Over the course of the Earth's history, climate has changed dramatically. Some periods are extremely warm; in the Eocene, around 55 million years ago, there was a period of time, known as the PETM, where average global temperature was around 7o C warmer than it is today (13.39o C). We are currently in an "icebox" time. These are relatively rare, and are defined as points in time where there is ice at the poles. Because of this, the Earth would naturally warm again. Virtually no scientist disputes this; there is a solid base of evidence.
The controversy about climate change comes not from whether or not it exists, however. It's more a question of how much of an impact humanity has had on it. I'd like to take a moment and address a few of the myths and facts about climate change.
Myth #1a: The current warming trend is entirely natural.
Well, no. CO2, a major greenhouse gas, is stored in fossil fuels: natural gas, oil, and coal. These fuels are compressed, ancient organic matter, which is full of CO2. Burning these fuels puts lots of CO2 into the atmosphere. CO2 traps heat energy and reflects it back at the planet. So, when we put carbon dioxide in the atmosphere, we do contribute to the warming of the planet, especially when you consider the rate at which we add this gas to the atmosphere.
Myth #1b: The current warming trend is entirely man-made.
This is a popular converse to #1a. No, humans are not entirely responsible for climate change. The planet undergoes climate changes on a fairly regular cycle, and we are nearing a warm stretch anyway. The rate is what is different; the fact that the Earth is beginning to warm again is not.
Myth #2: Carbon Dioxide is the only greenhouse gas. So, if we can get rid of that, then the Earth will cool back down.
Nice try, but no. If we could remove all greenhouse gases from the atmosphere, we'd need to get rid of a lot more that just CO2. Methane (CH4), nitrous oxide (N2), and water vapor (H2O) are all greenhouse gases as well. In fact, water vapor has the strongest of these greenhouse gases. We could not possibly remove all the water from the air, and doing so would be far worse to life than climate change. The water cycle keeps water vapor from being too large of a problem, with respect to climate.
Also, simply removing greenhouse gases wouldn't fix the warming trend. There are other factors, such as the solar cycle and changes in Earth's orbit. Airborne particles and aerosols can also affect climate change.
Myth #3: Climate change would be great! It's way too cold where I live.
This one is especially tempting to those living in places like Minnesota, the Dakotas, or anywhere else where the average winter temperature is below 0. Unfortunately, it's not necessarily true. The term "global warming" is incredibly misleading in this respect. The Earth will not uniformly warm up by 5o C. Some areas will get warmer, sure. Others will get colder. The entire planet, land and sea surface, is warming, on average. This is not a promise of South Dakota becoming the new Arizona.
Myth #4: The Earth is warming faster each year, especially over the last decade.
Factually wrong. 2008 tied with 2001 for being the 8th warmest year on record. It's certainly still warmer than, say, 100 years ago. However, it's not exponential growth of the annual global temperature.
Myth #5: The weather's weird this year. It's global warming!
The weather is weird this year. But, no, it's not due to climate change. The unusual weather patterns this year (for instance, the repeated afternoon rainshowers early this summer in areas like Colorado) are due to the El Niño. It's an interesting weather phenomenon, but it a much shorter cycle than the climate cycle.
There is a hint of truth in this one, though. Weather patterns will change, causing drought, flooding, and other changes in weather globally.
Climate change is a complex issue. It's definitely science: it's occurring, and we can't stop it. We couldn't prevent it, no matter what we did. It's a natural process. However, we have had some impact on the speed that the warming trend has occurred. So far, it's not the fastest climate change: the PETM was a larger jump. in 10,000 years. We haven't had that long for this one yet, so it has yet to be seen if this is the fastest climate has changed. However, on the bright side: life didn't die out during the PETM. Instead, they flourished. The fact that we have polluted the air with so much carbon dioxide is problematic, but not as much as the other pollutants we've released. The Earth will survive and recover from any human impacts on climate change. A bigger question is how we humans will adapt and ride it out.
Thanks to Blog Action Day for posing the question about climate change, human impacts, and what action we need to take.
Graph credit: Paleomap Project
Credit for the annual temperature data to Science Daily.