Advances in high-yield agriculture over the latter part of the 20th century have prevented massive amounts of greenhouse gases from entering the atmosphere – the equivalent of 590 billion metric tons of carbon dioxide – according to a new study led by two Stanford Earth scientists.
The yield improvements reduced the need to convert forests to farmland, a process that typically involves burning of trees and other plants, which generates carbon dioxide and other greenhouse gases.
The researchers estimate that if not for increased yields, additional greenhouse gas emissions from clearing land for farming would have been equal to as much as a third of the world's total output of greenhouse gases since the dawn of the Industrial Revolution in 1850.
There's an interesting twist here for greenies to note: Genetically engineered crops reduce CO2 emissions because genetic engineering raises crop yields. Funny but true. So Europeans opposed to genetic engineering of crops (and the center of such opposition seems squarely in Europe) are inadvertently working against a goal that the vast majority of them support: reduction of CO2 emissions in order to prevent global warming.
This report reminds me of Jevon's Paradox where part of improvements in fuel efficiency goes toward more energy usage as people do more things with the money saved on buying fuel. Well, in a similar manner improvements in agricultural efficiency raised living standards and boosted population growth. So how much of the improvements in agricultural efficiency really reduced the amount of farm land shifted into agriculture? Use of technological advances in farming to lower the cost of growing a ton of grain increases incentives for using more grain to feed animals (some of which emit warming gas methane btw).
For example, People respond to lower cost grain by feeding more grain to cattle, pigs, and chickens. So then they eat more meat and their indirect consumption of grain soars. Also, higher crop productivity per acre reduces the the amount of labor needed per ton of grain produced. That frees up labor work in factories and develop more capital equipment with which to burn fossil fuels. This cancels some of the effect of reduced CO2 emissions that would otherwise come from higher crop yields.
Speed is not a word typically associated with trees; they can take centuries to grow. However, a new study to be published the week of Feb. 1 in the Proceedings of the National Academy of Sciences has found evidence that forests in the Eastern United States are growing faster than they have in the past 225 years. The study offers a rare look at how an ecosystem is responding to climate change.
For more than 20 years forest ecologist Geoffrey Parker has tracked the growth of 55 stands of mixed hardwood forest plots in Maryland. The plots range in size, and some are as large as 2 acres. Parker's research is based at the Smithsonian Environmental Research Center, 26 miles east of the nation's capital.
Parker's tree censuses have revealed that the forest is packing on weight at a much faster rate than expected. He and Smithsonian Tropical Research Institute postdoctoral fellow Sean McMahon discovered that, on average, the forest is growing an additional 2 tons per acre annually. That is the equivalent of a tree with a diameter of 2 feet sprouting up over a year.
If this trend continues the amount of biomass tied up in these forests will continue to increase.
The researchers suspect higher temperatures, longer growing seasons, and more CO2 (which is nutritious for a plant) as causes.
It was not enough to document the faster growth rate; Parker and McMahon wanted to know why it might be happening. "We made a list of reasons these forests could be growing faster and then ruled half of them out," said Parker. The ones that remained included increased temperature, a longer growing season and increased levels of atmospheric CO2.
During the past 22 years CO2 levels at SERC have risen 12%, the mean temperature has increased by nearly three-tenths of a degree and the growing season has lengthened by 7.8 days. The trees now have more CO2 and an extra week to put on weight. Parker and McMahon suggest that a combination of these three factors has caused the forest's accelerated biomass gain.
Ecosystem responses are one of the major uncertainties in predicting the effects of climate change. Parker thinks there is every reason to believe his study sites are representative of the Eastern deciduous forest, the regional ecosystem that surrounds many of the population centers on the East Coast. He and McMahon hope other forest ecologists will examine data from their own tree censuses to help determine how widespread the phenomenon is.
Some plants benefit from more CO2 because they open their stomata to let in CO2 for shorter periods of time. This reduces moisture loss. Of course, if warming causes a drought in an area then the net effect on plant growth from warming will be negative.