Our planet runs on sunlight. The steady stream of free energy that rains down on us from above keeps us warm, drives our cycles of wind and rain, and powers the photosynthesis that ultimately feeds very nearly every living thing on Earth.

In 1998, the Earth's photosynthesizing plants, algae and phytoplankton used sunlight to bind up an estimated 104.9 petagrams (104.9 billion metric tonnes) of carbon into biomass. (That's net production, not gross . . . this is the total after the primary producers used some of their own energy for their own basic metabolic needs.) Production was split almost evenly between land and water . . . ~54% came from land plants, and ~46% from the oceans.

That's the (net) primary production for our entire planet, before anything else (like us!) gets to eat. One year of sunlight, across every photosynthetic organism on earth . . . 104.9 billion tonnes of carbon.

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Left: Earth's net primary productivity (on land), over 14 years of data. Public domain/NASA.


Every fossil fuel in existence today was once living things: mostly plankton, but also plants, algae, fungus, bacteria, and the occasional animal. And like everything else in the food chain web, those living things were ultimately fed by photosynthesis, by sunlight. The coal, oil, and natural gas that daily powers our machinery represents scattered pockets of photosynthetically-trapped sunlight, removed from circulation and buried in stone for hundreds of millions of years.

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Since 1870, humans have released an estimated 375 billion metric tonnes of trapped fossil fuel carbon back into the atmosphere. That total is heavily weighted to the recent side (over a third of it was since the year 2000), and lately we've been adding 9 more tonnes each year.

Assuming 1998's 104.9 petagrams was an average-ish year, 375 billion tonnes of carbon represents 3 years, 6 months, and 27 days of net primary production for the entire planet. 3½ years of every plant and plankton on earth converting sunlight to glucose. And our "9 billion tonnes more per year"? That's more than another month of global photosynthesis, stacked onto all the rest, year after year after year.

And that's before anybody else (including us!) gets to eat. Net primary production is not the same as a net gain in biomass . . . from year to year—at least, before the Industrial Revolution—there's a pretty good balance between production and consumption, as producers get eaten. And then their consumers get eaten, and then those consumers get eaten, and eventually Simba is born. In the end, 100 billion tonnes of carbon might mean little or no (or even negative!) change in global biomass.

There are other places for carbon to go than into primary production. But regardless, we've built up a massive surplus of carbon, equivalent to what would be tied up after three and a half full years of global photosynthesis. Three and a half extra years of sunlight with nowhere else to go. That's a deep hole to dig ourselves out of.

Top photo in the public domain. Via Wikimedia Commons.