German scientists contend that two natural cycles will combine to lower global temperatures throughout the 21st Century.
The scientists show that there is an approximate 200-year solar cycle, supported by historical temperature data and proxy data from stalagmites in caves. “The solar activity agrees well with the terrestrial climate. It clearly shows in particular all historic temperature minima.”
There is also an approximate 65-year cycle of the Atlantic/Pacific oscillation (AMO/PDO) which is well-established by multiple lines of observations.
The 200-year solar cycle has just passed its maximum and will decline during the 21st Century. It is at least in part responsible for the warming of the last decades of the 20th Century. The AMO/PDO cycle is also beginning its cool phase and will reach a minimum in 2035.
The scientists say that “Non-periodic processes like a warming through the monotonic increase of CO2 in the atmosphere could cause at most 0.1°C to 0.2°C warming for a doubling of the CO2 content, as it is expected for 2100.” This positive forcing will be overwhelmed by the stronger negative forcing of natural cycles. They conclude that “the global temperature will drop until 2100 to a value corresponding to the “little ice age” of 1870.” Read more here. Below is a graph of historical temperatures and temperature predictions.
This work has been published in two papers:
H.-J. Lüdecke, A. Hempelmann, and C.O. Weiss: Multi-periodic climate dynamics: spectral analysis of long-term instrumental and proxy temperature records, clim. past, 9, 447-452, 2013
F. Steinhilber and J. Beer, Prediction of solar activity for the next 500 years, Jour. Geophys. Res. Space Phys., Vol. 118, 1861-1867 (2013)