A major heat wave is about to fry the East Coast — here's what's coming

On the heels of a heat wave that brought scalding temperatures and smog to the US Midwest and the Northeast last week, the thermometer is set to reach the mid-to-high 90s this weekend in upstate New York and Pennsylvania. 

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On hot days, emissions from vehicles and power plants can react with sunlight and other naturally occurring gases to create ground-level ozone, which can hang over cities on hot summer afternoons. Ground-level ozone is especially dangerous to children, the elderly, and people with respiratory illnesses like asthma.

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Summer officially started in the northern hemisphere last week with the June solstice, and forecasts suggest it will be a hot one. The US Climate Prediction Center says there's more than a 50% chance that the Northeast will be warmer than average from July through September.

This heat forecast is part of a trend of rising temperatures across the globe due to climate change. The five hottest years on record since 1880 have all occurred since 2010, with 2016 setting the record for highest average temperature. Projections suggest that by 2075, strong heat waves that currently occur once every 20 years could become annual events on 60% of the Earth's land areas.

According to a Harvard study, climate change will also contribute to an additional three to nine days per year of unhealthy ozone levels by 2050 — amounting to a 70-100% increase in ozone days, depending on the region.