The United Nations Paris agreement to stop dangerous global warming could cost $12.1 trillion over the next 25 years, according to calculations performed by environmental activists.

“The required expenditure averages about $484 billion a year over the period,” calculated Bloomberg New Energy Finance with the assistance of the environmentalist nonprofit Ceres.

That’s almost as much money the U.S. federal government spent on defense in 2015, according to 2015 spending numbers from the bipartisan Committee For Responsible Federal Budget. The required annual spending is almost 3.7 times more than the $131.57 billion China spent on its military in 2014.

Bloomberg’s estimates are likely low, as they exclude costly energy efficiency measures. The amount spent to meet global carbon dioxide emissions reduction goals could be as high as $16.5 trillion between now and 2030, when energy efficiency measures are included, according to projections from the International Energy Agency. To put these numbers in perspective, the U.S. government is just under $19 trillion in debt and only produced $17.4 trillion in gross domestic product in 2014.

American taxpayers spend an average of $39 billion a year financially supporting solar energy, according to a report by the Taxpayer Protection Alliance. The same report shows President Barack Obama’s 2009 stimulus package contained $51 billion in spending for green energy projects, including funding for failed solar energy companies such as Solyndra and Abound Solar.

[dcquiz] Solyndra was given a $535 million loan guarantee by the Obama administration before filing for bankruptcy in 2011. Abound Solar got a $400 million federal loan guarantee, but filed for bankruptcy in 2012 after making faulty panels that routinely caught fire.

Despite relatively high levels of taxpayer support, in 2014 solar and wind power accounted for only 0.4 and 4.4 percent of electricity generated in the U.S., respectively, according to the Energy Information Administration.

Ironically, solar and wind power have not done much to reduce America’s carbon dioxide emissions. Studies show solar power is responsible for one percent of the decline in U.S. carbon-dioxide emissions, while natural gas is responsible for almost 20 percent. For every ton of carbon dioxide cut by solar power, hydraulic fracturing for natural gas cut 13 tons.

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