In the past, just as today, the bulk of carbon dioxide emissions came from just a few major polluters—large countries that were economically and industrially powerful.
The World Resources Institute has recently compiled information showing how countries' carbon emissions have changed since 1850. This is a big push back in time, says Slate. Previously, the WRI's database stretched back only to 1990. What the data reveals (and can be seen quite clearly on a pretty, animated map that Slate created) is that different major polluters came online at different times.
[A]t the beginning of this time period—1850—the United Kingdom was the top emitter of CO₂, with emissions nearly six times those of the country with the second-highest emissions, the United States. France, Germany, and Belgium completed the list of top five emitters. In 2011, China ranked as world’s largest emitter, followed by the United States, India, Russia, and Japan. Tellingly, while the United States was the world’s second-largest emitter in both years, its emissions in 2011 were 266 times greater than those in 1850.
Though at various times different countries have taken the top slot as chief carbon polluter, the overall global trend is up, up, up. According to Slate, in 1888—when the U.S. first took the top spot away from the U.K.—the total emissions coming from the entire country were the same as California alone emits today. (Granted, at 38 million people, California today isn't too much smaller than the U.S. of 1888, where 50 million people were spread across 38 states.)
There's a finite pool of carbon dioxide that can be added to the Earth's atmosphere before we push the climate into unprecedented and destabilizing territory. Though the carbon dioxide we emit does eventually get pulled back out of the air, by plants and bacteria and by dissolving into the ocean, to a large extent much of the carbon dioxide that we've emitted since the Industrial Revolution is still hanging around.
Looked at this way—if we wanted to be fair about it—countries' allotments to emit carbon dioxide in the modern era would be skewed by how heavily they contributed to the pool in the past.
In 2007, says WRI, the total emissions from developing nations first outpaced the emissions from industrialized countries. Though everyone on Earth needs to work together to combat the threats of global climate change, it's important to remember that some countries—by getting to the table first—may have used their slice of the pie already.