It happened because the temperatures quickly rose above the normal upper temperature limit. (theinconvenientskeptic.com)
The EU's support for a 1.5 C upper temperature rise limit is disingenuous when it is not committing to more action. (foeeurope.org)
(Athanasiou and Bear 2002) The 2oC upper temperature limit is quite controversial scientifically because, as we shall see, some scientists believe that lower amounts of additional warming could set into motion rapid climate changes that could greatly harm people around the world and increases of as little as 1oC will likely greatly harm some people in some regions. (ethicsandclimate.org)