Lessons from the Past: Change Happens

The fossil record has a lot to say about the effects of climate change.  We can see the sensitivity of the world’s ecosystems; we can see how life responds to temperature changes; and we can put the current trends in perspective. While we can’t go back and read a thermometer, we can look at preserved temperature proxies, like oxygen and hydrogen isotopes. These heavier isotopes get trapped in polar ice sheets15 and the shells of creatures on the ocean floor and we can relate their abundances to specific average global temperatures.  

Thrinaxodon fossil

When you look back at the history of life two big warming events stand out.  The first follows the Permian-Triassic mass extinction.  Isotopic data from fossilized Benthic remains in China shows that equatorial surface waters, at that time, reached around 40 degrees Celsius.  Today equatorial surface waters average around 27C.  To put that in prospective, 40 degrees C is 104 degrees F, most hot tubs are set to 102 degrees F.4 The world was incredibly hot and life struggled.  The extreme temperatures and CO2 levels found during that period are believed to be responsible for long lag time in the recovery life’s biodiversity.  The species that managed to survive the mass extinction merely clung on to life, but nothing thrived in the heat. In fact all mammals owe their existence to one survivor of that period, Thrinaxodon, a small burrowing carnivore, who was the lone mammal-like reptile to survive the period. That’s how close WE came to not being.20

Water Color of alligators in a mangrove swamp

Another period of rapid global warming took place 55 million years ago and is known as the Paleocene-Eocene Thermal maximum. Isotopic data from the Arctic Coring Expedition show an average temperature of 23.3C or 74F for the Arctic Circle during that time.  When you combine the isotopic data with fossilized palm trees and crocodilian remains found in the same cores, you start to get the image of an arctic circle that looked more like the Everglades do today then the frozen tundra we know.1  This warming event opened up previously inhospitable terrain and saw great migrations between the continents and may have sparked the great diversification seen in the age of mammals.21

The first of these warming events nearly ended the mammalian line entirely, while the second spurred a period of great migration and radiation, so it’s hard to tell what end result of the current warming will be.  Climate change tends to bring 4 types of changes in mammalian populations:2

• The relative abundance at the species level shifts
• The taxonomic makeup of any given area changes
• Species richness changes
• Phenotypic expressions can alter.

The bottom line is everything is subject to flux, and in the face of such unpredictable futures it seems detrimental to be tightly linked to any one way of life or to any one other creature.  The Canadian Lynx is tightly linked to both its terrain and its prey and that doesn’t bode well.  

Thrinaxodon photo by Allison Beck
Mangrove Water Color by Jennifer Branch. Available at jenniferbranch.com