The Climate DeskExtreme weather has been grabbing headlines this summer. A major heat wave and wildfires in Russia and flooding in Pakistan have had devastating effects. The United Nations estimates that 6 million Pakistanis are in need of emergency aid.

Alison Stewart of PBS’s Need to Know speaks with Dr. Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research in Boulder, Colo. He explains the meteorological dynamics at work and speaks about the human cost of climate change.

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This story was produced by PBS: Need to Know for the Climate Desk collaboration.