Since this weekend marks the unofficial beginning of summer, and since we know the U.S. has been warming up since at least the 1970’s, it’s natural to wonder how Memorial Day temperatures been changing over that time. The graphic above has the answer: it shows average Memorial Day weekend (including all 3 days Saturday through Monday) temps for Denver during the 1970s, 80s, 90s, 2000s, and 2010s so far - with the 2010s highlighted in red since that bar only covers 3 years of data. Some areas have warmed up faster than others. But thanks largely to heat-trapping greenhouse-gas pollution, just about every location in the lower 48 states have seen the mercury go up over that period.
There has been a lot of talk about climate and climate change after this week’s deadly tornado outbreak - especially the complete devastation in Moore, where the second F/EF-5 twister in just 14 years has torn a path of destruction with a separate F4 striking a similar path in the years between. Was this just weather or was climate change partly to blame? We don’t know - yet.
While the atmosphere is warming and changing, the current research shows no clear climate change connection with tornadoes. We do know that two main ingredients of severe thunderstorm are on the rise – moisture and heat. But we don’t know how climate change will affect a crucial factor in tornado formation - wind shear. Research suggests that climate change is influencing weather patterns in ways that could lead to less shear, which could mean fewer tornadoes.
Climate change may also lead to swings between extreme drought and extreme rainfall, which could also suppress tornado numbers. But “could” is the important word here. There is simply not enough information to make that definitive connection — yet.
We’ve included another graphic (see below) showing how much confidence scientists have in understanding the relationship between climate change and various extreme weather events. If you look on the left hand side, you will see where things stand in the understanding of how tornadoes may be linked to climate change.