1. www.worldometers.info/world-population/.
2. https://www.statista.com/statistics/238610/projected-world-electricity-generation-by-energy-source/.
3. https://www.bp.com/content/dam/bp/en/corporate/pdf/energy-economics/statistical-review/bp-stats-review-2018-full-report.pdf.
4. Introduction;Letcher,2014
5. https://www.iea.org/etp/tracking2017/transportbiofuels.