TOKYO -- As Prime Minister Yoshihide Suga declared recently that Japan will become carbon neutral by 2050, the country has begun to move toward effectively slashing carbon dioxide emissions to zero within the next three decades.
Japan will now expand the previous policy goal of an 80% cut by 2050. But, as one researcher familiar with scenarios for fighting climate change said, "Zero emissions are not an extension of an 80% reduction."
If Japan is to achieve the new 2050 target, revolutionary technological innovations and bold social changes will be crucial.
In order to keep average global temperatures below 1.5 C above preindustrial levels, major carbon dioxide-emitting countries must lower their emissions to effectively zero by the middle of this century.
The Japanese government had already pledged to the world to cut emissions 80% by 2050 and set a target of achieving a "decarbonized society" by "the earliest possible date in the second half of the 21st century."
Demonstrating his political initiative, Suga has brought the target forward without input from experts. In Japan, there are existing scenarios assuming an 80% reduction by 2050 but not many studies estimating a 100% cut -- zero emissions.
One study that does estimate a 100% cut is an analysis by a group of researchers including Ken Oshiro, an assistant professor at Kyoto University, and Shinichiro Fujimori, an associate professor at the same university.
The expansion of low-carbon power sources such as solar, thorough energy conservation and the promotion of demand for electric power sources make an 80% reduction within reach.
But the realization of zero emissions of greenhouse gases -- including those like methane -- "is not a simple extension of an 80% reduction," Oshiro said.
Even if Japan pushes ahead with thorough electrification and decarbonization of power sources, it cannot stop using fossil fuels completely at industrial plants and steel plants where high-temperature heat sources are essential.
Some thermal power plants also must be retained in order to adjust for fluctuating outputs from solar and wind power plants. To cope with these sources of carbon, technologies for the capture and storage of carbon dioxide will be crucial.
Japan will also have to think about using heat sources such as hydrogen, including that produced by using surplus electricity from renewables, and synthetic fuels made from hydrogen, such as methane and ammonia.
Negative emission technologies leading to reductions of carbon dioxide will be essential, including bioenergy with carbon capture and storage, a technique that generates electricity by burning biomass such as wood and then captures and stores the carbon dioxide emitted.
At the same time, "major social system changes are required on the energy demand side," such as reducing the movement of people by expanding remote work, Oshiro said.
In the zero-emissions scenario, it is important to replace existing facilities using heat, such as boilers at plants and household water heaters, at an early stage with ones leading toward decarbonization.
In the scenario compiled by Oshiro and fellow researchers, solar power and wind power account for about 56% and 21% of power sources, respectively.
Nuclear power accounts for about 10%. The scenario is based on the current Japanese government plan. It assumes that nuclear plants that can be brought back online will operate until their 60-year life expires and that replacements and expansions will not be considered.
Many nuclear plants now remain shut in Japan due to safety concerns in the wake of the 2011 Fukushima nuclear disaster.
The zero-emission scenario also does not take into consideration cross-border transactions of low-carbon fuels and electricity, such as producing hydrogen overseas and importing it.
Another group of researchers including Etsushi Kato, a senior researcher at the Institute of Applied Energy, a private think tank in Tokyo, extended the scenario for an 80% emissions reduction by 2050 and calculated a scenario for a 100% cut by 2070 under various conditions.
If per capita energy demand increases until 2050 amid relatively high economic growth -- 1.7% per year until 2030 and then about 0.55% until 2050 -- the path to zero emissions will not come into sight.
The path to zero emissions will come into sight only if Japan either curbs per capita energy demand while achieving relatively high economic growth or else if it limits growth to about 1% until 2030 and then to about 0.55% until 2050.
But in either case it will only be possible if negative emission technologies such as bioenergy with capture and storage and also direct air capture, which removes carbon dioxide from the atmosphere, are available.
As the costs of negative emissions, which are needed to achieve zero emissions, will fall on society as a whole, "it will be important to rush to develop efficient negative emission technologies and commercialize them at an early date," Kato said.
The Japanese government panel discussing growth strategy unveiled a "green growth strategy" in December to achieve its target of going carbon neutral by 2050. But it cannot be denied that the green growth strategy is tentative, as it has not been analyzed by experts.
The green growth strategy calls for renewable energy to account for between 50% and 60% of power sources in 2050 as a reference range for future discussions. But the analysis by Oshiro's research team calls for a much higher percentage.
A total of 92 so-called RE100 Japanese companies, which have declared their commitment to go 100% renewable, are calling for the government to revise its basic energy plan to raise the 2030 target to between 40% and 50%. The government’s current basic energy plan calls for boosting the percentage of renewable energy in power sources to between 22% and 24% by 2030. The plan is expected to be revised this year.
Discussions based on scientific analysis will be needed, including those about bringing forward the current 2030 target and quickly introducing negative emission technologies.