Peer reviewed science: No Direct Human Health Risk Under a CO2 Exposure of 3000 ppm. “Increasing CO2 to 3000 ppm at 35 °C caused no significant changes in responses.”
(Note: 3000 ppm is 7.5 times (750%) higher concentration than the approximate 400 ppm average CO2 concentration in air today. It is unlikely CO2 could ever reach 3000 ppm due to any activity of humans burning fossil fuels. Humans contribute less than 5% of 400 ppm CO2. Even if humans tried in some giant misguided geoengineering project to increase CO2 – for example to stop an ice age – it would take hundreds of years to reach 3000 ppm. And then there would be no harm to humans. Don’t hold your breathe. Enjoy the blessings.)
http://www.sciencedirect.com/science/article/pii/S0360132316305121
Review: http://www.co2science.org/articles/V20/aug/a1.php