Why are we interested in ocean circulation? A short trip to the Earth's past.

Many people today are worried about the future of the earth when thinking of climate change. To most humans, climate and natural settings were considered the one stable concept in their otherwise unstable life. Hence, the thought of a 4˚C warmer Earth, as it is postulated by the IPCC and many newspapers often triggers communal fears of mass extinction that may even include the human race.

You may panic.

http://www.demonsinthedark.com/panicandalcohol.htm

However! Here is the interesting bit. During the last century, climate scientists have found evidence for long term climate changes throughout the earth’s history (e.g. Daansgard et al., 1982; Daansgard et al., 1993). Proxy data (eg by converting information found through biological and abiological indicators into climate variables) or even direct measurements (eg trapped air bubbles in ice cores) in geological records have shown that Earth has went through climates much more aggressive than the one we know.

-          Precambrian (600-3500 Ma): Snowball Earth: The whole of the earth’s surface was covered in ice (Hydeet al., 2000; Donnadieu et al., 2004)

-          Cretaceous (65-144 Ma): Greenhouse Earth: Ice did not exist. Fun fact: CO₂ pressure was above 1000 ppm vs today at 400 ppm (Barron et al., 1981; Barron,1983; Kuypers et al., 1999)

This shows that the Earth has a much greater climate span than we would have initially believed. Since our climate today includes ice on Earth (glaciers and permafrost) we are actually closer to the snowball earth climate than the Cretaceous version; meaning, we are stuck in an Icehouse Climate, while an ice free earth represents a Greenhouse Climate.

To get a more accurate understanding of our current climate situation, we should take a closer look at the recent past of our climate.

Vostok Ice core time series and Insolation, taken from Petit et al. (1999)

Petit et al. (1999) have managed to characterize climate for the last 400,000 years. We see that temperature (line b) has fluctuated strongly between cold glacial and warm interglacial periods. The Insolation curve (line e) suggests that those fluctuations are initiated by changes in solar energy on earth. Thanks to Milankovitch, we know today that climate over the last ice ages was indeed forced by three external variables (Eccentricity, Obliquity and Precession) with different oscillations (Zachos et al., 2001).

Now put yourself in the shoes of a climate change scientist and try to answer the following question using the graph above:

What is the difference between warming phases and cooling phases?

Post your answer if you like and see whether you were right next time J