Nuclear fission produces radioactive fission products.
One ton of fissile material produces just less than a ton of fission products.
The tiny difference of mass turns into a great deal of energy.
By Einstein's mass-energy equation: E = M.c2
c is about three hundred thousand kilometers per second.
That's why the sun has lasted more than 4.5 thousand million years, pouring out energy. It is also the reason for all geothermal activity.
Methane is CH4
CH4 + 2O2 = CO2 +2H2O
16 tons of methane consume 64 tons of oxygen to produce 44 tons of carbon dioxide and 36 tons of water vapor.
The smelting of iron requires the removal of oxygen from the compound ferric oxide, which is derived from iron ore. The equation is
2 Fe2O3 + 3 C = 4 Fe + 3 CO2
So, using the atomic weights again, the production of 4x56 = 224 tons of iron involves, even if you use a solar-powered furnace (I don't think it's actually been done) the emission of 3x44 = 132 tons of carbon dioxide. This means that building a thousand large steel structures involves a considerable investment or debt of carbon dioxide.
As defined by the European Standard EN197.1,
Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates (3CaO.SiO2 and 2CaO.SiO2), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0. The magnesium content (MgO) shall not exceed 5.0% by mass.
Now the calcium oxide in the above paragraph is also known as quicklime, the 'live' form of lime which is used agriculturally after 'slaking' it with water. Calcium oxide is strongly rather than violently alkaline, and the slaking process produces calcium hydroxide, and quite a lot of heat.
Quicklime is produced by an ancient proces which involves heating calcium carbonate rocks, chiefly limestone or chalk, to drive off the carbon dioxide
CaCO3 = CaO + CO2.So to get 56 tons of calcium oxide for your cement, you start with 100 tons of limestone and release 44 tons of carbon dioxide, not counting the carbon dioxide cost of your furnace. So large concrete foundations for tall structures also involve a significant carbon dioxide debt.
The great physicist William Thomson, professor of physics at Glasgow University, did such impressive work in thermodynamics that he was raised to the peerage as Lord Kelvin. But when he endeavoured to estimate the age of the Earth, on the unimpeachable basis of how long it would take for such a mass of molten rock and iron to cool to its present temperature, he arrived at 40 to 100 million years. This is far too short to allow for the biologist's estimates for the evolution of mammals, or for the geologists to account for the remains of deep sea organisms (limestone) high in the Himalayan mountains. The current best estimate is 4500 million years. Kelvin did not know about radioactivity, or the astounding consequences of converting mass to energy. He was off by a factor roughly in the range 45 to 110. We know that the radioactive elements which provided this heat have decayed in quantity, and that volcanic and tectonic activity thousands of millions of years ago was probably somewhat more violent than it is today.