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Climate scientists on Earth's two futures

Climate change's worst possible outcome
Climate change's worst possible outcome 01:42

For more than three decades, climate scientists have accurately forecast how carbon emissions would cause a global rise in temperatures. Now they're looking ahead at the decades to come. 

When it comes to predicting the future, scientists do not see just one possible outcome. Rather, they say the actions humans take in the near-term will have a major effect on how Earth changes for generations beyond. 

"We need to change our course in the next few years because it's still possible, I think, to avoid the worst outcomes," Former NASA scientist James Hansen told 60 Minutes correspondent Scott Pelley.

Hansen has been called the father of climate change science. In the 1980s, he determined that a recent rise in temperatures was a result of increased carbon emissions into the atmosphere. In 1988, he testified before Congress, indicating that human activity was the reason for the increase and tracing the rise of global temperatures through the year 2020.  

Now in that once-far-off year, California is facing the largest wildfires in its history, the East Coast has already been pummeled by nine powerful storms, and what may be the highest temperature ever recorded on Earth scorched California's Death Valley.

But as bad as they are, Hansen believes, raging forest fires and destructive hurricanes will not be Earth's worst crises if humans fail to change their actions. The worst consequences will come from permanent changes — rising sea levels and the potential extermination of species. 
"We can get back to the old climate if we haven't caused irreversible things," Hansen said. "If we lose our coastal cities, that's irreversible on any time scale that we would care about. And also, the loss of species. So those are the things that I worry about. But those are … late-in-century effects which our children and grandchildren will feel."

The "bit of good news" on climate change 02:54

Stopping climate change before irreversible effects have damaged the planet is possible, some scientists believe.

Michael Mann, a geophysicist whose work has shown today's elevated rate of warming began with the industrial revolution, sees this bit of good news through the climate models scientists work from today. Current projections create a more comprehensive look at how the climate responds to carbon dioxide, including how the ocean and plants can absorb some of the carbon humans have released into the atmosphere. 

According to the latest models, how much the planet will warm is mostly a function of how much carbon humans have burned up to now. If all carbon emissions were to cease today, Mann said, both plants and the ocean would increase the amount of carbon they take out of the atmosphere. As a result, temperatures would remain fairly flat.

"We are only committed to the warming that has happened already," Mann said. "If we stop burning carbon now, we stop the warming of the planet. In a sense, that is empowering. It tells us we can have a real impact."

That does not necessarily mean the damage that has been done is reversible. Future generations may be able to figure it out, Mann said—but only if humans halt the planet's warming. 

"We have never failed as a society to come up with ingenious technical achievements down the road," Mann said. "We can't do that now. In decades from now, we might be able to do that. So, the critical thing now is to stop turning the thermostat up. We can do that." 

The videos above were edited by Will Croxton. 

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