The Last Ice Age: A Reference Point

Written By: Michael Tsang, Ph.D. | Date: 2020

The last glacial maximum, or what is more commonly referred to as the most recent ‘ice age’, occurred about 21,000 year ago. This was a time when large continental ice sheets extended far into mid-latitude regions of Europe and North American, covering present day areas such as London and New York City. Clearly this was a time when the Earth’s climate was completely different for many parts of the planet (i.e. where shelves of ice used to occupy what is now some of the world’s busiest cities in the world). It is interesting to reflect on this in terms of our current trajectory for greenhouse gas emissions (GHG) and climate change.

So, what was the CO2 concentration at the time of the last ice age? Around 180 parts per million (ppm). Putting this into comparison, the CO2 concentration just after the last ice age and leading up to the industrial revolution (i.e. 1750) hovered more or less around 280 ppm. In other words, it only took a 100 ppm increase (i.e. a 55% increase) over the CO2 concentrations of an ice age to get to the climate conditions at the start of the industrial revolution.

Since the industrial revolution, CO2 concentrations have risen to 407ppm as of 2018’s records, which is an increase of 45% from the industrial revolution, meaning that in the last 150 years, humans have increased the planet’s CO2 concentrations by nearly the same relative amount as had occurred when exiting from the last ice age.

What about temperatures? The global annual mean temperatures that resulted in conditions suitable to create the last ice age were just 4–5°C (7–9°F) cooler compared with the mid-20th-century. Today, we are seeing an average global surface temperature that is roughly 0.87°C (likely between 0.75°C and 0.99°C) higher than mid-19th-century average. However, continuing with business as usual and not lowering our GHG emission rates is expected to lead to a warming of 4.1-4.8°C by 2100. Again, a similar relative change compared to exiting the last ice age.

So, given the impacts that a 100 ppm change in CO2 concentrations and a 4-5°C change in temperature had on the planet, it is not hard to see why scientists, policy makers and companies are pushing for limiting warming to 1.5°C or lower. But while the vision is there, the current plan is not fool-proof. With current policies for lowering GHG emissions, it is expected that warming will be limited to an increase of just 2.8-3.2°C. And even with the Paris Agreements and Pledges, warming in 2100 is expected to still be 2.5-2.8°C higher than current averages. Thus, more needs to be done, and more can be done, to limit climate change’s impacts.