With climate change, yields might decline 30-46 per cent over the next century if the globe warms slowly and by 60-82 per cent if emissions continue at the current levels. Yields increase up to 29°C for corn, 30°C for soybean and 32°C for cotton. Anything above that affects the crops, said economist Michael Roberts of North Carolina State University, USA. He conducted the study, using a climate change prediction model, with fellow economist from Columbia University.

They took data on the crop yields for the years 1950-2005 from the US Department of Agriculture. They showed the temperature range that exists historically in croplands and the temperature range that was likely. If yields go down in the US, it would drive up prices of staple food commodities all around the world, Roberts said. While there is a consensus on changes in yield, there is no agreement on the extent of changes and the factors causing them, said Josef Schmidhuber, lead author of a chapter on agriculture in Intergovernmental Panel on Climate Change’s fourth assessment report.
He has identified 200 factors such as rainfall and soil acidity that would affect yield. Three caveats could ease the problem, said Roberts. One, the greening theory in which more CO2 could offset some negative effects, which is a topic of intense debate; two, development of heat-tolerant crops by companies like Monsanto, which has little evidence of adaptation in the past; and three, farmers shifting the area of cultivation. A scientist from Yale contested the study’s findings and said agriculture in the US would improve with climate change. “These results focus on grains in the US grown on rainfed land, which is a fraction of US crops. Irrigated land is also crucial. The study does not necessarily apply to non-grains, irrigated crops, or livestock,” said Robert Mendelsohn, professor of the School of Forestry and Environmental Studies, Yale University.
Gauri Kashyap
Down To Earth Feature Service

Snows of Kilimanjaro: History soon?
The famous Snows of Kilimanjaro that cap Africa’s highest mountain are melting so fast they could be gone within two decades, according to a study of the mountain’s ice fields that used data going back nearly a century. Scientists believe global warming rather than local weather changes is chiefly to blame for the rapid loss of ice from the Tanzanian peak. A study comparing new measurements with those taken in 2000 show that a layer of ice between six and 17 feet thick has vanished from the summit since that time.
Not only are the mountain’s glaciers retreating at an unprecedented rate, but its remaining ice is thinning. The researchers predict that if current conditions persist, the mountain could be ice-free as early as 2022. The snows of Kilimanjaro will then exist only as a memory — and the title of a short story by Ernest Hemingway. Scientists made their forecast after combining data from aerial photographs and ground measurements of ice thickness. They found that the total area of Kilimanjaro's ice fields had shrunk by nearly 85 per cent between 1912 and 2007. More than a quarter of the ice present in 2000 was now gone.
The Guardian

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