TOKYO - Japan is likely to face increasingly long and dangerously hot summers as global temperatures continue to rise, with advanced climate simulations also pointing to more frequent torrential rain, rising seas and accelerating ice loss by the end of the century.
The latest projections were presented by Masahiro Watanabe, a professor at the University of Tokyo and a leading climate-change researcher specializing in computer simulations. Watanabe has played a central role in the Intergovernmental Panel on Climate Change, or IPCC, which brings together researchers from around 200 countries to assess the latest scientific findings on the global climate.
Recent summers have already changed how people spend their time outdoors. Residents interviewed on the street said temperatures feel considerably higher than in the past, when 30 degrees Celsius was regarded as exceptionally hot. Some said the heat now discourages them from leaving home, while others recalled that summers once felt drier and more comfortable.
The Japan Meteorological Agency has also added new terminology to its forecasts to communicate the threat posed by exceptionally high maximum temperatures, reflecting growing concern about extreme heat.
While temperatures still fluctuate naturally from year to year, Watanabe said the long-term average is clearly rising and abnormal weather events are becoming more common. "Unless carbon dioxide emissions are stopped, temperatures will continue to rise," he said.
Watanabe studies the climate by constructing a virtual Earth inside a computer. Researchers enter conditions such as rising atmospheric carbon dioxide concentrations and use supercomputers to calculate how the planet’s complex climate system may respond over decades.
Because the climate cannot be solved through simple calculations, Watanabe’s team uses the Earth Simulator, a supercomputer developed to analyze natural phenomena. A simulation covering the period from 1950 to 2100 shows temperatures spreading progressively above late 20th-century levels.
Areas shown in red, yellow and white become increasingly widespread as the simulation advances into the future. By around 2050, much of the world is substantially warmer, even under a middle-range scenario in which carbon dioxide emissions neither increase nor decrease to an extreme degree.
"This is not the worst-case scenario," Watanabe said.
The Arctic shows the greatest warming. Unlike a uniform increase across the planet, global warming is strongest around the North Pole, where average temperatures could rise by 8 to 10 degrees Celsius in some projections. Because those figures represent annual averages, temperatures during some seasons could rise above freezing.
The Northern Hemisphere also warms more sharply because it contains more land. Land heats faster than the oceans, which absorb heat more slowly.
Japan also becomes warmer in the simulation. Short-term changes in color from one year to another represent natural climate variability, but areas that remain persistently red or yellow indicate the underlying effect of global warming.
Researchers continually compare simulation results with actual observations to improve their accuracy. At Watanabe’s laboratory on the University of Tokyo’s Kashiwa campus, scientists analyze decades of observed sea-surface temperature data and examine changes in broad ocean patterns.
Temperatures in the tropical Pacific are particularly important because they have a major influence on large-scale atmospheric circulation and the occurrence of abnormal weather around the world. Rather than focusing on a single location, researchers study changes across the entire ocean pattern and compare them with computer-generated results.
Japan’s recent heat records already show that summer conditions are changing. Data measuring the cumulative number of observation sites recording maximum temperatures of at least 35 degrees Celsius indicate that extremely hot days are beginning earlier in the year.
The previous summer, described as reaching disaster-level heat, saw the number of such observations rise rapidly at an early stage. By July, the cumulative figure was already approaching 4,000 to 5,000, although August was roughly comparable with the year before.
The findings indicate that Japan’s summer is becoming longer, Watanabe said. The period of intense heat is beginning earlier rather than being confined to the traditional peak of summer.
Average global temperatures have already risen by about 1.1 degrees Celsius since the Industrial Revolution, when carbon dioxide concentrations began increasing significantly.
Researchers have calculated how Japan and the wider world could change if global temperatures by the end of the 21st century rise by 2 degrees or 4 degrees Celsius above preindustrial levels. The projections examine how frequently torrential rain may occur, how far sea levels may rise and how much additional ice may disappear compared with conditions at the end of the 20th century.
Source: テレ東BIZ
