Trees and Plants Losing Capacity to Stop Climate Change

Trees and plants absorb carbon dioxide, mitigating climate change. Find out why a new study concludes that this C02 fertilization effect is getting weaker.

People who deny that climate change is happening, caused by humans, and a crisis are becoming few and far between. Even so, I do still run across members of this declining population now and then.

Against my better judgement, I continue to engage specimens of this disappearing breed in a debate when challenged. One of the climate myths they often resort to is that carbon dioxide (C02) can’t be bad for the environment because it’s “plant food.”

The notion here is that the more C02 there is in the air, the better it is for plants. So, the more carbon emissions we generate, the better it is for the environment. 

Wishful Thinking and Motivated Reasoning

Even if C02 raises the temperature, plants thrive in warmer conditions, so that will create a lusher, greener Earth for all of us, the myth goes. This is nothing more than wishful thinking and motivated reasoning.

Everyone learns about photosynthesis in public school. We know that we inhale oxygen and exhale carbon dioxide while plants do the reverse.

At the same time, we’ve also all experienced situations where “too much of a good thing” did more harm than good. If one dose of medicine is good, two doses usually aren’t better.

C02 Fertilization Effect (CFE)

NASA has just published a new study in the journal Science. The study looked into what scientists call the C02 fertilization effect (CFE).

The CFE is the tendency for rising levels of C02 to stimulate plant growth. We’ve been counting on the CFE to play a vital role, causing plants to absorb C02 levels in the atmosphere and mitigating climate change.

The research findings suggest that this model is unduly optimistic. The study found that the capacity of plants to absorb and benefit from C02 is declining.

CFE Has Dropped from 21% to 12%

The CFE has dropped from 21% down to 12% per 100 ppm of CO2 since I was in university back in 1982. This means that land-based ecosystems won’t absorb the excess carbon we emit at the levels we expected to prevent warming.

The researchers used data from field studies, satellite observations and computer models. Their goal was to better understand how the CFE works and what trends they could identify.

They found that the efficiency of the CFE is dropping. If we think back to our biology classes, we’ll remember that C02 wasn’t the only photosynthesis component.

Raising C02 but Not Moisture and Minerals

Water, sunshine and nutrients like nitrogen or phosphorus are also vital to the process. Raising C02 levels without boosting the soil’s moisture and mineral content seems to work against the CFE rather than enhancing it.

Ben Poulter is a scientist at NASA’s Goddard Space Flight Center. He’s a co-author of the study. 

Professor Poulter explained, “According to our data, what appears to be happening is that there’s both a moisture limitation as well as a nutrient limitation coming into play. 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.”

Can’t Depend on Land Ecosystems as Carbon Sinks

This implies that, as climate change has increased, it has weakened the plant fertilization process from C02. This means that we can’t depend on our land-based ecosystems to act as carbon sinks in the ways they have up until now.

Trees and plants in many global regions are becoming less able to draw in our extra C02 from the atmosphere. Suppose the carbon dioxide stays suspended in the air. In that case, the greenhouse effect will intensify, and global warming will increase even faster than predicted. Climate change weakens the ability of plants to mitigate further climate change.

The vicious cycle became more apparent when the investigators looked at remote sensing data from sources like NASA’s Advanced Very High-Resolution Radiometer (AVHRR) and the Moderate Resolution Imaging Spectroradiometer (MODIS). They concluded that the CFE is deteriorating much faster than current land-based models have forecast after reviewing the data.

CFE is Deteriorating Much Faster than Forecast

The inaccuracy in earlier projections is because scientists have difficulty taking the effects of moisture and nutrients into account. They haven’t had access to enough global information to take the water and soil feedback into account.

Professor Poulter went on to say, “By combining decades of remote sensing data like we have done here, we’re able to see these limitations on plant growth. As such, the study shows a clear way forward for model development, especially with new remote sensing observations of vegetation traits expected in coming years.”

By “remote sensing data” Professor Poulter means any technique that allows people to study an object without touching it. We’re seeing a sweeping revolution of this type of technology in ecology, especially from orbital satellites.

Sweeping Revolution in Remote Sensing

Besides MODIS and AVHRR, scientists have access to the Sentinel satellites from Europe and the Dove satellites from the Planet organization in San Francisco. The Google Earth Engine is also available for this kind of work.

Even more importantly, there are powerful new software tools for processing and interpreting the data. 

As Professor Poulter puts it, “These observations will help advance models to incorporate ecosystem processes, climate and CO2 feedbacks more realistically.”

Exciting as the new research capabilities are, the conclusions that science is drawing from them are less hopeful. The more we learn about ecosystems’ role in the global carbon cycle, the more challenging the task of mitigating climate change seems to be.

Land Ecosystems Will Not Be as Reliable For Climate Mitigation

“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,” Professor Poulter explained. “And because of this weakening, land ecosystems will not be as reliable for climate mitigation in the coming decades.”

Returning to the “carbon dioxide is plant food” argument, science shows that’s not how things work. Plants won’t benefit from the added C02 in the atmosphere because it’s out of synch with moisture and nutrient levels in the soil.

Nature always operates in a delicate balance. It’s also far more complex and intricate than simplistic models can account for.

Bring Our Activities into Harmony with Nature

Humanity needs to bring our activities into harmony with the ecosphere. We can’t expect nature to accommodate our activities instead.

Understanding the story of how life evolved on our planet and the interrelatedness of all living things is vital to our survival. If we don’t all grasp that story, our future is looking bleak and dismal. Fortunately, our minds can adapt.

We always have more to learn if we dare to know.
Learn more:
Land Ecosystems Are Becoming Less Efficient at Absorbing CO2
Recent global decline of CO2 fertilization effects on vegetation photosynthesis
Climate Crisis Becomes Undeniable
Hottest Decade Ever Recorded Announced by UN
Soil Animal Biomass Declining Sharply

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