Intrinsic, Extrinsic, and Anthropogenic Controls Defined

Geoscientists like to classify factors or variables as either intrinsic, extrinsic, or anthropogenic to the earth system.

• Intrinsic factors are variables that relate to changes in Earth's internal systems (i.e., changes in the lithosphere, hydrosphere, biosphere, etc.) and the cycling of earth materials between each.
• Extrinsic factors are variables that relate to factors originating outside of the Earth (variations in planetary orbits, output of solar energy, historic and future meteorite impacts, etc.)
• Anthropogenic factors are variables that have been influenced by human activities and are, thus, adding to or subtracting from natural signals produced by normal earth system activities. In the climate change and sea level rise debate, it is often this factor that is most at the center of controversy. How exactly do human activities (i.e., burning fossil fuels) impact sea level? Do anthropogenic factors overwhelm natural factors inherent in the normal functioning of the earth system? These questions are important to think about later in the module when you project the future of sea level rise from your historic tidal data sets and critically analyze the patterns and trends that you observe.

Clearly, some factors that influence sea level originate from processes/influences active outside of the planet while others are influenced by processes that are more local. For nearly as long as the Earth has had liquid oceans, there is evidence that sea levels have risen and fallen for a variety of reasons. For those of you who may have visited Cincinnati, Ohio, and have picked up a rock on the side of the road... You can attest to the fact that the rocks are full of marine fossils which clearly demonstrate that the bedrock under Cincinnati, at some time in the past, was submerged by ocean waters. If you have never traveled to Cincinnati, no worries, many locations globally have sedimentary rocks within which are the remains of marine sea-creatures (fossils) that help demonstrate that sea-levels today are not where they were when those organisms were living.

In addition to thinking about driving factors in terms of source, the driving forces for sea level change can also be investigated via the temporal framework and the spatial scale over which the process occurs. Hence, it is critical in the investigation of sea level change to explore all factors regardless of whether they are rooted in local or global phenomena. In order to evaluate these factors further... geoscientists often look at temporal scale to contextualize discussions and separate short-term (episodic and periodic) from long-term changes in sea level.