The world has slid into "ecological debt", having used up all the natural resources the planet can provide this year, according to the New Economics Foundation.
The think-tank said humans were using up resources such as forests and fisheries faster than they can be regenerated and producing more waste, mainly carbon dioxide, than the planet can absorb.
As a result, we have been increasingly "overshooting" nature's budget each year since the 1980s, NEF said.
Tuesday marks the date when we have exceeded the natural resources the planet can provide for this year - a day which has been creeping steadily earlier each year.
From now until the end of the year, humanity is "dipping into our ecological reserves, borrowing from the future," according to Dr Mathis Wackernagel, executive director of the Global Footprint Network.
Each year, the network calculates humanity's ecological footprint - the demands it puts on the planet - and compares it to the capacity of the Earth's ecosystems to generate resources and absorb waste.
Human beings are currently using up the capacity of 1.4 planets, and consumption is increasing.
Last year, Ecological Debt Day, formulated by NEF based on data from the Global Footprint Network, was October 6 - although new data has been taken into account this year including emissions from slash and burn agriculture and biofuels.
Incorporating the new data into last year's calculations would have put Ecological Debt Day 2007 on September 28, showing human consumption is still on the rise, NEF said.
According to the foundation, the failure to live within our ecological means is the root of many of the most pressing environmental concerns, including climate change, collapsing fisheries, declining biodiversity and factors contributing to the current food crisis.
