What is climate change? Why’s everyone getting all huffy about a tiny change in the temperature of the Earth? Doesn’t it all seem just a little bit silly?
There’s a good chance that, if you’re reading my blog, you’re already somewhat familiar with the basics of climate change. But maybe when you’re sitting around, talking with your friends or family, they ask you questions that you don’t know the answer to: ”It was the coldest winter here in fifteen years! How can global warming be happening?”, “There’s no scientific consensus on global warming! Fox News said so!”, etc.
So, for your benefit and review, here’s my little guide to Climate Change. There’ll be some resources at the end for further reading, in case you’d like them. Also, if you’re new to climate change, or if you’re a skeptic, please keep an open mind as you read; the only way you get anything out of anything is by going in with a positive attitude.
In any case, let us begin with:
A BRIEF OVERVIEW OF THE RECENT HISTORY OF OUR PLANET
In order to really understand climate change, we have to take a look at how the Earth has worked for the past few million years. Right now, we’re living in what scientists call the Quaternary Period, a period of geologic history that began about 1.6 million years ago. In geologic time, that’s not too old; considering the fact that the planet was formed about 4.5 billion years ago, the Quarternary Period is relatively short.
Also, it’s important to note that we are living in an Ice Age. The Quarternary Period is relatively cold compared to other time periods, and during the last 1.6 million years, the ice caps have been constantly growing and shrinking, expanding and contracting. (The ice caps go all the way from the point at which they are now, all the way down to Seattle! Imagine a five mile high glacier in the middle of downtown Seattle…crazy.)
So, if we look at the graph above, we can notice a few things. One is that the graph begins about 650,000 years ago and charts time on the y-axis, and another is that the graph charts the parts per million (ppm) of CO2 in the atmosphere. That’s on the x-axis. Also, you’ll notice that the lines charted on the graph go up and down, in cycles.
Scientists note that the times when we’ve had lots of glaciers covering the surface of the Earth are the same times that there has been a relatively small amount of CO2 in the atmosphere (look at the graph: see how the blue areas, which are the times representing glacial periods, are all times during which the amount of CO2 in the atmosphere is below 230 ppm?). Also, they notice that the exact opposite is true: the times when there have been few glaciers, called “interglacial periods,” have had relatively high amounts of CO2 in the atmosphere (the times outlined in yellow).
So we can clearly see that the amount of CO2 in the atmosphere can at least somewhat account for changes in climate. When there’s a low amount of CO2 in the atmosphere, we’re going to have a period of really cold temperatures and glaciers; when there’s a high amount of CO2 in the atmosphere, we’re going to have an interglacial period with relatively fewer glaciers and warmer temperatures.
So, do you think we live in an interglacial period, or a glacial period? If you guessed interglacial period, you are correct! We’re smack in the middle of what’s called the Holocene, an interglacial period that began around 9600 BC, so the levels of CO2 in the atmosphere are naturally higher than what they are during a glacial period.
Looking back at the graph, we have to notice two more things. First, notice the variation in levels of CO2. The lowest amount of CO2 we’ve had is probably around 180, and the highest CO2 we can see is about 290, or perhaps a bit above 300. But generally, the amount of CO2 in the atmosphere has remained in a comfortable space of between 190 and 290.
The last thing we see when we look at that graph is the amount of time that it takes for CO2 levels to change. The changes in temperature and in the amounts of CO2 take place over thousands of years, sometimes even tens of thousands of years. That’s a long time!
Now that we have seen how the Earth has behaved in the past, and can see the patterns and cycles that have occurred naturally on account of CO2 levels, let’s move on to:
HUMANS BEGIN TO USE FOSSIL FUELS, AND CO2 LEVELS RISE
In the nineteenth century, a curious phenomenon began to occur on our planet. Humans had discovered the power of fossil fuels (coal, oil, natural gas, and a few others), and the CO2 levels in our atmosphere began to increase dramatically.
Let’s take a look at a graph from the IPCC, the Intergovernmental Panel on Climate Change. (They’re the 2,000 or so scientists that recently won the Nobel Peace Prize along with Al Gore for their work studying global warming, and the effects global warming has on our climate.)
