So, it’s the first of January, 2014. I didn’t quite make it to the my 50 posts/5000 hits goal, but 45 and ~4700 is pretty close. I’m incredibly excited to move forward with Mostly Harmless Science in the new year and have a few treats planned, including a video entry on the formation, geology, and landscapes of the Rocky Mountains. For now though, there is research and thesis work to do, so I’ll be laying low for the next couple of weeks until I’m caught up. I’ll still try to post an article a week and stay active with reading and commenting. In the meantime, check out some of my earlier articles that you might not have read yet!
Let’s talk evolution. Of climate. In the pre-industrial Holocene – the geological period spanning from 11,700 years ago to the present. We’ve heard countless times how CO2 and methane emissions since the late 18th and early 19th centuries have wreaked havoc with the global climate. Below you can see the infamous ‘hockey stick curve‘, which shows the near-exponential temperature rise during this period. You’ll notice that prior to the Industrial Revolution, there are two labels on the graph – the Little Ice Age and the Medieval Warm Period. What are these intervals?
Well for starters, how do we know what the temperature was like thousands of years ago? We use proxy records – climate ‘indicators’ preserved in the geological record. Some examples include lake and ocean sediment cores, tree rings, and my personal favorite – ice cores. As ice forms, bubbles of air are trapped inside and sealed within the crystal structure of the ice. Ice forms in seasonal layers; thus, records such as the Antarctic ice cap store annual ‘samples’ of air. Oxygen and hydrogen isotopes (‘signatures’) have known relationships to temperature, and carbon dioxide concentrations can also be measured directly. Antarctic ice cores have allowed us to look almost 800,000 years back in time. The Medieval Warm Period appears as a temperature peak and the Little Ice Age as a trough.
Since both of these periods also fall into the realm of recorded history, we also have documented evidence of the impact of these climate fluctuations on societies at that time. During the Medieval Warm Period, the Norse established settlements in Greenland and Iceland. In Europe, populations grew and agriculture flourished, while in North America and Asia, drought fueled the collapse of civilizations. With the onset of the Little Ice Age, glaciers advanced and Norse colonies were abandoned. Winters across Europe and North America grew longer and colder, and rivers and canals in major cities such as London froze deeply enough that skating was possible. The famous Stradivarius violins are made from wood from this period, which is purportedly denser and contributes to the richness of the tone.
An abandoned Norse settlement in Greenland
A 17th Century painting of the frozen Thames River, London
As far as the ‘why’, that’s a little harder to judge. Potential causes include changes in the North Atlantic thermohaline circulation (ocean currents), solar cycles, and large-scale volcanic activity. The key point here is that climate can be driven by a number of different factors. The strong relationship between atmospheric CO2 and global temperature in the past century shows that CO2 is presently the dominant driver, but no such certainty exists for times long past.
Be warned: you may have just sustained a lethal dose of mostly harmless science.
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Cover photo courtesy of Scott Ableman. All other images from Wikimedia Commons.