Human activities and the built environment trap heat and prevent cities from cooling down, said UCLA geography professor Dennis Lettenmaier.

“Everything’s warming up, but the effect is amplified in urban areas,” Lettenmaier said after studying  217 urban areas across the globe and finding that prolonged periods of extreme heat increased significantly in 48 percent of them between 1973 and 2012.

The findings, published in the journal Environmental Research Letters, show that about only 2 percent of those urban areas experienced a significant decline in heat waves. And the change was more dramatic at night: Almost two-thirds of the urban areas showed significant increases in the frequency of extremely hot nights.

Climate: Urban areas amplify global warming impacts | Summit County Citizens Voice

Scientists have discovered a huge increase in UHI since 1973, yet USHCN makes essentially no adjustment in post 1973 temperatures.

And why did the author cherry-pick 1973 as the start year? Because it was right at a local minimum. Had he started in almost any prior year, it would have wrecked his story.

These academics spend months writing a paper completely full of crap, on a topic which it takes 10 minutes to write an informative blog post about.