We review a range of recent studies of natural cycles in climate change on the scale centuries to millennia.The time span 0 to 2000 CE has been considered by multiple groups with results ranging from only a minor signature of natural cycles, to dominant natural cycles without an AGW signature.The Luedecke-Weiss analysis finds three overwhelmingly dominant centennial cycles which represent theglobal warming from 1850 to 1990, thus casting doubt on human-caused global warming as the sole factorin global temperature change of the past century.The Abbot-Marohasy analysis used records for the years 50-1830CE and machine learning methodology;projecting from 1830 they find a fit between predicted and observed proxy global temperatures wasachieved by incorporating an AGW component with a value ECS=0.6 °C.The Scafetta et al approach uses proxy data 0-2010 CE to fit 8 harmonic components together with acomposite GCM, and find an optimal fit using ECS=1-2.3 °C.Asten studied alkenone temperature proxies from four temperate-zone ocean cores identifying with periodsof order 10k, 6k and 2.3k years especially well developed in a core from the Okinawa trough.The documented natural cycles invite predictions of future temperature trends. Differing projections rangefrom a sharp sunspot-related cooling this century; a cooling of 1 °C by 2200 CE; a warming of 1.5-2°C by2100 CE, and an additional cooling component from millennial cycles acting over the next 1000 years. Wediscuss compatibility/incompatibility of these results inview of parameters and assumptions used in thedifferent studies.
|Number of pages||1|
|Publication status||Published - 2018|