Outdoor air pollution caused by humans is currently responsible for over two million deaths per year, according to a new study that highlights the effects of humans and downplays the role of natural climate change on our health.

The study, published in the Institute of Physics (IOP) journal Environmental Research Letters, shows that 2.1 million deaths each year are the result of fine particulate matter (PM2.5) spewed into the air by humans. Fine particulate matter refers to tiny particles in the air that can enter the respiratory system and create everything from breathing problems to cancer.

Most of the PM2.5-related deaths occur in East and South Asia, where air pollution is so severe that entire metropolitan areas like Beijing can be enveloped in a fog of smog. The study also claims that 470,000 deaths a year are the result of human-induced increases in the ozone level.

"Our estimates make outdoor air pollution among the most important environmental risk factors for health," said co-author of the study Jason West from the University of North Carolina.

The team of scientists found that naturally-occurring climate change plays a very small role in the large number of human deaths, with an estimated 2,200 people dying from natural PM2.5 levels and 1,500 from natural increases in ozone.  

"Very few studies have attempted to estimate the effects of past climate change on air quality and health. We found that the effects of past climate change are likely to be a very small component of the overall effect of air pollution," West explained.

One thing the scientists stressed, however, is the uncertainty when dealing with climate models. A number of models were used to calculate the PM2.5 and ozone levels between 1850 and 2000, and depending on which one was used, results varied. Rather than looking at the hard numbers, the team simply wishes to stress the importance of dealing with human-induced pollution, which will only grow more deadly as population concentrations increase and more regions industrialize. Dealing with the problem effectively will require broad-sweeping social and metropolitan policies, not a playbook based on numbers.

"We have also found that there is significant uncertainty based on the spread among different atmospheric models," West said. "This would caution against using a single model in the future, as some studies have done."