Make no mistake – the earth is warming. I’m not going to get into the politics of global warming here, this isn’t the place for that. Whether you believe that the rise of global atmospheric carbon dioxide gas concentrations (CO2) and subsequent warming is a direct result of man-made activities or not, the indisputable facts are: 1) the levels of CO2 in the atmosphere are higher than they have been in hundreds of thousands of years, and 2) the rate with which they have risen is unprecedented in the recent climate record of our planet.
Think of Earth floating in the cold vacuum of space as if it were a glass-walled greenhouse full of plants in a very cold, dry desert environment. Sunlight hits the greenhouse, and only some of it’s heat rays escape back out into the desert. The glass of the greenhouse traps some of the heat and keeps it in, warming the air in the greenhouse.
The climate of our planet behaves in a similar fashion, in that the greenhouse gases in our atmosphere work like the glass of the greenhouse, trapping some of the sun’s heat. The higher the concentrations of the gases, the thicker the glass and the more efficient it is at keeping heat in and warming the greenhouse. Earth’s greenhouse gases are, in order of abundance, water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Carbon dioxide is the most important, as there are direct correlations between the levels of CO2 in the air and the global mean temperature.
Whales know that ~70% of the surface of the earth is covered in water. Penguins know that about 10%, or six million square miles is covered in ice. For now. Those values will change as the earth continues to warm and the ice sheets melt at an accelerated rate. There are three major repositories of ice left on the earth – the ice sheets of Antarctica and Greenland, and various small mountain glaciers and ice caps. Between Greenland and Antarctica, they contain 99% of the fresh water on our planet.
Just how much ice is sitting in Antarctica and Greenland? The answer is staggering. The volume of ice in Antarctica is around 30 million cubic kilometers (7.2 million cubic miles), spread over around 14 million square km, or an area about the same size as the United States and Mexico combined (5.4 million square miles). About 2.2 million cubic kilometers of this ice lies trapped in the West Antarctic Ice Sheet (530,000 cubic miles). It is so massive that is has depressed the rocks on which it lies by around 0.5 to 1 km (Anderson, 1999). Up north, the Greenland ice sheet has a volume of ~2.9 million km3 (695,000 cubic miles).
What would happen if observed trends in CO2 levels and global temperature rise continue or even accelerate and these ice sheets melted? One recent calculated value states that melting of the West Antarctic ice sheet will raise global sea level by 3.3 m (Bamber et al., 2009). If the ice in Greenland were to melt, this would add an additional 6-7 m to mean sea level (Houghton et al., 2001). If the entire Antarctic ice sheet melted, sea level could rise as much as 70 m (200 feet). That would not be good for us humans.
Check out the incredible footage of glaciers in Greenland and Alaska melting, by Dr. James Balog of the Extreme Ice Survey:
Some people might think that a few meters of sea level rise isn’t a lot, especially when tides and waves are on the order of tens of meters. But the average sea level is a whole different beast. A rise of even 5 meters will have HUGE, global consequences on billions of people. Entire countries will be wiped off the earth, islands will disappear beneath the waves, and global coastline geography will change forever. Check out this interactive sea-level rise map:
Here’s what San Francisco would look like with a global mean sea level rise of 5m, just think of all that new waterfront real estate along I-5 in Stockton:
A few weeks ago, I wrote about the Adirondack mountains, and in that post I included a model sketch of the layout of ancient continents. In that sketch, the seas and continents looked very different than they do today. Over the span of geologic time, continents drift, the climate fluctuates between warm periods and ice ages, and continental ice sheets come and go. Climate change is a natural process, and it has occurred hundreds of times through the long history of Earth. What’s happening right now has happened before, long before humans were around, in fact, just 21,000 years ago we were in the grips of an ice age, and sea levels have risen 120 meters since then to their present levels.
So what’s the big deal, you might ask? The big deal is that the change we are in the midst of right now is happening at an unprecedented rate, and a whole lot of us humans live at the coast. Take a look at this graph of global average temperature – notice how the far right side value (closer to the present) skyrockets upwards way higher than it has in the last 400,000 years, and way faster than it has in the last 1,000 years.
Most people would agree that this is a direct result of man-made greenhouse gas levels rising during the industrial revolution and beyond into the present day – there is a nearly perfect correlation between CO2 level rise since the industrial revolution and the upward climb of global average temperatures.
Here’s some resources to learn more about global warming. Read the evidence for yourself and make up your own mind. I may be biased due to my scientific background, but I think we’re careening down a dangerous path, at the end of which lies a very different earth, one in which the coastlines will be very different than they are today, and one that could potentially be devoid of any winter snow in the United States….
A really interesting article about Dr. Charles Keeling, the scientist who created the instruments that have provided the longest-running continuous measurements of atmospheric Co2 levels on Mauna Loa volcano in Hawai`i: http://www.nytimes.com/2010/12/22/science/earth/22carbon.html
The role of the cryosphere in sea level change:
Melting threat of the West Antarctic Ice Sheet and risk to US coastal cities:
Climate change in Mountain Ecosystems:
Current CO2 levels and trends back in time: