Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.

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The concept of megadroughts came to prominence with research into Common Era (CE; Year 1-present) palaeo climate droughts over western North America 1-5 . This research documented multi decadal periods of extreme aridity (or various hydrological deficits 1-5 ) before 1600 CE, as well as widespread ecological disturbances [6][7][8] and societal disruptions [9][10][11][12] . Although recurrent and persistent droughts are an intrinsic feature of North American hydroclimate variability, these megadroughts were primarily distinguished by their much greater per sistence (for example, multiple decades) than even the most extreme decadal length instrumental era droughts during the 1930s and 1950s 13,14 .Since then, extreme droughts across the globe have been increasingly referred to as megadroughts, despite often large differences in their severity, duration, or spatial extent. These include multi decadal periods of enhanced aridity in Australia 15,16 , South America 17 , Europe 18 , Central Asia 19,20 , and Mesoamerica 21 ; a multi season drought in 1540 CE over Europe 22 ; spatially extensive multi year droughts in India 23 ; the late Ming Dynasty drought in China 24,25 ; and an early twenty first century decadal drought in Chile and Argentina [26][27][28] . As anthropogenic warming is expected to increase drought severity and risk in many regions of the world 29,30 , the term has also been increasingly applied to droughts amplified by climate change, both in observations 26,31 and in model projections 32,33 .The use of the megadrought label has therefore been inconsistent, owing partly to an absence of applicable objective criteria that define when a drought becomes a megadrought, or when a period of moisture deficit

Since the 1980s, the subtropical jet stream has generally moved poleward, but its behavior varies by region and season. Here we examine the interannual variability and trends in the latitudinal position of the spring subtropical jet over the Himalayas. During the modern period (1948 to 2018), the spring (March-April-May) jet is typically anchored immediately south of the Himalayas but has rarely (in 1956, 1971, 1984, and 1999) moved poleward to pass over Kyrgyzstan and northwest China. A tree-ring reconstruction of the jet's latitude indicates that such poleward excursions may have become more frequent after 1950, but it is not clear whether that behavior is unprecedented within the past four centuries. These insights into the behavior of the Himalayan subtropical jet may improve seasonal weather forecasts for the region and provide a target for climate simulations to test whether the recent spate of excursions is unusual and due to anthropogenic warming. Plain Language Summary The subtropical jet stream (STJ) is a band of high-speed westerly winds in the upper atmosphere located near the subtropics. Since the 1980s, the STJ has generally moved poleward, but its behavior varies strongly by region and season. We studied the STJ over the Himalayas and found, during 1948-2018, that the spring STJ is typically anchored near the Himalayan foothills. In a few years (1956, 1971, 1984, and 1999); however, it has moved far north to pass over Kyrgyzstan and northwest China. A tree-ring reconstruction of the jet's north-south position suggests that this type of poleward tracks has happened before, but the past few decades may be unusual due to the number of such events. Including the potential north-south range of the Himalayan subtropical jet into forecasting models might help improve the accuracy of spring weather predictions in this region. Our multicentury record can be used to test how well models simulate the Himalayan jet and investigate whether anthropogenic warming is the cause of the recent poleward extremes.

The climate of Nepal has changed rapidly over the recent decades, but most instrumental records of weather and hydrology only extend back to the 1980s. Tree rings can provide a longer perspective on recent environmental changes, and since the early 2000s, a new round of field initiatives by international researchers and Nepali scientists have more than doubled the size of the country’s tree-ring network. In this paper, we present a comprehensive analysis of the current tree-ring width network for Nepal, and use this network to estimate changes in forest growth nation-wide during the last four centuries. Ring-width chronologies in Nepal have been developed from 11 tree species, and half of the records span at least 290 years. The Nepal tree-ring width network provides a robust estimate of annual forest growth over roughly the last four centuries, but prior to this point, our mean ring-width composite fluctuates wildly due to low sample replication. Over the last four centuries, two major events are prominent in the all-Nepal composite: (i) a prolonged and widespread growth suppression during the early 1800s; and (ii) heightened growth during the most recent decade. The early 19th century decline in tree growth coincides with two major Indonesian eruptions, and suggests that short-term disturbances related to climate extremes can exert a lasting influence on the vigor of Nepal’s forests. Growth increases since AD 2000 are mainly apparent in high-elevation fir, which may be a consequence of the observed trend towards warmer temperatures, particularly during winter. This synthesis effort should be useful to establish baselines for tree-ring data in Nepal and provide a broader context to evaluate the sensitivity or behavior of this proxy in the central Himalayas.

This study aims to understand the influence of climate on radial growth of Abies pindrow growing in the plateau of mixed forest in Khaptad National Park in Western Nepal Himalaya. Based on the dated tree-ring samples, 362-year long tree-ring width chronology was developed dating back to 1650. The studied taxa of this region was found to have dendroclimatic potentiality that was evident from the chronology statistics calculated. The tree-ring chronology was correlated with climate (temperature and precipitation) data to derive the tree-growth climate relationship. The result showed significant negative relationship with March-May temperature and positive relationship with March-May precipitation. This indicates that the availability of moisture is the primary factor in limiting the tree growth.Banko Janakari, Vol. 23, No. 2, 2013