The sunscreen rebound effect

I’ve just returned from a few days at thebeach with my family.  One thing that stands out as a key function of aparent in the summer beach environment is making sure your child avoids gettingsunburnt.

This got me thinking about a world withoutsunscreen.  This cheap little cream enables us to withstand sun exposurelike super-humans, avoid painful sunburn, and partake in activities that wouldbe out of the question in a 'no sunscreen' world. 

Since sunscreen allows us to tolerate so much more exposure to the sun,is it actually contributing in some way to increased incidence of skincancer?  Are the net health benefits of sunscreen 

actually much lowerbecause of our change in behaviour?  How big is the sunscreen reboundeffect?

There seems to be some acceptance of thesunscreen rebound.  This article statesthat “Sunburn may even protect against melanoma - by keeping people outof the sun.”

Again here:

The Australian experience provides thefirst clue. The rise in melanoma has been exceptionally high in Queenslandwhere the medical establishment has long and vigorously promoted the use ofsunscreens. Queensland now has more incidences of melanoma per capita than anyother place. Worldwide, the greatest rise in melanoma has been experienced incountries where chemical sunscreens have been heavily promoted.

And here:

sunscreen use tendsto prolong the amount of time people spend in the sun whilethey are on vacation—and thatonly sunburn modifies the behavior of sun-seekers

And here:

Sunscreens suppress naturalwarnings of overexposure to the sun and allow excessive exposure towavelengths ofsunlight which they do not block.Because sunscreens create a false sense of security, moreeffective measures to reduce sunlight exposure, such as limitingtime spent in the sun or use of hats and clothing, may be ignored.

My experience suggests that all of thesestatements are true to some degree.  

If everything was held constant - time inthe sun, covered clothing, etc (notice the decline in hat wearing in the pastfew decades?) - then sunscreen may be quite effective at preventing skincancer.  But humans have a tendency to adjust their behaviour to takemaximum advantage of such innovations. 

The question that remains is whether thereis still a net health benefit from sunscreen.  But due to the plethora ofuncontrollable variable in any longitudinal study, I'm not sure that we willever have definitive statistical evidence for this.