What might cause more gradual changes in climate and what might cause more abrupt changes in climate?

What are fundamental questions with regard to solar variability Foukal focuses upon?

Recognition of chaotic behavior:

• log-log size-frequency linear relationship (also gives the fractal dimension).
• significance: can predict size and recurrence interval of larger events from a shorter record of small events. Done with earthquakes and faults.
  • caveats:
    • scale limits.
    • mode changes in behavior.

Any temporal correlations between sunspots and global climate?

• Maunder minimum - middle of Little Ice Age.
• historic winter warmings statistically connected to sunspot cycle.
• tree rings and the C-14 production good correlation.
• Sporer minimum from 1450-1550 based on C-14.

What are long term constraints on major fluctuation of solar output?

What are mechanics of solar sunspot cycles and why might they be instructive as to long term behavior?

• tied to magnetic fields and fluxes: reversals
• feedback cycles and self exciting dynamo
• might expect to be chaotic (magnetic reversals of earth are claimed to be), but the earth does not show anyting equivalent to the relative regularity of the 22 year solar cycle.

EUV cyclcity and potential feedback cycles in our system? E.g. ozone destruction leads to increase of UV at sea level a decrease in phytoplankton activity and a decrease in uptake of CO2.

Comments or thoughts on such a mechanism?

• basic research question: are climatic fluctuations periodic or aperiodic? Focus on changing orbital variables - Milankovich cycles.
• the previous literature cited emphasizes periodicities found in other records.
• methodology: statistical analysis of time-spectra of grain size in lake core.
• construction of a time scale necessary.
• assumption for purposes of this paper: silt fraction -> climate
• results: can identify periodicities and focus on a 1500 year cycle. R2 of .8 great.

Discussion questions:

• Did you find their arguments persuasive?
• If you have n periodicities with which to fit a line, what are your chances of finding a fit as n increases?
• Does this address the aspect of abruptness of change?
• How many 1500 cycles were sampled in their curve?

Readings:

• Schneider, D., 1997 (March), The Rising Seas, Sci. Am., 112-117.