Cold Waves Used to Be More Frequent, and Now That We're Not Used to Them, They Seem Worse

CC BY 2.0. XKCD C.C.

Polar Vortex might not have been newsworthy a few decades ago

Explaining a joke might make it less funny, but there's an important point in there: Our rather short-term human memory means that we quickly forget how things used to be decades ago (if we were even alive back then), and so if things that used to be more frequent become more rare, they could seem like evidence that things are moving in the opposite direction because we're not used to them anymore.

A good example of this is that people who are younger than 28 have never lived a month of below average global temperatures. So what seems normal to them is actually part of an abnormal warming long-term trend. In other words, a long-term normal temp would seem unusually cold to these people based on personal experience.

The only way to have an informed, scientific opinion about long-term trends like climate change is to look at the hard data over long periods, which is what climate scientists are doing. You can't just anecdotally look at regional weather and compare it to what you remember to make up your mind.

A good example of this: Despite the cold wave in the US, December 2013 was the third hottest December since records began in 1880.

nasa global warming maps image

Via XKCD (comic made by geek god Randall Munroe, published under Creative Commons license)

See also: Most Important Pie Chart You'll See Today: 13,950 Peer-Reviewed Scientific Articles on Earth's Climate