Continuing our discussion of global warming and climate change, we’ll focus in this session on the human impact on our global surroundings. Previously, we’ve noted the importance of the Earth’s greenhouse effect and how this effect is driven by less than 1% of the gases in Earth’s incredibly thin atmosphere. We discussed that water vapor, while being a powerful greenhouse gas, only remains in the atmosphere for a period of a few days, preventing It from driving long term changes in the greenhouse effect. Carbon dioxide, on the other hand, while a relatively weak greenhouse gas, can accumulate in the atmosphere due to its very long atmospheric lifetime,, enabling its impact to be both global and long term. But what role is being played by human activities? One of the characteristics that separates us from other species is the ability to utilize complex tools to perform work. And, if you ask me, this is one impressive piece of tooled machinery right here. This is the Bagger 288.
It’s length is ½ the height of the Empire State Building, and it can dig a hole the size of a football field to a depth of 98 feet in a single day. The purpose of the Bagger 288? To dig open pit coal mines. And here is an example of a mountaintop removal coal mine. While not dug by the Bagger 288, it is an example of how humans can completely alter the face of our environments. But we’re capable of much more than that. Let’s step back a little further and take a look at an area just northeast of Santa Cruz, Bolivia. Here you see over the course of only 28 years, thousands of acres of dense jungle replaced by villages and fields. And scenes like this are repeated across the globe. But let’s keep going and step back even further. This is the Earth at night, showing the lights of human civilization. Despite being from space, it’s very easy to pick out the areas of greatest population density and industrialization. In my mind, no other single image so clearly demonstrates the ability of our one species to change the face of our entire planet.
But what effect do we have? Very few people go out with the specific purpose of destroying their natural surroundings. More often than not, our intents are respectable. We seek to build homes in which to live, grow food for our sustenance, and provide means to make a financial living. And these actions are generally done with regard given to the local environment. But oftentimes it is difficult to predict and ascertain the long-term and widespread impacts of our actions, and, as a result, we encounter some very unintended consequences. Pictured here is what’s called an oceanic “dead zone”. This particular dead zone covers thousands of square miles off the coast of Louisiana in the Gulf of Mexico. Found near the mouths of rivers around the world, dead zones are created when fertilizer from upstream crops accumulates and reaches the ocean, leading to an overgrowth of oceanic phytoplankton, seen in the light green coloring in the picture.
As a result, there can be little to no dissolved oxygen in the water within these dead zones. Animals that cannot escape the impacted area, such as shrimp, crab, lobsters, and so on, die as a result, giving the “dead zones” their name. And many of these dead zones are growing larger and larger each year. In recent years, widespread forest fires have garnered attention around the world. When a forest fire starts, the first and natural reaction is a desire to suppress and extinguish it as quickly as possible. However, fires serve a very vital purpose in the natural processes of the forests. Rapid extinguishment of fires can lead to an overgrowth of underbrush. And, when such an overgrowth exists, it can result in new fires becoming much more intense and difficult to contain, resulting in much greater damage.
As a result, many localities, particularly with forests near heavily populated areas, have adopted the practice of having what are called “controlled or prescribed burns” where the underbrush alone is burned periodically in a very controlled way. This process seeks to lower the intensity and aid the containment of any natural or accidental fires which occur. Few other natural occurrences in recent years have had the impact of Hurricane Katrina, which made landfall as a strong Category 3 storm back in 2005. But the impact of what would have been a very destructive storm under any circumstances was inadvertently made considerably worse. Development along oceanic coastlines can result in the destruction and elimination of natural wetland areas and barrier islands, natural impediments which help dissipate the strength of storm surges. Along the Louisiana coast, such wetlands are being lost at a rate of 40 square miles a year and have been for decades. When Hurricane Katrina struck, it brought with it more than a 20 foot wall of water that surged miles inland along the Louisiana, Mississippi, and Alabama coastline, destroying much of everything in its path.
Landslides can also be impacted. Human activities related to deforestation, development, and crop irrigation can remove stability-providing root and tree structures and modify water penetration into natural earth formations. These changes can greatly influence the stability of these environments, resulting in sudden, violent, and devastating slides of tons of soil, rock, and debris at speeds of up to 200 mph. This landslide, from January 2005 in La Conchita, California, released 250,000 cubic yards of earthen material, destroyed or damaged 36 homes, and killed 10 people. A lawsuit brought by those impacted found the ranch located at the top of the hillside, where lemons and avocados were grown, partly to blame, due to improper drainage of the ranch’s irrigation system. Looking at our global impact, the atmospheric level of carbon dioxide has increased 39% in 130 years of the industrial period, despite large-scale natural opposition. This rapid rise of CO2 is unprecedented in the geologic record, and the current levels of CO2 are higher now than they have been in the last 650,000 years and likely the last several million years.
Human activities have literally driven the atmosphere into uncharted territory, pushing the primary long-term greenhouse gas to a level it has not seen in hundreds of thousands of years and at a rate the planet has never seen. So, in this section, we’ve noted that humans, as a species, are unprecedented in the 4.5 billion year history of the planet. Never before has a species been able to consciously alter its surroundings on such an immense scale. However, our history is replete with examples that these actions are often accompanied by severe, unintended, and difficult to predict consequences. Now, human activity has pushed the atmospheric concentration of carbon dioxide to a level it has not seen in hundreds of thousands, if not millions, of years and at a rate that is unprecedented in the geologic record. But exactly how does the climate react to such influences? That will be the subject of our next section.