It doesn't smell any different and it doesn't feel any different but we have changed the atmosphere. It has not been like this for about 3 million years. No humans have ever breathed air like this and we should be very worried about its implications.
Carbon dioxide (CO2) levels in the atmosphere have just passed the symbolic but significant milestone of 400 parts per million (ppm). A few hundred years ago, at the dawn of the industrial age, the CO2 concentration was only 280ppm but it has increased exponentially since then as a direct result of our burning of fossil fuels. When the concentration of this greenhouse gas was last at the current high, the arctic was completely ice free and the sea level was 120 feet higher. Average polar temperatures were more than 14 degrees Farenheit higher and overall, the world was 5 to 6 degrees warmer than today. These conditions are expected to return with incalculable costs unless we act soon.
As a result of industrialization, global temperatures are now rising 75 times faster than in prehistoric times and have increased by almost 2 degrees in recent history. While the world's governments supposedly agreed to limit the increase to approximately 3 degrees, little has been done to limit the emission of causative greenhouse gasses. While it is good to have some CO2 in the atmosphere, its natural ability to retain heat like a greenhouse stops the Earth from freezing, we now have too much of a good thing.
If we fail to limit future greenhouse gas emissions, the Earth is predicted to pass through a series of tipping points, temperatures at which runaway global warming will occur. Once the summer ice in the Arctic melts completely, all that solar heat energy will be absorbed by the oceans instead of being reflected back into space. As atmospheric temperatures reach a critical point, frozen tundra circling the Arctic will melt releasing immense quantities of methane, another greenhouse gas that traps 20 times more heat than CO2 thus leading to even greater warming.
As the poles get warmer, air and water currents that move solar heat energy from the equator to the rest of the planet will change and based on geological precedent, scientists predict that this may cause the release of massive amounts of methane hydrate from the deep ocean that will further inflame the rising temperatures. Scientists have determined that there is more carbon stored in these frozen water and methane deposits than in all the coal, oil and natural gas on the planet and if it is released, it will contribute to runaway warming.
Climate patterns will change and rainfall redistribution around the globe will result in some areas receiving more precipitation and others less. We do not fully understand when these tipping points will be reached or how they might interact but many climate scientists believe the evidence demonstrates that we only have a few years to act.
In this new world we are creating, evidence suggests land ice in Greenland and Antarctica will melt and that the sea level will be potentially hundreds of feet higher than at present leaving vast swathes of land underwater and hundreds of millions of people homeless. The loss of mountain glaciers and changes in precipitation will render much of the planet devoid of water and thus uninhabitable. All scientific indications are that our grandchildren will live in a world that is drastically different from the one in which we grew up. They will face famine, conflict and death on a scale never before imagined and no amount of denial will help them.
We can probably still avoid this future if we act quickly; many scientists believe that there is still time, but we cannot wait much longer to make the necessary changes in CO2 emissions. As the first humans to breathe this atmosphere that we have created, it remains in our power to act and we will be responsible for the catastrophes to come if we fail.
n Dr. David S. Richard is a professor of Biology at Susquehanna University.