What has been the greenhouse gas impact of shutting down Japanese nuclear power plants post-Fukushima?

Question

Japan shut down virtually all nuclear power plants after the March 11, 2011 earthquake, tsunami and nuclear power plant accident.

What has been the greenhouse gas impact of this decision? Have people merely consumed less power, or have other forms of electricity generation increased as a result? If the latter, have they been forms of electricity that have been more greenhouse gas intensive, or less greenhouse gas intensive, than nuclear power?

For the sake of simplicity, I'm asking only about Japan's decision, not about other countries that are phasing out nuclear post-Fukushima.

(As a pre-emptive reply to any criticisms: I acknowledge that nuclear power is not sustainable as it indirectly generates greenhouse gases, and there's a limited supply of nuclear material. Also, that electricity generation and electricity usage could well have changed without the shutdown of nuclear power plants)

Answer 1

Change in capacity

From 2004 to 2014, nuclear capacity did not change substantially:

Change in generation

However, the generation mix did change quite a bit (2014 nuclear data not available, so this chart ends in 2013):

Summary of data

Here's a summary of the data from 2011, along with the two years before and after:

                                2009    2010    2011    2012    2013
    CAPACITY (Million kW)                   
Fossil Fuels                    182     182     185     189     191
Nuclear                         47      47      44      44      42
Hydroelectricity                22      22      22      22      22
Non-Hydroelectric Renewables    7       8       9       11      18
TOTAL                           258     259     260     266     273
    GENERATION (Billion kWh)                    
Fossil Fuels                    616     685     795     863     862
Nuclear                         263     280     156     17      14
Hydroelectricity                76      81      82      75      77
Non-Hydroelectric Renewables    27      41      43      56      55
TOTAL                           982     1087    1076    1011    1008

Effect of Fukushima incident

In order to determine how much more greenhouse gases were emitted as a result of the move away from nuclear after the Fukushima incident, let's assume:

• Hydroelectric capacity is stable and not affected by the change
• Solar and wind capacity would have grown anyway, and maybe grew a bit faster than if the accident had not occurred, but is still such a small percentage that we can safely ignore it
• Therefore, nearly all generation shifted away from nuclear was replaced by fossil fuel generation

Prior to the incident, fossil fuels accounted for about 63% of generation, and nuclear was about 26%. After, these numbers shift to 86% and 1%. That means that 23% of the total annual production moved from nuclear to fossil fuel.

If for simplicity's sake we assume the annual consumption of Japan is 1 trillion kWh, this means that about 230 billion kWh's worth of fossil fuels were burned to produce electricity, that would not have been used if the Fukushima incident had not occurred.

Change in fuel sources

Prior to Fukushima, coal and natural gas each accounted for roughly 50% of primary fuels for electricity generation. Nearly all of the added generation after Fukushima came from natural gas (values are in metric tonnes of oil equivalent):

            2009    2010    2011    2012    2013
Coal        108     116     112     117     104
Natural gas 97      103     119     124     124
TOTAL       205     219     231     241     228

Note this data comes from "Annual primary fuel consumption," and thus includes more than just what is used for electricity production - some of the natural gas is likely used for heating, and some of the coal for steel production. However this shouldn't matter too much as we're most interested in the increase in consumption.

Net increase in GHG emissions

As @EnergyNumbers pointed out, it's really hard to give a definite answer to this question. I've made a whole series of assumptions here, and my numbers are rough as a result. But in the end, we could estimate that after Fukushima:

• An additional 230 billion kWh of electricity was produced using natural gas instead of nuclear energy
• Per kWh of electricity produced, about 0.55 kg of CO₂ is produced
• Thus, roughly 127 million metric tonnes of CO₂ was emitted that would have been avoided if Fukushima had not occurred
• This represents roughly 10% of Japan's total CO₂ emissions

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Sources:

• EIA International Energy Statistics
• How much carbon dioxide is produced per kilowatthour when generating electricity with fossil fuels?