Field of Science

Microbes and Climate Change

Since the very first little blobs of entropy-defying life first appeared around four billion years ago, micro-organisms have played a major role in shaping the temperature of the planet by adjusting the balance of gases in the air. It could even be argued that global warming was one of the first effects of life, when the first methanogens (methane producing bacteria) started pumping greenhouse gasses into the new atmosphere. The evolution of photosynthesis lead to the great oxidation event, and over time the balance of gasses in the atmosphere stabilised into its current composition: lots of nitrogen (controlled by nitrogen fixing bacteria), medium amounts of oxygen (controlled by photosynthesis) and much smaller amounts of carbon dioxide (also controlled by photosynthesis, of both plants and bacteria).

Until humans, the general gaseous air composition was controlled almost exclusively by bacteria, with plants (mostly algae) having a lesser effect on carbon and oxygen levels. Animals didn't really get much of a look in until humans started releasing all the locked up carbon in fossil fuels.

Bacteria that are currently contributing to global warming are the methanogens, most notably those in the gut of ruminant mammals (i.e cows, sheep and other edible things). Cows and sheep can't break down cellulose in the plant material that they eat, so they have bacteria that do it for them. Unfortunately this process releases huge amounts of methane, and methane is around 20 more planet-warming than carbon dioxide.

When I went to Copenhagen last year (I didn't go for the conference, in fact I didn't realise it was on until I started wondering why it was so hard to find a hostel room!) someone handed me a leaflet saying that climate change could be prevented if everyone in the world became a vegetarian. It was an ... interesting point of view, but you could see where the idea came from. Cows are little methane factories.

Just in case anyone forgot what a cow was.

However bacteria are also heavily involved in keeping climate change under control with photosynthesis, which uses up carbon and releases oxygen into the environment. Despite being very leafy and green, forests (even rainforests) tend not to be huge carbon sinks, they take up carbon during the day certainly, but at night they respire and use most of it up again, and anything they've stored tends to be released once they die and decompose. Marine cyanobacteria, however, take in carbon like its going out of fashion, and when they die they sink down to the bottom of the ocean and lock it all away in calcified rocks. One of the most prolific carbon-eating bacteria is Prochlorococcus. Around 100 million Prochlorococcus can be found in every litre of seawater and, along with fellow bacteria Synechococcus it removes about 10 billion tons of carbon from the air every year.

In terms of helping to moderate climate change, there are plenty of ideas floating around as too how bacteria could be useful, but one of the more helpful ones is trying to make a bacterial-based carbon neutral biofuel. The idea is that if you find bacteria that take up as much carbon for their growth as they release while being used as fuel they are technically 'carbon-neutral'. You can grow pretty much anything in bacteria, up to and including oils that can drive cars, it's just currently not very efficient.

Whether or not anything can be done to stop climate change (or, more importantly, whether or not people can agree to do anything) may be an unresolved issue, but its becoming clear that the issue of how the worlds climates are changing is a subject for microbiologists and plants-scientists as much as for meterologists. Whatever happens to the climate in the future, bacteria will still have a large part to play.


Exams and course-work are all over, so from now on I am hoping to keep this blog purely for the prokaryotes:


Lucas Brouwers said...

Isn't the real difficulty to create such an environment, where producing way too much carbon is actually beneficial, as opposed to nature where bacteria are probably to produce 'just enough' for their own survival?

It would be such a great synthesis of science if synthetic biologists, microbiologists, climatologists etc. could tackle this problem.. It might be a bit utopian, but I think it is much more likely that the 'solution' comes from biology, rather than some of the ambitious geo-engineering approaches that have been proposed.

Lab Rat said...

@lucas: Thing is, for methanogens etc. producing way too much carbon is beneficial, it's just the general surroundings of algae and cyanobacteria can control that to produce what is essentially the optimal gas conditions for Rubisco (or maybe Rubisco just evolved to specialise for those conditions or more likely a bit of both!)

With the burning of fossil fuels and increase in farmed ruminants there's suddenly this massive influx of carbon and methane on a relatively very small time scale. I think the main thing about humanity is that it does things *quickly*. Events like bringing down mountains, cutting holes in rocks, and releasing tons of carbon would previously take evolutionary or geographical time-scales and are now being achieved incredibly fast.

I think you linked to that diagram of the life-time of the earth in one hour (or one day). When you think of how much humanity has managed to do in that short period it seems quite spectacular.

As for the 'solution' I have a hunch that it might come more from engineering; possibly because I know some engineers working on solution ideas and their a lot more realistic than microbiologists and more useful than climatologists. But more people working from different disciplines together would be the ideal solution.