Energy and Human Ambitions on a Finite Planet, 2021a

Selected AnswersC
Numerical answers are given as ranges or other hints, meant to facilitate checking for gross departures
from the right track, without revealing the precise answer so that shortcuts are discouraged. Questions
for which the answer is already known (questions asking to verify an answer), easily validated in the
text, or that are a matter of original thought or opinion may not be included here.
The ranges sometimes may be annoyingly large, but think of them as guard rails to prevent a tragic
miscalculation or to catch a fundamental misunderst<strong>and</strong>ing of the underlying concepts. It can help
catch errors like dividing the wrong things or swapping numerator <strong>and</strong> denominator, or multiplying
when division is called for. In many cases, intuition, or guessing, might lead you already to similar
answers or ranges. With practice, students may be able to anticipate what they think are reasonable
ranges for answers. In fact, it is a great practice to think about expectations before working on the
problem.
This appendix, then, might be thought of as an “intuition implant” that simulates how problems are
for experts. Real life does not provide “answers at the back of the book,” so experts rely on experience,
intuition, <strong>and</strong> a sense for “reasonable” results to help them underst<strong>and</strong> when they’ve taken a wrong
turn. A successful use of this appendix would help train students to develop their own “common
sense” guard rails.
Chapter 1
4. Between 250 <strong>and</strong> 300 years
5. Between 250 <strong>and</strong> 300 years
6. Between 10 18 <strong>and</strong> 10 20
7. Between 100 <strong>and</strong> 150
8. More than 10 40
9. Between 5 <strong>and</strong> 500
10. Later than 23:50
11. Before 12:10 AM
12. Between 10 <strong>and</strong> 40 years
14. Between 75 <strong>and</strong> 100 years
15. Between 300 <strong>and</strong> 500 billion
16. It’s not 100 times longer
17. A few millennia
19. Between 50 <strong>and</strong> 100 W
20. A smidge higher then boiling
21. Between 200 <strong>and</strong> 250 K
22. Between 150 <strong>and</strong> 250 K
23. Between 100 <strong>and</strong> 275 K
Chapter 2
1. Nearly $100 billion
2. 4%: ∼$1 trillion; 5%: more than $100 trillion
4. On the low end of advanced countries
5. Between 25 <strong>and</strong> 100 MJ/$
6. Between 5% <strong>and</strong> 50%
7. The text had trading art, singing lessons,
therapy, <strong>and</strong> financial planning
8. Between 100 <strong>and</strong> 1,000; Less than 10 to go
9. Between 20 <strong>and</strong> 100 years