The problem with any extreme weather event is that it’s impossible to say what role global warming has had. The reason being that the heatwave could have happened without any global warming.
What we do find is that since global warming began to kick off in a big way in about 1980, there has been a doubling in the number of heatwaves and tripling in the number of days in which heatwave conditions occur. Modern heatwaves are more frequent and more intense than their predecessors.
We also find that the deadliest heatwaves on record are all recent events. Prior to 1980 the highest death toll of any heatwave was 946, this happened in LA in 1955. Since 1980 there have been six heatwaves where the death toll has exceeded 1,000, the worst being the European heatwave of 2003 which claimed 70,000 lives and the 2010 Russian heatwave where 52,000 people died.
The heatwave is being caused to a large extent by the jet-stream. This is an atmospheric phenomena that is currently trapping a hot air mass over the southwestern states. Normally the jet stream flows in a wavy line but at the moment there’s a loop in it and within that loop is a hot air mass that can’t escape. When this happens the heat intensifies day after day until the jet-stream moves.
It’s rare for it to happen in this particular way and on this scale but it is an event that’s becoming more common – the 2010 Russian heatwave was caused by exactly the same thing, but on that occasion the loop in the jet-stream was centred over Moscow.
So where does global warming come into it?
The average global temperature is higher than it used to be so any heatwave is bound to be that bit more intense but it’s the effects on the jet-stream that are perhaps of more concern.
It’s too early to say how, or even if, global warming is affecting the jet-stream, but as more and more data are gathered it’s certainly looking like this is the case.
Fortunately many people in the affected areas are no strangers to high temperatures and many properties are air-conditioned, hospitals are used to dealing with casualties of heat related conditions and the authorities have provisions in place for looking after their citizens. Had this happened elsewhere, where people aren’t used to dealing with the heat, then the consequences would have been much worse.