In today’s video, we learned about the medieval village Hound Tor, and how short term changes in climate caused the village to cease to exist a mere few hundred years later. We also examine what natural factors that affect climate change, as well as various indicators we have for recording the weather and overall climate.
Natural Factors Affecting Climate Change
I like this part, because I’m an engineer and a space nerd, and it involves variables, periods, and the orbit of earth.
E = eccentricity
Eccentricity is a term that describes how elliptical or circular the orbit of a planet is – in this case, we’re referring to Earth. The eccentricity of Earth’s orbit increases and decreases over time, with a period of about 100,000 years. As the earth gets closer to the sun while it has a higher eccentricity, it sees more solar energy than during parts of the year where it is farther than the sun. In periods when the Earth’s orbit is more circular, the Earth sees nearly equal amounts of solar energy throughout the year.
T = obliquity
Obliquity refers to the angle of the Earth’s axis in relation to the axis that is perpendicular to the plane of the Earth’s orbit. Or, more simply put, the tilt of the earth. This can vary between 21.5 degrees and 24.5 degrees and has a period of 41,000 years. The tilt of the Earth affect which parts of the surface see more or less sunlight throughout the year.
P = precession
Precession refers to the wobble of the axis of the earth. As the earth spins, it wobbles like a top on the axis. The amount of precession the earth sees has a period of 23,000 years.
All of these factors together have an effect on the climate of the earth.
Natural Indicators of Climate Through the Years
There are a few ways we can see what the climate was like before we started recording it. Among them are ice cores and tree ring studies. The picture below is a (poor) representation of a bored out piece of a tree trunk:
Tree ring studies involve pulling a core out of a tree and seeing the distance between the rings to determine how much sun a tree got in a given year. More width between the rings means more growth, and therefore more sun. Less width means the opposite. This tells us how the climate has changed over the years in the trees life span. We can also look at wood samples from dead trees and correlate their later years with living trees to see even further back into the past. Comparing the data of many trees gives us a reliable look at what the weather and climate was like in recent history.
So what drove people away from Hound Tor?
Volcanic eruptions, most likely. Volcanic activity presents the most unpredictable changes in climate over short term periods. When volcanoes erupt, they spread ash and aerosols into wide areas of the atmosphere, which can drastically affect the amount of solar radiation reaching the earth, and therefore the temperature. An eruption at Mount Pinatubo, for example, caused the world’s temperatures to drop 0.5 degrees Celsius all on its own!
What does all of this tell us?
In examining the recent history of climate on the earth, we get a sudden sharp rise in temperature over the last 100-150 years that can’t be explained by natural factors. When we look at the rise in temperature along with the rise in the amount of C02 in the atmosphere (which is almost entirely driven by human activity), the rise in temperature directly corresponds to the rise in CO2.
The lesson this week concludes with a stark reminder of what climate change did to the people of Hound Tor, and what it may do in the future on a much larger scale.
Climate Change - Challenges and Solutions 