Guest essay by Eric Worrall
Paleo-climate experts have advanced a theory that weathering of Indonesian mountain ranges is starving the planet of CO2, which is keeping the Earth locked in the ongoing Quaternary ice age.
Rise of carbon dioxide–absorbing mountains in tropics may set thermostat for global climate
By Paul VoosenDec. 28, 2018 , 3:00 PM
Hate the cold? Blame Indonesia. It may sound odd, given the contributions to global warming from the country’s 270 million people, rampant deforestation, and frequent carbon dioxide (CO2)-belching volcanic eruptions. But over much longer times, Indonesia is sucking CO2 out of the atmosphere.
Many mountains in Indonesia and neighboring Papua New Guinea consist of ancient volcanic rocks from the ocean floor that were caught in a colossal tectonic collision between a chain of island volcanoes and a continent, and thrust high. Lashed by tropical rains, these rocks hungrily react with CO2 and sequester it in minerals. That is why, with only 2% of the world’s land area, Indonesia accounts for 10% of its long-term CO2 absorption. Its mountains could explain why ice sheets have persisted, waxing and waning, for several million years (although they are now threatened by global warming).
Now, researchers have extended that theory, finding that such tropical mountain-building collisions coincide with nearly all of the half-dozen or so significant glacial periods in the past 500 million years. “These types of environments, through time, are what sets the global climate,” said Francis Macdonald, a geologist at the University of California, Santa Barbara, when he presented the work last month at a meeting of the American Geophysical Union in Washington, D.C. If Earth’s climate has a master switch, he suggests, the rise of mountains like Indonesia’s could be it.
Kimberly Lau, a geochemist at the University of Wyoming in Laramie, calls the work “exciting in idea and novel in execution.” Lee, however, would like to see direct evidence from ancient sediments that the collisions drove up rock weathering. “They have to go to the sink and study those,” he says. And a recent study challenges the mountain thermostat idea with evidence for the importance of volcanoes. The study used ages from thousands of zircons, durable crystals that can indicate volcanic activity, to show that upticks in volcanic emissions were the dominant force driving the planet’s warm periods. It’s likely both teams have at least one hand on the truth, adds Lee, who contributed to the zircon paper.
The beauty of his team’s model, Macdonald said at the end of his talk, is that it explains not just why glacial times start, but also why they stop. A hothouse Earth appears to be the planet’s default state, prevailing for three-fourths of the past 500 million years. An Indonesia-style collision may push the global climate into a glacial period, but only for a while. Mountains erode and continents drift. And the planet warms again.
The abstract of the paper;
PLATE TECTONIC DRIVEN CHANGES IN PLANETARY WEATHERABILITY AS THE LONG-TERM CONTROL OF EARTH’S CLIMATE STATE
SWANSON-HYSELL, Nicholas L.1, MACDONALD, Francis2, PARK, Yuem2, JAGOUTZ, Oliver3 and GODDERIS, Yves4, (1)Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, (2)Department of Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106, (3)Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 54-1212, Cambridge, MA 02139, (4)CNRS, GET, Toulouse, 31400, France
Long term changes in Earth’s climate resulting in shifts between prolonged non-glacial and glacial intervals are widely considered to result from plate tectonic processes. However, the primary tectonic drivers for long-term climatic variability remain unclear. On geological time-scales, CO2 is emitted primarily by volcanism and consumed primarily by the chemical weathering of silicate rocks. Prolonged imbalances between sources and sinks would catastrophically manifest in either the onset of a Snowball Earth or a runaway greenhouse. The relative clemency of Phanerozoic climate requires that CO2 sinks scale with sources, which can be explained through the silicate weathering feedback where elevated CO2 leads to higher temperatures and invigorated hydrological cycling that enhances chemical weathering and vice versa. Given that CO2 sources and sinks must equal on long timescales, what sets steady-state CO2 levels on Earth at a given time? And what determines whether Earth is in a glacial or non-glacial climate state? The concept of global weatherability is a useful framework to address these questions. On a more weatherable planet, the CO2 concentration needed for the sink to equal the source is lower than on a less weatherable planet where CO2 increases until high enough levels are reached for the chemical weathering flux to be sufficiently large. Global weatherability is the product of variables such as lithology, tectonic uplift rates, and paleolatitude, which are set by evolving plate tectonic boundary conditions. In this contribution, we evaluate long-term changes in paleogeography and mountain-building and their connections to Phanerozoic climate. We seek to test the hypothesis that ocean basin closure, arc-continent collision and ophiolite exhumation exert a major control on Earth’s climate state by enhancing global weatherability. Using paleogeographic models, we reconstruct the past position of a new database of ophiolite-bearing sutures. We find that when extensive arc-continent collisions have occurred in the tropics the Earth has experienced a glacial climate, and otherwise, the Earth has been in a non-glacial climate state. We interpret plate tectonic driven changes in rock type and topography in the tropics to be the most significant control on Earth’s long-term climate state.
Despite the ongoing alarm about anthropogenic global warming, the reality is that in paleo-climate terms the Earth is currently experiencing a very cold climate, with vast areas of the planet rendered uninhabitable by permanent ice sheets, and the constant ongoing threat that further cooling and glaciation could drive us out of regions we currently inhabit.
The following quote from Wikipedia puts the cold of our current Quaternary ice age into perspective.
… The Current or Quaternary Ice Age is the last of five known major glacial periods, or ice ages, during Earth’s history, the preceding ones being the Karoo Ice Age (360–260 Ma), Andean-Saharan (450–420 Ma), Cryogenian (720–635 Ma) and Huronian (2,400–2,100 Ma). …