Global thermostat?

Fears of global warming have funded a huge volume of scientific investigation over the past decade, and the more that has been learned the more complicated has become the climate picture.

The latest twists come in the form of carbon-dioxide (CO2) absorbing mountains, and greenhouse-gas producing, leaf-cutter ants.

At an American Geophysical Union meeting in Washington, D.C. last month, Francis Macdonald – a respected geologist at the University of California, Santa Barbara – offered a theory to explain global Ice Ages that tied them to a global thermostat controlled by CO2-absorbing mountains in Indonesia and nearby New Guinea.

In theory, Macdonald said, a giant, natural CO2 sponge is created when  “ancient volcanic rocks from the ocean floor that were caught in a colossal tectonic collision between a chain of island volcanoes and a continent” are pushed out of the sea by the collision of four different tectonic plates, reported Paul Voosen at Science.

“Lashed by tropical rains, these rocks hungrily react with CO2 and sequester it in minerals,” Voosen wrote. “That is why, with only 2 percent of the world’s land area, Indonesia accounts for 10 percent 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).”

Voosen’s story on Macdonald’s provocative presentation was headlined “Rise of carbon dioxide–absorbing mountains in tropics may set thermostat for global climate.” The climate twist attracted almost no mainstream media attention despite its suggestion that climate issues might be more complicated than just the human burning of fossil fuels.

“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,” Voosen reported. “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.”

Macdonald’s theory doesn’t directly contradict the prevailing belief that human-derived CO2 has been significantly boosting atmospheric CO2 levels since the beginning of the Industrial Age, but it does complicate the picture in that there might also be forces bigger than human-kind involved in driving climate shifts.

Planetary norm

“Over the past few years, Macdonald and his collaborators have searched for other times when tectonics and climate could have conspired to open an Indonesia-size CO₂ drain,” Voosen observed. “They found that glacial conditions 90 million and 50 million years ago lined up neatly with the collisions of a chain of island volcanoes in the now-vanished Neo-Tethys Ocean with the African and Asian continents. A similar collision some 460 million years ago formed the Appalachians, but it was thought to have taken place in the subtropics, where a drier climate does not favor weathering. By reanalyzing ancient magnetic fields in rocks formed in the collision, Macdonald’s team found the mountains actually rose deep in the tropics. And their uplift matched a 2-million-year-long glaciation. ‘They’re developing a pretty compelling story that this was a climate driver in Earth’s past,’ says Lee Kump, a paleoclimatologist at Pennsylvania State University in University Park.”

Macdonald’s team has been examining sites of past volcanic uplifts over the past half-million years and mapping them to see which might have formed in the tropics before drifting north or south into temperature regions.

Where uplifted rocks are located is vital to CO2 absorption. The CO2 removed from the air is bound to rock as calcium carbonate (CaCO3). The conversion happens most rapidly in warm, moist climates.

Some scientists have for years been studying how humans might duplicate this natural process and use rocks to suck CO2 out of the air. The costs, however, appear prohibitive.

“Current (human) CO2 emissions are around 40 billion tons a year; (current) natural weathering absorbs roughly 1.1 billion tons. Enhanced weathering could remove up to 4.9 billion tons per year if basalt is used, and up to 95 billion tons for dunite,” according to the Potsdam Institute for Climate Impact Research.

Unfortunately, the Institute added, “dunite – the rock type most discussed amongst experts – contains harmful substances, such as chromium or nickel, that could get released during the process. This is why for the present study dunite is an important benchmark, but the researchers focus on basalt as a more sustainable option.”

The Institute concluded that for humankind to do artificially what the mountains of Indonesia do naturally would be cost prohibitive if mined and ground basalt was used to suck up CO2.

Costs were pegged at about $200 per ton of CO2 removed – more than three times the $60 per ton cost of dunite, which the Institute considered economically viable.

Most European nations now impose “carbon taxes” on fossil fuels. The taxes have pushed gasoline prices to over $6 per gallon in France with taxes accounting for about 60 percent of the cost, the New York Times noted in a December report on the “Yellow Vest” riots in that country.

Climate costs

The “protests against the tax increase have become the biggest obstacle yet to such attempts to encourage conservation and alternative energy use. The protests point to the difficulties facing nearly all industrialized countries committed to pulling the world back from the cliff’s edge of catastrophic climate change,” Alissa J. Rubin and Somini Senguptat reported for the NYT.

