USA Today: Climate change — due primarly to human-produced greenhouse gases but also because of natural variability — is the cause of most of the temperature increases observed in the USA since 1951, according to a new report released Thursday by the federal U.S. Climate Change Science Program. The report found that average surface temperatures over the USA have increased about 1.6 degrees since 1951, nearly all in the last 30 years. Last year, the United Nations’ International Panel on …