Impatti, adattamento e vulnerabilita Le cause e le responsabilita dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilita” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

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Climate Change 2007: Impacts, Adaptation and Vulnerability.

저작근 근전도에 관한 정상교합자와 ii급 부정교합자의 비교 연구

Global Land Cover (GLC) information is fundamental for environmental change studies, land resource management, sustainable development, and many other societal benefits. Although GLC data exists at spatial resolutions of 300 m and 1000 m, a 30 m resolution mapping approach is now a feasible option for the next generation of GLC products. Since most significant human impacts on the land system can be captured at this scale, a number of researchers are focusing on such products. This paper reports the operational approach used in such a project, which aims to deliver reliable data products. Over 10,000 Landsat-like satellite images are required to cover the entire Earth at 30 m resolution. To derive a GLC map from such a large volume of data necessitates the development of effective, efficient, economic and operational approaches. Automated approaches usually provide higher efficiency and thus more economic solutions, yet existing automated classification has been deemed ineffective because of the low classification accuracy achievable (typically below 65%) at global scale at 30 m resolution. As a result, an approach based on the integration of pixel- and object-based methods with knowledge (POK-based) has been developed. To handle the classification process of 10 land cover types, a split-and-merge strategy was employed, i.e. firstly each class identified in a prioritized sequence and then results are merged together. For the identification of each class, a robust integration of pixel-and object-based classification was developed. To improve the quality of the classification results, a knowledge-based interactive verification procedure was developed with the support of web service technology. The performance of the POK-based approach was tested using eight selected areas with differing landscapes from five different continents. An overall classification accuracy of over 80% was achieved. This indicates that the developed POK-based approach is effective and feasible for operational GLC mapping at 30 m resolution.

Global land cover mapping at 30 m resolution: A POK-based operational approach

We have produced the first 30 m resolution global land-cover maps using Landsat Thematic Mapper TM and Enhanced Thematic Mapper Plus ETM+ data. We have classified over 6600 scenes of Landsat TM data after 2006, and over 2300 scenes of Landsat TM and ETM+ data before 2006, all selected from the green season. These images cover most of the world's land surface except Antarctica and Greenland. Most of these images came from the United States Geological Survey in level L1T orthorectified. Four classifiers that were freely available were employed, including the conventional maximum likelihood classifier MLC, J4.8 decision tree classifier, Random Forest RF classifier and support vector machine SVM classifier. A total of 91,433 training samples were collected by traversing each scene and finding the most representative and homogeneous samples. A total of 38,664 test samples were collected at preset, fixed locations based on a globally systematic unaligned sampling strategy. Two software tools, Global Analyst and Global Mapper developed by extending the functionality of Google Earth, were used in developing the training and test sample databases by referencing the Moderate Resolution Imaging Spectroradiometer enhanced vegetation index MODIS EVI time series for 2010 and high resolution images from Google Earth. A unique land-cover classification system was developed that can be crosswalked to the existing United Nations Food and Agriculture Organization FAO land-cover classification system as well as the International Geosphere-Biosphere Programme IGBP system. Using the four classification algorithms, we obtained the initial set of global land-cover maps. The SVM produced the highest overall classification accuracy OCA of 64.9% assessed with our test samples, with RF 59.8%, J4.8 57.9%, and MLC 53.9% ranked from the second to the fourth. We also estimated the OCAs using a subset of our test samples 8629 each of which represented a homogeneous area greater than 500 m × 500 m. Using this subset, we found the OCA for the SVM to be 71.5%. As a consistent source for estimating the coverage of global land-cover types in the world, estimation from the test samples shows that only 6.90% of the world is planted for agricultural production. The total area of cropland is 11.51% if unplanted croplands are included. The forests, grasslands, and shrublands cover 28.35%, 13.37%, and 11.49% of the world, respectively. The impervious surface covers only 0.66% of the world. Inland waterbodies, barren lands, and snow and ice cover 3.56%, 16.51%, and 12.81% of the world, respectively.

https://www.tandfonline.com/doi/pdf/10.1080/01431161.2012.748992

Finer resolution observation and monitoring of global land cover: first mapping results with Landsat TM and ETM+ data

