Note from Kathy: We live and work in a very complex system that doesn’t always correspond with some of the simple explanations I’ve encountered in the grazing world. I believe that the more we know about what is happening, the better decisions we can make, and that’s why I share higher degrees of complexity with you. The downside, is that what you learn may feel daunting or even downright depressing if you don’t have some additional good news to consider as well. So at the end of this article, I include some good news that gives us an opportunity to take a deep breath and maybe make lemons from our lemonade.
Thanks to Esprit Smith of NASA’s Jet Propulsion Laboratory for this article. I made a few minor additions to speak to interests and concerns of On Pasture readers.
Land ecosystems currently play a key role in mitigating climate change. The more carbon dioxide (CO2) plants and trees absorb during photosynthesis, the process they use to make food, the less CO2 remains trapped in the atmosphere where it can cause temperatures to rise. But scientists have identified an unsettling trend – as levels of CO2 in the atmosphere increase, 86 percent of land ecosystems globally are becoming progressively less efficient at absorbing it.
Because CO2 is a main ‘ingredient’ that plants need to grow, elevated concentrations of it cause an increase in photosynthesis, and consequently, plant growth – a phenomenon aptly referred to as the CO2 fertilization effect, or CFE. The CO2 Fertilization Effect, is considered a key factor in the response of vegetation to rising atmospheric CO2 as well as an important mechanism for removing this potent greenhouse gas from our atmosphere – but that may be changing.
For a recent study, researchers analyzed multiple field, satellite-derived and model-based datasets to better understand what effect increasing levels of CO2 may be having on the CO2 Fertilization Effect,. Their findings have important implications for the role plants can be expected to play in offsetting climate change in the years to come.
“In this study, by analyzing the best available long-term data from remote sensing and state-of-the-art land-surface models, we have found that since 1982, the global average CO2 Fertilization Effect, has decreased steadily from 21 percent to 12 percent per 100 ppm of CO2 in the atmosphere,” said Ben Poulter, study co-author and scientist at NASA’s Goddard Space Flight Center. “In other words, terrestrial ecosystems are becoming less reliable as a temporary climate change mitigator.”
What’s Causing It?
Scientists have been concerned about how long the CO2 Fertilization Effect could be sustained because, while an abundance of CO2 won’t limit growth, a lack of water, nutrients, or sunlight – the other necessary components of photosynthesis — will. To determine why the CFE has been decreasing, the study team took the availability of these other elements into account.
“By combining decades of remote sensing data, we’re able to see these limitations on plant growth. What our data shows appears to be happening is that there’s both a moisture limitation as well as a nutrient limitation coming into play,” Poulter said. “In the tropics, there’s often just not enough nitrogen or phosphorus, to sustain photosynthesis, and in the high-latitude temperate and boreal regions, soil moisture is now more limiting than air temperature because of recent warming.”
In effect, climate change is weakening plants’ ability to mitigate further climate change over large areas of the planet.
You can learn more about this change in this week’s article on declining forage quality.
What Does This Mean?
“What this means is that to avoid 1.5 or 2°C warming and the associated climate impacts, we need to adjust the remaining carbon budget to account for the weakening of the plant CO2 Fertilization Effect,” he said. “And because of this weakening, land ecosystems will not be as reliable for climate mitigation in the coming decades.”
Now Some Good News
There are two reasons scientist give us for the weakening of the CO2 Fertilization Effect: limited nutrients and in some places, a lack of water. There is something that we can do about this: Spread compost.
Compost helps us in a lot of ways. First, it’s a great source of nitrogen and other plant nutrients. It helps solve the limited nutrients problem plants are facing. Second, just one application acts as a kind of medicine for the soil. As my good friend John Wick says, “Life comes from life. Compost is living substrate that reinvigorates the system and begins carbon sequestration.” You can read more about how much and for how long your soil will begin sequestering durable carbon in this month’s Grazier’s Focus. While compost can’t make more rain, it helps soil hold more water. So plants can stay greener longer, and continue doing their job of pulling CO2 from the air. Finally, compost solves another greenhouse gas problem we have, food waste that rots and releases methane into the atmosphere.
How can you get started? Visit your local Natural Resources Conservation Service office and ask them about Conservation Standard Practice Code 336. It’s a new standard practice that provides for technical and financial assistance for spreading compost. You can also take a page from the book John Wick helped write for how to work with your local communities and governments to encourage support for composting and for providing assistance to farmers and ranchers. You’ll find more about that in this week’s article on