the growing season and colder, more variable soil temperatures in winter. Warmer growing seasons generally increase ecosystem uptake and storage of carbon and nitrogen, whereas a smaller snowpack and colder soils in winter reduce rates of ecosystem nutrient cycling and plant growth. My dissertation aims to understand how climate change in the growing season and winter interact to affect function and nitrogen cycling in northern hardwood forest ecosystems. I accomplished this goal through formal literature review and two climate change manipulation experiments at Hubbard Brook Experimental Forest, NH. I found that although 67% of climate change experiments were conducted in seasonally snow covered ecosystems, only 14% take into account the effects of distinct climate changes in winter. By simulating climate change across seasons, I demonstrated that changes in nitrogen cycling caused by increased soil freezing in winter are not offset by warming in the growing season. Moreover, shifts in plant function due to winter climate change are mediated through a combination of changes in snow depth, soil temperature, and plant-herbivore interactions that differentially affect above- and belowground plant components. These results would not be evident from examining climate change in either the growing season or winter alone and demonstrate the need for considering seasonally distinct climate change to determine how nitrogen and carbon cycling will change in the future
Northern Eurasia Future Initiative (NEFI): facing the challenges and pathways of global change in the twenty-first century
During the past several decades, the Earth system has changed significantly, especially across Northern Eurasia. Changes in the socio-economic conditions of the larger countries in the region have also resulted in a variety of regional environmental changes that can have global consequences. The Northern Eurasia Future Initiative (NEFI) has been designed as an essential continuation of the Northern Eurasia Earth Science Partnership Initiative (NEESPI), which was launched in 2004. NEESPI sought to elucidate all aspects of ongoing environmental change, to inform societies and, thus, to better prepare societies for future developments. A key principle of NEFI is that these developments must now be secured through science-based strategies co-designed with regional decision-makers to lead their societies to prosperity in the face of environmental and institutional challenges. NEESPI scientific research, data, and models have created a solid knowledge base to support the NEFI program. This paper presents the NEFI research vision consensus based on that knowledge. It provides the reader with samples of recent accomplishments in regional studies and formulates new NEFI science questions. To address these questions, nine research foci are identified and their selections are briefly justified. These foci include warming of the Arctic; changing frequency, pattern, and intensity of extreme and inclement environmental conditions; retreat of the cryosphere; changes in terrestrial water cycles; changes in the biosphere; pressures on land use; changes in infrastructure; societal actions in response to environmental change; and quantification of Northern Eurasia’s role in the global Earth system. Powerful feedbacks between the Earth and human systems in Northern Eurasia (e.g., mega-fires, droughts, depletion of the cryosphere essential for water supply, retreat of sea ice) result from past and current human activities (e.g., large-scale water withdrawals, land use, and governance change) and potentially restrict or provide new opportunities for future human activities. Therefore, we propose that integrated assessment models are needed as the final stage of global change assessment. The overarching goal of this NEFI modeling effort will enable evaluation of economic decisions in response to changing environmental conditions and justification of mitigation and adaptation efforts
Study on Regional Responses of Pan-Arctic Terrestrial Ecosystems to Recent Climate Variability Using Satellite Remote Sensing
I applied a satellite remote sensing based production efficiency model (PEM) using an integrated AVHRR and MODIS FPAR/LAI time series with a regionally corrected NCEP/NCAR reanalysis surface meteorology and NASA/GEWEX shortwave solar radiation inputs to assess annual terrestrial net primary productivity (NPP) for the pan-Arctic basin and Alaska from 1983 to 2005. I developed a satellite remote sensing based evapotranspiration (ET) algorithm using GIMMS NDVI with the above meteorology inputs to assess spatial patterns and temporal trends in ET over the pan-Arctic region. I then analyzed associated changes in the regional water balance defined as the difference between precipitation (P) and ET. I finally analyzed the effects of regional climate oscillations on vegetation productivity and the regional water balance.
The results show that low temperature constraints on Boreal-Arctic NPP are decreasing by 0.43% per year ( P \u3c 0.001), whereas a positive trend in vegetation moisture constraints of 0.49% per year ( P = 0.04) are offsetting the potential benefits of longer growing seasons and contributing to recent drought related disturbances in NPP. The PEM simulations of NPP seasonality, annual anomalies and trends are similar to stand inventory network measurements of boreal aspen stem growth ( r = 0.56; P = 0.007) and atmospheric CO2 measurement based estimates of the timing of growing season onset (r = 0.78; P \u3c 0.001).
