Climate Change
This is the kind of problem where the stakes are so high that you don’t wait till - 
“all the evidence is in” before taking action.  
If you lived at the top of a steep hill and someone told you your brake fluid had all leaked out, would you “take it for a spin” to see if the brakes still worked?  Probably not but if you think like a politician in a developed country in the last few decades you just might.  They were informed by their advisers and did nothing.  
So what is Climate change?
Here are few possibilities...
We’ve burned so much fossil fuel in the last 150 years that we may have started a self reinforcing feedback loop in the world climate.  
The parts per million of CO2 has risen from 280 to 387 over the last 200 years.  
Please visit: the web site for more information.
This could have begun a warming trend that could melt the permafrost.  The permafrost holds millions of tons of methane that could be released into the atmosphere.  Methane is a much stronger greenhouse gas than CO2.
Do you remember the dust bowl phenomenon that occurred in the mid-west.  That wasn’t so long ago.   The mid-west could become a desert.
Think about it...
CO2 levels in ppm

Nick Stanton made the graph below from two sources. 

The years 1000 through 2000 are from a graph of the Law Dome Ice Cores

The period 2000 to 2100 is an extrapolation based on Current Data for Atmospheric CO2 at  the website.  This extrapolation assumes that we do not do enough to mitigate emissions of green house gasses. 

Sadly, if this happens it’s likely that no one will be around to see it.  On the other hand if we get to work and do everything we can as soon as possible we will have a much better life than we have been suffering the last 200 years or more.