Concrete article – 2 things

The paragraph below is from this article from the University of California’s news center; 

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The manufacturing of Roman concrete also leaves a smaller carbon footprint than does its modern counterpart. The process for creating Portland cement, a key ingredient in modern concrete, requires fossil fuels to burn calcium carbonate (limestone) and clays at about 1,450 degrees Celsius (2,642 degrees Fahrenheit). Seven percent of global carbon dioxide emissions every year comes from this activity. The production of lime for Roman concrete, however, is much cleaner, requiring temperatures that are two-thirds of that required for making Portland cement.

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1. 7% of global CO2 emissions is a huge number; good little factoid but do they mean global human-produced CO2 or all the CO2 produced by everything?

2. Roman concrete only requires 2/3 the temperature of modern concrete; 2/3 of what? 2/3 of the absolute temperature, or the celsius (or fahrenheit) temp? I was taught that it’s wrong to talk about fractions of temperatures in the first place.

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