Avoiding A Frozen Earth

  • Date: 22/03/14
  • Doug L. Hoffman, The Resilient Earth

It would appear that planet Earth’s current configuration has created feedbacks that prevent a runaway climate catastrophe.

Forty million years ago, Earth began slipping from a “hothouse” climate to an “icehouse” climate. Currently the planet is in a brief warm interlude know as an interglacial—a period of retreating ice sheets and shrinking glaciers. As the word interglacial suggests, our current comfortable climate is not permanent, but merely a pause between frigid ice age conditions. Though climate alarmists and media talking heads continue to natter on about uncontrollable rising temperatures a more devastating climate change would be a descent into an ice age so cold and so deep that the entire globe freezes over—it has happened before. A new scientific paper reveals what researchers say is a feedback mechanism that acts as a natural thermostat and keeps Earth from cooling to the point of uninhabitability.

Most of the news regarding climate change is focused on warming and the mechanisms that regulate heat retention. The chosen culprit in the global warming brouhaha is the trace gas carbon dioxide, a known greenhouse gas. What is seldom mentioned is that CO2 does not have a linear effect on heat rate in the stratosphere or elsewhere. It has a much greater impact, proportionately, at low relative concentrations and a decreasingly weaker impact as atmospheric concentrations grow.

One of the upshots of this nonlinearity is that dropping CO2 should yield accelerated cooling, perhaps to the point of runaway global cooling. It is known that Earth has been totally frozen over at a number of times in the past, a condition called “Snowball Earth” by paleoclimatologists. The big question is how can Earth cool without plunging into another Snowball Earth period? That is the subject of a new paper, “Hydrologic Regulation of Chemical Weathering and the Geologic Carbon Cycle,” published in the journal Science.

Katherine Maher and C. Page Chamberlain, both of Stanford University, report that Earth’s temperature is regulated by a negative feedback between atmospheric CO2 levels and chemical weathering of silicate rocks. This feedback operates over million-year time scales and is strongest when global topography is elevated, as it is today. When mountain rangers are worn and low the mechanism is at its weakest. Here is how they frame the situation in the paper.

Despite substantial changes in solar luminosity, plate tectonics and atmospheric composition, over billions of years temperatures on Earth have remained favorable for liquid water, and by extension, life. A requirement for maintaining such clement conditions is a chemical weathering process that converts atmospheric CO2 and silicate rocks to alkalinity and divalent cations, which are then buried on the seafloor as carbonate minerals. Chemical weathering rates cannot be out of balance with the supply of CO2 from volcanic and metamorphic sources for very long without catastrophic consequences. Fortunately, such imbalances have been infrequent. Yet, Earth’s climate has varied between warm, ice-free conditions and cold, extensively glaciated states, suggesting a climate system with variable regulation. The stability of Earth’s climate thus requires both a negative feedback between chemical weathering rates and temperature, and a mechanism that allows the strength of the feedback, or extent of regulation, to vary. The strength of the feedback is dictated by the functional relationship between the weathering rate and climate, and when balanced against CO2degassing rates, determines planetary temperatures. Several processes could allow the strength of the feedback to vary, suggesting the mechanisms underlying one of the most profound features in the sculpting of Earth’s history remain unresolved.

The geologic portion of the carbon cycle operates on a much longer time-scale than the cycling of carbon through plants and other living things. Volcanoes supply carbon dioxide that can warm climate. But CO2 also dissolves in water, turning into carbonic acid (H2CO3)that can dissolve rock. The products of this weathering become runoff, flowing down rivers to the sea, where microscopic animals combine them with more carbon dioxide from the air to build hard skeletons. When the animals die all that carbon falls to the bottom of the ocean where it becomes sea floor sediment, which is eventually buried and becomes geologically sequestered for millions of years.

Since spare Earths that can be used for experimentation are in short supply, the authors created a model to test out their hypotheses. The proposed model combines two equations: “(1) a solute transport equation that quantifies weathering-derived solute as a function of the mean fluid travel time in a catchment; and (2) an equation that relates the supply of fresh rock from erosion to the downward propagation of a weathering front.” Fundamental to their calculations is a measure called the Damköhler number. [...]

In other words, a doubling of atmospheric carbon dioxide levels did not terminate the ongoing glacial period. For an excursion to 1000 ppm to register in the proxy record it must have been much longer than anything humanity will generate. This tells us that all of the hand-wringing about drastic and irreversible changes to the climate from human emissions are overblown. By the way, current thinking is that the Great Dying was caused by extensive and long term vulcanism spewing massive amounts of CO2 into the environment.

More over, on shorter time scales CO2 levels are always bouncing around, contrary to what some would have you believe. Friederike Wagner, Bent Aaby, and Henk Visscher, in “Rapid atmospheric CO2 changes associated with the 8,200-years-B.P. cooling event,” found a great deal of natural variation. Quoting from their PNAS paper: “In effect, there seems to be every indication that the occurrence of Holocene CO2fluctuations is more consistent with current observations and models of past global temperature changes than the common notion of a relatively stable CO2 regime until the onset of the Industrial Revolution.”

So it would appear that Earth’s current configuration has created some feedbacks that prevent the bottom from falling out of global temperatures when the climate dips into an Ice Age. It is logical to assume that there are similar feedbacks that prevent a runaway in the opposite direction, preventing the global warming catastrophe that the climate change alarmists are always babbling on about. Currently, global temperatures aren’t rising and there is conclusive evidence that elevated CO2 levels are good for plants. It seems that all of the bad things predicted by the climate alarmists are not coming true, but the good thingsthey deny are, so let’s stop all the scaremongering and deal with the real problems facing humanity.

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