Increasing levels of carbon dioxide in the atmosphere have been blamed for planetary warming with resulting climate change. But what do we really understand about it? How much is out there and how much do we need to remove to blunt the worst effects of climate change? How would we do a project so big?

Good questions all. Some answers below.

Estimates vary but according to the U.S. Energy Information Administration (EIA), there are between 5 and 6 trillion tons of greenhouse gasses (GHGs) in the atmosphere, most of them carbon dioxide. It’s difficult to get an exact number because until recently it has been increasing and concentration fluctuates with the northern hemisphere’s growing season. When green plants grow during the summer months concentration abates somewhat. Lately, with the replacement of some coal-fired power generation and other efficiencies, the rise in the quantity of CO₂ in the air has slowed, however we’re still pumping between 35 and 45 gigatons of CO₂ into the air each year.

Because 5 trillion tons is such a big number, precision is less important than magnitude. More often, CO₂ is reported as a concentration in the air we breathe. The current CO₂ concentration is just over 400 parts per million (PPM) compared to about 280 ppm at the dawn of the Industrial Revolution.  Simply put, this means that in an air sample containing a million molecules, 400 of them would be CO₂—not much but enough to cause significant climate change. It also means that since the Industrial Revolution we’ve pumped an additional 120 ppm into the air.

A trillion can also be written as one thousand-billion, and taking one billion tons of CO₂ out of the air annually, as some have suggested, may be a worthwhile demonstration project, but it is really table stakes unless we can ramp up our efforts significantly. For example, a few years ago, Sir Richard Branson introduced the Virgin Earth Challenge for anyone who could produce a method of removing 1,000 tons of CO2 from the atmosphere per year for ten years. The expectation was that the eventual solution would be scalable to meet the climate need. The challenge came with a prize of $25 million. Despite all this the prize goes Unawarded to this day.

Now to put this in perspective, there’s no need to take all 5 or 6 trillion or so tons of CO₂ out of the atmosphere. Simple math suggests that on the order of 3.85 trillion tons of CO₂ have been introduced into the environment by the consumption of fossil fuels since the Industrial Revolution. It would be inadvisable to remove all carbon dioxide from the air because green plants need it right where it is if they’re going to do the job of making food for the rest of the world.

If we could remove just one trillion tons of CO₂ from the air though we’d see an appreciable improvement in climate quality. But even with that reduced ambition, if we could only take a billion tons of CO₂ out of the air per year it would take 1,000 years. We will need a faster solution.

Let’s take a look at the natural process of photosynthesis, for instance, to see what’s possible. Today green plants, including food crops, grasses, trees, mosses, and tiny sea creatures like algae and phytoplankton, capture solar energy at an annual rate estimated at 130 terawatts, which equals more than 6 times the power consumed by human civilization. With all that energy, green plants turn this solar energy into biomass equal to between 100 and 115 billion tons—again, not all of it is food.

So here’s a suggestion: If we could find ways to double the photosynthetic output on the planet and if we could prevent even some of that biomass from decaying back into its starting products, including CO₂, we’d have a solution that could remove one trillion tons of CO₂ from the air in about a decade. If our effort went slower we could still save the environment, after all, we’ve been adding carbon to the atmosphere for more than 250 years and the fact that we’d be moving in the right direction counts for a lot. But the scale of any effort needs to be in the many tens of billions of tons per year, not a just one billion.

This is purely hypothetical since we don’t have the arable land, fresh water, or as-yet unspecified storage capacity for that much biomass. Still, the idea is thought provoking because it at least lets us conceptualize the need, and with that concept as a goal we can perhaps iterate toward a solution. Actually, there are suggestions for how to boost photosynthesis on the planet and that’s a subject for another post.