Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics—and its influence on the deep Earth and climate—it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of ‘full-plates’ (including oceanic lithosphere) becomes increasingly challenging with age. Prior to 150 Ma ∼60% of the lithosphere is missing and reconstructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles; in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these ‘continental’ reconstructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding (or only loosely applying) plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geodynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic (410–250 Ma) together with a review of the underlying data. Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it will also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.

Plate tectonics in the late Paleozoic

In recent decades, intense droughts, insect outbreaks, and wildfires have led to decreasing tree growth and increasing mortality in many temperate forests. We compared annual tree-ring width data from 1,097 populations in the coterminous United States to climate data and evaluated site-specific tree responses to climate variations throughout the 20th century. For each population, we developed a climate-driven growth equation by using climate records to predict annual ring widths. Forests within the southwestern United States appear particularly sensitive to drought and warmth. We input 21st century climate projections to the equations to predict growth responses. Our results suggest that if temperature and aridity rise as they are projected to, southwestern trees will experience substantially reduced growth during this century. As tree growth declines, mortality rates may increase at many sites. Increases in wildfires and bark-beetle outbreaks in the most recent decade are likely related to extreme drought and high temperatures during this period. Using satellite imagery and aerial survey data, we conservatively calculate that ≈2.7% of southwestern forest and woodland area experienced substantial mortality due to wildfires from 1984 to 2006, and ≈7.6% experienced mortality associated with bark beetles from 1997 to 2008. We estimate that up to ≈18% of southwestern forest area (excluding woodlands) experienced mortality due to bark beetles or wildfire during this period. Expected climatic changes will alter future forest productivity, disturbance regimes, and species ranges throughout the Southwest. Emerging knowledge of these impending transitions informs efforts to adaptively manage southwestern forests.

Forest responses to increasing aridity and warmth in the southwestern United States

Plate Tectonics in the Late Paleozoic

There is a broad consensus that the Solonker Suture Zonemarks the final closure of the Paleo-Asian Ocean, which led to the formation of the eastern segment of the Central Asian Orogenic Belt. However, when and how the final closure occurred still remains controversial. To address this issue, provenance analysis of Permian sedimentary rocks of arc basins along the Xar Moron River was carried out. Geochemical analysis revealed a close relationship between the sedimentary and volcanic rock suite in the study region suggesting short transport distances and a complex convergent arc setting. Detrital zircon U-Pb analysis identified two major age provenances: (1) the Precambrian basement of the North China Craton (~2497 Ma and ~1844 Ma) and (2) the Paleozoic Southern Accretionary Orogen along the northern margin of North China (~436 Ma and ~269 Ma). The present locations of identified age provenances indicate southward subduction beneath the northern margin of North China. A comparison of the youngest age population in the sedimentary rocks with U-Pb ages obtained for subduction-related volcanic rocks implies that the Solonker Suture Zone formed from the Late Permian to Early Triassic. The results of our study advocate a complex Permian arc system which was probably similar to present-day Southeast Asia.

Final closure of the Paleo‐Asian Ocean along the Solonker Suture Zone: Constraints from geochronological and geochemical data of Permian volcanic and sedimentary rocks

Remote sensing, hydrological modeling and in situ observations in snow cover research: A review

Assessment of flash flood risk based on improved analytic hierarchy process method and integrated maximum likelihood clustering algorithm

Monitoring changes of NDVI in protected areas of southern California

An investigation of temporal dynamics and spatial patterns of dryness/wetness conditions over the eastern part of Northwest China (including Shaanxi, Ningxia, the eastern part of Gansu, and a part of southern Inner Mongolia) during the period 1960–2009 is presented. The analysis of this study is threefold. First, the dryness/wetness conditions over the study area were characterized using the self-calibrating Palmer Drought Severity Index (PDSI). The spatiotemporal variability of dryness/wetness conditions in the study area was then investigated by the rotated empirical orthogonal function (REOF) and Mann–Kendall trend test. Third, we examined the periodical oscillations of dryness/wetness conditions and the multi-scale relationships between dryness/wetness conditions and El Nino-Southern Oscillation (ENSO). The results indicate that most parts of the study area were characterized by a dry trend in both the rainy season (May–September) and winter. Four sub-regions of dryness/wetness conditions across the study area were identified. Based on the wavelet analysis, the periodical features in the PDSI time series for each sub-region were explored. Negative relationships between the PDSI in the sub-region I (representing the central and southern parts of Shaanxi and the southeastern Gansu) and the Nino 3.4 index can be consistently detected on 2–6 year scales during the entire period 1960–2009. This suggests that the strong El Nino events generally lead to very dry conditions in the sub-region I on multi-year scales. In addition, we further investigated how the ENSO cycle modulates the strength of the East Asian summer monsoon (EASM) in both developing and decaying phases of El Nino and La Nina events. The results of this study could be beneficial for efficient water resources management and drought assessment in the current study area and also provide a valuable reference for other areas with similar climatic characteristics.

Temporal dynamics and spatial patterns of drought and the relation to ENSO: a case study in Northwest China

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019GL082137

Chunyu Dong

Papers

Remote sensing, hydrological modeling and in situ observations in snow cover research: A review

Assessment of flash flood risk based on improved analytic hierarchy process method and integrated maximum likelihood clustering algorithm

Monitoring changes of NDVI in protected areas of southern California

Temporal dynamics and spatial patterns of drought and the relation to ENSO: a case study in Northwest China

Vegetation Responses to 2012-2016 Drought in Northern and Southern California