By Dr. Sebastian Lüning
(Translated/edited by P Gosselin)
The climate of the last 10,000 years has not been as stable as leading IPCC scientists assume. Over the last 10 years there has been a flurry of papers from studies conducted all over the world (Figure 1) and they reveal cyclic fluctuations of the climate on a 1000-year scale. The climate changes are synchronous with solar activity, which indicates that the sun is the main driver behind climate change. The same can be said about the climate over the last 1000 years, and for the recent warming of the 20th century.
Figure 1: Overview of literature on solar activity and global millennial cycles. Black dot indicates the location of Matthew Schmidt’s area of studay of his recent publication.
The newest publication appeared in the journal Paleoceanography in July, 2012. A team of scientists led by Matthew Schmidt of Texas A&M University studied a sediment core taken 200 meters below the sea surface in the Florida Strait. The core covers the last 10,0000 years of climate (see black dot in Figure 1). The Gulf Stream passes through this narrow strait on its way north, thus making it an important connecting link between the tropics and the high Atlantic latitudes.
It’s been long known that the climate history of the Florida Strait is closely coupled with the climate development of the high Atlantic latitudes. As temperatures in the North Atlantic plummeted during the Little Ice Age, the Florida region became much drier.
Matthew Schmidt and his team focused on the first half of the post Ice Age period, from 9000 to 6000 years before today. Did climate patterns similar to those during the Little Ice Age exist back then as well? To answer that question the scientists reconstructed the temperature development over the 3000 year period using an array of techniques.
The result was not surprising
Also during the early post Ice Age times dry periods over the Florida region occurred with regularity. When the climate cooled in the North Atlantic, along with other regions of the world, the rains failed over the Florida Strait region. In the Pacific, the El Nino-events become more frequent (Figure 2). Solar activity also set the beat in other parts of the world, as confirmed by the results of studies by Gerard Bond.
There was one exception. The authors found a dry Florida period at the 8200 year mark (gray bar, Figure 2). Here they interpreted regional deviations and the effects of system-internal cycles.
Overall, Schmidt and his colleagues determined that solar activity fluctuations also played a very important role on the global atmospheric circulation system during the early post Ice Age time. Here there are clearly recognizable solar-driven climatic cycles on a millennial scale.
Figure 2: Climate development during the early post Ice Age was synchronous with solar activity (exception: cool phase 8200 years ago, marked with a gray bar). Phases of low solar activity led to cold temperatures in the North Atlantic and dry conditions over the Florida region (blue dashed lines). In periods of high solar activity (red dashed lines), Florida was wetter. Schmidt et al. (2012)
The American scientists also performed a frequency analysis of the climatic fluctuations and found the characteristic cycles with periods of 1500, 90 and 60 years (Figure 3). Schmidt and his colleagues interpreted the 1500 year cycle as those that Gerard Bond described earlier. The data set also contained the 60-year cycle, which likely mirrored the Atlantic Decadal Cycle.
Figure 3: Frequency analysis of the oxygen isotope cycles of the sediment core for the period 9100 to 6200 years before today. From Schmidt et al. (2012).
The study by Matthew Schmidt and his colleagues is yet another important piece to the puzzle in understanding the sun as a major factor in driving climate. Are the media going to report on this? Don’t hold your breath.