The simulated monthly ET results agree well (RMSE = 8.3 mm month-1; R2 = 0.89) with tower measurements for regionally dominant land cover types. Generally positive trends in ET, precipitation and available river discharge measurements imply that the pan-Arctic terrestrial water cycle is intensifying. Increasing water deficits occurred in some boreal and temperate grassland regions, which agree with regional drought records and recent satellite observations of vegetation browning and productivity decreases.
Climate oscillations including Arctic Oscillation and Pacific Decadal Oscillation influence NPP by regulating seasonal patterns of low temperature and moisture constraints to photosynthesis.
The pan-Arctic water balance is changing in complex ways in response to climate change and variability, with direct linkages to terrestrial carbon and energy cycles. Consequently, drought induced NPP decreases may become more frequent and widespread, though the occurrence and severity of drought events will depend on future water cycle patterns
Assessment of the status of the development of the standards for the Terrestrial Essential Climate Variables - T7 - Permafrost and seasonally frozen ground
Decadal changes in permafrost temperatures and depth of seasonal freezing/thawing are indicators of changes in climate. Warming may result in an increase in active layer thickness, melting of ground ice and subsequent reduction in permafrost thickness and the lateral extent of permafrost. These changes can have an impact on terrain stability leading to ground subsidence or erosion, vegetation, ecosystem function and soil moisture and gas fluxes. Permafrost and seasonally frozen ground also influence surface and subsurface hydrology. Standardized in situ measurements are essential to understanding how permafrost conditions are changing, to improve predictions of future changes, and to calibrate and to verify regional and global climate change models. Long-term monitoring sites are contributing to the Global Terrestrial Network for Permafrost (GTN-P). These sites exist throughout the permafrost regions and have provided data that have facilitated the characterization of trends in permafrost conditions over the last two to three decades and in a few cases over much longer periods. Under the leadership of the International Permafrost Association a coordinated field campaign is under way during the International Polar Year to obtain a snapshot of global permafrost temperatures and active layer measurements. The main parameters and measurement methods are: Permafrost: sub-surface earth materials that remain continuously at or below 0°C for two or more consecutive years. Parameter is ground temperature (°C) at specified depths. Permafrost temperature measurements are obtained by lowering a calibrated temperature sensor into a borehole, or recording temperature from multi-sensor cables permanently or temporarily installed in the borehole. Measurements may be recorded manually or by data loggers. The depth of boreholes varies from less than 10m to greater than 100m. Data loggers may be utilized for daily measurements of shallow temperatures to reduce the frequency of site visits and provide a continuous record of ground temperatures. Ideally (although not always feasible at all sites), temperatures at shallow depths (upper 10 m to 20 m) should be collected at monthly or more frequent intervals as this allows the annual temperature envelope (i.e. range in temperatures at depth) and mean annual temperatures to be determined. Active layer: the surface layer of ground, subject to annual thawing and freezing in areas underlain by permafrost. Parameters are thickness (cm) and temperatures (°C). Several traditional methods are used to determine the seasonal and long - term changes in thickness of the active layer: mechanical probing annually, frost tubes, and interpolation of soil temperatures. The minimum observation required under the Circumpolar Active Layer Monitoring (CALM ) protocol is a late season mechanical probing of the thickness of the active layer on a gridded plot or transect. Interpolation of soil temperature measurements from a vertical array of sensors can be used to determine active-layer thickness at a point location (see www.udel.edu/Geography/calm/) Seasonally frozen ground: refers to soils without permafrost that are subjected to seasonal freezing and thawing. Parameters are depth (cm) and temperature (°C). Winter frost penetration in regions of seasonal ground freezing is determined by measuring soil temperatures or by use of frost tubes; similar to methods used for active layer measurements. The methods described above are presented in a combined draft manual developed for the International Polar Year Thermal State of Permafrost (IPY/TSP) which is available on the International Permafrost Association (IPA) Web site (www.ipa-permafrost.org/). Deriving ISO standards from this manual should encourage the adoption of these standard methodologies and promote the expansion of the observational networks. Unlike ice and snow covers, properties of permafrost terrain are currently not directly detected from remote sensing platforms. However, many surface features of permafrost terrains and periglacial landforms are observable with a variety of sensors ranging from conventional aerial photography to high-resolution satellite imagery in various wavelengths._
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