David M. Romps, Jacob T. Seeley (Berkeley), David Vollaro, and John Molinari (Albany) published a report in Nature whose title reads
Let me tell you: I find this number conceivable.
They decided that the lightning frequency is approximately equal to the product of the precipitation rate and a potential energy (CAPE). It probably isn't exact but it's probably good enough for some estimates. Combined with some empirical data, 1 °C of warming adds 12% to the warming strikes. When combined with some nonsensically overrated projections about the rise of the mean temperature in the rest of the century, they may get a 50% increase of lightnings.
More realistically, the Earth may experience at most something like additional 0.8 °C of warming by 2100 so the increase of the lightnings will be about 10%.
It's interesting to see how many people are killed (click) by lightnings in the U.S. (the same country that the paper analyzes). Since the beginning of 2014, there have been 25 casualties. So in a climate warmer by 1 °C, there would be about 2 more deaths in the U.S. each year – unless something else changes, of course.
This should be compared with the thousands that freeze to death and whose lives could be saved if there's some warming. Obviously, lightnings are negligible relatively to those. But despite the small numbers, lightnings are interesting because it's a rare example of a process by which "warming may indirectly kill people".
You may see that only 1/5 of the 2014 fatalities are women (pink color). This percentage actually isn't true just in this year – you find a similar percentage of 80% of men in previous years, too. Why is that? Is Nature misandrist or feminist? Or do penises act as lightning rods? Well, both of these explanations are unikely.
It's more likely that the explanation hides in the activities of the victims. Women are probably less likely to be closing car windows on a construction site, roofing car dealerships and other things, fishing, riding motorcycles, fixing windshield wipers, swimming, building tree house, doing a maintenance work, sheltering in storm, and (to explain some previous years) playing golf. So even though women are competitive in horseback riding, picking blueberries, walking, perhaps swimming, trimming hedges, the "men's excess" can't be eliminated.
Incidentally, you could argue that this ratio of deaths – four-to-one "favoring" men – roughly represents the ratio how much the two sexes work, especially when it comes to risky jobs (although you shouldn't forget that they're less likely in doing various types of work at home). So the "apparent meritocratic gender gap" is actually larger than the 1.5-to-1 gap in their average salaries.
But back to the lightnings. It's likely that the lightning rate increases with the temperature and is of order 100% already for temperature changes comparable to 10 °C. We could find some alternative methods to get this dependence from looking at the weather in different seasons – or different climatic zones – and do some regression. I am convinced that the dependence would be "comparable".
Lightnings are examples of phenomena where the warming matters; and where there are some fatal consequences, too. In principle, all the necessary conditions are fulfilled for the climate change hysteria to be relevant. But when we look at the problem quantitatively, we see that the casualties are tiny and negligible in comparison with the casualties of freezing that may be avoided with a degree of warming.