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The polar regions are warming more than any other region on Earth. And statistically speaking, the temperature difference between the tropics and the Earth's poles is shrinking. But this contrast of temperatures is the reason for our westerly winds, for our jet stream.
When there are large contrasts, the jet stream blows strongly. This is easily derived from the thermal law of wind. However, if the temperature contrast decreases, the jet stream weakens and there are more areas of high pressure that remain quasi-stationary longer.
And where the high pressure lasts for maybe a few weeks, it will be dry and then hot in the summer. But between two areas of high pressure there always remains a zone of low air pressure. And here there is constant precipitation, which is even more abundant due to warming. (Janeen Townsend, more at weather.com)
