As we discussed Monday, the spread of development across the earth has occasioned changes in the land. Agriculture, settlement, even recreational uses of land and resources modify those resources in various ways.

Before going into details, let’s posit types of transformations:

Purposeful: changes made with the goal and intent of that change to accomplish a social goal (e.g., cultivation for food production)

Inadvertent: changes resulting from the purposeful goal that were not explicitly sought, but may be positive or negative. Ancillary to this is the:

"Law of unintended consequences": the principle that seems to hold in most cases of human disturbance or transformations of nature: that along with the intended outcomes (e.g., a grassland is turned into a wheat field) come a set of unintended outcomes (and negative) outcomes. This is perhaps most clear in cases of introduced species we’ll discuss in class.

Direct vs indirect (often purposeful and inadvertent): direct is immediate outcome of human action; indirect flows through an extended "chain of causality" (e.g., carbon flux to atmosphere warms climate which then causes area of tundra or glaciers to shrink)

• Terrain/roughness (cut trees down and roughness declines; add buildings and it increases---this can change climate,erosion, etc.)
• Biodiversity (species per area) (added and subtracted, native and exotic); here’s a chance to examine unintended consequences: purposeful introduction of species like Kudzu, Russian Olive, cheat grass. Also plenty of inadvertent species introductions
• Hydrology (runoff vs. infiltration): the most obvious change here is urbanization that yields more impermeable surfaces, thus less infiltration and more runoff. Can go the other way: farmers may want to absorb rainfall I to the soil, so keep it loosened with plowing, less runoff.
• Radiation/thermal properties (more of less solar radiation absorbed or reflected by the surface, this affects the thermal regime); urbanization tends to create more heat-absorbing surfaces, and less heat loss thru evaporation (because increased runoff), so cities are hotter.
• Bio-geochemical cycles, like carbon absorption or emission from the vegetation and soil; the cycling of nutrients like nitrogen and phosphorous. One of the most widespread purposeful change is increased flow of nitrogen into soil and into plants thru fertilizers (way above natural baseline rates). Inadvertent change is loss of carbon from soil thru cultivation and accelerated erosion.

These changes propagate thru the main earth systems:

• Biogeochecmical cycles (carbon and nitrogen, to be discussed next week);
• Terrestrial and oceanic ecosystems (soil, vegetation, animals)
• Hydrologic system (evaporation, condensation, precipitation, infiltraiton, runoff)
• Atmospheric system (storage and transport of energy –momentum and heat) through atmospheric circulation, and resulting climate and weather conditions)

Let’s return to the notion of natural or baseline conditions. Is any part of the earth’s surface in a fully "natural" state? How do we define ‘change"?

The rate and intensity of transformations varies greatly across space.

Now let’s return to the human driving forces: production/consumption of goods and services, settlement, etc. The need and desire for food, housing, transportation, recreation, etc. Detailed goals like increasing crop yields with fertilizers, cloud seeding to make rain or snow; building reservoirs, can have obvious consequences. But so can increasing demand for outdoor recreation, changes in food preferences, and energy use. Think about these in recitation exercise 4.

Recitation tie in: you are asked to describe the transformation of a place with which you are familiar.