The recent warming in the Arctic is affecting a broad spectrum of physical, ecological, and human/cultural systems that may be irreversible on century time scales and have the potential to cause rapid changes in the earth system. The response of the carbon cycle of the Arctic to changes in climate is a major issue of global concern, yet there has not been a comprehensive review of the status of the contemporary carbon cycle of the Arctic and its response to climate change. This review is designed to clarify key uncertainties and vulnerabilities in the response of the carbon cycle of the Arctic to ongoing climatic change. While it is clear that there are substantial stocks of carbon in the Arctic, there are also significant uncertainties associated with the magnitude of organic matter stocks contained in permafrost and the storage of methane hydrates beneath both subterranean and submerged permafrost of the Arctic. In the context of the global carbon cycle, this review demonstrates that the Arctic plays an important role in the global dynamics of both CO2 and CH4. Studies suggest that the Arctic has been a sink for atmospheric CO2 of between 0 and 0.8 Pg C/yr in recent decades, which is between 0% and 25% of the global net land/ocean flux during the 1990s. The Arctic is a substantial source of CH4 to the atmosphere (between 32 and 112 Tg CH4/yr), primarily because of the large area of wetlands throughout the region. Analyses to date indicate that the sensitivity of the carbon cycle of the Arctic during the remainder of the 21st century is highly uncertain. To improve the capability to assess the sensitivity of the carbon cycle of the Arctic to projected climate change, we recommend that (1) integrated regional studies be conducted to link observations of carbon dynamics to the processes that are likely to influence those dynamics, and (2) the understanding gained from these integrated studies be incorporated into both uncoupled and fully coupled carbon-climate modeling efforts. (Less)

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Sensitivity of the carbon cycle in the Arctic to climate change

Nitrous oxide is a potent greenhouse gas whose concentration is increasing in the atmosphere; the highest emissions have been observed from agricultural and tropical soils. Now, measurements in subarctic East European tundra show that bare surfaces on permafrost peatlands, known as peat circles, release large quantities of nitrous oxide. Nitrous oxide is a potent greenhouse gas whose concentration is increasing in the atmosphere1. So far, the highest terrestrial nitrous oxide emissions have been measured in agricultural and tropical soils2,3, and nitrous oxide emissions from northern natural soils have been considered negligible4,5. Pristine tundra, one of the largest natural land cover types in the world, is a mosaic of different surface types including bare surfaces created by cryoturbation6,7. Here we used a static chamber method to measure nitrous oxide emissions from the discontinuous permafrost zone in subarctic East European tundra. We show that nitrous oxide emissions from bare peat surfaces in the region, known as peat circles, range between 0.9 and 1.4 g nitrous oxide m−2 from June to October, and are equivalent to those from tropical and agricultural soils. Extrapolation of our data to the whole Arctic reveals that the emissions from these hot spots could amount to ∼0.1 Tg nitrous oxide yr−1, corresponding to 4% of the global warming potential of Arctic methane emissions at present. Therefore, not only carbon, but also nitrogen stored in permafrost soils, has to be considered when assessing the present and future climatic impact of tundra.

Large N2O emissions from cryoturbated peat soil in tundra

Large N2O emissions from cryoturbated peat soil in tundra. Nat Geosci 2:189-192

[1] We studied the carbon dioxide and methane fluxes from early June to mid-September 2001 in the Russian tundra of northeast Europe. Gas fluxes were measured with chamber techniques to determine the seasonal (100 days) carbon gas balance for terrestrial ecosystems representing various vegetation types. Also, the gas balance for aquatic ecosystems in the region was measured. The 2001 fluxes were compared to colder and wetter season fluxes from 1999. The Sphagnum sp. dominated peat plateau fen and Carex sp. and Sphagnum sp. dominated intermediate flarks were carbon sinks of 106 and 110 g C m−2, respectively. In addition, methane emissions were highest from these sites. Other terrestrial surfaces lost carbon to the atmosphere (28–118 g C m−2). The thermokarst lake and the river had seasonal carbon losses of 15 and 34 g C m−2, respectively. For areal integration, the distributions of the various functional surfaces were classified based on Landsat TM satellite image and on-site validation. This data was used to integrate the carbon fluxes for the entire Lek Vorkuta catchment. The upscaling indicated that the catchment (114 km2) lost 4 (±3.5) Gg C to the atmosphere in summer 2001. The results suggest that predicted warming in the tundra region would induce a substantial loss of carbon. In the warm summer of 2001, the carbon gas released from the whole northeast European tundra (area 205,000 km2) was 8 Tg C when calculated from the Lek Vorkuta data.

