One way to express how warm as summer has been is to calculate Thawing Degree Days (TDD). To calculate TDD, you simply add the average temperature for each day.  The later in the summer, the more TDD accumulate.  Likewise warmer summers have greater TDD.

To the right are two different graphs showing the calculation of Thawing Degree Days (TDD) and Growing Degree Days (GDD), the only difference is what you use as the base temperature.  

For simplicity the assumption for Arctic plants is the base temperature for growing degree days is 0 degrees Celcius, thus GDD = TDD.  However, for temperate plants the generalization is growth starts at 10 degrees Celcius.  In reality every plant is probably different based on their internal enzymes and antifreeze compounds within their tissues.    

We collect temperature at standard screen height (2 meters above the ground) and within the plant canopy at between 10 and 15 cm height. 

In most locations it is a little warmer near the ground during the day. 

Throughout the summer TDD accumulate. 

As you can see from this example from Atqasuk Alaska in 2022, TDD were greatest in the experimentally warmed plots, then near the ground in ambient plots, and screen height (2m) had the fewest TDD.