Yasuyuki Aono

Global impacts of the 1980s regime shift

Abstract 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 Earths 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.

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.

Effect of urban warming on blooming of Prunus yedoensis

Abstract An attempt is made to estimate the shift of blooming dates of Prunus yedoensis (the Japanese cherry tree) by urban warming. The ‘number of days transformed to standard temperature’ method is used to estimate blooming dates from temperature data. It is shown that the accuracy of this estimation is good enough to use this method for our purpose. Urban effects on blooming dates are obtained by subtracting the estimated blooming dates calculated using the urban-effect-eliminated temperature from those obtained using the observed temperature. It is found that the amount of shift of blooming date is almost proportional to the amount of urban warming at each site. It is also shown that the proportional constants are closely related to mean blooming dates at each place. The range of the constants is 2.5–5.5 days/°C with smaller values in southern and larger values in northern Japan. General quickening trends due to an increase of urban warming are observed in large cities in Japan. A relatively rapid increase to earlier blooming days was obtained during the 1950s through mid-1970s, then the increasing tendency stopped. In Kyoto, computational results showed a decrease in quickening tendency after the mid-1970s. By comparing variations of actual and estimated blooming dates, it is postulated that this reversal of trend at this site had actually occurred. Methodology and possible sources of errors are discussed. Examples of shifts in number of days of blooming of Prunus yedoensis by urban warming at stations in five large cities in Japan are given.