Look in the mirror

Global warming?  Maybe.

Climate change?  Probably.

Man-made?  More likely than not.

The United States as the largest contributor?  Depends.

Depends on what?  Depends on whether or not you consider the US CONSUMER as part of that contribution.  And NOT just considering what your daily fossil-fuel usage might be; heating, cooling, electricity, travel fuels. 

Consider first what device upon which you may be viewing this.  Consider how much energy it takes to locate, mine, process, and refine those milligrams of rare earth metals that are used in IT and every other phone, pad, laptop, computer, server, switch, and satellite needed to type and see this message.

Consider next how the country in which these resources are produced cares LITTLE about how it hurts our world's environment, and cares more about an economy strong enough to keep its peoples employed and fed.  Consider how NOT doing so would result in MILLIONS of its citizens revolting, showing the world another failed communist/socialist attempt at government.

The leaders and governments of both India and China are in NO position to have a concern about how an American consumer might need to dispose of another lithium-ion battery, how much arsenic there might be in the pigments that color that child's toy or drinking cup, or how many tons of pollutants are spewed into the atmosphere or oceans.  They need to provide their manufacturing firms the opportunity to provide just enough employment wages for a majority of their population to keep them housed and fed.  If the air everyone breathes or the water everyone drinks causes a deadly disease, so much the better; fewer people to worry about.

So, saying that the United States and its citizens are the largest contributors to climate change, you'll have to qualify that by asking how much "new" is enough.  We've raised generations on "disposable" to the point where anything that lasts longer than 10 years is TOO old-fashioned to be worthwhile. 

There's a reason that some of these items have lasted that long.  And very little of it has to do with heavy metals.