Figure 6: Human-nature interactions can be complex and surprising. As parks in Africa protect
ecosystems and the animals that thrive in them, animals sometimes leave the park and cause
problems in nearby farms. Baboons in particular are a serious source of crop destruction in the
areas near national parks in Africa, as are elephants and other species. Protecting farmers is
critical for maintaining public support for wildlife protection. Credit: Fred Roberts.
So to properly understand any of these problems involving HESs, themodel of the human system and the model of the environmental system need to
be fully coupled.
Such fully coupled systems are still in their infancy, and building them willrequire solving a host of mathematical problems. First, we have to tease out how
the different aspects of the system interact, which requires identifying all the
feedbacks in the system. Particularly when linking human and natural systems,
this can be extremely tricky. For example, integrated assessment models attempt
to predict the impact of climate change on the economy. However, they rely on
United Nations projections for population and don’t consider the effect variations
in climate might have on population size. This extremely complex feedback loop
presents a challenge for mathematical modelers. The problem is further
complicated by the differing time scales over which environmental systems and
human systems evolve.
Next, we have to encode interactions in a computer model, whichinevitably requires clever simplifications. For example, models inevitably require
parameters – that is, numbers that capture an aspect of how the system works.
In a climate model, for example, the reflectiveness of the clouds might be