Global Warming 2020

Global Warming News : Rising Surface Ozone Reduces Plant Growth And Adds To Global Warming

Scientists from three leading UK research institutes have just released new findings that could have major implications for food production and global warming in the 21st century.

Experts from the Met Office, the University of Exeter and the Centre for Ecology & Hydrology, have found that projections of increasing ozone near the Earth’s surface could lead to significant reductions in regional plant production and crop yields. Surface ozone also damages plants, affecting their ability to soak up carbon dioxide from the atmosphere and accelerating global warming.

Near-surface ozone has doubled since 1850 due to chemical emissions from vehicles, industrial processes, and the burning of forests. Dr Stephen Sitch, a climate impacts scientist at the Met Office Hadley Centre and lead author of the article, said: “Climate models have largely ignored atmospheric chemistry but in this research we have identified a cause of potentially increased warming with elevated levels of surface ozone likely to suppress plant growth.”

Plants and soil are currently slowing–down global warming by storing about a quarter of human carbon dioxide emissions, but the new study suggests that this could be undermined by further increases in near-surface ozone. As a result more carbon dioxide would accumulate in the atmosphere and add to global warming. Co-author, Professor Peter Cox of the University of Exeter, explains: “We estimate that ozone effects on plants could double the importance of ozone increases in the lower atmosphere as a driver of climate change, so policies to limit increases in near-surface ozone must be seen as an even higher priority.”

Source: http://www.sciencedaily.com/releases/2007/07/070725143612.htm

Global Warming – Climate Change News : Increased Carbon Dioxide In Atmosphere Linked To Decreased Soil Organic Matter, Decreased Plant Growth

A recent study at the University of Illinois created a bit of a mystery for soil scientist Michelle Wander — increased carbon dioxide in the atmosphere was expected to increase plant growth, increase plant biomass and ultimately beef up the organic matter in the soil — but it didn’t. What researchers found instead was that organic matter decay increased along with residue inputs when carbon dioxide levels were increased and they think the accelerated decay was due to increased moisture in the soil.

“Going into the study, the assumption was that higher levels of carbon dioxide in the atmosphere will increase crop yield and soil organic matter,” said Wander. “We did see a 30 percent increase in above- and below- ground soybean biomass so we expected that to be mirrored in soil organic matter, but there wasn’t an increase. In fact, organic matter levels may have even been lower than in plots not exposed to elevated carbon dioxide levels.”

The study was conducted at U of I’s SoyFACE facility — an open air laboratory in which rings of pipes surround corn and soybean crops and can be exposed to various levels of carbon dioxide, ozone or both pumped through the pipes.

“My student Adriane Peralta and I were looking at younger soil organic matter that would be most influenced by today’s practices and we were expecting a big change — a 30 percent increase in soil organic matter, reflecting the changes we saw above ground.

“The source of carbon is plant biomass, so we would expect increased yield, increased biomass, increased soil organic matter in the soil. This kind of positive feedback would be good because it could offset the increases in decay that will result from rising temperature,” said Wander. She explained that the increases in carbon dioxide levels in the atmosphere insulate the earth and contribute to global warming. Average annual air and soil temperatures are increasing while winters are getting shorter. By the end of the century, maximum daily temperatures could rise by 5 to 12 degrees Fahrenheit in winter and 5 to 20 degrees Fahrenheit in summer.

“We know that microbial activity is directly influenced by an increase in temperature if other factors, like moisture aren’t limiting their growth,” she said. “Increased decomposition of organic matter is undesirable from a soil quality and climate perspective; microbial degradation of organic stocks releases carbon and nitrogen and over the long term this reduces soil’s productivity and ability to resist erosion, plus it returns the carbon dioxide to the atmosphere.” All of this talk about using agricultural lands to mitigate climate change depends upon our ability to keep the carbon in soil reserves.

Wander said that carbon dioxide is rising every year in the atmosphere because of human use of fossil fuel and deforestation. “We attribute the higher soybean yields over the past several decades to the rising carbon dioxide levels in the Earth’s atmosphere — some attribute a 10 percent increase in soybean yields already due to this carbon dioxide fertilization effect.

“Most models or projections of the future assume the carbon dioxide fertilization effect would be a good thing for agriculture and the world’s food supply and have a benefit to soil organic matter, but more and more we are finding things are a little more complicated. What our study shows is that in this system, rising carbon dioxide levels are not contributing to soil health after all.

“So, we had a bit of a mystery to solve. Where did the organic carbon that was added by increased plant growth go” We know for certain that soil organic matter stocks result from the balance of inputs and decay so we had to look at factors influence decomposition. Nutrient levels soil pH and available N were all high in this fertile field and so we ruled these factors out.”

Wander and Peralta suspect soil moisture plays a role. Wander points out that changes in rainfall are another important aspect of climate change and notes that we are already seeing shifts in the distribution of rainfall with increases in winter and spring rains with drier summers. Dry conditions can constrain plant growth and microbial decay rates. So, what they saw in the SoyFACE plots, was evidence of an important feedback — where crops exposed to elevated carbon dioxide became more water use efficient.

“When plants take up moisture they open their stomata — the pores through which they transport both carbon dioxide and water and when plants satisfy their need for carbon dioxide they can close those stomata and conserve water. This appears to have happened at SoyFACE in both corn and soybean crops. So, moisture feedbacks that increased microbial activity might solve the mystery”. Wander said it’s a little tricky to project the future with these findings, because they are manipulating carbon dioxide but not rainfall in the SoyFACE test plots.

“We have learned that we can’t say ‘yield equals organic matter.’ We have to understand the nuances of the time and place. SoyFACE is giving us early clues about what could happen in the future and where to direct our research attentions.” The frontier of science right now includes anticipation of these interactions –reality might be stranger than the fiction that we create in the laboratory- even in an open field study like SoyFACE.

The findings from the study are published in the February issue of Plant and Soil.

Adapted from materials provided by University of Illinois at Urbana-Champaign.

Source: http://www.sciencedaily.com/releases/2008/03/080311123413.htm