See also: climate change. "No need to worry" -> "Well, there isn't really hard proof" -> "Other countries aren't doing anything about it either" -> "Well, it's too late anyway so I'll just continue to do what I was doing before".
Spencer is a lukewarmer - he believes the Earth is warming, and it's partially due to human activity. I'm also a lukewarmer (we are not only still coming out of the last ice age, but we a recovering from the Little Ice Age, when you sometimes could walk from Manhattan to Staten Island on the harbor ice). (I'm unconvinced about the role of CO2, though). His book, Global Warming Skepticism, is a fair assessment of the skeptical case, I think.
The main thing about Spencer is UAH: to me, it's the only reliable data on global warming, and it's telling us there's not much happening. On top of which, I expect the rest of the world to get off fossil fuel long before there's any noticeable problems due to global warming. All the fuss is about computer model projections, which are not being confirmed by reality over forty years of satellite measurements.
In the space of 10 years or so.