640,000 Years Of Climate Change

Written by Doug L. Hoffman

A new study of the Asian Monsoon record has shed light on Earth’s changing climate over the past six-hundred and forty millennia. Drawn from an exhaustive and painstaking examination of the relative proportions of the oxygen isotopes 16O and18O in stalagmites, records from Chinese caves characterize changes in both the Asian monsoon and global climate. This record supports the idea that the 100,000-year glacial/interglacial cycle is an average of discrete numbers of precession cycles. Further more, changes in insolation, the amount of energy received from the Sun, triggers deglaciations and shorter term millennial events. No evidence supporting the upstart theory that CO2 controls climate change is reported.

While the theory that CO2 might contribute to warming the Earth has been around for more than a century, the idea that it is the climate control knob that dictates climate change is relatively recent. This idea, simplistic and easy to sell to an unwary public, has severely damaged the young field of climate science. Thankfully, the carbon dioxide global warming kerfuffle has not deterred conscientious scientists from pursuing other research. In a paper appearing in the 30 June, 2016, edition of the journal Nature, a team of researchers lead by Hai Cheng, of the Institute of Global Environmental Change, Xi’an Jiaotong University, China, has shed new light on historical climate change history. In “The Asian monsoon over the past 640,000 years and ice age terminations,” a wealth of new information on past climate variability over an exceptionally long time period, and with precise dating, is presented. Here is the paper’s abstract:

Oxygen isotope records from Chinese caves characterize changes in both the Asian monsoon and global climate. Here, using our new speleothem data, we extend the Chinese record to cover the full uranium/thorium dating range, that is, the past 640,000 years. The record’s length and temporal precision allow us to test the idea that insolation changes caused by the Earth’s precession drove the terminations of each of the last seven ice ages as well as the millennia-long intervals of reduced monsoon rainfall associated with each of the terminations. On the basis of our record’s timing, the terminations are separated by four or five precession cycles, supporting the idea that the ‘100,000-year’ ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands, and is nearly in anti-phase with summer boreal insolation. These observations indicate that insolation, in part, sets the pace of the occurrence of millennial-scale events, including those associated with terminations and ‘unfinished terminations’.

Cheng et al. measured the relative proportions of the oxygen isotopes 16O and 18O in stalagmites to determine the intensity of past monsoons in central China. Rainwater, turned into weak carbonic acid by soil carbon dioxide, leaches calcium carbonate (CaCO3) and traces of uranium (U) from limestone rock. As the water percolates into the cave, it loses part of its CO2, depositing calcium carbonate that forms stalactites and stalagmites. The carbonate retains the rainwater’s original oxygen-isotope composition and uranium traces. The uranium slowly decays to thorium (Th), acting as a record of the time since calcite deposition. The ratio of oxygen isotopes (δ18O) provides an indication of conditions when the rain that caused the leaching fell. The researchers used these processes to compile a remarkable time series of monsoon variability over 640,000 years.

While this new, exacting record has allowed scientists to reconfirm the importance of orbital cycles in forcing changes in Earth’s climate this research has brought new insights as well. The new record covers much of the time since the so-called Mid-Pleistocene revolution and crosses the Mid-Brunhes Event (MBE). The MBE marked a change in the glacial/interglacial cycle. “The amplitude of glacial–interglacial cycles in CO2, Antarctic temperature, and global ice volume (or sea level) increased substantially after the MBE,” the researchers report. The details of this can be seen in the figure below, taken from the paper.

This paper contains a wealth of information and observations, far too many for this short post. But I want to draw particular attention to the author’s conclusions regarding what causes the coming and going of glacial ice, the waxing and waning of the current ice age. Here WMI stands for Weak Monsoon Interval and HS stands forHeinrich Stadial. Again, quoting from the Nature paper:

The unparalleled length and temporal precision of our cave record allow us to extend the aforementioned approach to robustly test ideas about the classic ‘100-kyr problem’. Our data indicate that glacial terminations T-VII to T-V were also associated with WMIs. The T-V WMI occurred between ~430.5 ± 1.5 and ~426 ± 2 kyr bp. The T-VI WMI, centred at 532.3 ± 3.5 kyr bp, has a duration of ~4.5 kyr, assuming a linear growth rate of sample SB-32 around this time period. The T-VII WMI is broadly similar to that of T-II, T-IV and T-V, ending abruptly at 627 ± 6 kyr bp. Each coincides presumably with a major HS, a sea level rise marking each glacial termination, a CO2 rise, and an Antarctic temperature rise. These observations, now for the past seven terminations, support the hypothesis that rising NHSI triggers an initial ice-sheet disintegration, which in turn perturbs the oceanic and atmospheric heat and carbon cycles,resulting in a CO2 increase, which further drives the termination.

As scientists suspected, long before the current CO2 hysteria, carbon dioxide does not cause changes in climate on its own. Yes, it is a greenhouse gas and, yes, it does contribute marginally to warming the globe, but it is a feedback caused by other forcing events. It does not cause glacial periods to end, nor does it cause warm interglacials to slip back into frigid glacial conditions. It simply isn’t that potent. In fact, its impact is limited, otherwise once a warming started the climate would experience thermal runaway. That this has not happened, with humanity gleefully pumping carbon dioxide into the atmosphere for centuries, is an indication of just how weak the impact of CO2 really is.

Will these new data cause the climate change alarmists to change their ideas? Probably not. They are too invested in the CAGW fiction, and too addicted to government grant money, to change their views at this point. The only thing that will erase the CO2 hoax will be the onset of the next glacial period, and that could be several thousand years in the future. Until then, we shall have to endure the ravings of environmental prophets of doom and global warming scam artists. Ignore them as best you can.

Be safe, enjoy the interglacial and stay skeptical.

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