Carbon dioxide levels hitting historic high is the final wake-up call - The Week

At 415 ppm, carbon dioxide level is at highest ever in human history

Earth's CO2 hits highest recorded level in human history - exceeding 420 parts per million

MeCCO Monthly Summaries :: Media and Climate Change Observatory

What is climate change? A really simple guide - BBC News

RealClimate: Not just another dot on the graph?

The carbon skyscraper - International Science Council

Effects of acute exposures to carbon dioxide on decision making and cognition in astronaut-like subjects

Just how 'Sapiens' in the world of high CO2 concentrations?

Increased levels of carbon dioxide could reduce brainpower, study finds

RealClimate: Not just another dot on the graph?