Reuters: In the 1930s, fierce dust storms created by drought conditions and farming techniques that led to soil erosion swept the prairies of the western United States, causing widespread ecological calamity. But this so-called Dust Bowl period was just a small example of a huge increase in dustiness in the US West in the past 150 years due to human activities such as settlement, farming and livestock grazing, scientists said on Sunday. The researchers drilled into lake-bed sediments …