are nukes the most urgent environmental threat?

Time | Why are nuclear bombs an environmental problem? We have long known that a large-scale nuclear war would lead to a sudden change in climate—called a nuclear winter—that could threaten all life on earth. But in the past decade, climate scientists have used advanced climate modeling to show that even a small exchange of nuclear weapons—between 50-100 Hiroshima-sized bombs, which India and Pakistan already have their in arsenal—would produce enough soot and smoke to block out sunlight, cool the planet, and produce climate change unprecedented in recorded human history.

Scary? It gets worse. New research by the National Center for Atmospheric Research (NCAR) suggests that the above scenario of a "limited" nuclear war would also burn a hole through the ozone layer, allowing extreme levels of ultraviolet radiation to reach the Earth's surface, which would greatly damage agriculture and most likely lead to a global nuclear famine.

It seems it does not take a cold war posture of MAD—mutually assured destruction—to threaten civilization as we know it.

Presenting the research at the American Association for the Advancement of Science (AAAS) conference in Washington D.C. last week, NCAR scientist Michael Mills explained that the heat and soot in the stratosphere following limited nuclear war would lead to "low-ozone" columns over cities, which would increase cancer rates and eye damage dramatically. But the ozone loss would be so great that it would also have serious repercussions for plant life, including “plant height reduction, decreased shoot mass, and reduction in foliage area” and long-term genetic instability. Another risk is depletion of phytoplankton that feed sea life.

“It would be very difficult for us to grow the type of crops we grow today,” Mills said, according to Global Security Newswire. “In addition to ecological damage, there would be a global nuclear famine.”