The inexorable rise of carbon dioxide levels in the atmosphere and the steady increase in global temperatures raise the frightening prospect of significant change in Earth’s climate. Indeed, the evidence seems clear that our climate is altering rapidly.
So scientists and politicians the world over are looking for ways to halt or reverse these changes, a task that is fraught with difficulties in a world hooked on fossil fuels. One option increasingly discussed is terraforming—deliberately altering the environment in a way that cools the planet, perhaps by absorbing carbon dioxide or reflecting sunlight
To have an impact, these kinds of plans changes must have a global reach require engineering projects of previously unimaginable scale. That’s set bioengineers thinking that there might be an alternative option.
Instead of creating global engineering projects, why not create life forms that do a similar job instead. The big advantage of this approach is that organisms grow naturally and can spread across huge areas of the planet by the ordinary mechanisms of life. Thus the process of terraforming the landscape would occur with minimal human input. What could possibly go wrong?
Plenty. The big fear is that these approach could have unexpected and unintended consequences for the planet. One nightmare scenario is that the organisms might unintentionally trigger feedback mechanisms that accelerate global warming rather than mitigate it. So an important question is how to prevent this scenario.
Today, we get some answers thanks to the work of Ricard Sole and pals at the ICREA-Complex Systems Lab in Barcelona, Spain. These guys explore various ways of creating synthetic organisms that make it almost impossible to trigger unintended feedback loops that harm the planet.
They begin by pointing out that a particular problem is the possibility of explosive growth of populations of synthetic organisms when they are introduced or their spread to a particular environment. “One way of preventing undesired explosive growth is to use a modified version of an extant organism that exhibits a strict relationship with another species associated to the target habitat,” they say.
So the growth of one population of organisms depends on the population dynamics of another. “Recent experimental studies indicate that such designed mutualistic link can be created by artificially forcing a strong metabolic dependence and also with the help of genetic engineering,” they say.
Sole and co spend some time exploring this idea. They point out that this interdependence requires a double positive feedback where the synthetic species benefits, and is benefited by, its host. “This scenario is tied to the symbiotic relationships that characterize several types of natural associations, such as nitrogen-fixing bacteria living in plant root nodules,” they argue.
There are less direct forms of interdependence as well. Cooperation can also arise when one species modifies the existing environment in way that allows a partner species to thrive and create more growth opportunities for the first.
For example, it may be possible to engineer a microbe to release some kind of protein capable of enhancing water retention. Other organisms such as plants can then make use of this retained water.
There is another way of influencing population growth: by limiting the food supply. Sole and co suggest genetically modifying organisms so that they can feed only on human waste, such as garbage or sewage. Outside this environment, they simply die off.
“A good candidate could be plastic garbage in the ocean which is known to be colonized by many different species, including several microbial genus, such as Vibrio,” say Sole and co. They point out that despite the rapid increase in plastic waste dumped in the ocean, the amount observed is much less than expected. “[This suggests] (among other possibilities) that some microbial species capable to attach to plastic polymers are also degrading them,” they say.
That’s an interesting idea. If we’re going to actively modify the environment to tackle problems like global warming, it makes sense to use the growth and colonizing potential that life offers. That’s surely easier than engineering a structure of some kind to influence the planet on a global scale.
But it’s also a controversial idea. Sole and co say that the interdependence built into these models prevents runaway growth or feedback loops because it must happen to both species at the same time and that’s highly unlikely.
But it is by no means impossible. And there is evolution to contend with as well. While the synthetic organisms released into the wild may be safe, a few million generations down the line, their ancestors may not be.
Sole and co seek to dampen these fears by pointing out that humans have already changed Earth. “Despite the long, sustained and profound anthropogenic impact on many of these novel ecosystems, they can display a richness and resilience that reminds us the potential of nature to reconstruct itself,” they say. On the other hand, they also show how tenacious lifeforms can be and how hard it is to reverse these changes once they have occurred.
Releasing synthetic life forms with the specific goal of terraforming Earth may one day be an urgent necessity. If and when that day comes, let’s hope we’ll be glad of the research that has characterized how this terraforming will occur.
Ref: arxiv.org/abs/1503.05043 : Synthetic Circuit Designs for Earth Terraformation