As he welcomed Brazil's Foreign Minister Aloysio Nunes to Washington, Tillerson boasted that the US has a "terrific record" in reducing the emissions blamed for global warming.
But, in a nod to concerns that US global leadership has been damaged by the decision to quit the Paris deal, he urged partners "to keep it in perspective."
Reports suggest Tillerson was one of the advisors who counselled President Donald Trump not to pull Washington from the accord, fearing a blow to US influence abroad.
But if that was the case, the former oil executive put a brave face on the decision, which has seen Europe and China pull together to renew their support for the 2015 agreement.
"That was a policy decision," Tillerson told reporters.
"I think it's important that everyone recognizes that the United States has a terrific record of reducing our own greenhouse gas emissions.
"It's something I think that we can be proud of, and that was done in the absence of the Paris agreement.
"I don't think we're going to change our ongoing efforts to reduce those emissions in the future either, so hopefully people can keep it in perspective."
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