The unknowns in the problem of biodiversity change

In summarizing the state of knowledge on biodiversity change in both natural and managed systems the major assessments (the Global Biodiversity Assessment, the MA, the IAASTD, and the Global Biodiversity Outlook) usefully clarified the limits of our current understanding of biodiversity change. They showed that our knowledge is still extremely patchy. We know much about changes in species richness and abundance for birds, for example, but little about many invertebrates. We have many data on the ecological consequences of biodiversity change in temperate grasslands, but relatively few on tropical forests. At the same time none of the assessments offers much insight into the value of one type of biodiversity change relative to another. In the opening chapters of Part II of this book I have considered what this means for the information needed to underpin management of biodiversity change. Chapter 8 considers the information requirements of the main management options, adaptation and mitigation, and what this means for the way we project the causes, consequences, and character of biodiversity change. In Chapter 9, I address the issue of valuation, and the challenges involved in generating information that can inform macro-economic policy.

In the best of all worlds, however, we will still be called on to make decisions on the basis of incomplete information. There are two dimensions to the problem of biodiversity change that complicate both calculation of what it costs society and development of options for its management: the irreversibility of some aspects of biodiversity change and the fundamental uncertainty that induces. For all practical purposes the extinction of species is forever. Its effects are unknown and unknowable at the moment it occurs. People undertaking activities that change either the survival prospects of a species or its range cannot imagine all possible consequences of their actions. Nor are they able to assign probabilities to the consequences they can imagine. Similarly, it is not possible to reverse the changes wrought by many invasive species, or to assess the potential costs and benefits of actions that irreversibly affect the future evolution of the system.