>> [Meehl] Imagine a baseball player 
who's been taking steroids.
This player steps to the plate 
and hits a home run. 
And he asks: 
Was that home run due to the steroids?
If you look at the number of home runs
he hits over a season when he's taking steroids
and compare that to a previous season 
when he wasn't, it's only then you can figure out
that the steroids have made him 
more able to hit a home run
because it made him stronger, 
and the chances of him hitting a home run are greater.
So by adding just a little bit more to those
naturally occurring steroids in the human body
we change the background base state of our systems.
>> [Narrator] O.K., got it. But a lot of bad things happen when you take steroids, right?
>> [Meehl] The greenhouse gases we're adding to the atmosphere by burning fossil fuels
are the steroids of the climate system.
The atmosphere has very small amounts of
greenhouse gases that occur naturally. 
By adding just a little bit 
more of those greenhouse gases to the air
we change the background state 
of the climate system.
We increase the temperatures just a little bit, 
but that increase
is enough to shift the odds toward a much
greater chance for extreme heat events
and extreme precipitation events.
>> [Narrator] Normally you'd expect record lows 
and record highs to balance out over time.
But now we're getting almost three record highs
for every record low.
>> [Meehl] So just as a baseball player on steroids
can occasionally strike out...
>> [Umpire] You're out!
>> Awwwww!
>> [Meehl] the climate system can still experience record cold temperatures. 
But the chances of record highs
are still much greater.
>> [Narrator] And that's what steroids and baseball
have to do with climate change. 
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