The rough and ready consensus among climate scientists is that if we want to prevent global temperatures from rising more than 2 degrees C above pre-industrial levels and avoid drastic climate change, the world will have to cut greenhouse-gas emissions 50 percent or more by 2050. And what, exactly, will that require? The International Energy Agency just released a new report today laying it all out:

Among the International Energy Agency’s chief messages is that current policies are unsustainable with carbon dioxide emissions expected to rise 130 percent and demand for oil expected to rise 70 percent by 2050. [IEA Executive Director Nobuo] Tanaka warned that oil demand could be five times the current production of Saudi Arabia by that time. ...

The agency also mapped out a second situation aimed at bringing emissions to half their current levels by mid-century by emphasizing technologies and strategies for "weaning the world off oil." The agency estimated the cost of that process at $45 trillion, or 1.1 percent of annual global output, over the period to 2050. Investments of $100 billion to $200 billion would be needed each year over the next 10 years, rising to $1 trillion to $2 trillion each year in the coming decades.

Yes, those are staggering sums, but they're hardly unaffordable—$100 to $200 billion per year is, after all, cheaper than your average ill-advised war in the Middle East. And, as the report makes clear, our current oil-dependent course is totally unsustainable. The logistics, though, do sound daunting: A 50 percent cut in global emissions would entail building 17,000 wind turbines and 32 new nuclear power plants each year, along with achieving an eight-fold reduction in carbon intensity for the transportation sector. Oh, and every year we'd have to outfit 50 coal and gas plants with (not-yet-viable) technology to sequester their carbon emissions. That said, the IEA seems to believe this is all very much "both necessary and achievable," so long as the world gets started, like, yesterday. Er... which is not quite where Congress is at.

--Bradford Plumer