The media are reporting stories with a new theme: More CO2 is bad for plant life. This flies in the face of biochemistry, but the activist motivation is clear: They want people thinking CO2 is bad in every way. They don’t want the warming scare undermined by the idea that CO2 along with warming actually helps plant life and agriculture.
The current stories are coming from researchers involved with an outdoor laboratory site called Jasper Ridge, affiliated with Stanford University, my alma mater and home to famous alarmist Stephen Schneider (deceased). The headlines are occasioned by a new paper appearing Sept. 5 in the journal Proceedings of the National Academy of Sciences, authored by Chris Field, director of the Stanford Woods Institute for the Environment..
Headlines Claim, Details Deny
Headlines and claims like those below are appearing this week, but as we shall see, the details do not support the conclusions claimed; a leap of faith (bias) is required.
“There’s been some hope that changing climate conditions would lead to increased productivity of grasses and other plants that draw down carbon dioxide from the atmosphere,” said study lead author Kai Zhu, a global ecologist and data scientist at Rice “In northern California, it was hypothesized that net grassland productivity might increase under the warmer, wetter conditions that are predicted by most long-term climate models. Our evidence disproves that idea.”
Plants like carbon dioxide — the main heat-trapping gas. Some people argue that because of that, climate change isn’t so bad and will mean greener Earth. But the experiment’s findings contradict that. At least in the California ecosystem, plants that received extra carbon dioxide, as well as those that got extra warmth, didn’t grow more or get greener.
“This experiment really puts to bed the idea of a greener hypothesis where ecosystems save us from the implications of human-induced climate change.” Chris Field, director of the Stanford Woods Institute for the Environment.Field, whose study appears Monday in the journal Proceedings of the National Academy of Sciences, theorizes that there’s a limit to how much carbon dioxide plants can use.
The Principle of Limiting Factors
Botanists subscribe to the principle that each species has a range of conditions that it can tolerate, and each factor has an ideal level for that species. When a factor deviates from ideal, it constrains the growth and becomes the limiting factor.
- The following are regarded as the most important environmental factors
· Moisture supply
· Radiant energy
· Composition of the atmosphere
· Soil aeration and soil structure
· Soil reaction
· Biotic factors
· Supply of mineral nutrients
· Absence of growth-restricting substances
The first four factors can be considered as climate factors, while the others vary for other reasons. Scientists are conducting experiments in many places to measure the effects of climate factors, both singly and in combination.
Empirical Tests of CO2 and Plant Life
With respect to CO2 the Free-Air CO2 Enrichment or FACE technology was developed as a means to enrich the air with CO2 around vegetation while having minimal effects on the surrounding microclimate. Some of those experiments were conducted on various grassland species, many of which were growing naturally in pastures. CO2 science provides details here.
Dr. Sylvan H. Wittwer, professor emeritus of horticulture at Michigan State, describes the results:
Thousands of scientific experiments have been conducted to measure the effects of carbon dioxide enrichment on specific plants. In most green plants, productivity continues to rise up to CO2 concentrations of 1,000 ppm and above. For rice, the optimal CO2 level is between 1,500 and 2,000 ppm. For unicellular algae, the optimal level is 10,000 to 50,000 ppm. Bruce Kimball, a research leader of the Water Conservation Laboratory of the U.S. Department of Agriculture in Phoenix, Arizona, has pulled together nearly 800 scientific observations from around the world measuring the response of food and flower crops to elevated CO2 concentrations. The mean (average) response to a doubling of the CO2 concentration from its current level of 360 ppm is a 32 percent improvement in plant productivity, with varied manifestations in different species.
Dr. Wittwer directed the Michigan Agricultural Experiment Station for 20 years, and chaired the Board on Agriculture of the National Research Council. He provides details on the interaction of CO2 and plants in his article Rising CO2 is Great for Plants
What’s Different about Jasper Ridge
The attempt to overturn vast evidence of CO2 benefiting the biosphere involves manipulating several factors, including non-climatic ones. Chris Field, director of the project in an interview:
In order to create a realistic possible future environment for these grasslands, we’re manipulating four environmental factors. We’re doubling the concentration of atmospheric CO2. It’s currently about four hundred parts per million, or 0.04 percent in the atmosphere. Our targeted level for the experiments is 0.07 percent, seven hundred parts per million, which is a level that, depending on CO2 emissions, we might reach anywhere in the second half of the century.
We’re increasing the average temperature using heat lamps by about three degrees Fahrenheit. This is at the low end of the projections for the second half of the century. But it’s a practical level for us to achieve without a really massive infrastructure.
We’re also adding nitrogen pollution. It’s better known as acid rain. But it’s biologically available nitrogen that comes also from fossil fuel combustion and other industrial processes. We’re adding it at a level that’s typically experienced now in areas in Northern Europe, in the Northeastern U.S., which are relatively polluted.
The fourth environmental factor that we’re manipulating is rainfall. In general, at the worldwide scale, we know that as it gets warmer, the amount of precipitation basically has to increase because more water is evaporating from the ocean. We don’t know whether a given spot will be wetter or dryer. But by having a precipitation increase, we can untangle the interaction between the other treatments and the precipitation, and more or less create a framework where we can evaluate the impact of precipitation in each of the other factors.
The way our experiments are designed is that we have two levels of each of these four major factors, CO2, warming, Nitrogen pollution, and extra precipitation. And we have all of the different combinations of the two levels. So we have all the two treatment combinations, the three treatment combinations, and the four treatment combinations. Each of those is replicated eight times. Because we’re imposing these treatments on a natural ecosystem, we have lots and lots of variability from place to place and time to time. And the only way that we can be confident that we’re seeing the true effects of our treatments and not just environmental variability, is if we have enough replicates of each treatment that we can extract out the signal from the noise.
One of the most unexpected results we’ve had in the Jasper Ridge Global Change Experiment is the realization that under a wide range of conditions, increased atmospheric CO2 does not lead to increased plant growth. In fact, under many conditions, elevated atmospheric CO2 actually prevents plants from taking full advantage of other resources that are available in the environment. This has quite profound implications for our understanding of ecosystem response to global change and for future climate change. If plants, in fact, don’t grow more under elevated carbon dioxide, it means that atmospheric CO2 is likely to grow faster in the future than we have been anticipating. It basically puts a lot more pressure on societies to figure out how to control emissions of carbon dioxide rather than stepping back and hoping that ecosystems will help us solve the fossil fuel problem.
Once we realized this, it was really important to figure out what the mechanism was; because we know from lots of laboratory studies that the instantaneous rate of plant growth or photosynthesis almost always increases under elevated atmospheric CO2 . We did a variety of experiments that tried to infer the mechanisms from the observations that we were able to take in the existing experiment; these lines of evidence pointed to the fact that there was another mineral nutrient, another kind of fertilizer, that was required for plant growth that was preventing them from taking advantage of the elevated atmospheric CO2 and it might even be becoming less available under elevated CO2. But we couldn’t be sure unless we did a separate experiment. The evidence suggested that this limiting resource was probably phosphorus.
There you have it. The experiment confirms the principle of limiting factors. At present concentrations, rising CO2 always increases plant productivity unless another factor is sub-optimal and constrains growth. The researchers, aided and abetted by the media are spinning this to say more CO2 is not good for plants. In reality, the lack of phosphorus or other nutrients is not the fault of CO2, and will not be enhanced by somehow reducing CO2.
Dr. Wittwer’s conclusion stands: Rising CO2 is Great for Plants.
Crabs really love CO2 as well.