Climate change deniers often sing the frustrating song that carbon dioxide emissions are harmless, but a groundbreaking study by scientists at Harvard, the University of Wisconsin, and Oregon State University has produced a paper which the authors claim to be the first to “definitively show the role carbon dioxide played in helping to end the last ice age.” CO2 concentrations rose from 185 parts per million to 260 ppm over the roughly 10,000 years during which the last ice age ended, according to Physorg. Compare that with our man-made emissions, which have raised CO2 concentrations by the same amount in the past two centuries alone, and we all have something to be very concerned about.
So what caused the increase in carbon dioxide emissions? During the ice age, it’s important to keep in mind that all increases in CO2 emissions were a natural phenomenon — until someone successfully clones a Wooly Mammoth, we won’t be seeing one anywhere near a car. Rather, the theory goes that natural shifting of the earth, a ‘wobble,’ if you will, caused warmer summers in the Northern Hemisphere some 21,000 years ago.
As temperatures increased over the polar caps of the Northern Hemisphere, glaciers melted and freshwater flowed into the oceans and sat there, remaining on the surface rather than sinking and joining the natural flow. Simply speaking, this freshwater intrusion slowed a natural current — the Atlantic meridional overturning circulation — in which water would normally “flow northwards across the equator, stealing Southern Hemisphere heat and exporting it to the Northern Hemisphere. The AMOC then sinks in the North Atlantic and returns southward in the deep ocean.”
This retention of heat in the oceans of the Southern Hemisphere is believed to have caused carbon dioxide from deep oceans to be “uncorked” and released into the atmosphere, beginning sometime around 17,500 years ago.
The paper, “Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation,” published in the journal Nature, has some incredible research behind it. The scientists constructed the “first-ever record of global temperature spanning the end of the last ice age based on 80 proxy temperature records from around the world,” according to Jeremy Shakun, a National Oceanic and Atmospheric Administration (NOAA) Climate and Global Change postdoctoral fellow at Harvard and Columbia Universities and first author of the paper.
These 80 local temperatures records, calculated from ice cores and ocean and lake sediments, provided scientists with data from which they could derive a history of global mean surface temperature. Additionally, Physorg notes “samples of ancient atmosphere are trapped as air bubbles in glaciers, providing a direct measure of carbon dioxide levels through time that could be compared to the global temperature record.” Having found a clear correlation between CO2 emissions and climate change during the ice age, the researchers plugged their data into a “climate model that couples interactions between atmosphere, oceans, lands, and sea ice.”
When taken in total, the study found that “global temperature mirrored and generally lagged behind rising carbon dioxide during the last deglaciation, which points to carbon dioxide as the major driver of global warming,” stated Shakun.
The natural increase in carbon dioxide levels caused by a sun-warmed Northern Hemisphere pushed the world into the end of the ice age at a relatively slow rate. Man-made carbon dioxide emissions have vastly outpaced those of such a natural phenomenon. In 2011 we reached a global CO2 concentration of 392 ppm – an amount higher than any time in the last 800,000 years. And we aren’t in an ice age.