Yes, that's right: 50 years ago. Read it. It's amazing how much they knew back then, and how the basic concept hasn't change at all.
Was the article perfect? Not quite.
Quite accurate records of the amount of fossil fuel consumed in the world each year show that in the past 100 years man has added about 360 billion tons of carbon dioxide to the atmosphere. As a result the atmospheric concentration has increased by about 13 per cent. The carbon dioxide theory predicts that such an increase should raise the average temperature of the earth one degree F [0.6 deg C]. This is almost exactly the average increase recorded all over the world during the past century! If fuel consumption continues to increase at the present rate, we will have sent more than a trillion tons of carbon dioxide into the air by the year 2000. This should raise the earth's average temperature 3.6 degrees [2 degrees C].Instead of 2°C, the world warmed about 0.5 - 0.6 °C. It concludes:
We shall be able to test the carbon dioxide theory against other theories of climatic change quite conclusively during the next half-century. Since we now can measure the sun's energy output independent of the distorting influence of the atmosphere, we shall see whether the earth's temperature trend correlates with measured fluctuations in solar radiation. If volcanic dust is the more important factor, then we may observe the earth's temperature following fluctuations in the number of large volcanic eruptions. But if carbon dioxide is the most important factor, long-term temperature records will rise continuously as long as man consumes the earth's reserves of fossil fuels.