Historical data show that if a country wishes to cut its CO2 emissions by a meaningful amount it has two options that can be guaranteed to work – expand nuclear or reduce energy consumption. There are as yet no clear instances of a country achieving significant CO2 reductions by expanding intermittent renewable energy.
In this post I use CO2 emissions and other data from BP for the period 1965-2014 to identify cases where a country or a group of countries’ CO2 emissions have decreased by at least 20% over a decade or two and to identify the cause of the decrease. (Note that the BP data include only CO2 emissions from consumption of oil, gas and coal.) It follows on from Euan Mearn’s recent post “CO2 Emissions Reduction, Renewables and Recession”.
Emissions Reduction Option 1 – Expand nuclear:
Of the many countries that have built nuclear plants only France and arguably Sweden have built enough to make a serious dent in their CO2 emissions. Nevertheless they serve as examples of what nuclear does. Figure 1 plots emissions versus the percentage of nuclear energy in France’s total energy consumption since 1965:
Figure 1: CO2 emissions (red, left scale), percent nuclear in the generation mix and carbon intensity (blue & orange, right scale), France
A complicating factor in attributing emissions reductions to nuclear is that most countries started to expand nuclear generation around the time of the 1973/4 and 1979/80 “oil shocks”, which also tended to reduce emissions, although for economic reasons. To Figure 1 I have therefore added a line (orange, plotted inverted) showing the tons of CO2 emitted per ton of oil equivalent consumed in generating electricity, which is a measure of carbon intensity (values were calculated by dividing CO2 emissions by total energy consumption). The close match between this line and the percentage of nuclear in France’s generation mix shows that the expansion of nuclear has roughly halved France’s carbon intensity since 1970 and that nuclear was indeed the dominant contributor to the ~25% reduction in France’s emissions between the late 1970s and the late 1980s.
Sweden also achieved a 25-30% CO2 emissions reduction over roughly the same period (Figure 2). Here the relationship between the reduction and nuclear expansion is less obvious, but nuclear probably made a significant contribution:
Figure 2: CO2 emissions (red, left scale), percent nuclear in the generation mix and carbon intensity (blue & orange, right scale), Sweden
Emissions Reduction Option 2 – Reduce Energy Consumption
Nuclear expansions can be planned, but reductions in energy consumption have historically been caused by unplanned economic downturns. Probably the best example is the economic collapse of the Soviet Union in the early 1990s, which led to a ~25% decrease in energy consumption and a ~40% decrease in CO2 emissions in the East Bloc countries by the late 1990s:
Figure 3: CO2 emissions and total energy consumption, Soviet Union & Former Soviet Union
A more recent example is provided by the PIIGS countries (Portugal, Ireland, Italy, Greece and Spain), which between 2007 and 2014 reduced their combined energy consumption by about 15%, or more correctly had it reduced for them by a combination of indebtedness and the 2008/9 global recession. This reduction in energy consumption was accompanied by a ~30% drop in combined CO2 emissions:
Figure 4: CO2 emissions and energy consumption, “PIIGS” countries
Most European countries have in fact recorded emissions reductions that coincide with reductions in total energy consumption in recent years (the only countries outside Europe that have are the US and Japan, but the reductions here are minor). The question is whether these reductions were caused by reduced energy consumption or by increased renewables generation, or maybe by a combination of both. Performing a country-by-country evaluation was not possible, so I short-circuited the process by constructing two XY plots with all the European countries lumped together.
Figure 5 compares the decrease in emissions, measured as the difference between 2014 and the highest emissions year going back to 2004, against the decrease in total energy consumption over the same period. The two are quite strongly correlated (R squared = 0.65, increasing to 0.77 when Portugal is discarded. Note also how a 10% reduction in consumption generates a ~16% reduction in emissions, indicating that some kind of amplification mechanism is in operation, although it’s not clear how it works. This effect is also seen in Figures 3 and 4):
Figure 5: Percent reduction in total energy consumption versus percent reduction in CO2 emissions, 22 European countries
Figure 6 now compares the emissions reductions shown in Figure 5 against the increase in the percentage of renewable energy (excluding hydro) in the generation mix. This plot is similar to the one Euan Mearns presented in the first Figure of his recent post and like Euan’s plot it also shows no correlation (R squared = 0.00):
Figure 6: Increase in percentage of renewables in energy mix versus percent reduction in CO2 emissions, 19 European countries (Bulgaria, Romania and Slovakia not plotted owing to incomplete data)
These results create at least a strong presumption that the recent CO2 emissions reductions in Europe were dominantly a result of reductions in energy consumption caused by the 2008/9 global recession and the European debt crisis, and that renewables made no significant contribution. This is potentially bad news for renewables aficionados and also for Europe as a whole, because it suggests that the only way Europe can make further dents in its CO2 emissions is by further collapsing its economy.
There is. however, one country that claims to have reduced its energy consumption by other means – Denmark (Figure 7). Since 2006 Denmark has reduced its total energy consumption by 20%, and once again the reduction looks much like a response to the 2008/9 global recession:
Figure 7: CO2 emissions and energy consumption, Denmark
The Danish Energy Agency, however, attributes it to taxation:
Energy taxes on electricity and oil were introduced in Denmark in 1977. Since then the taxes have been increased several times and taxes have also been put on coal and natural gas. In 1992 the taxes were supplemented by CO2 taxes. The exact impacts of the energy taxes on Danish energy consumption cannot be measured, but there is no doubt that the taxes have had a big impact on energy consumption.
Although it doesn’t help much if the DEA is correct. Punitive taxation is just another form of economic hardship.
A final question is how much of the 34% reduction in Denmark’s CO2 emissions since 2006 can be attributed to its expansion of wind capacity over this period. By assuming zero emissions for wind and plugging in the Volcker-Quaschning kgCO2/kWh estimates for oil, gas and coal to the BP annual energy-by-source data I came up with an estimate of 17%, or half of it. This estimate must, however, be taken with a grain of salt. Denmark is able to generate as much wind power as it does only because it can export its surpluses to Scandinavian reservoirs via the Nordic grid. Denmark also assumes that most if not all of its wind generation is consumed domestically while in fact maybe as little as half of it is.
Summary of Findings
This brief review of historical data teaches us the following:
1. Any country that wishes to do so can make substantial cuts in its CO2 emissions by replacing its fossil-fuel generation with nuclear generation. Another advantage of “going nuclear” is that development can be planned in advance to meet a specific emissions target. The danger is that another sudden burst of anti-nuclear hysteria could bring the program to a halt at any time. Public and governmental attitudes towards nuclear have not been completely rational in recent years.
2. Substantial cuts in emissions can also be made by reducing energy demand. However, the reductions that have so far occurred have been dominantly a product of varying degrees of economic collapse, and while many governments pontificate about the urgent need to save the planet from global warming none of them are presently prepared to collapse their economies to save it.
3. With the arguable exception of Denmark no country has yet succeeded in significantly reducing its emissions by expanding intermittent renewable energy generation, and neither history nor Denmark (which is a special case) gives us any guidance on how intermittent renewable energy might be expanded to the point where it does achieve signficant emissions reductions. But previous Energy Matters posts here, here, here and here suggest that it can be done by keeping enough load-following capacity to fill demand when the wind doesn’t blow and/or the sun doesn’t shine. The problem with this option is that the generation system becomes progressively more inefficient and more costly as more renewable capacity is added until eventually a point is reached where it threatens to bring on economic collapse all by itself.
In summary, history brings us back to square one. Barring major and presently unforeseen advances in technology the only practicable option for reducing CO2 emissions is nuclear.