In his new paper, S. Matthew Liao proposes biomedical modifications to help humans consume less: 

[A] car uses more fuel per mile to carry a heavier person, more fabric is needed to clothe larger people, and heavier people wear out shoes, carpets and furniture at a quicker rate than lighter people, and so on.  And so size reduction could be one way to reduce a person's ecological footprint. For instance if you reduce the average U.S. height by just 15cm, you could reduce body mass by 21% for men and 25% for women, with a corresponding reduction in metabolic rates by some 15% to 18%, because less tissue means lower energy and nutrient needs.

Ronald Bailey finds that this isn't the first time the idea has been suggested. Steve Clark doesn't believe the proposal counts as "voluntary":

Unless the techniques that are being proposed are somehow made reversible then the children in question will have no choice in the matter. Their parents are deciding for them. As a society we do not give parents an unlimited right to make decisions on behalf of their children. 

Duncan Geere offers a critique to another of Liao's bioengineering suggestions, using hormones to make people more empathetic:

Hormone tweaking can have unintended side-effects, and a community that's more empathetic and altrustic could be taken advantage of by others who have less scruples. Liao's response to these criticisms? "These risks should be balanced against the risks associated with taking inadequate action to combat climate change. If behavioural and market solutions alone are not sufficient to mitigate the effects of climate change, then even if human engineering were riskier than these other solutions, we might still need to consider it."

Leo Hickman rounds up the paper's harsher critics:

Climate sceptics were the first to vent their anger. Somewhat inevitability, terms such as "eugenics", "Nazis" and "eco fascists" were quickly being bandied around. One sceptic blogger said that the "sick" Liao and his co-authors should be "kept in Guantanamo". Another said the paper "presages the death of science, and indeed the death of reason, in the West". But prominent environmentalists were also keen to denounce the paper. Bill McKibben tweeted that the paper contained the "worst climate change solutions of all time". Mark Lynas tweeted that he thought it was an "early April Fool". It was hard to disagree.