[2] He is the Cyrus Fogg Brackett[3] Professor of Physics, emeritus, at Princeton University,[2] and a long-term member of the JASON advisory group,[1] where he pioneered the development of adaptive optics.

In 2018, Donald Trump appointed him to the National Security Council to counter evidence linking carbon dioxide emissions to global warming.

[2] He is credited with a key insight in 1982 that made adaptive optics possible: there is a layer of sodium in the mesosphere, at around 90 to 100 km of elevation, which could be lit by a laser beam to make an artificial guide star.

[16] Michael Oppenheimer, co-founder of the Climate Action Network, said that Happer’s claims are "simply not true" and that the preponderance of evidence and majority of expert opinion points to a strong anthropogenic influence on rising global temperatures.

[18] A petition that he coauthored to change the official position of the American Physical Society to a version that raised doubts about global warming was overwhelmingly rejected by the APS Council.

Posing as consultants for a Middle Eastern oil and gas company, they asked Happer to write a report touting the benefits of rising carbon emissions.

Happer declined a fee for his work, calling it a "labor of love", but said that they could donate to the "objective evidence" climate-change organization CO2 Coalition, which suggested that he contact the Donors Trust to keep the source of the funds secret as requested by the Greenpeace sting operation.

[23] In an interview, Happer responded to the sting operation: "I was only interested in helping the 'client' to publicize my long-held views, not to peddle whatever message the 'client' had in mind ...

[25] Hannah Devlin of The Guardian wrote that Happer "supports a controversial crackdown on the freedom of federal agency scientists to speak out about their findings, arguing that mixed messages... have led to people disregarding all public health information.

[26] He resigned from the Council in September 2019, reportedly because his plan to review climate science did not receive sufficient support from the White House.