The picture below is from Oregon State Climatologist George Taylor. You may have heard of him, the Governor of Oregon tried to get him fired for not jumping on to the global warming bandwagon because he doesn’t see enough supporting evidence.
The picture is of Forest Grove, Oregon, and the temperature plot below shows how it is warming. But George says:
“Yes, it’s a window air conditioning unit to the east and the edge of a large asphalt parking lot to the north, northwest, and west. The pic is shot looking northeast. For those of you that may not immediately realize this, air conditions exhaust hot air to the outside.
Not only that, but Forest Grove is located in Washington County, Oregon’s fastest-growing county (in terms of population growth, not percentage) for the last 40 years. No wonder it’s seeing unprecedented high temperatures…”
It looks like the air conditioner may have been installed around 1985, notice the sustained 1 degree jump that started about then and sustained a plateau.
And this is a station of record, a US Historic Climatology Network station that is used in global climate models by NASA, in fact the plot is from that database.