Here's the thing about a warming climate: the march upward is not going to be smooth nor is it going to be even.
Take a look at this year's temperatures by state. California was five degrees—five degrees!—warmer than its 20th-century average, whereas Michiganders and Mississippians were experiencing near record cold.
That is to say, climate change doesn't mean it will never be cold again, but it does mean that when a heat wave hits, it is more likely to be more extreme than the ones preceding it. "It is very likely that heat waves will be more intense, more frequent and longer lasting in a future warmer climate," the Intergovernmetnal Panel on Climate Change wrote back in 2007.
Any individual weather event or pattern can't be blamed directly on the atmospheric changes caused by burning fossil fuels. But if we ask the question a little bit differently, we can discern a climate trend: how likely is it that California would be experiencing the kind of heat we've seen without the human influence on the climate? It might happen, but it'd be very, very unlikely.
Take San Francisco, not exactly a place known for being hot. The California Energy Commission's Cal-Adapt predicts that by the end of this century there will be 126 extreme heat days per year in the city.
Cal-Adapt program defines an "extreme heat day" as those above very close to the maximum temperature (above the 98th percentile) recorded for a location between 1961-1990. I think we can safely classify these days as the ones where you might say, "Man, this is like the hottest day of the year." So, take that in: a third of the year will be hotter than the hottest days between 1961 and 1990.
The only good thing about the spikiness of the changing climate is that during the peaks we can get a sense of what the new normal will be. And maybe that will spur us to change the climate path that we're on towards ever hotter temperatures. Here's the number of extreme heat days we might expect in the coming decades:
