It's hardly news that human beings have had a hand in the planetary warming that began more than 30 years ago. For nearly a century, scientists have known that increasing atmospheric carbon dioxide would eventually result in warming that was most pronounced in winter, especially on winter's coldest days, and a cooling of the stratosphere. All of these have been observed.
However, actually "doing something" about warming is a daunting endeavor. The journal Geophysical Research Letters estimated in 1997 that if every nation on Earth lived up to the United Nations' Kyoto Protocol on global warming, it would prevent no more than 0.126 degrees F of warming every 50 years. Global temperature varies by more than that from year to year, so that's not even enough to measure. Climatically, Kyoto would do nothing.