Cold
Cold
[It's cold, two Guys wearing knit caps (one knit cap is white the other black) are walking outside and the White Knit Cap Guy is shivering.] White Knit Cap Guy: It is brutal out. So much for global warming, huh? Black Knit Cap Guy: *sigh* This used to happen all the time. White Knit Cap Guy: What?
[A dot plot showing number of days with lows below zero Fahrenheit by year since 1970.] Black Knit Cap Guy (off-screen): You're from St. Louis, right? Black Knit Cap Guy (off-screen): On average, it used to get below 0 °F there a handful of days per year. Black Knit Cap Guy (off-screen): But you haven't had a day like that since the nineties. [Above the dot plot to the left is a label in a black frame:] Days with lows < 0°F [Below the dot plot are written the years:] 1970 1980 1990 2000 2010 [Below again is written in small letters:] Source: rcc-acis.org/climatecentral
[Black Knit Cap Guy has stopped walking.] Black Knit Cap Guy: Then, in 2014, when the first polar vortex hit, it dipped below zero for two days. Black Knit Cap Guy: And everyone freaked out
[They continue walking.] Black Knit Cap Guy: because what used to be normal Black Knit Cap Guy: now feels too cold. White Knit Cap Guy: It is too cold!
[Above the last panel is written in a black frame:] The Future: [Cueball is pointing at a patch of ice.] Cueball: Look at this— ice! In St. Louis! So much for global warming. Person off-screen: *sigh*
Note that this is not the same data set as mentioned in xkcd as this is regarding freezing days and not subzero days!
With the full excel dataset of the number of freezing days (i.e. below 32 °F) as obtained from the National Oceanic and Atmospheric Administration 's homepage NOAA you get the following plot:

From the same dataset excel dataset we can also get the number of sub-zero days i.e. below 0 °F (which are those mentioned in the XKCD strip) - plotting those and you get the following plot:
Note that this IS the same data set as mentioned in XKCD. This is subzero days!

While there were a number of very cold years with outliers in the 1970s - then the clear overall trend is still that there are fewer days with cold weather over the years.
So while weather is different every year (which is also illustrated by the outliers) the climate is defined by the long term trend - which is the point of this cartoon.

In this comic, Cueball (wearing a white knit cap with a pom-pom) and Cueball's friend (wearing a black knit cap) are walking outside in sub 0 °F (-17.8 °C). White Knit Cap Guy complains about the brutal cold and as a result questions whether global warming is real. Black Knit Cap Guy explains that this kind of weather used to happen all the time back before the year 2000, showing that global warming is, in fact, very real.
This is illustrated in panel two by a graph showing the number of days with sub 0 °F as a function of year from 1970 to 2013 in the city of St. Louis , (where we learn that Cueball is from). It shows that these days used to be rather common between 1970 and 1999, only to be completely absent for the next 14 years until and including 2013. A source link for this graph is provided (though as of June 2014, the link is dead - see Trivia below).
Cueball's friend uses this graph to explain that not a single day like this has happened since 2000, until here in 2014 where a polar vortex pushed the temperature down below zero again for two days. Since this weather is now unusual and infrequently experienced, people in St. Louis perceive it as being very cold because they have since adapted and are now unused to this sort of temperature, even though this was a common temperature to reach in past decades. This is further demonstrated when Cueball remarks that it's "too cold". Subzero Fahrenheit temperatures are very cold to be out in. See for instance the first panel of 526: Converting to Metric .
In the last panel, in a future St. Louis, a Cueball discovers a thin sheet of ice, suggesting the temperature has fallen just below 32 °F (0 °C), the freezing point of water. The suggestion here is that the environment has warmed to such an extent that temperatures below 32 degrees F are very unusual, and the future Cueball repeats the same short-term fallacy that such "extreme cold" disproves global warming. Someone off-panel, presumably another Black Knit Cap Guy, sighs as the cycle continues.
The comic reacts to a simplified view of global warming by amateurs, including media, who fail to understand (or choose to ignore) the difference between climate and weather . Short, random weather fluctuations like the polar vortex are taken as examples or counter-examples of climate change and global warming. To understand climate change, one must look at global (not local) and long-term (not short-term) temperature trends.
Debates on the theory of global warming/climate change often center on whether the current warming trend is primarily caused by humans or is a natural change, as has happened in the past. Within the scientific community, there is an overwhelming consensus that the current trend is anthropogenic (i.e. man-made), but many in the general public (including many politicians) are hesitant to accept this. There is clearly no doubt about where Randall stands on this debate, as many of his comics and blog posts continue to plead for humanity to do something about the man-made global warming trend - especially in comic 1379: 4.5 Degrees .
The title text suggests that gathering data about global warming is time-consuming and is the kind of stuff only a real nerd would do. Most people would rather hang out with friends, or at least spend their time with some more fun nerd activity. Randall has been known to use the title text to poke fun at himself over how much time he has spent researching topics and more generally how geeky his interests tend to be. Although the title text tries to deny this geeky behavior, he cannot help himself at the end by mentioning another interesting climate subject: Snowfall records .
Climate change, especially global warming, is a recurring theme in xkcd.
[It's cold, two Guys wearing knit caps (one knit cap is white the other black) are walking outside and the White Knit Cap Guy is shivering.] White Knit Cap Guy: It is brutal out. So much for global warming, huh? Black Knit Cap Guy: *sigh* This used to happen all the time. White Knit Cap Guy: What?
[A dot plot showing number of days with lows below zero Fahrenheit by year since 1970.] Black Knit Cap Guy (off-screen): You're from St. Louis, right? Black Knit Cap Guy (off-screen): On average, it used to get below 0 °F there a handful of days per year. Black Knit Cap Guy (off-screen): But you haven't had a day like that since the nineties. [Above the dot plot to the left is a label in a black frame:] Days with lows < 0°F [Below the dot plot are written the years:] 1970 1980 1990 2000 2010 [Below again is written in small letters:] Source: rcc-acis.org/climatecentral
[Black Knit Cap Guy has stopped walking.] Black Knit Cap Guy: Then, in 2014, when the first polar vortex hit, it dipped below zero for two days. Black Knit Cap Guy: And everyone freaked out
[They continue walking.] Black Knit Cap Guy: because what used to be normal Black Knit Cap Guy: now feels too cold. White Knit Cap Guy: It is too cold!
[Above the last panel is written in a black frame:] The Future: [Cueball is pointing at a patch of ice.] Cueball: Look at this— ice! In St. Louis! So much for global warming. Person off-screen: *sigh*
Note that this is not the same data set as mentioned in xkcd as this is regarding freezing days and not subzero days!
With the full excel dataset of the number of freezing days (i.e. below 32 °F) as obtained from the National Oceanic and Atmospheric Administration 's homepage NOAA you get the following plot:

From the same dataset excel dataset we can also get the number of sub-zero days i.e. below 0 °F (which are those mentioned in the XKCD strip) - plotting those and you get the following plot:
Note that this IS the same data set as mentioned in XKCD. This is subzero days!

While there were a number of very cold years with outliers in the 1970s - then the clear overall trend is still that there are fewer days with cold weather over the years.
So while weather is different every year (which is also illustrated by the outliers) the climate is defined by the long term trend - which is the point of this cartoon.
