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Sound like a trivial pursuit?

No. It's huge. That rise in average global temperatures would put us in a world never before known in recorded history

The potential consequences? Think of a dystopic desert out of "Mad Max."

That 4-year extreme drought parching California? Try a 20-year megadrought drying out about eight states , desperate fights for drinking water and forest fires eight times the size of current ones.

Mad about hunters killing rhinos and lions? How will you feel watching animals and plants go extinct like falling dominoes? Crops failing; waves of refugees driven out of coastal cities by rising seas, begging for shelter and food?

Right now, we're at about 0.85 degrees Celsius (1.53 degrees Fahrenheit) above the average temperature on Earth before massive carbon emissions began. We should hit 2 degrees Celsius (3.6 degrees Fahrenheit) by about midcentury.

Deal

So, back to Paris, where nearly 150 world leaders are working fight global warming at the COP21 -- it stands for Conference of Parties, and this is its 21st annual meeting.

There has been a deal -- or treaty -- in the works to try to corral nearly 200 countries into getting a handle on the carbon emissions, which most all scientists agree is driving global warming.

It's a very bare-bones agreement hammered out last year in Lima, Peru, at the COP20 . Back then, delegates came up with a basic principle -- that the burden to cut emissions would be different for developed and developing countries.

Rich countries would help poor countries meet their goals and also help out with calamities caused by global warming -- like refugee crises triggered by coastal flooding.

The details of the treaty to be hopefully signed this year in Paris were left pretty open.

Hope

The leaders of the two biggest players in the deal met Monday in Paris. China and the United States are also the biggest emitters of greenhouse gasses.

Afterward, Obama said the two were on the same page about lowering carbon emissions. "Nowhere has our coordination been more necessary or more fruitful than the topic that we're here to discuss during the Paris conference, and that is how the world can come together to arrest the pace of climate change."

For the first time in China, there'd be a cost to companies for emitting carbon into the environment. With a cap on carbon emissions for individual companies, firms would trade or buy permits from each other to emit additional pollution.

Despair

But there has been despair as well.

Though it's a start, critics don't think China can accurately measure its output of carbon dioxide and other gasses and fear enforcement could easily get muddled.

Then there's the United States.

Early in his presidency, Obama attempted to enact a cap-and-trade system , but was unable to overcome bipartisan opposition, partly fueled by fears that such a law could hamper economic competitiveness with emerging economies like China's.

Failure

And then there's a major historic fail.

It shows how hard it can be to get the world to work together on climate change.

Remember the Kyoto Protocol? It was adopted at the COP3 in 1997.

It was the best-known milestone to come out of a previous COP -- a nonbinding agreement by 192 states to lower greenhouse gas emissions to 5% below 1990 levels between 2008 and 2012.

The United States did not ratify it and dropped out of it completely in 2001.

Canada dumped it, too, in 2011.

And China, India and other developing countries were exempt from it.