&gt; What exactly about this is possible?<p><a href="http:&#x2F;&#x2F;www.lowtechmagazine.com&#x2F;2007&#x2F;06&#x2F;green-slow-air.html" rel="nofollow">http:&#x2F;&#x2F;www.lowtechmagazine.com&#x2F;2007&#x2F;06&#x2F;green-slow-air.html</a><p>Long-term, helium looks to have issues though, especially if we slow down natural gas mining.  Perhaps we could find a tenable balance between helium and hot air.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Thermal_airship" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Thermal_airship</a>