How the Date of Earth Overshoot Day 2021 Was Calculated

Earth Overshoot Day marks the date when humanity’s demand for ecological resources and services in a given year exceeds what Earth can regenerate in that year. To determine the date of Earth Overshoot Day, Global Footprint Network calculates the number of days that Earth’s biocapacity can provide for humanity’s Ecological Footprint, as explained on this page. The methodology relies on the latest edition of the National Footprint and Biocapacity Accounts, which unavoidably presents a “time gap” with the present time due to United Nations’ reporting procedures.

To address this “gap” and determine Earth Overshoot Day for the current year, Global Footprint Network establishes trendlines from the National Footprint and Biocapacity Accounts data and extends those trendlines to the present year. Where possible, more recent data from reputable sources (Global Carbon Project, International Energy Agency (IEA), etc.) are incorporated to strengthen the assessment for the “gap” years.

Changes in carbon emissions and forest biocapacity from January 1^st to Earth Overshoot Day 2021 were evaluated. The research team concluded a 4.6% increase in the global Ecological Footprint compared to 2020. As reported by IEA, the global pandemic induced lockdowns caused an initial sharp drop on CO2 emissions in 2020. However, emissions increased again during the second half 2020. At the end of the year, total emissions were reported to be 5.8% lower than 2019 emissions due to the global pandemic. Combined with the most recent data from the Global Carbon Project, we estimate a 6.6% increase in the carbon Footprint for 2021 compared to the year prior. The second notable change was the effect of Amazon deforestation and degradation on global forest biocapacity. The research team estimates a 0.5% decrease in global forest biocapacity.

The downloadable research report documents these drivers. The result of all data extrapolations and analyzed factors concluded that Earth Overshoot Day 2021 lands on July 29.