Friday Headlines, September 6, 2019


This week in geology

  • Is Pluto a planet or what?

This week in the environment

  • What caused the little ice age and the medieval warm period?

Why Pluto isn’t a planet – And might become one again

When I was a kid, Pluto was the ninth planet.

Then it wasn’t a planet anymore.

Now… Oh dear.

Photograph of Pluto from NASA's New Horizons probe
Photograph of Pluto from NASA’s New Horizons probe. Source: NASA/New Horizons

Astronomers today define planets as objects in the universe that meet the following requirements:

  • Spherical (roughly)
  • Orbits the Sun (or another star)
  • Is the only occupant of its orbit. That is, it had “cleared its neighborhood.”

Dwarf planets are defined this way:

  • Spherical (roughly)
  • Orbits the Sun (or another start)
  • Has NOT cleared its neighborhood. There’s other ‘stuff’ in its orbit.

According to this definition, Pluto is a dwarf planet, because there are other occupants of its orbit.

But a NASA Administrator Jim Bridenstein stated on August 23 that he still regarded Pluto as a planet.

NASA Sdministrator Jim Bridenstine states that he considers Pluto a planet.

So… You decide

What caused the Little Ice Age?

First, let’s define some terms. The Medieval Warm Period is an episode of warmer climate that affected the North Atlantic region of the Earth from about 950 to 1250 AD. This was followed by a period of overall cooler climate, the Little Ice Age, from about 1550 to 1850 AD. There are arguments about the exact timing of the Little Ice Age.

The reconstructed depth of the Little Ice Age varies between different studies (anomalies shown are from the 1950–1980 reference period)
Source: Robert A. Rohde, CC By-SA 3.0

The question is, what caused this episode of cooling? Six potential causes have been identified:

  • Orbital forcing (Milankovitch Cycles)
  • Solar activity (e.g. sunspots)
  • Volcanic activity
  • Ocean circulation patterns
  • Variability in human populations
  • Natural variability in climate

Most researchers blame volcanic activity for the onset of the little ice age. None of the other criteria seem to work, although a recent paper suggests that the genocide of indigenous North American peoples may be the cause.

Koch et al. (2019) attribute a decrease in global atmospheric CO2 to the loss of cleared land that was once worked by Native Americans. Increased vegetation in once clear areas drew CO2 from the air and fixed it into new plant growth, resulting in overall cooling of the global climate.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s