Too high screwed
Poor prospects are easier to cope with if there is at least a small silver lining somewhere. In the case of climate change, this was the expectation that rising carbon dioxide levels could increase harvests, at least in some regions, and thus iron out other negative effects. A misconception, as is always evident.
What will our world look like in fifty years, with an estimated 550 ppm carbon dioxide in the air? The we alth of scenarios is as great as the range of horrors associated with them. Even the International Panel on Climate Change (IPCC) harbored only a glimmer of hope: The increasing concentrations of the greenhouse gas should at least heat up food production in some regions and thus compensate for crop failures caused by drought on a global scale. Because theoretically, at 25 degrees Celsius, rice, soybeans and wheat would have to deliver 38 percent more yield - provided other effects are excluded. After all, researchers observed values between twenty and thirty percent in climate chambers and artificial greenhouses.
However, the first limitation follows immediately: The CO2 should probably actually boost photosynthesis in rice, soybeans and wheat, because the effectiveness of the process here is directly influenced by the carbon dioxide content of the air becomes. But not with maize and sorghum, which are among the most important grains in the tropics and subtropics: in these so-called C4 plants, photosynthesis is already running at full speed, decoupled from the CO 2 ambient concentrations. An increase in the greenhouse gas content in the environment therefore has no effect. Nevertheless, the IPCC assumes that there will be a slight increase in the harvest of C4 plants, as they will be able to make better use of their water reserves in the future. Because of the higher carbon dioxide content in the air, the plant can cover its need for the gas more quickly and keep its stomata, through which it controls the gas and water balance, more closed - this curbs the water loss.
But the forecasts from the IPCC and Co all face a major problem: the data they are based on - in particular on the growth behavior of plants under the assumed environmental conditions - are often from the 1980s and therefore comparatively old. And probably they are also useless because they come from laboratory conditions. But life in a glass greenhouse or in a climate chamber has very little to do with being in the open air. To remedy this deficiency, the FACE experiments were developed. The Free- Air gas Concentration Enrichments become plots additionally ventilated with carbon dioxide or ozone in the open air in order to simulate realistic future conditions. And the results of these long-term tests have already shaken many a climate model.
The University of Illinois' Stephen Long and his colleagues are also coming out with worrying data again. They used FACE to study the growth of traditional food plants. And with regard to expected growth in 2050, they came to just half of what climate chambers and greenhouse experiments suggested. In the case of rice, the increase in photosynthesis was only a quarter. And with C4 plants, FACE researchers saw no growth at all.
Even fertiliser, which in some experiments was chosen as the means of choice to further improve the yield, was hardly successful under FACE conditions: the yields of wheat and rice increased by nine percent - but only by a third compared to their conspecifics in the climate chamber. The FACE data thus make a mockery of current forecasts: According to the model, the increase in production due to carbon dioxide should easily compensate for expected harvest losses due to other climatic factors such as drought in the tropics by ten to thirty percent.
Enough bad news? Not for a long time. Long and his collaborators also point out that there is little research to date that reveals the coupled effect of rising carbon dioxide and ozone concentrations. Ozone is harmful to plants at very low levels, and its levels will also increase with climate change. However, while harvest declines of eight percent occurred in climate chambers, FACE tests easily showed losses of twenty percent and more. If the effects could simply be added together, the world would not see the 23 percent increase forecast by the IPCC, but actually a five percent drop. Globally speaking, climate change would not increase crop yields, but rather decrease them.
And now what? First of all, it is important to update the previous factors in the models and, of course, to investigate other interactions such as the influence of soil moisture and temperature. And then there is the discrepancy between theory and practice. What feedback mechanisms prevent photosynthesis from increasing to the calculated extent? Where else can leverage be applied in order to get more out of it? Could new plant varieties bring the solution? With impressive creativity and naivety, humans have found ways and means to upset the delicate balance on this planet. Now he has to do something similar to limit the damage as much as possible.
