Some people will deny anything that displeases or scares them: unusual pain in their chests, unwanted lumps beneath their skin, or the fact that humans share ancestry with apes are a few examples. Another is climate change.
Many climate scientists say their biggest fear is that warming could melt the Arctic permafrost - which stretches for thousands of miles across Alaska, Canada, and Siberia.
Most reputable scientists agree that climate change is real and that the effects are likely to be bad. But nobody can say for sure exactly what 'bad' means. The safest and most equitable way out of this horrific mess is simple: cut fossil-fuel emissions.
Deliberately modifying the earth's atmosphere would be a desperate gamble with significant risks. Yet the more likely climate change is to cause devastation, the more attractive even the most perilous attempts to mitigate those changes will become.
The best way to deal with climate change has been obvious for years: cut greenhouse-gas emissions severely. We haven't done that. In 2010, for example, carbon emissions rose by six per cent - the largest such increase on record.