Tiny metal nanoparticles can damage DNA, essentially by triggering toxic gossip.

There are 33 days until the opening of formal negotiations in Copenhagen on the next global climate-protection treaty. The hoped-for accord would take up where the current treaty leaves off. But to get some perspective on just where that is, a new United Nations report describes for negotiators and the public just how much the Kyoto Protocol has achieved. And real strides have been made in slowing the growth of greenhouse-gas emissions, thanks to many European nations (albeit with little help from North American ones or Japan).

A NASA model incorporates how atmospheric aerosols and greenhouse gases interact, yielding better estimates of the gases' warming and cooling effects.

Trees near high-traffic areas accumulate tiny particles.