Extreme temperatures, wild weather mark official start of summer

UNDATED (NBC) - A record-setting warm spring has given a quick start to potentially dangerous summer heat.

Forecasters say high temperatures and humidity can be a recipe for such storms, and there's no letup in sight.  

For decades, warmer temperatures have been arriving earlier because of climate warming, which affects everything from blooming plants to animal migration.  

The fastest-warming region on the planet is the Arctic, with the summer melt of sea ice usually in full swing by the summer solstice. This year it happened three weeks early.

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