By 2050, in these scenarios the total cropland Footprint increases by 10 percent, and built-up land by nearly 50 percent. The forest Footprint doubles, the carbon Footprint grows nearly two and a half-fold, and the grazing land Footprint almost triples its current size. Projecting out to 2050, the IPCC B1 scenario results in the lowest Footprint value, with carbon making up 47.4 percent of the total Footprint. The A1 scenario represents the highest value, with carbon comprising 60.9 percent of the total Footprint. Thus even if the most aggressive IPCC carbon reduction scenario is realized, the level of overshoot is still projected to be more than 1.5 times what is was in 2005. Unfortunately, recent data shows that carbon emissions are accelerating, and are now close to the IPCC worst-case scenario (IPCC 2006), while other data suggests the capacity of global carbon sinks may be declining (IPCC 2006). The IEA Reference scenario and the IPCC A1B scenarios are very closely aligned, with only a 0.07 percent difference between the two projections in 2030. The IEA Alternative scenario falls 2 percent above the IPCC B1 scenario. Figure 17 shows the projected trends in Footprint components through 2050, using the carbon projection from the IPCC A1B scenario. The level of overshoot shown in these scenarios may or may not be physically possible. For example, the scenarios assume that by 2050 a growing ecological debt will not have resulted in depletion and collapse of the resource base to an extent that would limit some of the projected growth in demand. The model also fails to take into account feedback loops that exist
in many biophysical systems. For example albedo changes accompanying the loss of Arctic ice, methane released from warming tundra, and the declining carbon sink capacity of a warming and acidifying ocean all have the potential to accelerate the rate of climate change, even if anthropogenic emissions of carbon are held constant or are reduced. A more rapidly changing climate may then render future estimates of available biocapacity overoptimistic. Unlike financial capital, one type of which can easily be exchanged for another of matching monetary value, ecological assets are not readily interchangeable. The overuse of fisheries, for example, cannot be offset by decreasing demand on forests. Further, these assets are often in competition, with additional cropland expanding into forest land and subsequently compromising fuelwood and timber resources, and carbon storage capacity. This lack of substitutability makes the challenge of ending overshoot even greater. Wealthier countries may temporarily buffer themselves from overshoot by importing resources and exporting wastes. Early adopters of aggressive sustainability strategies may be able to eliminate local overshoot, not only enhancing their own wellbeing but also potentially being able to derive economic benefit from an ability to provide resources to others in need. Thus, addressing overshoot early is in the self-interest of individual nations, as well as in the interest of the world as a whole. The alternative, failing to address overshoot, means accepting its consequences, with the greatest initial impact on the world’s poorest and most vulnerable nations.
Figure 17. Estimated ecological overshoot in 2050 based on IPCC A1B and other projections (see text). 28