We have a pretty good idea of what Earth's atmosphere has been like over the past 800,000 years.
People like us – Homo sapiens – did not develop until about 200,000 years ago, but ice core records show intricate details of our planet's history long before humans existed. By drilling more than 3 kilometers deep into the ice cover over Greenland and the Antarctic, scientists can see how the temperature and carbon dioxide levels in the atmosphere have changed to this day.
From this record, we know that the atmosphere and the air we breathe never contained as much carbon dioxide as today.
For the first time in recorded history, average monthly CO2 levels in the atmosphere surpassed 41
The new record is no coincidence – people have quickly transformed the air we breathe through CO2 pumping in the last two centuries. In recent years, we have driven these gas volumes into uncharted territory.
This change has inevitable and frightening consequences. Research shows that unchecked this trend could directly lead to tens of thousands of pollution-related deaths, reaching a point where it slows down human perception and leads to sea-level rise, burning heat waves and super storms.
"What interests me most as a scientist is what this continued ascent actually means: that we continue to advance with an unprecedented experiment on our planet, the only home we have," says climate researcher Katharine Hayhoe said on Twitter about the new record.
Breathing the Breath of a New World
In the 800,000 years that we have recorded, average global CO2 levels fluctuated between about 170 ppm and 280 ppm. When people started burning fossil fuels in the industrial age, things changed quickly.
It was not until the industrial age that the number has risen above 300 ppm. For the first time in 2013, the concentration climbed above 400 ppm and continues to rise.
Scientists discuss when the CO2 levels were last so high. It could have happened during the Pliocene era 2 to 4.6 million years ago, when sea levels were at least 60 to 80 feet higher than today. It may have been in the Miocene, 10 to 14 million years ago, when the oceans were more than 100 feet higher than they are now.
In our 800,000-year record, it took about 1,000 years for the CO2 content to increase by 35 ppm. We are currently seeing an increase of more than 2 ppm per year, which means that within the next 45 years, if not earlier, we could reach an average of 500 ppm.
People never had to breathe so much air. And it does not seem to be good for us.
The global temperature closely follows the atmospheric CO2 concentration. Possible effects of higher average temperatures include tens of thousands of deaths from heat waves, increased air pollution leading to lung cancer and cardiovascular disease, higher levels of allergy and asthma, more extreme weather events, and the spread of ticks and mosquito diseases – an effect we have already see.
Global annual temperature and CO2 values, 1959-2016
Higher CO2 concentrations also exacerbate ozone pollution. A 2008 study found that for every degree Celsius, the temperature rises due to CO2 levels, ozone pollution can kill another 22,000 people through respiratory disease, asthma and emphysema. A recent study has calculated that air pollution kills 9 million people each year.
Other research has given more cause for concern. The average CO2 content does not match the air that most of us breathe. Cities tend to have much more CO2 than the average – and those values are even higher indoors. Some research suggests that this could have a negative impact on human cognition and decision-making. (There is a complete list of possible impacts of climate change on human health on an archived EPA page.)
President Obama's EPA ruled in 2009 that CO2 is a pollutant that had to be regulated under the Clean Air Act, though The Trump administration is reviewing this decision again.
Drowning in CO2
The effects of CO2 on human health are only part of the larger story.
The change we have seen recently in CO2 levels has been much faster than natural historical trends. Some experts believe that by the end of the century we are on our way to achieving 550 ppm, which would cause global average temperatures to rise 6 degrees Celsius. (The increase in superstorm, sea-level rise, and spread of tick-borne disease, which we are already seeing, comes after a 0.9-degree increase.)
Sea level rise only increases as CO2 levels continue to rise.
At present, carbon dioxide emissions are still rising. The goal set out in the Paris MOU is to limit global temperature rise to 2 ° C or less. But as it was called recently in Nature, we are currently tuned to more than 3 degrees of warming.
The latest measurements from Mauna Loa show that if we want to avoid that, we need to make some dramatic changes very quickly.