International Herald Tribune: If uncertainty runs rampant in the global-warming debate, it is in part because scientific data is often too complex to be well understood by anyone but climate scientists.
This month, however, the world is likely to reach a scientific milestone that appears impressively scary even to those with only a cursory knowledge of climate science.
For the first time in human history, atmospheric carbon dioxide levels will surpass 400 parts per million, according Scripps Institution of Oceanography,...