What will happen with climate in the future is speculative, but there is a scientific consensus that humans have played a role in a well-documented increase in atmospheric CO2, one of three important greenhouse gases that have been steadily rising since the 1800s.

The other two important gases are methane (CH4) and nitrous oxide (N20), which is where those leaf-cutter ants enter the picture.

They are big producers of N20, a gas which is 100 times as powerful as CO2 in helping warm the planet over the long term. A 2017 study singled N2O out as potentially significant threat to Arctic environments, Scientific American reported. 

Like the other greenhouse gases, it is also vital to survival on earth. The planet would be just another cold, dead rock spinning through space without these gases.They let solar radiation penetrate to warm the planet, but slow the release of infrared radiation back into space.

In that way, the gases work much like the glass enclosing a greenhouse with the big exception being that the greenhouse gases are steadily trickling off into space and must be steadily replaced by new gas generated by natural processes on Earth.

“Without (these gases), the average surface temperature of the Earth would be about 33ºC (60ºF) lower than it is now, and life as we know it would be impossible,” according to Climate Central, which adds that it is also possible to have too much of a good thing.

“Venus has a much thicker atmosphere than Earth, most of it CO2, and the surface temperature there is above 444ºC (800ºF). Part of that is because Venus is closer to the Sun, but almost 389ºC (700ºF) of it is a result of Venus’ powerful greenhouse effect.”

Humanity evolved to survive in a relatively narrow range of temperatures between not too hot and not too cold.

“…Many of the factors forming the natural living conditions of human societies, such as climate, are largely depending on the distance to the equator,” geographers studying the distribution of the human animals concluded in a 2010 paper….We found that only less than one-eighth of the human population lives south of the equator while around 50 percent of the population dwell within the area between 20 degrees North and 40 degrees North (latitude).”

Madrid and Philadelphia are near 40 North. Mexico City is near 20 North. Los Angeles, Tokyo, Shanghai, New Delhi, Cairo and a host of other major global communities are within the band.

Global warming threatens to upset this balance of human occupation as it exists today. People are concentrated along the coasts, which could be flooded by rising seas as glaciers melt, and in that middle-of-the-planet band where some regions could become too hot for occupancy or suffer from losses of agricultural productivity because of heat and shifts in rainfall patterns.

Our fault?

Many now believe all of this is the result of humans messing with the planetary environment for thousands of years in various efforts to make life better for themselves, but humans aren’t the only animals so engaged.

“Leaf cutter ants are prominent ecosystem engineers throughout Neotropical forests,” observes a peer-reviewed study published earlier this month at Proceedings of the Royal Society: Biological Sciences. “Their foraging and colony construction behaviours relocate plant biomass and excavate soil, altering nutrient distribution and patchiness, and influencing forest structure, understory microclimate and regeneration patterns. As dominant forest herbivores, LCA harvest a wide range of material including leaves, twigs, flowers, fruits, seeds…and can remove up to 8 percent of standing live forest foliage annually The majority of this foraged plant material is relocated to subterranean gardens where it is used as a substrate to cultivate the mutualistic fungus that feeds the colony.”

Those subterranean gardens, in turn, crank out large volumes of N20. Think human farmers, cows and methane, and you’ll get the picture. 

“Together, our findings suggest that LCA activities can engineer substantial N2O hot spots in tropical forest ecosystems, actively creating sites with unique physical and biological conditions to support N₂O production rates many orders of magnitude greater than those typically observed in natural systems,” concluded Fonia Soper from the University of Montana, Missoula, and colleagues from the University of Nevada and Brown University.

Ant emissions, they reported,  appear “comparable to or greater than those produced by engineered systems such as wastewater treatment tanks. Refuse-concentrating Atta species are ubiquitous in tropical forests, pastures and production ecosystems, and increase density strongly in response to disturbance. As such, LCA colonies may represent an unrecognized greenhouse gas point source throughout the Neotropics.”

There is nothing to indicate the ants worry about their pollution, and for most of human history and for all of human prehistory, humans didn’t worry about theirs either. Now, they know better on many fronts, and worry about the fronts on which they don’t really know but believe they can forsee.