Probably the second most important (only to preventing nuclear war) issue humanity has ever addressed will be discussed at Copenhagen in less than a month. At this conference, delegates from all over the world will work out a global agreement on how to prevent this catastrophe from occurring. In light of this, the next few weeks' Science Fridays will discuss the various aspects of climate change.
The change humans are causing to the climate is known most commonly as global warming or climate change, though the terms global change and climate crisis are also used. The meaning of these is essentially the same. Some people care a lot about which is best; I don't, except that I think global change is vague and likely to be misunderstood. I will use the other terms interchangeably in this series.
I'll start with an overview on how the Earth's climate has worked for most of recorded history, and how we should make sure it returns to.
Currently, when sunlight falls on the Earth, about 30% is reflected—most prominently by ice, though deserts also reflect sunlight well. (The percent of incoming light a surface reflects is called its albedo. So, the Earth's average albedo is 30%, though different parts reflect varying amounts of light.) The light that isn't reflected is absorbed and converted into heat.
All objects get rid of some of their heat energy by radiation—“glowing” to convert the heat into light. Most things we encounter “glow” in the infrared, so we can't see it. Only very hot objects, like lightbulbs and the sun, glow in the visible spectrum. So, the Earth loses heat by radiating infrared light away. The amount of energy it radiates is roughly equal to the amount of radiation it absorbs—if it weren't, the system would not be in equilibrium and the temperature of the Earth would be changing rapidly.
Of course, that isn't the whole story, because we haven't accounted for the greenhouse effect. The greenhouse effect is a natural process by which certain gases, most importantly carbon dioxide (CO2) and methane, trap some of the infrared light the Earth radiates in the atmosphere. This makes the Earth warmer than it otherwise would be. It's very fortunate for us that it exists—without it, it would be too cold to support civilization as we know it.
Just because it's natural and makes our existence possible does not mean we can't hurt ourselves with it. The Mississippi River is natural, and New Orleans wouldn't exist without it, but human stupidity with a little help from nature caused it to flood the city. The dumbest of the global warming deniers claim that CO2 is fine because it's natural, but “natural” does not always mean “beneficial” or “immune to reacting violently to human stupidity.”
So, humans did a whole lot of things to put tons of CO2 and methane in the atmosphere. Since the beginning of the industrial age, atmospheric levels of CO2 have increased by more than 30%, mainly due to deforestation and the burning of fossil fuels. Methane levels have increased by more than 150% over the same time, mainly as a result of agriculture, particularly beef cows. This has strengthened the greenhouse effect, causing global temperatures to rise.
A few side effects of this warming have helped increase it. The biggest is called the ice-albedo feedback. As the Earth warms, sea ice in the Arctic melts. As the ice melts, less-reflective water is exposed to the surface. Water has a much lower albedo than ice, so it absorbs more light, and gets hotter. So, the Earth warms, causing ice to melt, causing more light to be absorbed, causing the Earth to warm, and so on.
This feedback loop is very bad for us. Unfortunately, it's not unique. As the Earth warms, permafrost melts. Permafrost has a very high CO2 and methane content that is released as it melts. So, Earth warms, melting permafrost, releasing greenhouse gases, causing the Earth to warm. Another example is how much CO2 the ocean absorbs. The ocean naturally absorbs a chunk of CO2, helping mitigate the effects of our carbon emissions. However, it absorbs less and less as it warms. This is another way global warming feeds on itself.
So, emitting as much CO2 and methane as we have opened up a really complicated can of worms. Basically, because of these feedbacks, there is a point we hopefully won't reach where even if we drop emissions to zero, we won't be able to stop runaway warming. We have to make sure we curb our emissions before we reach that point.
What happens if we don't? A lot of really bad things. And not just that it'll be uncomfortably hotter.
If temperatures rise enough to melt the Greenland and Antarctica ice sheets, global sea levels will rise a lot. More than half the world's population lives close to the sea. If sea level rises, tons of people get displaced. The map below shows what parts of the east coast would vanish into the sea in a 10 meter sea level rise (which is not the worst case scenario here.) Imagine the impact of losing Boston, New York, Virginia Beach, Wilmington, Charleston, Miami, Mobile, New Orleans, and Galveston. Then add the west coast.
It isn't just the ice at the poles that could melt, either. The Himalayas are sometimes called the “third pole” because of all the ice there. The Himalayan glaciers grow high in the mountains and flow downhill. The Ganges, Indus, Brahmaputra, Mekong, Thanlwin, Yangtze, and Yellow rivers are fed primarily by their meltwater. Most of the Chinese, Indian, Pakistani, and Southeast Asian populations depend on those rivers. If the Himalayan glaciers vanished, the economies of those countries would be devastated, and, given our close ties to them, so would ours. Compounding the problem, three of those countries are nuclear powers, so instability in the region could have dire global consequences.
The two effects I mentioned above would cause a greater displacement of people than has ever occurred. You can be sure that a global wave of refugees would have dire political and economic implications for everyone, not just those directly displaced.
Global warming would affect us many other ways, mostly bad. Most agricultural centers would become more arid and less suitable for growing crops. Diseases would grow in range and epidemics would become more common. The frequency and severity of storms would increase (imagine a few more Hurricane Katrinas.) Deserts would expand. Ultimately, North Carolinians might have to go to New Hampshire to find a climate similar to what we have now.
This is what will happen if we fail to prevent it. It is not inevitable. Over the next three weeks, I'll discuss the ways it can be stopped, and how the politics for stopping it look.
This week's science news is a little terse because I'm in a rush.
Storm Video Hatteras:
Lightning and Space Weather:
NASA & ESA team up for Mars: