Climate Change Seminar - The Climate record and temperature gradients in the earth.

The types of record of climate change are myriad. One type of evidence that is often neglected, but has some advantages, is analysis of the shallow thermal gradient. Imagine a tracker finding a campfire pit, touching the ground, and saying, "they left only two-three hours ago." In courses on remote sensing infrared photos are sometimes shown of a thermal shadow left on the tarmack after the planes have left. The ground remembers its past thermal history.

A bit of heat-flow science:

• steady state heat flow through a slab given by:
• q = k ((T2-T1)/h)
• q is heat flow W m-2, energy per surface area unit
• k = thermal conductivity W m-1°C-1
• T2 and T1 bounding temperatures with T2>T1
• h = thickness of a plate

Thermal diffusivity:

• k = K/(p*cp)
• where K is thermal conductivity, p is density, cp is specific heat (pressure dependent).
• For rocks k = 15-60 km2/Ma. This means heat moves through rocks slowly.
• Relationship between depth of anomaly and age of occurrence:
• above circa 15 m can see seasonal signal.
• down to about 150 m a century long signal would be seen.
• down to about 500 m a millenial signal would penetrate.
• the ice age signal is 1 km or deeper.
• Deepening frost during spring thaw? Observation by farmers.

Discussion questions:

• What might be ideal situation to uncover this thermal record, or flip side, what are potential complications? Key to understanding this is the relationship between atmospheric T and ground T, i.e. the nature of "thermal coupling" between atmosphere and lithosphere.
• Where would be good sites?
• What will information about one locality tell you?
• What are the general results?
• What can the results be compared with to look for consistency?

Summary: This crude but robust technique provides results consistent with global warming in the last century. However, it doesn't address the causes.

Convergent validity and explanatory power in the context of multiple records.

Discussion question for next time: Concentrate in on the graphs showing various signals (dust/ash content, methane, carbon dioxide, various isotope values) in the vertical ice core successions. Which ones correlate well with each other? Which ones ones don't? What are some of the system links behind these correlations or lack thereof.