If carbon dioxide kills so many children, why has the global mortality rate for children plunged since 1990?

BBC News - Child deaths: Unicef says global mortality rates fall

The number of children dying before the age of five has fallen significantly over the past 20 years, the UN children's agency Unicef has said.

Some 6.9 million children died before the age of five last year, compared to 12 million such deaths in 1990. Almost 19,000 under-fives died daily in 2011.

Flashback: When Heat Kills: Global Warming As Public Health Threat : Shots - Health Blog : NPR

The current poster child for global warming is a polar bear, sitting on a melting iceberg. Some health officials argue the symbol should, instead, be a child.