Warmer atmosphere means more water

A109 Light Utility Helicopter flight with mayor Gisborne City from the air in November 2023.

Re: ‘Atmospheric rivers’ pummel California, Saturday page 10.

“Heavy rain flooded California roadways and much-needed snow piled up in the mountains as the first of back-to-back atmospheric rivers pummelled the state yesterday. The storm focused its energy on the southern and eastern parts of the state . . .”

Coincidently, this northern hemisphere report comes one year after devastating summer-time Cyclone Gabrielle hit New Zealand.

It has been well established that atmospheric rivers will occur more frequently with higher intensity and heavier precipitation in a warming climate, because of the greater availability of water vapour in the atmosphere.

These are long, concentrated regions in the atmosphere that transport moist air from the tropics to higher latitudes. The moist air, combined with high wind speeds, produces heavy rain.

Tropical cyclones feed off the energy provided by hot ocean waters. In recent summers there has been “unusually warmer water” in the Tasman Sea; the ongoing warming trend from human-induced climate change is playing a big role.

In New Zealand, the result is “moist, rainy conditions” in the north and east of the country and warmer-than-average sea and air temperatures. And there could be more like Gabrielle on the way, sooner than you might expect.

A basic rule of climate science is that the atmosphere can hold more moisture as it warms; the Clausius-Clapeyron relationship.

The main driver of climate change is the greenhouse effect. Today’s atmospheric CO2 levels are over 422.21 ppm, the highest in more than 14 million years.

The best we can do is, worldwide, all must stop using fossil fuels right now.

Bob Hughes