An article claimed — in its headline — that a ~5ºC (~10ºF) increase in temperature was an increase of 18.7 percent, by calculating using the relative temperature scale. Which is wrong, of course; e.g. 2ºC does not represent twice as much thermal energy as 1ºC. The site has since made a correction.
If you really want to do a percentage based comparison, you need to convert to an absolute temperature scale like Kelvin, which shows you that it’s actually a 1.8 percent increase in temperature (306.75 / 301.45). This is middle school science.
Sadly, I don’t think that this is generally taught in middle school. Or possibly even high school, except to a few students.