This graph is almost identical to the first graph we looked at, but instead of looking at 650,000 years, this one above only graphs C02 levels from the past 10,000 years. So, the y-axis charts time, from about the present to 10,000 years ago. This amount of time covers just about the entire Holocene period. The x-axis charts the parts per million (ppm) of CO2 in the atmosphere, just like first graph. Also, in the right hand corner, the scientists have taken the past two hundred years and made an additional graph. It’s the same thing: time on the y-axis, CO2 in ppm on the x-axis, except the chart is dealing with an even smaller amount of time than the big graph it’s sitting on. Pretty cool.
Now, do you notice anything interesting? It’s pretty obvious. Look at how quickly the amount of CO2 in the atmosphere rose starting in the last two hundred years. On the big graph, it’s almost a vertical line that just shoots straight up, from about 280 ppm of CO2 to about 375 ppm of CO2. Whoa! That’s pretty fast, isn’t it?
Think about the first graph that we looked at. Remember the interglacial periods and the glacial periods? Remember how in order to create these two vastly different environments, it only took a fluctuation of CO2 levels in between 190 and 290 ppm? And remember how these fluctuations and cycles took place over thousands of years?
Wow. Now look at our newest graph. The amount of CO2 in the atmosphere is the highest it’s been in the last 650,000 years, to what looks to be about 375 ppm, or 85 ppm more than what’s normally the highest! Even more astonishing is the fact that this amount of CO2 was put in the atmosphere in less than two hundred years, not the thousands of years that is considered typical. If we were to graph 375 ppm on the first graph we looked at, it would be literally off the charts.
So, now we can clearly see that there is a lot more CO2 in the atmosphere than is normal. “Okay,” you may be thinking, ”why does that matter?”
Good question. Now is when we must ask:
DO RISING CO2 LEVELS RESULT IN GLOBAL WARMING?
Scientists often use computer models to figure out how the climate acts, or would act given certain conditions. Since we don’t have another planet Earth to mess around with, we use climate models to create scenarios we can use to tell the differences between what’s going on and what would be going on if we didn’t have a certain factor affecting climate.
So, for instance, we could construct a climate model that would show what would happen if there were no human-created (or, “anthropogenic”) CO2 emissions that got into the atmosphere. That would give us a model of the temperature of the planet without anthropogenic CO2 levels interfering, which we can think compare to our current, real life world temperatures.
And luckily for us, scientists have done just that.
This graph shows in gray the results of the model. The y-axis graphs the average global temperature (in degrees Celsius), and the x-axis graphs time from 1850 until 2000. The gray area is what the climate model predicted would be what happened if there were no anthropogenic CO2 levels affecting the temperature, whereas the red line shows the real temperature data recorded since 1850.
Hmm…they don’t seem to match up too well, do they? Notice especially how the red and gray really start to diverge starting in the 1960s and ’70s. If the two graphs matched up, we could say positively that our climate is acting naturally, without being affected by humans. But the graphs don’t match up very well at all.
Looking at this graph, we can now be sure that whatever is happening to our climate is not natural. Things would not be acting the way they are if it were happening naturally. So now we ask ourselves, “What could be the cause of the sudden increase in temperatures?”
Well, to answer that question, we can create another climate model, but this time, we’ll include only anthropogenic sources of CO2. Then we’ll take that model and see how it matches up to the real life data.
The graph is the same as the one directly above, and the only thing that has changed is the model results (the gray). Interestingly, the gray seems to be matching up with the red a little bit more, doesn’t it? In the first model that was made, the red line seemed to jump way above the gray line once we hit the 70s, but in this graph, the red line seems to be sitting right on top of the gray line for a good part of the graph.
So, it seems to fit that anthropogenic CO2 is causing warming. But just to be sure, let’s look at a model that combines the data from both natural and anthropogenic CO2 sources.
Whoa! Notice how perfectly the lines seem to match up. This model is by far the most accurate of any of the other two. Thus, it seems that we can accurately say that humans have caused the global temperature to go up, and that this was more likely than not caused by the amount of CO2 we’ve been releasing into the atmosphere.
Conclusion
These are just some of the data that are availble out there. If you’d like to learn more, I’d strongly suggest that you check out the IPCC (Intergovernmental Panel on Climate Change). They are the major authority on climate change and global warming. Their latest report came out in 2007, and the summary for the scientific data can be found here:
http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf
Also, if you’re a climate skeptic who still doesn’t think global warming and climate change could be possible, take a look at Grist Magazine’s guide to climate change:
http://gristmill.grist.org/skeptics
Thanks! And if you’ve got ideas for more information to add, please let me know.
Bryson Nitta, 2008
AMDG
