Right now, there is an observed trend in numerous areas: higher ocean temperatures, melting polar icepacks, a consistent trend of stronger storms, and higher air temperatures. There is also a plausible cause - greenhouse gasses from combustion of fossil fuels. You can say that the trend of increasing temperature is a coincidence. 40 years ago, one could also have said that the reduction in population of birds mirrored the extinction of dinousaurs. Of course, the true cause was DDT. In the past 50 years, numerous environmental concerns have been shown to be significant problems. Some of these include MTBE, clear-cutting trees, leaded fuel, mercury poisoning, and smog.