Either clarification or citation humbly requested. The United States alone has conducted over 1000 nuclear tests, without rendering global agriculture impossible.
Citations first:
http://climate.envsci.rutgers.edu/pdf/ToonRobockTurcoPhysicsToday.pdf
http://climate.envsci.rutgers.edu/nuclear/
Now, to clarify:
Nuclear testing in the old days was done in deserts, or in remote polar areas (mostly the Soviet Union there, though many of their tests were conducted in desert areas of Central Asia). Those sites were chosen partly because they avoid massive vegetation burnoffs. Underground tests don't have that problem at all (and they became standard practice for the biggest players in 1963 with the signing of the Limited Tes...
A reminder for everyone: on this day in 1983, Stanislav Petrov saved the world.
It occurs to me this time around that there's an interesting relationship here - 9/26 is forgotten, while 9/11 is remembered. Do something charitable, and not patriotic, sometime today.