How about 307 ppm? That is far below Hansen’s safe level of 350 ppm.

We could have a dust bowl and a depression! Just like the 1930s.

Maybe 310 ppm? Before global warming, there wasn’t much moisture in the atmosphere to produce snow. Snowfalls must have been very light prior to 350 ppm.

http://climate.umn.edu/doc/journal/top5/top5.htm

Maybe we should go all the way back to 290 ppm?

The Great Blizzard of 1888 or Great Blizzard of ’88 (March 11 – March 14, 1888) was one of the most severe blizzards in United States’ recorded history. Snowfalls of 40-50 inches (102-127 cm) fell in parts of New Jersey, New York, Massachusetts and Connecticut, and sustained winds of over 45 miles per hour (72 km/h) produced snowdrifts in excess of 50 feet (15.2 m). Railroads were shut down and people were confined to their houses for up to a week.[1]

http://en.wikipedia.org/wiki/Great_Blizzard_of_1888