We enjoyed reading “Nuclear Nemesis” and thank Professor Ali for reading and engaging with our work. His blogpost nicely broadens the discussion of nuclear power and branches out to explore numerous speculative but nevertheless interesting themes. Rather than focus on the entire post, we do have some very specific but important corrections to make concerning the points advanced in his blogpost that are most directed at our own study.

First, although the strap-line for Professor Ali’s blogpost highlights general questions of the “virtue or vice” of nuclear power, he then actually pushes these broader questions aside to focus more exclusively on climate change alone. The focus of our own article is very explicitly on this point, but it is (as we point out), only one among a series of challenges – for instance in relation to sustainability goals around land degradation, water quality, atmospheric pollution, safety risks and other even more climate-related difficulties like sensitivities to rising temperatures and sea-levels.

Given the initial general scope of Professor Ali’s post, his discussion might have been expected also to address these issues. It is in many of these kinds of way, that we point out that, although a nuclear “stabilization wedge” may look positive in climate terms alone, it’s potential is severely limited compared to energy efficiency and renewable energy which perform manifestly better in many of the above terms. As we also discuss in our own paper, this point is amplified by the clearly slower and more costly nature of nuclear climate change mitigation measures, which threaten to crowd out other more effective options. As highlighted in our paper, these issues apply especially in developing country settings.

Second, as gratified as we were to read that Professor Ali holds “immense respect for the intellectual integrity” of our research, we do challenge the notion that our “invested analytics could have been better channeled towards evaluating prospective nuclear technologies rather than a reflexive and asymmetric regression.” In fact, it is consideration of prospective approaches that actually underscores a key reason for recognizing the complementary value of our own retrospective analysis.

One key problem often diagnosed in debates around nuclear power and its various alternatives are the persistent pressures disproportionately to address nuclear power in ways that are far too prospective – in what Professor John Byrne calls the “future tense”. At the present time of crisis for existing nuclear designs, this is the case, for instance with the present shift of attention to untested new kinds of future “small modular reactor”. There is a general tendency across the board (with all options), for prospective analysis to display “appraisal optimism.” But this has arguably proven to be especially pronounced in the nuclear field.  Despite this, assessments of competing options like offshore wind power, have in recent years, by contrast,  actually often proven systematically pessimistic. Either way, to compare a prospective pictures of SMRs with retrospective pictures of renewables presents a clear risk of bias.

Without denigrating the value of prospective analysis as part of the debate, what our own analysis sought to do is address a conspicuous gap. It is as we note (but on which Professor Ali does not comment) remarkable that the relatively simple question has for so long lain unanswered, as to whether any empirical basis can be discerned for claims that nuclear investments associate with reduced carbon emissions – and how the scale of this might compare with similar associations in respect of renewables. There is no necessity to claim this query to be singularly decisive (nor is this argued in our article), in order to appreciate that it is relevant. It is in this light, that it is odd (given the frequency of the claims). that our analysis should be the first to clearly directly address this question.

Furthermore, there arises another argument for retrospective analysis beyond the historical tendency of prospective claims around nuclear to be so consistently seriously over-optimistic. This lies in the fact that analysis of past performance is especially useful as a complement and source of validation for prospective analysis. Although retrospective analysis like our own is indeed (as we acknowledge) subject to ambiguities over causal relations, this offers a way to compensate for true vulnerability of prospective analysis to extreme sensitivity to analytic bias. Each approach has its shortcomings. The two together are stronger than either alone. But this means retrospective analyses like ours must at least be done.

So, the challenge here is (of course) not (as Professor Ali implies) one of choosing in a zero-sum way between two mutually exclusive analytical options. It is rather a question of combining mutually complementary kinds of analysis. With both prospective and retrospective research offering value, our own focus on the latter is doubly justified by the fact that this kind of work has remained so surprisingly neglected. Given this value of triangulating contrasting forms of analysis in a complex policy field like this (each with their upsides and downsides), it would be odd indeed to say that there is no place for retrospective empirical work. It is strange that Professor Ali should suggest so.

A third and final issue is that we respectfully disagree with Profess Ali’s notion that our “regression analysis” is “not well-suited to the core societal question at hand”. We question his claim that “the correlations are based on asymmetric units of comparison (given that only 31 countries are nuclear power producers while the full sample of countries with renewable portfolios is 123 in their data set).”

We sought to test whether national attachments respectively to nuclear power or renewable energy can be seen to associate with evident mitigation of emissions. We did test for these associations in four samples (i.e. nuclear countries and renewable countries in two timeframes each). Given this, doing a regression analysis between variables of nuclear and renewable energy supply and carbon emissions is both logical and sensible, as the regression analysis is one of the most common and potent statistical procedures that even made the transition to modern machine learning techniques.

Furthermore, if it is apt at all, it is very unusual in statistics to use the word “asymmetric” with respect to correlations. If the fact that the samples have different sizes is regarded as a potential reason of concern, then let us again state clearly that by all rules of statistics, this is already taken care of (and evaluated correctly) by the indicated presence or absence of statistical significance. This is how we deal with this issue in our own analysis.

Ultimately, we agree with Professor Ali (as in our own blogpost that he cites) that “the global energy transition will require us to resist positional temptations and be willing to embrace revisionism”. But this must not blind us where it becomes very clear that one option displays very real downsides compared to others. Analysis that simply tries to maintain a “middle of the road” position between different alternatives, will become irrationally biased if one of these alternatives grows manifestly less favorable under any view.

The importance of the climate change imperative makes it vital to avoid “do everything” rhetorics that simply reflect entrenched special interests in this field. If policymaking is thus pressurized into pursuing decarbonization pathways that are slower, less effective, more costly, and more risky than diverse forms of energy efficiency and renewable energy, then the result may not only be irrational, but catastrophic.