Michael Barbaro

So that really ties the hands of not just California, but other like-minded states that might want to do something very ambitious on automobiles.

So in the absence of major new state regulation and a federal government that doesn't want to regulate most of these greenhouse emissions at all, what do scientists say that the world starts to look like?

Scientists are worried.

I mean, the United States is the largest historic emitter of climate change.

It's the second largest annual emitter of carbon pollution and greenhouse gases.

If the U.S.

is not doing its part, a lot of countries could start to wonder, why should they?

And the most important is China.

And that's the big fear that a lot have relayed to me.

If the United States is successful in not just failing to reduce its own emissions, but convincing other countries that they don't need to either, scientists feel that could have a really dangerous domino effect for the planet.

And where do those dominoes eventually fall?

I mean, they fall in more severe rising temperatures and more droughts and hotter droughts, more frequent and severe wildfires, rising sea levels from melting glaciers that are threatening coastal communities.

These kinds of changes also directly damage human health, scientists tell us.

They damage food security, water supplies.

They lead to an increase in vector-borne diseases, Lyme disease, dengue.

There's a whole sweeping landscape of impacts that scientists are warning will get worse if emissions continue to go up.

I feel like what's quite remarkable about the story that you've told here is how quickly this country's relationship to greenhouse gases, the idea that they create climate change and that this is something to be addressed by the government, how quickly...

really just in a decade and a half, that's changed.

If you go back to the mid-early 2000s, when the endangerment finding was written, it seemed like much of the business and even political world was starting to become aligned in this sense that there was a problem and that something could be done about it.

Add where Nancy Pelosi and Newt Gingrich are sitting on a couch together in front of the Capitol.