Desde el pensamiento científico

This section provides a summary of the effects of options compared on the indicators of natural area, wilderness area, and mean species abundance (MSA). We concentrate on terrestrial biodiversity. However, there are some caveats to bear in mind when comparing the effects of the options to reduce biodiversity loss. They are briefly mentioned at the end of this section (see also Chapter 7).

Most of the options considered in this chapter show a net positive effect on global biodiversity in terms of MSA natural area and wilderness. However, from the overview (Figure 4.31). It is clear that none of the options will be able to bring further biodiversity loss to a halt. While this implies that there is 'no silver bullet' for bringing biodiversity loss to a halt, we could determine an acceptable level of biodiversity, below which it is not to deteriorate any further.

Most options show a prevented MSA loss of around 10%, while closing the yield gap and a dietary shift could prevent more than 30%. All basic options, but one, increase the extent of natural area, and all but one increase the wilderness area. For natural area, a dietary change would yield the strongest savings (about 10 million km2_{). For}

wilderness, the climate change option without bio-energy would have the largest effect (8 million km2_{). However, like for the MSA indicator, much of the baseline’s}

loss cannot be reduced.

Options address drivers of biodiversity loss in various ways

The main drivers of biodiversity loss introduced in Section 3.1 are: i) expansion of agricultural area and associated change of habitats, ii) overexploitation of natural habitats (e.g., grazing and logging); iii) pollution (e.g., eutrophication), iv) invasive species and v) climate change. All but invasive species are mitigated by one or more of the options presented but in different ways and to different extents. Given these multiple pressures and distinct drivers, and the limited working range of each option, it is not surprising that no single option will be able to bring further biodiversity loss to a halt. Moreover, options often have trade-offs and rebounds, relieving one or more pressures only to see another increase, or see prices and demand for land respond. Thus, given the inability of one option to address all drivers of biodiversity loss, the 40% of prevented MSA loss and the gains in wilderness and natural area that would result from changing diets to healthier Implementing climate change mitigation without using bio-energy results in increases of

wilderness area in almost all biomes, with the highest increases in boreal forests and scrub- land and savannah.

Figure 4.30

Boreal forest Temperate forest Tropical forest Grassland and steppe Scrubland and savannah Ice and tundra Desert

-0.2 0.0 0.2 0.4 0.6 million km2 Mitigating climate change – Without bio-energy

levels is quite large. Part of that large effect is due to the ambition level set for the option, and another part results from changing consumption patterns instead of increasing efficiency with which a consumption pattern is satisfied.

Increased efficiency in economic sectors significantly reduces pressure The options Closing the yield gap, Reducing post-harvest losses, Improving forest

management, and Reducing marine fishing efforts all focus on production systems. Increasing production efficiency of crops, livestock, fish and also timber in the coming decades seems to contribute significantly to reducing future biodiversity loss. The extent to which the effect of these options overlap is explored in Chapter 5. Also, increasing production efficiencies may increase local impacts, as demonstrated by the eutrophication effects in the Closing the yield gap option. Global gains in efficiency and associated benefits for global biodiversity can imply large local impacts.

Most of the basic options reduce losses in global biodiversity by 2050, on all three indicators MSA (left), natural area (middle), and wilderness area (right). Change in global biodiversity of options expanding protected areas and reducing deforestation by 2030.

Figure 4.31

Expanding protected areas – 20% Expanding protected areas – 50% Reducing deforestation Closing the yield gap Reducing post-harvest losses Changing diets – Healthy diet Changing diets – No meat Improving forest management – High ambition Mitigating climate change – Without bio-energy Mitigating climate change – With bio-energy 25%

-20 0 20 40 60 % of baseline MSA loss Basic options Sensitivity variants

Change in global biodiversity of options expanding protected areas and reducing deforestation by 2030

Prevented MSA loss, 2000 – 2050

Change in global biodiversity per option compared to baseline scenario

-5 0 5 10 15 20 million km2 Basic options Sensitivity variants Natural area, 2050 -5 0 5 10 15 20 million km2 Basic options Sensitivity variants Wilderness, 2050 Figure 4.31

Benefits for climate change mitigation and food supply

Most options benefit climate change mitigation and food supply simultaneously while contributing to reducing biodiversity loss. Reduced conversion of natural habitats keeps carbon stocks and uptake capacity intact. A more efficient and less wasteful agriculture and food sector would contribute to stable food supply especially in developing countries. These effects are elaborated in Chapter 5. Caveats when comparing the implications of the options for biodiversity First, the level of implementation assumed for each option is not the technical maximum, but is a lower target that is ambitious but also more realistic (see Section 4.1). These targets have not been specifically selected for the purposes of this study and therefore differ in ambition level. Consequently, comparisons of the effects of the options on biodiversity must be made with due consideration to the level of implementation of each option.

Second, the possible effect of combining separate options cannot be estimated by simply adding up their individual scores. Options have implications for prices of land and commodities, allocation of agricultural production across regions and environmental pressures. A first attempt at combining options for identifying interactions and second-order effects is presented in Chapter 5.

Third, the three indicators presented focus on naturalness as representative of the state of biodiversity. They exclude rarity and risk of species extinction. Thus, it would be incorrect to state that a single option is better for biodiversity in all respects. This depends on the indicator used for or definition of biodiversity (see also Chapter 2).