More extreme weather is one of the three most destructive effects of climate change, Hansen told the crowd. The two others are sea level rise and species extinction.

Taken by themselves, floods such as those that occurred in March in Nebraska and Iowa don’t prove much, he said, but a look at weather globally does. “There is an increased frequency of climate extremes, which is not natural,” he said with the slide as his backdrop. “People around here should recognize climate extremes.”

An Iowa native and former director of the NASA Goddard Institute for Space Studies, Hansen has been credited with bringing global warming to the national consciousness during testimony before Congress in 1988.

Global warming is amping up the worst kinds of weather, from greater heat and drought to more intense storms and heavier precipitation.

“The 100-year flood now occurs more than once a century, and don’t be surprised by a 500-year flood,” he said.

“Dry places (like the Middle East and U.S. Southwest) become drier, wet places (like Southeast Asia) become wetter,” he said. “At a place that is sometimes wet and dry (like Nebraska), those extremes tend to get greater.”

On Sunday, Hansen noted that the Missouri River is running higher more frequently than it once did. Five of the top 10 river stages at Omaha have occurred in the last 10 years, according to the National Weather Service. Three of those records have been set this year.

In the last 10 years, Nebraska and Iowa have seen two historic floods on the Missouri River, in 2011 and 2019, and Nebraska has seen its hottest, driest year on record, the costly flash drought of 2012.

While much has been made of news stories saying that there are just “12 years left to act,” Hansen advised against getting caught up in numbers. Yes, the window for manageable solutions is closing, he said.

“We’ve already passed the safe level of CO2 (carbon dioxide emissions),” he said. “We know we’re on the knife’s edge of giving young people a situation that could be out of their control.”

By acting now and not waiting additional decades, it remains possible to more affordably harness Earth’s natural cleansing systems for carbon, such as the ocean, soil and biosphere, he said. Delayed action could put doing so technologically or economically out of reach.

Hansen advocates for shifting to nuclear energy as a way to move away from fossil fuels.

“The world needs energy,” he said. Fossil fuels, he noted, lifted the developed world out of poverty. Now, though, the path forward is for the U.S. to put a price on fossil fuels that reflects their true cost to society.

The best way to do so is to attach a fee at the point of origin for fossil fuels, such as the coal mine in the U.S. or the port of entry for foreign oil. The money from that fee would be returned to American households in the form of a dividend. Hansen estimated that 70% of Americans would make more money from the dividend than they would pay in increased prices.

If the U.S. leads the way, other countries will have an incentive to follow, he said.

Hansen advocated that people join the Citizens Climate Lobby to lobby Congress for the fee and dividend.

“We have to save this world,” he said. “It is not an unsolvable problem.”