Ecological Overshoot; Three Scenarios

Scenarios are "What if" explorations to understand the consequences of choosing a deadline to eliminate global ecological overshoot. 

What is overshoot?

In simple terms, Overshoot is the shortfall in earth's biological capacity to meet the consumption demands of all humanity.

SCENARIO #1 Business-as-usual

Demand grows faster than supply

By 2050 accumulated ecological debt may be irreversible

Business-as-usual scenario and ecological debt

Using several moderate United Nations projections, this scenario assumes:

  1. On the demand side: modest rates of growth for both population and demand for biocapacity

  2. On the supply side: Initially, biocapacity will continue increasing at the same rate as in the past 40 years. Later, continued overshoot would impact productive ecosystems and biocapacity gains will reverse.

As per this scenario, business-as-usual would lead to an increase in an average person's ecological footprint from 2.2 global hectares in 2003 to 2.6 global hectares per person in 2050.  The major contributors:

  • Ecological Footprint of cropland and CO 2 would increase by 60%
  • Demand for grazing land and fishing grounds by 85%
  • Forest use would rise by 110%

The resulting ecological deficit per year would add up to 34 years of planet's entire biologicial productivity by 2050.  What this means could be gauged by some contextual indicators.

A mature forest contains 50 years' worth of  productivity. Theoretically speaking, a forest could be harvested for 50 years before standing stocks are completely exhausted. However, in practice, overharvesting of a forest may prevent a forest from maintaining itself, resulting in ecological degradation and collapse long before the entire standing stock is harvested.

Compared to forests, other ecosystems like cropland, grazing land and fisheries, have considerably lower standing stocks. Therefore, the tolerance levels of these ecosystems would be much lower than the forests.

It is therefore clear that business-as-usual is unsustainable and this would result in an irreversible damage to earth's biological productivity.

SCENARIO #2 Slow-shift

Gradual effort to come out of overshoot by 2100

Accumulated ecological debt eliminated by 2080, a modest 10% biocapacity buffer by the end of the century

Slow-shift and ecological debt

This scenario assumes that on the demand side:

Humanity's ecological footprint can be reduced by 15% from 2.2 global hectares in 2003 to 1.5 global hectares in 2100, if the following can be achieved

    • Global CO 2 emissions down by 50%
    • Fishing harvests down by 50%
    • Demand on cropland and grazing land to increase at half the rate of population growth
    • Forest products consumption to rise by 50%

This would result in an elimination of overshoot by 2080 and a modest 10% biocapacity buffer which could be used by the wild species.

CO 2 reduction is the key

The largest component of the 2003 Ecological Footprint was the CO 2 emissions from burning fossil fuels. Many geologists expect that oil production will peak in the next 2 to 3 decades. Without stringent control this could result in sharp rise in emissions by the end of the century.

Very strong measures are required to achieve the 50% reduction required in this slow-shift scenario. There are no easy solutions. The main forms of renewable energy in use today - hydropower, wind power, and biomass - all reduce CO 2 emissions when substituted for fossil fuels but increase demand on land. Moreover, even a 50-fold increase in wind-power and 700-fold increase in use of solar power would only restrict the emissions to the current levels.

The challenge is to increase energy supply while reducing CO 2 emissions without shifting the burden to other parts of the biosphere.

SCENARIO #3 Rapid-reduction

Aggressive efforts to move out of overshoot by 2050

Accumulated ecological debt eliminated by 2040, 30% biocapacity buffer by end of the century

Rapid-reduction scenario and ecological debt

This scenario assumes that

1. On the demand side, humanity's ecological footprint could be reduced by 40% from 2.2     global hectares in 2003 to 1.3 global hectares in 2100. Achieving this would require:

    • Reduce in CO 2 emissions to 50% by 2050 and 70% by 2100
    • 23% decrease in per person cropland and grazing land footprints

2. On the supply side:

    • 30% growth in biocapacity by increase in cropland, fisheries, and forest yields through improved technology and management

This scenario requires greatest initial economic investment but it carries lowest ecological risk because it minimizes ecological debt the fastest.

Twin challenges: Securing biodiversity and increasing biocapacity

Animals compete with humans for food and habitat. Plant diversity can be drastically impaired due to widespread cultivation of a limited set of domesticated species. To leave a portion of Earth's productivity for the use of wild species is an additional challenge over bringing human demands within earth's productive capacity.

The success of this scenario hinges on the drastic 30% rise in earth's biocapacity. It is a huge challenge to achieve this without introducing further environmental imbalances in the form of energy intensive farming, cutting down forests to create grazing areas, irrigation causing salinization or excessive fertilizer use impacting downstream or downwind wildlife.