TOKYO -- Climate scientists unequivocally blamed human activity for the warming of the planet in a United Nations report released Monday, painting a bleak future of extreme weather, including worsening heat waves, floods and droughts.
The report by 234 scientists on the International Panel on Climate Change said humans have a brief window of opportunity to prevent the most catastrophic outcome. The world must make a coordinated effort now to limit the planet's average temperature rise to 1.5 C from pre-industrial levels, the report says. Warming of 1.5 C is considered the critical threshold above which the impact of warming will grow significantly.
Seita Emori and Masahiro Watanabe, two Japanese scientists who were among the 234 authors, spoke with Nikkei about the path forward.
Edited excerpts from their interviews follow.
Seita Emori, deputy director of the Earth System Division at the National Institute for Environmental Studies in Japan
Q: The report says the rise in the postindustrial revolution average global temperature will reach 1.5 C within 20 years. What needs to be done?
A: This time, we assessed the average temperature rise over the next 20 years more thoroughly based on five different climate response scenarios. It is clear that we will reach 1.5 C sooner than previously thought.
We should speed up preparations for damage resulting from the temperature rise. Building of costly infrastructure can be difficult due to budget constraints. But we should start with what we can do.
Q: The report used unequivocal language blaming humans for climate change. What's the reason behind this?
A: It is a result of an assessment based on multiple pieces of evidence, but the content is not that much different from previous reports. The report does not affect the goals set under the Paris accord and does not change what needs to be done.
At the same time, the science behind the report has become more accurate, making the document more convincing. I hope governments harden their resolve to pursue what they have promised to do.
Q: The report touched on the possibility of a 5-meter sea level rise, which is highly uncertain. What is your opinion?
A: Personally, the Fukushima Daiichi nuclear disaster in 2011 changed my thinking toward low-probability events. It is a scientist's responsibility to warn about an event, even if it's unlikely, if the impact is enormous.
Q: Interest in climate change is low in Japan. What can be done to change that?
A: Anti-climate change measures help raise the quality of life. But Japanese people tend to think of them as an added cost that brings down the quality of life. This is the opposite of the global trend. We need to change our message to change the public's awareness.
Masahiro Watanabe, professor at the University of Tokyo's Atmosphere and Ocean Research Institute
Q: The acceleration of global warming has raised concerns about extreme weather. What's your assessment?
A: The report concluded that extreme weather, like heat waves and torrential rain, has become more frequent. Right now, the global temperature has risen by 1 C from before the industrial revolution. The higher the rise, the higher the risk of extreme weather, the report says. The once-in-a-decade heat wave is occurring at a frequency 2.8 times that of the pre-industrial revolution era. If the temperature rises by 1.5 C, the frequency will rise by a factor of 4.1 and 5.6 if the temperature rises by 2 C.
East Asia has seen a clear impact of global warming. According to forecasts, if the global temperature rises by 2 C, Japan will experience 2.8 days of extremely hot weather. And if the temperature rises by 4 C, Japan will have 19 extremely hot days, up from the current 2.5 days.
Q: Will torrential rain become more frequent?
A: The report estimates that a 1 C rise increases precipitation from torrential rain by 7%. Japanese forecasts already show the frequency of torrential rain has increased by a factor of 1.7 from the late 20th century. But the frequency will increase by 2.6 times when the temperature rise is 2 C and 3.9 times if the rise is 4 C.
We need to assume extreme weather is a given. More frequent hot days will require us to change behavior to avoid a heat stroke. But individuals cannot respond to flooding. The government and localities will need to craft hazard maps and spell out rescue plans.
Q: Isn't it too late now to reduce global warming gases?
A: The report stressed that climate change caused by human activity is happening right now, not in a distant future. It is clear inaction will exacerbate the impact. Achieving carbon neutrality is indispensable to limiting the impact.
Even if we limit the temperature rise to less than 1.5 C as set by the Paris accord, rising sea levels cannot be prevented. We need long-term planning, like not building a town in areas threatened by rising seas.