## 3 The Important Questions Regarding Global Energy Futures
### How Much Primary Energy Will Be Used?  
In 2021, according to BP [21], commercial energy use totalled 595.2 EJ, an increase over the 2019 figure, after a drop in 2020 [21], with an estimated further 24 EJ [22] of traditional fuel, mainly burnt at low thermal efficiency in lower-income countries. This global commercial energy total consisted of 489.7 EJ of fossil fuels, 80.2 EJ of RE, and 25.3 EJ of nuclear power. Since the early 2000s, the various sources of RE have slowly gained share at the expense of FF and nuclear power, with solar and wind power showing the fastest growth rates [21]. Even so, all RE had only a 13.5% share of global commercial primary energy in 2021. For electrical energy only, RE produced 27.9% of total generation output in 2021: 15% hydro, and non-hydro 12.8%, up from 8.4% in 2017, with hydro roughly constant 2017-2021 [21].  
The latent energy demand in low-energy countries might suggest that demand will be much higher in future, and most energy scenarios for 2050 envisage most growth coming from nations outside the Organization for Economic Cooperation and Development (OECD), e.g., [21,29]. At present, primary use is broadly related to the country's GDP,  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Topic** & **Number of Papers** \\ \hline Climate change mitigation & 27 \\ Global environmental problems & 25 \\ Statistical data & 11 \\ Energy forecasts & 9 \\ Agriculture & 8 \\ Transport & 7 \\ Global equality & 6 \\ Miscellaneous & 6 \\ \hline
**Total** & **99** \\ \hline \hline \end{tabular}
\end{table}
Table 1: Breakdown of the 99 papers covered in this review.  
suggesting that if future global GDP could be predicted, then so could global energy use, but the unanticipated economic downturn caused by the COVID-19 pandemic showed the difficulties of even short-term economic forecasting.  
What do researchers interested in future energy use envisage for 2050 global energy consumption? For the eight energy-forecasting organisations listed in Section 2, the year 2050 global energy use extracted from their various scenarios covered the range 543-1140 EJ [34]. (Non-commercial fuel use was assumed to be negligible by 2050--nearly all energy used was seen as commercial.) The scenarios on which this range is based include some with optimistic controls on energy-related CO\({}_{2}\) emissions, together with others which are closer to 'business-as-usual' (b-a-u) conditions. However, [PERSON] et al. [35], after a careful analysis of global oil reserves and production, concluded that reserve figures given by both BP and the EIA were too high, and thus argued that the 'Stated Policies Scenario' (essentially, a b-a-u scenario) of the IEA [28] was not a feasible option.  
As an example of a very different forecasting approach, [PERSON] [36], using the logistic curve, estimated 2050 global primary to lie within the narrow range 639-758 EJ, with a central estimate of 704 EJ, which fits within the 543-1140 EJ range for energy organisation forecasts. Of course, the real figure could well lie outside this range, and the authors of this review argue that a 2050 primary energy value less than 543 EJ--perhaps much less--is needed for global sustainability. If most primary energy is from RE, then the exact figure depends on which energy accounting system is used [37]. None of the energy forecasts discussed above reflect the gravity of our predicament, focussed as they are solely on CC (or even only on CO\({}_{2}\) emissions).