I don&#x27;t know.<p>This gets into a whole mess of considerations, and there&#x27;s not a lot of agreement.<p>There&#x27;s little doubt that there isn&#x27;t a gross surplus of solar energy incident on Earth&#x27;s surface.  But that surplus is, by orders of magnitude, fairly thin relative to present human energy demands.  By the time numerous factors are applied, you end up with infrastructure requirements which are truly prodigious.<p>I&#x27;m increasingly coming to the conclusion that the real lesson of <i>Limits to Growth</i> has largely been missed -- not <i>what</i> limits are, but <i>that</i> they exist, and even highly generous assumptions of abundance (or effluent absorption capabilities) are rapidly overwhelmed with even modest rates of growth. That is, the lesson is <i>humans must embrace limits.</i>  There&#x27;s considerable more math on how far in advance clear warning signs do or don&#x27;t exist, though fundamentally the principles are simple.<p>This turns the typical statement of sustainability on its head. The question isn&#x27;t &quot;how do we provide energy, food, and other resources for the people we see coming&quot;, but &quot;how many people can be supported, at what level of affluence, for what duration?&quot; It&#x27;s not energy supplies that are insufficient, it&#x27;s humans which are overabundant.<p>Answers to &quot;how many&quot; vary, though I&#x27;ve seen published values ranging from 50 million to 50 billion -- three orders of magnitude.  Someone&#x27;s off by a lot.<p>Going by history, the range of 50 million - 2 billion corresponds to human population from early prehistory to about 1920.  At the dawn of the Industrial Revolution, the value stood at about 500 million.<p>Levels at or above present populations would require a large number of complex problems be solved for a very long time.<p>The answer to your question may well be not that you&#x27;re wrong, but that you&#x27;re asking the wrong questions.<p>Put another way: there&#x27;s nothing inherent to the Universe (or even this small speck of it) which gives humans any right to existence or level of affluence.  Predicating reality on what we&#x27;d prefer is the definition of wishful thinking.