The Millennium Ecosystem Assessment was one of the foundational efforts to assess and categorize direct and indirect drivers of change and trends in ecosystems.  Direct drivers include changes in local land use and cover, external inputs (like fertilizer use and irrigation), climate change, and harvest and resource consumption.  Indirect drivers of change include demographic factors, economic trends (e.g. globalization), and sociopolitical (e.g. governance) institutions.

According to this assessment, most of the direct drivers of ecosystem change are either increasing their impact or continuing at their current pace and are expected to grow under all future scenarios considered in the assessment.  The assessment highlighted the fact that between 1955 and 2005, 15 of 24 ecosystem services have been degraded, five have been neither enhanced nor degraded and only four have been enhanced.  (See the graph below.)  The services that have been degraded or utilized unsustainably were mostly due to the need for food, fresh water, timber, fiber, and fuel and include capture fisheries, fresh water, air quality regulation, water purification and waste treatment, and natural hazard regulation.  The reasons for the degradations are also noted in the graph, and include factors such as overharvesting, and generally are by-products of raising availability of other services, like for food production.

According to the assessment, these changes have been more rapid than at any other time in history. There is evidence of a greater probability of a degradation in ecosystems at an increasing rate or even sudden and irreversible damage to these systems, particularly after a certain threshold level or tipping point is reached.  It may be possible to reverse the degradation on ecosystems and still meet the needs and wants generated from the services of those ecosystems, but only with the institution of major changes.  Unless these problems are addressed, the benefits from natural capital available for future generations will be significantly lower.

A group of international scholars published a different approach to these issues in early 2015 in the journal Science. The authors identified nine planetary “boundaries” – specific points in the global environmental system - beyond which we risk irreparable harm to ecosystems.  These researchers found that we have crossed four of these bright lines: climate change, biosphere integrity (ecosystems and animal populations), biochemical flows (nitrogen and phosphorus specifically) and land use.  They consider two boundaries, climate change and biosphere integrity, as “core” (for their significance for the Earth system).  Transgressing these parameters risks the current functioning of the Earth and destabilizes it as a resilient system. 

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