We never know as much we think we know

From Photosynthesis fight: researchers see green over carbon dioxide results by Kimberly Riskas.

One of the challenges in forecasting around climate change is all the moving parts. These are complex dynamic, interrelated loosely coupled systems. As an example, rising CO2 levels in the atmosphere likely has some negative consequences, possibly on heat retention (though we cannot be certain because our knowledge is still fragmentary). On the other hand, while it might cause some problems, it might also be beneficial by accelerating plant growth (CO2 being plant food).

This article does not answer any of these questions. It illustrates the yeoman's work being done in labs across the world, trying to understand the complex interactions of many dynamic systems, in any of which, our theoretical understanding is partial and our empirical body of knowledge is limited. There are surprises all around.

Earlier this year, a study published in the prestigious journal Science shook up the biology world by turning an accepted paradigm of plant growth on its head.

But now a pair of researchers is calling the findings into question, but the authors of the original work are standing their ground.

In comment pieces in the current issue of Science, the two sides face off over issues of soil conditions, plant biology and experimental design.

The original work, led by Peter Reich at the University of Minnesota, US, sought to understand how plant growth is affected by long-term high carbon dioxide levels. For 20 years, the team compared two groups of plants that employ slightly different methods of photosynthesis: the C3 pathway and the C4 pathway. (Read our report of the study here.)

Prevailing plant biology dogma states that C3 plants are more sensitive to atmospheric carbon dioxide levels than are C4 plants. Therefore, plants using the C3 pathway should produce more biomass as levels rise.

Much to the researchers’ surprise, the C3 plants grew well initially, but then lost their edge after 12 years. Instead, the C4 plants showed accelerated growth in the last eight years of the study, with increases in biomass outstripping the control plants by as much as 24%.

To explain the switch in growth rates, Reid and colleagues hypothesised that long-term high carbon dioxide levels triggered changes in soil microbes and nutrient cycling — changes that favoured C4 plant growth but hampered that of C3 plants.

The findings suggested that it may be difficult to predict with certainty just how much atmospheric carbon can be captured by plants in the future. As the effects of anthropogenic climate change continue to unspool, Reich cautioned, “We shouldn’t be as confident [that] we’re right about the ability of … ecosystems to save our hides.”

The rest of the article is about respectful but divergent interpretations by different teams.

Reminds me of that line by Friedrich August von Hayek in The Fatal Conceit

The curious task of economics is to demonstrate to men how little they really know about what they imagine they can design.