Suchergebnisse

Maize (Zea mays L.) is one of the most important staple crops in Northeast China, and yield losses are mainly induced by climate anomalies, plant diseases and pests. To understand how maize yield loss is affected by global warming, daily precipitation and temperatures, together with provincial agricultural data sets, were analyzed. The results showed that the accumulated temperature, an important factor in agricultural productivity, increased by 5% in 1991–2017, compared to 1961–1990, and that the frequency of low temperatures decreased by 14.8% over the same time period. An increase in drought by 21.6% was observed from 1961–1990 to 1991–2017, caused by decreased growing-season precipitation by −4 mm/decade. In addition, days with heavy rain in August and September increased slightly in Northeast China. In general, maize growth responded positively to the increased thermal conditions; in 1961–1990, 22.7% of observed maize yield-loss cases were due to low temperatures, but only 10% in 1991–2017. However, during the same time, the number of drought-induced yield loss cases increased from 27.3% to 46.7%. Moreover, yield loss cases caused by heavy rainstorms increased from 4.5% to 13.3%, indicating that heavy rainstorms have become an increasing threat to agriculture in Northeast China over the last three decades. In total, at least 70% of cases of provincial yield losses in Northeast China over the last three decades could be attributed to climatic factors. The frequency of climate hazards has changed under global warming, resulting in new challenges for agriculture. While drought and low temperatures were the primary causes for climate-induced yield losses before the 1990s, negative impacts from extreme events, mainly drought but also heavy precipitation, have increased in the last three decades, associated with global change. Farmers, agricultural scientists, and government policy makers could use these results when planning for adaptation to climate change.

© 2020 Elsevier GmbH Climate reconstructions for the Common Era are compromised by the paucity of annually-resolved and absolutely-dated proxy records prior to medieval times. Where reconstructions are based on combinations of different climate archive types (of varying spatiotemporal resolution, dating uncertainty, record length and predictive skill), it is challenging to estimate past amplitude ranges, disentangle the relative roles of natural and anthropogenic forcing, or probe deeper interrelationships between climate variability and human history. Here, we compile and analyse updated versions of all the existing summer temperature sensitive tree-ring width chronologies from the Northern Hemisphere that span the entire Common Era. We apply a novel ensemble approach to reconstruct extra-tropical summer temperatures from 1 to 2010 CE, and calculate uncertainties at continental to hemispheric scales. Peak warming in the 280s, 990s and 1020s, when volcanic forcing was low, was comparable to modern conditions until 2010 CE. The lowest June–August temperature anomaly in 536 not only marks the beginning of the coldest decade, but also defines the onset of the Late Antique Little Ice Age (LALIA). While prolonged warmth during Roman and medieval times roughly coincides with the tendency towards societal prosperity across much of the North Atlantic/European sector and East Asia, major episodes of volcanically-forced summer cooling often presaged widespread famines, plague outbreaks and political upheavals. Our study reveals a larger amplitude of spatially synchronized summer temperature variation during the first millennium of the Common Era than previously recognised.