The ancient geo engineers would use volcanic ash to control rising temperatures on Earth such as what we are experiencing today, however normal weather conditions on Earth is usually spent in an ice age for 100 thousand years, and then 13 thousand years in a warming climate such as what we are enjoying today. So this pyramid/volcano (PV) control system would see most of its use during an ice age environment, as having a 1000 foot rise in sea level pales in comparison to our possible 20 foot rise in sea level. Now that being said we can still use this system to keep us in this temperate climate we love and enjoy today, but it must be used before total cloud coverage of the Earth happens, total planetary cloud coverage is where Earth is heading with the higher ocean temperatures more water vapor will consume the atmosphere and block out the sun light. The PV system will also block out sun light and cool the Earths oceans the same as total cloud cover will but to have both ash and cloud cover happen at the same time might cause a super cooling plunge that could be enough to plunge us into another ice age. The ancient geo engineers in their infinite wisdom would stay ahead of the curve and discharge ash into the atmosphere to keep the oceans cool and the cloud or water vapor to a correct ratio for the ideal global environmental balance.   

Shaughnessy 2013 ©