And so we move onto part 2! In this section of my EPQ I went on to talk about what the Ice Age and Medieval warming period actually were and why the changing climate of the time didn’t raise as many concerns as our current changing climate.
The Medieval Warming Period, the period between 900 AD and 1300 AD, was warmer than the Little Ice Age that followed between 1303 and 1860. Temperatures began to rise between 1.0 to 1.4 degrees above normal and different environmental and biological changes were occurring. The warming period also caused prolonged droughts in the southwest of the United States and Alaska began to get warmer but historical accounts confirm that the medieval warming period was much cooler than the current conditions. Paleoenvironmental records are used to reconstruct the climate during this warming period. An ice core sample that was retrieved in the Antarctic Peninsula shows that the temperatures during this period were somewhat higher.
In the last 800,000 years, there have been 8 ice ages, each of which lasting approximately 100, 000 years and were separated by interglacial periods of between 10,000 and 35,000 years. A typical ice age lasting 100,000 years can be characterised into phases of advancing and retreating ice where the ice; grows for 80,000 years, but it only takes 20,000 years for that ice to melt. Unlike the Medieval Warming Period, the Ice Age was a period of colder global temperatures that featured glacial expansion across the surface of the Earth. An Ice Age, also known as the glacial age, is any geological period during which thick sheets cover vast areas of land and drastically reshape the surface features of entire continents. This is caused by pulses of cold glacial phases interspersed with warmer interglacial phase and had a distinct regularity due to the Milankovitch cycles. Reduced levels of carbon dioxide, CO2, in the atmosphere create a suitable environment for glaciations.
During these times, there were no human causes of such change in weather as there were no ways for them to significantly impact the climate. However, natural processes such as the change in the Milankovitch cycle have affected the planet’s climate.
The Milankovitch cycles describe how reasonably small changes in Earth’s movement can have significant impacts on the climate. These cycles are named after Milutin Milankovitch, a Serbian astrophysicist who investigated the cause of Earth’s ancient ice ages in the early 1900s. Over a century ago, Milankovitch hypothesised the long-term effects of changes in Earth’s position relative to the Sun and these changes being the key driver to Earth’s long-term climate and are responsible for initiating the beginning and end of Ice Ages. Milankovitch investigated how the variations in the Earth’s orbital movements affects the amount of solar radiation that reaches the outermost layer of our atmosphere and most importantly, where these solar radiations reach. The cyclical orbital movement of the globe became known as the ‘Milankovitch cycle’ and cause variations of up to 25 percent in the amount of incoming radiation around the mid-latitudes – the areas between 30 and 60 degrees north and south of the equator. There are three factor, that can vary the incoming radiation which includes:
- – The shape of the Earth’s orbit – the eccentricity
- – The angle the Earth’s axis is tilted compared to the Earth’s orbital plane – the obliquity
- – The direction of the Earth’s axis of rotation- the precession
These three factors can change the amount of solar radiation that reaches the Earth and operate together and as a unit to influence the Earth’s climate over long periods of time. This leads to larger changes in our climate over tens of thousands to hundreds of thousands of years. Milankovitch combined the cycles to create an all-inclusive mathematical model for calculating differences in solar radiation at several Earth latitudes along with corresponding surface temperatures. In 1965, the British climatologist Hubert Horace Lamb examined historical records of harvests and precipitation, along with early ice-core and tree-ring data and concluded that the Medieval Warming Period was a time of unusually high temperatures. It was also discovered to be the result of higher-than-average levels of solar radiation and less volcanic activity. It was caused by a change in the ocean circulation pattern which played a very important role in bringing warmer seawater to the Northern Atlantic.
The exact causes of ice ages, and the glacial cycles within them, have not been proven, they are most likely the result of complex interactions between things such as solar output, distance of the Earth from the sun and ocean circulation. Milankovitch calculated that Ice Ages occur approximately every 41,000 years which was confirmed by many different research that followed. An example of this is the study, published in records of the National Academy of Sciences. However, about 800,000 years ago, the length of the cycle of Ice Ages increased to 100,000 years, matching Earth’s eccentricity cycle. Although several theories have been offered to explain this shift, scientists currently do not have a clear answer. Other studies have also confirmed Milankovitch’s work, including research using data from ice cores in Greenland and the Arctic that has provided strong evidence of Milankovitch cycles from many hundreds of thousands of years in ‘Evidence-Based Climate Science’ by D.J. Easterbrook.