Are we living in an "ice age"? Clearing up some terminology.

When talking about climate, the ice age is mentioned a lot. Sometimes it is said that "the last ice age" ended roughly 10,000 years ago, and sometimes we are still said to be living in an ice age. So which one is correct? Technically both are correct. This is due to a complexity in terminology.

The broader climate state of Earth is divided into two categories: Icehouse Earth and Greenhouse Earth (Maslin, 2014). The state when there are continental glaciers (those that cover continents, separate from glaciers seen on mountains) at any point on Earth is called the Icehouse Earth, and the state when they do not exist is called the Greenhouse Earth. Approximately 80% of the last 500 million years has been spent as a Greenhouse Earth (Spicer and Corfield, 1992). During the icehouse state of the Earth, there are glacial and interglacial periods. The glacial period occurs when the glaciers at the poles move towards the lower latitudes of Earth, that is, towards the equator. The interglacial period is the time when glaciers remain at the poles.

Both the Icehouse Earth state and the glacial period are called Ice Age, but this is misleading. The last so-called “ice age” occurred 11,700 years ago (Clark et al., 2016). This event refers to the glacial period seen on Earth. However, the Earth is still in an "ice age" because it is still in the Icehouse Earth state. Even though it is currently in the interglacial warming period, this warming is approximately 15 times faster due to climate change (Clark et al., 2016). As the anthropogenic global warming gets stronger, the rate of warming will also increase.

The glacial periods seen in the last 500,000 years can be seen in this picture. Source for the picture is here.

The cycle of glacial and interglacial periods is clearly visible. One of the main factors that caused the emergence of Icehouse Earth states and glacial periods is the amount of carbon dioxide in the atmosphere. It ended and started the ages by greatly changing the conditions on Earth (Maslin, 2014).

In conclusion, we are currently living in an ice age and also not. The reason for this is that the word ice age refers to two different phenomena. Therefore, it would be more useful to use the terms Icehouse Earth and glacial period instead of ice age. However, how this will be translated into everyday language remains a challenge.

Sources

• Clark, P., Shakun, J., Marcott, S. et al. (2016). Consequences of twenty-first-century policy for multi-millennial climate and sea-level change. Nature Clim Change 6, 360–369.
• Maslin, M. (2014). Climate change: a very short introduction. OUP Oxford.
• Spicer, R. A. & Corfield, R. M. (1992). A review of terrestrial and marine climates in the Cretaceous with implications for modelling the ‘Greenhouse Earth’. Geological Magazine, 129(2), 169-180 pp.