Solar Luminosity Cycles

Extrinsically, insolation derived from the sun is a very important factor in driving climate and sea level change. As mentioned, insolation will vary based on changes in the Earth's orbital fluctuations (i.e., Milankovitch Cycles). If nothing else changed, given Earth's current tectonic configuration and geography, modifications to the Earth's orbit, rotation, axis tilt, could produce some profound climate changes on the time scales discussed. Nevertheless, we are becoming increasingly aware that changes in solar energy output can be driven by processes taking place within the sun itself, processes which impact solar luminosity on even shorter time scales (timescales below Milankovitch cycles). Solar luminosity is defined as the power outputted from the sun. Changes in solar energy output have been detected (you may have heard about sun spot cycles), and it appears that increased frequency of sunspots may cause increased rates of energy delivery to Earth.

Some scientists have shown that a decadal cycle in sunspot activity is noticeable, and there is increasing evidence that time periods where the sun is dimmer result in colder climates on Earth and vice versa. For instance, there is a great deal of information about the Medieval Warm Period, and the Little Ice Age that are now linked to changes in solar output. As such, the so called "Maunder Minimum" correlates with the most severe part of the Little Ice Age and their co-occurrence suggests solar luminosity may have contributed to the growth and advance of glaciers at the time.

Additional information on paleoclimate research can be accessed at the NOAA Paleoclimatology website hosted by the National Climatic Data Center.This is a great resource that will provide you additional information on climate forcing factors at various time scales. We highly recommend that if you are unclear on ideas up to this point that you spend some time exploring the website.

Ultimately, it should be apparent that climate variability on centennial and millennial scales (less than a few 1000) years must also play a role in temperature and in sea level change as glacial ice melts and as seawater undergoes expansion as temperatures go up (again see the last web link for clarity on temporal scales).

If insolation and greenhouse gases have the capacity to produce large scale changes in global climate (temperature) as suggested by the data above, we must look at Holocene sea level data to see how it changed too. Remember that the latest Pleistocene warming leading into the Holocene is generally attributed to a rise in global temperatures of 5 degrees Celsius.