"350 ppm (parts per million) is required if humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted."  So says, James Hansen, the NASA Scientist who first warned us about global warming 20 years ago, when he testified to Congress a couple weeks ago about the future of the planet. 

In an article he wrote at Huffington Post shortly after the testimony, he talked about the climate changes already in progress as a result of an increase of an average of two degrees Fahrenheit, an amount that may seem innocuous.  But there is more warming on the horizon that may be too late to stop.   Unless we cut back to 350 immediately from our current level of 387 and rising at 2 ppm per year, we are in for a likely set of tipping points that could lead to much worse.

"Climate can reach points such that amplifying feedbacks spur large rapid changes. Arctic sea ice is a current example. Global warming initiated sea ice melt, exposing darker ocean that absorbs more sunlight, melting more ice. As a result, without any additional greenhouse gases, the Arctic soon will be ice-free in the summer."   

In his testimony before Congress, he talked in more detail about the damage already occurring and likely to occur and then discussed the solutions, which he said need to be implemented immediately in order to allow dispersed renewable energies to supplant fossil fuels for power generation:

1.  A carbon tax to wean us off fossil fuel addiction

2.  A national low-loss electric grid

A. Siegel, blogging at Firedoglake, adds some details about the immediacy of the problem. 

"Prior to the industrial era, the atmosphere was at about 280 parts per million of carbon dioxide.  The 'old' (a few years ago) scientific consideration was that it seemed we could stabilize, without utterly catastrophic risk, at 450 ppm or below. This is the guiding thinking behind cutting carbon emissions 80 percent by 2050."

Jim Hansen now looks at the research and tells us, we must stabilize at 350 ppm.