Because the energy transition has not yet been sufficient to reduce annual carbon emissions.
From Our World in Data, here's annual total CO2 emissions, by world region:
Since the 1960s, growth in low-carbon energy sources has only grown from about 6% to about 16% (source)-- not enough to make a dent, given that total energy use has grown faster than that.
What oxygen shortage?
Earth's atmosphere contains 20.9 percent oxygen. There's a lot of oxygen in the atmosphere and its depletion rate from burning fossil fuels has been small. Humans have been burning fossil fuels on an industrial scale for a long time: coal fired power stations, internal combustion engines in cars, trucks, train locomotives, aircraft and ...
The first coal deposits were laid during the Carboniferous period, between 358.9 million years ago and 298.9 million years ago.
Within this period, the early Mississippian period from 358.9 to 346.7 Mya, was when the first coal deposits were being laid. During this period, coal was being laid in what is now eastern North America, specifically the Kentucky ...
Depending on your definition of "major", here are a few things I could think of that affect our "Goldilocks" temperature that humans are so fond of.
the magnetic field
distance from the sun
the greenhouse effect:
infrared radiation from atmosphere
infrared absorption by the atmosphere from Earth/atmosphere.
Atmospheric oxygen levels have in fact been declining. Current estimates indicate that the level is decreasing at a rate of approximately 19 parts per million per year. This would mean that it would take approximately 500 years, at current rates of consumption, for the the oxygen concentration of the atmosphere to decrease by 1% relative to its current ...
When you say produced, do you mean chemically made from another substance, or you do mean released into the atmosphere, or do you mean captured and stored?
Methane, or CH4, is a biogas as it is gas biologically created by organisms. Methane is created in natural processes from which it may be immediately released into the atmosphere or on much slower time ...
As Jean-Marie Prival commented, methane is the biogas (after removing impurites such as $H_2S$ and $CO_2$).
Biogas is renewable because "From a carbon perspective, as much carbon dioxide is absorbed from the atmosphere in the growth of the primary bio-resource as is released, when the material is ultimately converted to energy."