Tipping points in the earth system: Surprise, resilience, and governance

Agriculture has often been considered a local issue, however it is a major driver of global environmental change. Globally agriculture is both intensifying and extensifying and intensifying due to increases in agricultural demand from a growing human population, increasing consumption of meat, increasing trade in agricultural products, and increasing use of biofuels. Increases in agricultural production globally haves hitherto lead to substantial declines in other ecosystem services, such as pollination, water purification, and wildlife habitat. Declines in these functions appear to decrease ecosystem resilience, increasing the likelihood of crossing “tipping points.” When ecological modification moves an ecosystem across a tipping point the past response of the system no longer predicts the future, as new organizations of ecological structure and process initiate a different self-maintaining regime. In the absence of tipping points unwanted ecological changes can usually be reversed, however when they exist ecological changes are difficult, costly or impossible to reverse. The existence of tipping points suggests management should focus on locating tipping points and building resilience to avoid having ecosystems shift into undesired regimes. In this talk I present a typology of tipping points and identify possible types of hydrologically mediated tipping points in agricultural ecosystems. Examples of these include eutrophication of freshwater and estuarine systems through nutrient runoff, grazing's impact on soil-moisture/vegetation interactions, and changes in climate from alterations of water flows from land to the atmosphere. While these tipping points have been monitored at small scales, there have been few synthetic attempts to understand and model large-scale regime shifts. Such understanding is necessary to develop agricultural and development policies that robustly increase human well-being while sustaining the biosphere.