For me Earth Overshoot Day was in the first seconds/minutes of January 1st not on 8th August. I provide a few of my reasons below.
Earth Overshoot Day is a measurement of the Ecological Footprint of all humanity calculated by considering all of the biological materials consumed and all of the carbon dioxide emissions generated.
Oil – 70% of current oil deposits are from the Mesozoic period, 65 million years to 150 million years ago. To replace the oil used until the Overshoot moment we need to sequester enough carbon material and wait circa 100 million years to make that consumed oil. However we are not really sequestering any carbon – most land space is covered by farming and no carbon material is left on the ground. The amount of oil we should use in 1 year to keep the status quo should be 1/100,000,000 of current reserves.
Coal – Takes circa 300 million years to form naturally so we should use only 1/300,000,000 of current coal reserves in a year. As Earth is not really sequestering any carbon material we are not beginning the process of forming new coal.
Iron – Most commonly used metal, circa 2 billion tonnes of raw ore are processed yearly. Lester Brown of the Worldwatch Institute has suggested iron ore could run out within 64 years based on an extrapolation of 2% growth per year. Iron ore was formed circa 1.8 billion years ago in environmental conditions vastly different to now – i.e. Earth is not making any noticeable quantities of new iron ore. It is not really possible to sustainably consume a finite resource.
CO2 Absorbtion – The Ecological Footprint takes into account CO2 absorption. From what I could find out it assumes the oceans are an endless CO2 sink and rising acidity is not an issue. To calculate how much CO2 can be sustainably emitted we need to look at how much the ocean can absorb without the aciditiy levels rising. As some other carbon sinks are now intermittently failing (e.g. Amazon) the calculation needs to take into account what levels of CO2 can be emitted without raising airborne CO2 or the acidity of the oceans.
If we were to take a target of 350ppm CO2 (safe level as per Mr. Hansen) in not too many years from now, then the real Overshoot calculation on CO2 should be how much we can emit, while bringing us to 350 CO2ppm in X number of years and allowing the oceans to return to an acidity level comfortable for it's current inhabitants. My finger in the air calculation tells me we overshoot in the first seconds of the year, or maybe we start in overshoot on the first second.