The Tsunami tragedy triggered a series of events leading to today's announcement.
As far as excuses go, the near-meltdown of one of your larger nuclear power stations might seem a good way to get out of your international climate obligations.
Essentially, Japan appears to be saying “I’m sorry , my nuclear plant went belly up, so I won’t cut my emissions by 25%... I’ll increase them instead, by about 3% between 1990 and 2020".
The crisis at Fukushima in 2011 has, after all, been followed by a litany of mishaps: from alleged incompetence and repeated catastrophe for Japan’s nuclear industry to the multiple radioactive leaks at the site itself which has now seen its clean-up deadline extended until 2017.
It has seen a group of previously solidly pro-nuclear Prime Ministers (including the current leader's mentor) come out against current plans to re-start the country’s reactors, some of which - the FT suggests - are probably too old, or too close to the stricken plant to come back online anyway.
So far, so compelling an excuse, even if it is based in part on a plea of accident and incompetence. But though Fukushima is by no means irrelevant - there is a flaw in this reasoning.
Nuclear power in Japan prior to the Fukushima disaster accounted for only around 11% of its primary energy use (click for far more detail on this).
That means that even if Japan replaced its entire nuclear fleet with gas plants - rather than say investing in efficiency or renewables - it would not adequately explain the country’s about-turn on emissions.
Cut far greater than needed
An analysis (click for Excel) by @laurimyllyvirta for Energydesk suggests that flipping from a 25% reduction in emissions to a 3% rise implies putting the equivalent of 340 million tonnes of CO2 extra into the atmosphere each year.
To put that in perspective: the rise isn’t so far from the entire annual emissions of the coal intensive summit hosts - Poland.
But simply flipping nuclear for gas power would add less than a third of that amount to Japan’s emissions - equivalent to a much more modest change in the country’s ambition (a cut of about 17% instead of 25%).
And Japan isn’t simply flipping from nuclear to gas.
Not only has the country cut demand by around 15% at key times, it has also approved more new renewable capacity since 2012 than its entire installed base up until that point (a total of 26.7GW about six or seven nuclear reactors).
Furthermore it isn’t even planning on phasing out nuclear. Instead the government is actually hoping to reopen a number of its closed reactors in the next few years.
All of which means that however bad Fukushima has turned out to be for Japan and its nuclear industry, it is doesn't explain most of the change in their climate ambition.
Editor's update 16:30
To reflect a thoughtful comment(s) below:
The Japanese government may argue that their reduced ambition reflects the costs of dealing with the Fukushima situation, which leaves them short of cash for new low-carbon energy of any type -though other governments doubtless have their own reasons to plead austerity.
Japan has also switched partially to oil - which is more polluting than gas - instead of nuclear, so emissions have risen more. This is true and the analysis is, in that respect, indicative of a 'best case' switch to fossil fuels over the medium term - which I think is reasonable.
Japan has also abandoned plans to build new reactors, that could be set against the fact it has scaled up its renewables and efficiency ambitions and could do so further though by how much and over what timescale is subject to reasonable debate. This article doesn't analyse that.
Some argue (see below) that Japan's original commitment was not achievable - meaning that Fukushima simply added to an already existing need to change the commitment. Again that appears a technical issue of what is, or isn't, achievable - which isn't examined here.
Overall, the point of this analysis is that it appears hard to pin such a dramatic change in commitment only on the closure of the country's plants after Fukushima and that to focus exclusively on 11% of the country's primary energy demand seems odd in the context of such a significant change in commitment.
However, that is not to say that the closure of the country's reactors in the wake of the disaster did not have an impact on the country's emissions - that would be frankly odd.
PS. Energydesk is part of Greenpeace but operates independently from it and accepts comment from a variety of people and does not represent the Greenpeace view. If you want this please see the main Greenpeace website.