環境經濟學家表示，今年的8月20日為生態負債日。到了這一天，人類已消耗掉今年地球可再生自然資源的總量。
「生態負債日」的概念是國際環境智庫全球生態足跡網絡（Global Footprint）最先提出的發想，是以自然資源總量、人類的資源消耗量以及誰消耗哪些資源等生態足跡數據為基礎。根據這樣的計算，2013年截至8月20日，人類已經耗盡這一年地球可產生的自然資源，今年接下來的時間，自然資源將進入透支狀態。
全球生態足跡網絡指出，2001年以來，生態負債日每年都比前一年提早三天，每十年提早一個月。1993年的生態負債日是10月21日，2003年提早到9月22日，今年則是8月20日。
全球生態足跡網絡開發出「國家生態足跡帳戶」，提供人類對自然資源需求的完整數據。每個國家每年都會產生約6000個數據點的資料，以便追蹤比較232個國家、領土和地區的需求量，計算出地球的生物承載力能否達到需求。數據顯示，人類對可再生生態資源和服務的需求約等同於1.5個地球以上。到了本世紀中，人類的需求將增加到2個地球。但是1961年，人類的需求只要0.7個地球即可滿足。
「森林砍伐、魚種生存崩潰以及大氣層二氧化碳累積等種種跡象顯示，人類需求很可能超過地球生物圈吸收和再生的能力。」全球生態足跡網絡指出，「隨著全球經濟膨脹和高生活水準的要求，人類對自然系統的需求也快速成長。許多研究指出，地球的各種臨界值均已經被跨越，未來生物圈供養人類的能力也面臨風險。」
根據全球生態足跡網絡2013年的報告，中國的總生態足跡為全世界最大，因為中國是全世界人口總數最龐大的國家。中國的人均生態足跡雖然比歐洲和北美的國家小，但過去七年來也已超過了世界人均。全球生態足跡網絡指出，「如果人人都過得和典型的中國居民一樣，將要花掉1.2個地球才能供養全球人口。」其他國家的人均生態系統需求更高。如果人人都過得和美國居民一樣，將會消耗掉4個地球才能供養全球人口。按照卡達的生活方式，則是需要6.5個地球的資源。
目前的自然資源趨勢已經無法滿足地球70億人口。但卻有20億人無法取得滿足基本生活所需的資源。今日，超過80%的世界人口生活在資源消耗大於資源再生的國家。這些「生態債務國」消耗的資源比境內的資源要多，因此他們不是耗盡自己的生態資源，就是從別處取得生態資源。日本居民消耗的資源等於7.1個日本。義大利約需消耗4個義大利。埃及的消耗約為2.4個埃及。
全球生態足跡網絡解釋，生態負債日僅是估計值，而非確切日期，「我們不可能100%精確計算出生態預算耗盡的日期。」2011年生態負債日來得比2010年晚幾周，但這不代表人類的生態負債減少。負債日期的微調是根據精算方式而來，而非人類在生態足跡上的實際進步。
雖然不是所有的國家都「欠債」，但即便是巴西、印尼、瑞典等「生態債權國」的自然資源也在萎縮當中。全球生態足跡網絡指出，「我們不能讓自然資源和人類經濟、基礎建設和生活方式間的預算缺口越來越大。」
「我們仍有機會挽回局勢。只要生態債務人能減少對自然資源的依賴，而債權人透過經濟、政治和戰略保存其生態資產。與其清算自然資源，不如將自然資源視為財富的來源。」全球生態足跡網絡和夥伴們正和各種全球組織、各國政府和金融機構合作，協助他們做出符合生態現狀的決策。
Environmental economists have identified August 20 as “Earth Overshoot Day,” the day when humanity has consumed as much renewable natural resources as the planet can regenerate in one year.
Earth Overshoot Day is an initiative of the international sustainability think tank Global Footprint. According to Global Footprint’s calculations, today humanity’s demands exceed Earth’s carrying capacity – we are in the red for the rest of 2013.
Human demand for renewable ecological resources and the services they provide is now equivalent to that of more than 1.5 Earths.
The data shows that humanity is on track to require the resources of two planets before mid-century. But back in 1961, human demand was met by the resources of just 0.7 planets.
The calculation of Earth Overshoot Day is based on Ecological Footprint data, which measures how much nature there is, how much humans use, and who uses what.
The National Footprint Accounts, developed by Global Footprint Network, provide comprehensive data about humanity’s demand on nature. Based on approximately 6,000 data points per country per year, they track how this demand compares across 232 countries, territories, and regions, and how it relates to the planet’s biological capacity to meet these demands.
“Environmental changes such as deforestation, collapsing fisheries, and carbon dioxide accumulation in the atmosphere indicate that human demand is likely to be exceeding the regenerative and absorptive capacity of the biosphere,” says Global Footprint.
“As the demands upon natural systems rapidly increase due to the swelling global economy and the need to attain better standards of living, several studies suggest that many of the Earth’s thresholds are being exceeded and that, because of this, the biosphere’s future ability to provide for humanity is at risk,” Global Footprint warns.
Global Footprint data now suggests that since 2001, Earth Overshoot Day has come three days earlier each year.
Each decade, Earth Overshoot Day appears to have arrived one month earlier. In 1993, Earth Overshoot Day fell on October 21. In 2003, Overshoot Day was on September 22. This year, August 20 is Overshoot Day.
China’s total Ecological Footprint is the world’s largest because it is the world’s most populous nation, according to the 2013 Global Footprint report. China’s per capita Footprint is smaller than those of countries in Europe or North America, but for the past seven years it has exceeded what is available per person worldwide. “If everybody were to live like the typical resident of China, it would take 1.2 Earths to support the global population,” the think tank says.
Other countries’ per capita demands on the planet’s ecosystems are even higher. If everybody were to live like United States residents today, it would take four Earths to support the global population.
In Qatar, the typical resident requires the resources of six and a half Earths.
Current resource trends already cannot meet the needs of the planet’s seven billion population. About two billion people lack access to the resources required to meet their basic needs.
Today, more than 80 percent of the world’s population lives in countries that use more than their own ecosystems can renew. These “ecological debtor” countries either deplete their own ecological resources or get them from elsewhere.
Ecological debtors are using more than they have within their own borders. Japan’s residents consume the ecological resources of 7.1 Japans. It would take four Italys to support Italy. Egypt uses the ecological resources of 2.4 Egypts.
Not all countries demand more than their ecosystems can provide, but even the reserves of such “ecological creditors” like Brazil, Indonesia, and Sweden are shrinking over time, says Global Footprint.”We can no longer sustain a widening budget gap between what nature is able to provide and how much our infrastructure, economies and lifestyles require.”
“It is possible to turn the tide. Ecological debtors have an incentive to reduce their resource dependence, while creditors have the economic, political and strategic motive for preserving their ecological capital,” says Global Footprint Network. “Rather than liquidating resources, it is wiser to treat them as an ongoing source of wealth.”
In 2011, Earth Overshoot Day came a few weeks later than it did in 2010, but this does not mean humans reduced the global overshoot.
Earth Overshoot Day is an estimate, not an exact date, explains Global Footprint on its website. “It’s not possible to determine with 100 percent accuracy the day we bust our ecological budget. Adjustments of the date that we go into overshoot are due to revised calculations, not ecological advances on the part of humanity.”
Global Footprint Network and its partners are working with organizations, governments and financial institutions worldwide to help them make decisions aligned with ecological reality.
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