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Carbon balance in East European tundra

[1] Methane (CH4) and carbon dioxide (CO2) fluxes on east European tundra wetland ecosystems (67°23′N, 63°22′E) were measured by static chamber techniques in 1999. The 29 microsites were divided into wet flarks (WF), intermediate flarks (IF), wet lawns (WL), intermediate lawns (IL), and hummocks (HCK) in accordance to the water table (WT) and vegetation. The seasonal net ecosystem exchange (NEE) varied from −104 mg emission to 249 mg CO2–C m−2 h−1 uptake. Regression models were constructed to estimate the seasonal gross photosynthesis and respiration on each of the microsites. The cumulative gross photosynthesis (and respiration) was 68 (37), 131 (77), 176 (126), 164 (129), and 189 (187) g C m−2 in a 100 day summer period in WF, IF, WL, IL, and HCK, respectively. The losses of carbon in winter accounted for 23.7%, 5.0%, 3.1%, 2.6%, and 2.3% of the net ecosystem production. CH4 emissions in summer (and winter) were 7.7 (7.8), 6.6 (0.8), 8.2 (0.4), 0.7 (0.3), and 0.1 (0.2) g C m−2 for WF, IF, WL, IL, and HCK, respectively. The modeled annual carbon balance for grouped microsites shows that dry HCKs were carbon sources −7.5 g C yr−1 while flarks and lawns were carbon sinks ranging from 2.2 to 35.9 g C yr−1. The results show the importance of WT and vegetation composition on annual flux dynamics in a tundra wetland. CH4 emissions from arctic peatlands seem to be sensitive to changes in the WT.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002GB001930

Carbon dioxide and methane dynamics and annual carbon balance in tundra wetland in NE Europe, Russia

We report here the carbon dioxide (CO 2 ) budget of a 98.6 km 2 subarctic tundra area in northeast European Russia based on measurements at two different scales and two independent upscaling approaches. Plot-scale measurements (chambers on terrestrial surfaces, gas gradient method and bubble collectors on lakes) were carried out from July 2007 to October 2008. The landscape-scale eddy covariance (EC) measurements covered the snow-free period of 2008. The annual net ecosystem exchange (NEE) of different land cover types ranged from −251 to 84 g C m −2 . Leaf area index (LAI) was an excellent predictor of the spatial variability in gross photosynthesis (GP), NEE and ecosystem respiration (ER). The plot-scale CO 2 fluxes were first scaled up to the EC source area and then to the whole study area using two data sets: a land cover classification and a LAI map, both based on field data and a 2.4 m pixel-sized QuickBird satellite image. The good agreement of the CO 2 balances for the EC footprint based on the different measuring techniques (−105 to −81 g C m −2 vs. −79 g C m −2 ; growing season 2008) justified the integration of the plot-scale measurements over the larger area. The regional CO 2 balance based on area-integrated plot-scale measurements was −41 or −79 g C m −2 yr −1 according to the two upscaling methods, the land cover classification and the LAI map, respectively. Due to the heterogeneity of tundra, the effect of climate change on CO 2 uptake will vary strongly according to the land cover type and, moreover, likely changes in their relative coverage in the future will have great impact on the regional CO 2 balance.

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Vladimir Elsakov

Papers

Large N2O emissions from cryoturbated peat soil in tundra

Large N2O emissions from cryoturbated peat soil in tundra. Nat Geosci 2:189-192

Carbon balance in East European tundra

Carbon dioxide and methane dynamics and annual carbon balance in tundra wetland in NE Europe, Russia

Carbon dioxide balance of subarctic tundra from plot to regional scales