DOCU-CLIM: A global documentary climate dataset for climate reconstructions.

Documentary climate data describe evidence of past climate arising from predominantly written historical documents such as diaries, chronicles, newspapers, or logbooks. Over the past decades, historians and climatologists have generated numerous document-based time series of local and regional climates. However, a global dataset of documentary climate time series has never been compiled, and documentary data are rarely used in large-scale climate reconstructions. Here, we present the first global multi-variable collection of documentary climate records. The dataset DOCU-CLIM comprises 621 time series (both published and hitherto unpublished) providing information on historical variations in temperature, precipitation, and wind regime. The series are evaluated by formulating proxy forward models (i.e., predicting the documentary observations from climate fields) in an overlapping period. Results show strong correlations, particularly for the temperature-sensitive series. Correlations are somewhat lower for precipitation-sensitive series. Overall, we ascribe considerable potential to documentary records as climate data, especially in regions and seasons not well represented by early instrumental data and palaeoclimate proxies.

Reconstruction of April temperatures in Kyoto, Japan, since the fifteenth century using the floral phenology of herbaceous peony and rabbit-ear iris.

We reconstructed April mean temperatures in Kyoto since the fifteenth century by investigating historical documents such as diaries and chronicles and compiling phenological data series of the full bloom date for herbaceous peony. In order to fill gaps in phenological data series, we used the full bloom date of rabbit-ear iris, an herbaceous plant that flowers at about the same time of the year as an herbaceous peony. We obtained floral phenological data covering a total of 278 years. Calibration using modern temperature data showed herbaceous peony phenology to be the preferred data source for April temperature estimation. Variations in the reconstructed April temperatures in Kyoto were synchronous with changes in the solar cycle. In particular, April temperatures were about 2 â„ƒ lower than at present around the ends of the Spoerer and Maunder grand solar minima, from 1550 to 1590 and from 1690 to 1730, respectively. In addition, the reconstructed April temperatures suggested a time lag in the climate response to solar activity changes that was about 10 years longer than the previously estimated lags in the responses of wintertime and March temperatures. However, further research is needed to accurately quantify this time lag.

Direct observations of ice seasonality reveal changes in climate over the past 320-570 years.

Lake and river ice seasonality (dates of ice freeze and breakup) responds sensitively to climatic change and variability. We analyzed climate-related changes using direct human observations of ice freeze dates (1443-2014) for Lake Suwa, Japan, and of ice breakup dates (1693-2013) for Torne River, Finland. We found a rich array of changes in ice seasonality of two inland waters from geographically distant regions: namely a shift towards later ice formation for Suwa and earlier spring melt for Torne, increasing frequencies of years with warm extremes, changing inter-annual variability, waning of dominant inter-decadal quasi-periodic dynamics, and stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution. Although local factors, including human population growth, land use change, and water management influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems, suggesting that global processes including climate change and variability are driving the long-term changes in ice seasonality.

Global impacts of the 1980s regime shift.

Despite evidence from a number of Earth systems that abrupt temporal changes known as regime shifts are important, their nature, scale and mechanisms remain poorly documented and understood. Applying principal component analysis, change-point analysis and a sequential t-test analysis of regime shifts to 72 time series, we confirm that the 1980s regime shift represented a major change in the Earth's biophysical systems from the upper atmosphere to the depths of the ocean and from the Arctic to the Antarctic, and occurred at slightly different times around the world. Using historical climate model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and statistical modelling of historical temperatures, we then demonstrate that this event was triggered by rapid global warming from anthropogenic plus natural forcing, the latter associated with the recovery from the El Chichón volcanic eruption. The shift in temperature that occurred at this time is hypothesized as the main forcing for a cascade of abrupt environmental changes. Within the context of the last century or more, the 1980s event was unique in terms of its global scope and scale; our observed consequences imply that if unavoidable natural events such as major volcanic eruptions interact with anthropogenic warming unforeseen multiplier effects may occur.

Cherry blossom phenological data since the seventeenth century for Edo (Tokyo), Japan, and their application to estimation of March temperatures.

The changes in March mean temperatures in Edo (Tokyo), Japan, since the seventeenth century, were reconstructed using phenological data for the cherry blossoms of Prunus jamasakura deduced from old diaries and chronicles. The observations of the time of full blossoming and of cherry blossom viewing parties were acquired and used to construct a full-blossoming phenological data series for P. jamasakura. Phenological data from 207 of the years from 1601 to 1905 were used for this study. The reconstructed temperatures suggested the existence of two cold periods (the second half of the seventeenth century and the beginning of the nineteenth century), during which times the estimated March mean temperatures were about 4 °C and 5 °C, respectively. These two cold periods at Edo coincided with those reconstructed at Kyoto in previous studies. These cold periods coincided with two less extreme periods, the Maunder and Dalton minima, in the long-term solar variation cycle.

Clarifying springtime temperature reconstructions of the medieval period by gap-filling the cherry blossom phenological data series at Kyoto, Japan.

We investigated documents and diaries from the ninth to the fourteenth centuries to supplement the phenological data series of the flowering of Japanese cherry (Prunus jamasakura) in Kyoto, Japan, to improve and fill gaps in temperature estimates based on previously reported phenological data. We then reconstructed a nearly continuous series of March mean temperatures based on 224 years of cherry flowering data, including 51 years of previously unused data, to clarify springtime climate changes. We also attempted to estimate cherry full-flowering dates from phenological records of other deciduous species, adding further data for 6 years in the tenth and eleventh centuries by using the flowering phenology of Japanese wisteria (Wisteria floribunda). The reconstructed tenth century March mean temperatures were around 7 degrees C, indicating warmer conditions than at present. Temperatures then fell until the 1180s, recovered gradually until the 1310s, and then declined again in the mid-fourteenth century.