We're Fertilizing the Heck Out of Our Planet and It's Not a Good Sign
The world is getting greener. A global analysis of satellite data finds that an area two times the size of the continental US has gone from brown to green over the past thirty years. Human carbon emissions are doing a hell of a job fertilizing the planet-but we probably shouldn't celebrate.
"This was very surprising to see," Ranga Myneni, an Earth scientist at Boston University and co-author on a new Nature Climate Change study detailing planet Earth's fresh look told Gizmodo. "A huge amount of greening is happening, nearly everywhere on Earth."
Along with sunlight and water, CO2 is the key ingredient plants need to build new biomass. So it isn't surprising that when you give plants more carbon, they have a growth spurt. Dozens of studies have documented this "
Pulling long-term data from two of NASA's Earth-orbiting satellite sensors, Myneni and his co-authors have discovered a dramatic 33-year increase in the global "leaf area index"-the amount of land surface covered by green things. The greening, which totals roughly 7 million square miles (18 million square kilometers), is distributed across the continents, from the Arctic tundra to tropical rainforests to the African savannah. Using sophisticated global vegetation models, the team showed that some 70 percent of the effect can be explained by CO2 fertilization.
First and foremost, most experts agree that CO2 fertilization is probably a temporary effect. The reason is simple: anything that limits growth, whether it's sunlight, water, carbon, or even physical space, can only simulate plants up to a point. Eventually, they run into some other resource limitation. This principle, called "
Liebig's law of the minimum
," was developed in agricultural
CO2 fertilization also stands to impact plant growth in unexpected ways. It's possible, for instance, that some plants are putting out more leaves at the expense of roots, which could have detrimental effects on their long-term health.
Finally, some ecologists worry CO2 fertilization will have dramatic feedbacks on the entire climate system. For instance, plants pump a lot of water from the ground into the atmosphere; a process known as transpiration. "When plants have more leaves, they can pump more water into the atmosphere, resulting in more clouds and rainfall," Myneni said. "This could make the hydrological cycle more vigorous."
Even if CO2 fertilization brings some benefits, we can't say burning fossil fuels is a good thing without looking at the big picture. That picture includes
ice sheet melting
sea level rise
"If you tally the harmful and beneficial impacts of having more CO2 in the air, I think the negatives are bigger," Myneni said.
At the end of the day, planetary greening is another shred of evidence that humans have become a dominant force of nature. As for what it means? We'll have to watch and wait as our global climate experiment unfolds.