Hydroclimatic variability in Santiago (Chile) since the 16th century

35 Pags.- 7 Figs.- 4 Tabls. The definitive version is available at: https://rmets.onlinelibrary.wiley.com/journal/10970088The long‐term hydroclimatic variability in Santiago (Chile) was analysed by means of a new 481‐year (1536–2016 CE) tree‐ring reconstruction of the Standardized Precipitation Evapotranspiration Index (SPEI) of August, integrating the hydroclimatic conditions during the preceding 14 months. Results show a high frequency of extreme drought events in the late 20th and early 21st centuries, while the frequency of extreme wet events was higher in the 17th–18th centuries. The mid‐20th century represents a breaking point for the hydroclimatic history in the region, including some significant changes: (a) the interannual variability increased; (b) the wet events became less intense; (c) the extreme dry events became more frequent; and (d) the most intense dry event of the entire period was identified, coinciding with the so‐called Megadrought (2006–2016). A correlation analysis between the reconstructed SPEI and three climate indices (PDO, SOI and Niño3.4) was performed at monthly scale, considering different multi‐annual aggregations. The analysis shows diverse impacts on the hydroclimatic variability, with positive correlations between SPEI and PDO as well as Niño3.4, and negative correlations between SPEI and SOI. The most significant correlations were, overall, found at multi‐annual time scales (>7 years). Results help to better understand the current hydroclimatic changes (Megadrought) in a long‐term context.R.S.N. is funded by a “Juan de la Cierva” postdoctoral grant FJCI-2017-31595. This work was developed under the project CAS/1900020 funded by the Spanish Ministry of Science and the Fulbright Foundation. O.M.R., P.S. and R.S.N. thank the Climatology Group (2017SGR1362, Catalan Government) and the CLICES Project (CGL2017-83866-C3-2-R). R.S.N. and M.D.L. are supported by the Government of Aragón through the “Programme of research groups” (group H38, “Clima, Agua, Cambio Global y Sistemas Naturales”) and thank the project CGL2015-69985-R. E.T. and M.V. were partially supported by NSF-PIRE (OISE-1743738) and NSF-P2C2 (AGS-1702439). M.F. is funded by a postdoctoral grant CONICYT PIA AFB170008 of the Institute of Ecology and Biodiversity (IEB).Peer reviewe

Global surface air temperature variations during the twentieth century: Part 2, implications for large-scale high-frequency palaeoclimatic studies

This paper is the second of a two-part series analysing details of regional, hemispheric and global temperature change during the twentieth century. Based on the grid box data described in Part 1 we present global maps of the strength of regional temperature coherence measured in terms of the correlation decay length for both annual and seasonal mean data. Correlation decay lengths are generally higher for annual rather than seasonal data; higher in the Southern compared to the Northern Hemisphere; and consistently higher over the oceans, particularly the Indian and central north Pacific oceans. Spatial coherence is relatively low in all seasons over the mid to high latitudes of the Northern Hemisphere and especially low in summer over the northern North Atlantic region. We also describe selected regional temperature series and examine the similarities between these and hemispheric mean data, placing emphasis on the nature of the relationships in different seasons. The Equatorial Indian and Atlantic oceans appear to be the best regional proxies for representing global mean temperatures. Temperature change in regions bordering the northern North Atlantic are less representative of hemisphere mean data, particularly in summer. The implications of these results for the large-scale interpretation of high-frequency palaeoclimate proxies are discussed. Strictly, given the length of the instrumental data, our results apply to temperature variability on timescales up to, at most, 50 years. Traditional inferences on global mean temperature change based on regional proxies originating around the margins of the northern North Atlantic must be viewed with some caution. Information on temperature change over the oceans, especially the tropical oceans, is an important prerequisite for accurate portrayal of global mean change. Care must be taken when integrating the evidence of different climate proxies to respect the seasonality of the response. Warm-season temperatures are most atypical of the various seasonal averages, especially in the Northern Hemisphere. Inferring annual temperature change on the basis of summer-responsive data is highly questionable

Tree-ring based reconstructions of northern Patagonia precipitation since AD 1600

Long-term reconstructions (400 years) of seasonal and annual precipitation variations were developed for northern Patagonia east of the Andes using a new set of 16 tree ring-width chronologies from Austrocedrus chilensis (D.Don) Endl. Reconstructions, which capture between 41 and 50% of the precipitation variance, show that the twentieth century contains the most extreme long periods of wetness and dryness in the past 400 years. Since about AD 1910, the reconstructions are also characterized by an increase in interannual variability and one of the highest rates of extreme events within the last 400 years. A prominent oscillation on the order of 2-2.1 years in length has been identified in the reconstructions using spectral analysis. Quasi-Biennial Oscillations have been shown to be very marked in some circulation indices of the Southern Hemisphere. Although significant oscillations within the preferred frequency domain of El Nino-Southern Oscillation (ENSO) are present in the reconstructions, no clear trod consistent responses to ENSO have been observed. Correlations of reconstructions with mean sea-level pressure around South America for the interval AD 1912-1984, reveal the influence of subtropical and high-latitude features of the atmospheric circulation on precipitation variations in northern Patagonia. Droughts result from an intensification of the subtropical Pacific anticyclone off the Chilean coast and the deepness of the circum-Antarctic trough over the South Orkney-Antarctic Peninsula sector. Mean sea-level pressure reconstructions for the South Atlantic sector of the Southern Oceans were used to evaluate the temporal stability of the relationships between northern Patagonia precipitation and high-latitude climatic variations since AD 1750. The influence of high-latitude circulation on precipitation appears to be more significant during the twentieth century, which in turn may respond to an intensification of wavenumbers 3 on the mean planetary wave structure over the Southern Hemisphere. Recent increase of precipitation variability in northern Patagonia may reflect stronger interactions between middle- and high-latitude atmospheric circulation in the Southern Hemisphere during the twentieth century

Investments in Global Warming Mitigation: The Case of “Activities Implemented Jointlyâ€\x9D

This paper examines bilateral cooperation between developed countries (home country) and developing countries (host country) to reduce greenhouse gas emissions and to enhance carbon dioxide sinks. With the home-host country pair as the unit of analysis, our logistic regression model examines 158 Activities Implemented Jointly (AIJ) investment projects from 1993 until 2002 across 2541 country-pairs. Because the marginal costs of reducing emissions may be lower in developing countries, the AIJ projects served as a policy laboratory to assess whether such investments might be advantageous to both countries in the event future regimes allowed emission credits from such bilateral projects. Instead of investing in home countries where maximum pollution reductions (or carbon sequestration) might be possible, home countries invest in locations where they can conduct their policy experiments at low transaction costs. Prior trade and aid relationships were used as a proxy. Regarding energy projects, location decisions are driven by home countries’ desire to reduce air pollution that they receive from abroad. Geography – proximity of a host country to a home country – in interaction with host country's coal production, is a very important driver of location decision in AIJ energy sector projects. Location of sequestration projects is impacted by the host country's potential for avoiding deforestation as well as by previous aid and trade patterns between a home and a host country. Proximity is not important in this case. Copyright Springer Science + Business Media B.V. 2006Global climate change policy, Global warming policy, International environmental policy, International environmental regimes, International cooperation, Global commons, Energy policy, Environmental policy, Activities implemented jointly, International regimes,