from your linked article: Some elements of the accord would be voluntary, while others would be legally binding. That hybrid structure was specifically intende

from your linked article: Some elements of the accord would be voluntary, while others would be legally binding. That hybrid structure was specifically intended to ensure the support of the United States: An accord that would have required legally binding targets for emissions reductions would be legally interpreted as a new treaty, and thus would be required to go before the Senate for ratification. But that proposal would be dead on arrival in the Republican-controlled Senate, where many members question the established science of climate change, and nearly all hope to thwart President Obama’s climate change agenda.