If economic development continues apace, in 2050 human carbon emissions will amount to around 15 billion tons per year.
Natural sources will still contribute around 200 billion tons, though. So a whopping 7.5% of annual carbon emissions will be due to human sources! That's more than double the current level of around 3%.
The world will overheat and everything will die, and Earth will turn into Venus!
No, it won't.
Until hurricane season actually arrived, climatologists were warning that we were heading into a record hurricane season, that we were going to see more and more hurricanes like Katrina! This hurricane season was going to be thick with super-hurricanes--why, we're going to have to add category six to handle these new super-hurricanes, and it's all because of man-made global warming!
(...Katrina was not all that strong, and the only reason it did as much damage as it did was because New Orleans is below sea level....)
And of course now that hurricane season is here, and that so far--on the very verge of October--there have been no serious hurricanes, no one in the media is asking the climatologists why they were so damned wrong about the severity of this year's hurricane season.
In fact, they are never asked tough questions like that. No one in the mainstream media ever asks, "Hey, you were predicting an ice age in the late 1970s--what happened to that?" More detailed and complex questions never come up, either, such as, "Your computer simulation models the effects of increased CO2 on the global environment, but how do you control for such forcings as incident solar radiation? Does your model also deal with methane and water vapor, which are both present in much higher concentrations in the atmosphere, and are more potent to boot?"
OH, that's right. The global warming community has spoken. The sun doesn't matter! That's right, the sun has nothing to do with increased global temperatures. It has output variability cycles which have been observed for over a century, including the "Maunder Minimum" which has a definite causal link to the "Little Ice Age", but--nope!--a recent study has "proven" that the sun has nothing to do with global warming. So we can forget the one about "solar forcings".
Strange, though, that Mars is experiencing global warming at about the same rate as the Earth. Guess the Martians that NASA never found are also driving too many SUVs.