What do mountains have to do with climate change? More than you’d expect: new research shows that the weathering rates of mountains caused by vegetation growth plays a major role in controlling global temperatures. Scientists from the University of Oxford and the University of Sheffield have shown how tree roots in certain mountains “acted like a thermostat” for the global climate.
In warmer climates, tree roots grow faster and deeper (aided by the decomposition of leaf litter), breaking up rock that combines with carbon dioxide. This weathering process removes carbon dioxide from the atmosphere, lowering the global temperature and decreasing the growth rate of vegetation.
This is the valley in the Southern Peruvian Andes where fine root growth and organic layer thickness were measured over several years. Photo credit: Cecile Girardin.
“This does seem to be a self-regulating process,” lead author Christopher Doughty told mongabay.com. “However, it is important to note that plants did not evolve to regulate climate in this way. It is likely a fortuitous coincidence or maybe life would have gone extinct without this process long ago and we wouldn’t be here to talk about it.”
The research helps resolve the enigma of how the climate remained stable enough to support life despite repeated global climatic events.
“It has always been a mystery why climate has remained stable for life despite several large changes in temperature that could have negatively impacted life,” Doughty said. “There are several mechanisms where life basically stabilized climate for life – we think that this is one of those mechanisms. It is important because it helps us to better understand how life has maintained itself on this planet for so long.”
Unfortunately, the authors don’t think these mountain thermostats will help prevent human-caused climate change.
“This is an important process to stabilize global climate, but also very slow,” Doughty explained. “It requires thousands to millions of years to stabilize climate. This is too slow a process to have any noticeable effect on the CO2 people are adding to the atmosphere by burning of fossil fuels. Over millions of years, the increased CO2 will accelerate weathering, but this will not help humans deal with anthropogenic climate change.”
Cloud forest in the Peruvian Amazon. Photo by Rhett A. Butler / mongabay.com
The effect also doesn’t work everywhere; some regions don’t absorb nearly as much carbon dioxide as others.
“Weathering happens in most regions, but most [significant] weathering occurs in regions of uplift and regions of granite and basalt,” Doughty said. “Therefore, mountainous regions are most important for this process. Mountains made of basalt in warm regions of the globe are the most important. Therefore, the mountains of Ethiopia are actually surprisingly important… more so than the much larger Himalaya Mountains, which are colder and not made of basalt.”
To study this effect, the researchers examined the weathering of rock at different locations in Peru, from the lowland Amazon to cloud forests in the Andes.
“We placed many mesh bags of root-free soil into the ground,” Doughty said. “We then waited three months, dug up the bags, counted and weighed the roots. We did this over a several year period so we have a good understanding of root growth patterns, which in the past has been notoriously difficult to study.”
The researchers discovered the thermostat effect almost by accident, while studying the ecology of tropical forests and how they allocate carbon. Only when analyzing the data did they realize that mountains were acting as climate stabilizers.
“We studied the growth of tree roots to better understand how tropical forest trees allocate their carbon as temperatures change,” Doughty said. “It was only later, after examining the data, that we realized that this mechanism could stabilize long-term climate too.”
While still in the early stages of research, this discovery may someday help further our understanding of the origins of life on earth, as well as providing clues as to how temperature changes might affect life in the future.
“It is very interesting to research the question of how life may stabilize climate for life, and also relatively understudied,” Doughty said. “It can be difficult to understand how large changes in temperature may affect life, which is why the Andes region of Peru was such a good area to study this. I think in the future we must take advantage of such natural laboratories as the 3,000-meter elevation transect in Peru to see the long-term impacts of changing temperatures on life.”
- Doughty C, Taylor L, Girardin C, Malhi Y, Beerling D. Montane forest root growth and soil organic layer depth as potential stabilizing Cenozoic global chnage. Geophys Res Lett. 2014;10:1–8. doi:10.1002/2013GL058737.