“Doubt, indulged and cherished, is in danger of becoming denial; but if honest, and bent on thorough investigation, it may soon lead to full establishment of the truth.” -Ambrose Bierce
About a week and a half ago, I wrote an article called The Power of Theory In Science, where I mentioned the Big Bang, Evolution, and Global Warming as some of the leading scientific theories describing a variety of natural phenomena.
And while no one took issue with my assertion that the Big Bang and Evolution were the best scientific theories describing (respectively) the origin of our physical Universe and the diversity of life found on Earth today, there were plenty of challenges to my assertion on global warming.
Let’s get the facts out on the table right to start:
- I’m a physicist, not a climate scientist.
- I do not run climate simulations or claim that I can accurately predict the climate.
- But I do understand the physical mechanisms behind heat transfer, thermal equilibrium, and what determines “temperature” for a body. Like, say, a planet.
- And I recognize that there are scientists — real, honest, competent and skilled scientists — that work on these problems. Some of them write about it, too.
So, what are some of the basic facts, if we’re really trying to understand what’s going on. First off, we need to know what the Earth’s temperature is doing. Because if there’s no warming, then humans certainly couldn’t be causing it. Let’s take a look.
You can’t simply measure the temperature at one location on Earth; local variations are too strong to get an accurate measurement that way. But if we look at many different locations over the Earth — if we take a global average temperature — we can measure how the average temperature changes over time.
And as you can see, if you take the average temperature from 1961-1990, temperatures now are consistently about 0.5° Celsius higher than they were over that time frame.
Has this held true recently, with the most up-to-date data that we have?
Yes it has. Even with strong year-to-year variations, as many things affect the Earth’s temperature, the overall trend is easy to see: the Earth is getting hotter, and it’s getting hotter at an increasing rate.
Of course, the big question is why? If this is happening because of something we’re doing, we’d better figure it out and stop. So what could be causing this increase in temperature?
Well, it’s possible that the recent increase in carbon dioxide in our atmosphere has caused it. The correlation is clear, and the rapid changes of both of these things together may suggest some kind of causation, but is this what’s really happening?
Let’s go over two basic things: figuring out where this carbon dioxide came from and what effects it could possibly be having. Like I said, I don’t know enough about climate science to come up with and test a particular model, but I know enough physics to look at the basic, overall picture, and have you look with me.
Humans use lots of energy, particularly humans in extreme climates, and particularly in North America. A kilowatt is a lot of energy; for the entire United States, a total of about 100,000,000,000,000,000,000 Joules of energy gets used every year. This is about 20% of the world’s total, a staggering amount of energy.
True, it’s only about 0.02% of the energy received by the Earth from the Sun, but we don’t get that energy from the Sun. Where do we get it from?
From lots of different sources, but mostly from Oil, Coal, and Natural Gas, which make up 85% of our planet’s energy sources. All three of these fuel sources — known as fossil fuels — take molecules where energy is stored (in the bonds of the molecules themselves), release that energy (via some form of combustion), and then emit the waste products (predominantly carbon dioxide) into the atmosphere.
And it’s not like this is wasted; quite to the contrary, we are not only using all of this energy, there is a demand for far more. Since the industrial revolution began, a huge amount of extra carbon dioxide has been released into the atmosphere by humans.
I know I put this graph up earlier, but it plots two very important things. The lower line shows how many billions of tons of CO2 were emitted each year since 1750. A little math tells us that about 1.4 trillion tons of CO2 have been added to the atmosphere thanks to human activity.
But the top line shows what the atmospheric concentration of CO2 is in any given year. And even though it’s risen dramatically — as we’ve known at the highest levels since the 1960s — it’s only increased by a percentage of what we’d expect if all of that emitted CO2 wound up in the atmosphere.
Because the atmosphere is in contact with the oceans, which absorbs carbon dioxide. Now, carbon dioxide combines with water to produce carbonic acid, which is toxic to ocean life in overabundance, as the Great Barrier Reef, among other places, is finding out.
But Carbon Dioxide is only a tiny fraction of the atmosphere, coming in — even after the increases of modern times — at only 0.04% of the total dry atmosphere.
Why should we care about something so inconsequential?
You see, most of the atmosphere, like Oxygen and Nitrogen, don’t really care about light of any type. Not the sunlight that falls on the Earth, not the infrared light that the Earth radiates away into space at night. But some molecules are sensitive to one much moreso than the other.
The reason, of course, is that different molecules are sensitive to different wavelengths of light, and different temperature objects emit light at different wavelengths. The Sun is very hot — nearly 6,000 Kelvin — and emits mostly visible light. Visible light mostly passes through our atmosphere unimpeded, and is blocked only by things such as clouds, aerosols, or things that help produce these sunlight-blocking things. (Such as pollution, oddly enough, which is the leading cause of global dimming.)
So if the amount of sunlight hitting the Earth is diminishing, why is the overall temperature of the Earth getting hotter? Why is the Earth’s average temperature increasing?
Because some gases — such as methane, water vapor and carbon dioxide — absorb the heat that the Earth tries to radiate back into space. Just as a blanket reflects your body heat back onto you, these gases reflect the Earth’s heat back onto the Earth, raising the overall temperature.
It isn’t perfect, which is good, otherwise we’d wind up like the hottest planet in the Solar System, Venus. Yes, not Mercury, but Venus, because of its thick atmosphere full of greenhouse gases. While Earth is nowhere near the 460 Celsius that Venus is on average, a similar fate awaits us the more and more greenhouse gases we dump into our atmosphere. The one we control the most is Carbon Dioxide, but don’t let that fool you into thinking that’s the only important one.
Because the most abundant greenhouse gas in the atmosphere wasn’t included on the above charts: water vapor. Water vapor is very highly variable, but there’s one thing that affects water vapor concentration more than any other. Temperature. This is not circular reasoning; this is a very important fact.
If you do anything to increase the temperature of the Earth, like emit more carbon dioxide, you increase the amount of water vapor in the atmosphere. Increasing the amount of water vapor in the atmosphere then further increases the temperature of the Earth, making it that much more difficult to fight those changes.
So how do we do it? If too much carbon dioxide in the atmosphere is bad for the planet, and we’re putting it there, and it’s definitely contributing to (if not causing it outright) global warming, what do we do about it?
The big problem, as anyone can plainly see, is that we’re using a lot of energy, our most productive energy sources have this harmful side effect of adding carbon dioxide to the atmosphere, and adding carbon dioxide to the atmosphere is causing the temperature of the Earth to rise. It isn’t the only thing causing the Earth’s temperature to rise, and it isn’t only causing the Earth’s temperature to rise, but that’s one of the things it’s definitely doing.
People still argue about “how much” and “how big will the effect ultimately be” for the amount of CO2 we’ve already released, but we know that we’ve already contributed very heavily to this problem, and we’re going to continue to do so unless we figure out a very different path from the one we’re currently on.
I don’t know what the solution — if we find one — will ultimately be, but there is nothing to be gained by pretending this problem isn’t real, and by pretending that it isn’t our problem. The “crisis” is what are we going to do about it, and the worst thing we can do is pretend it doesn’t exist, rather than recognizing that this is a real issue, and it’s our responsibility to deal with it responsibly. Because the consequences of ignoring it? Well, I refer you to this 1969 letter from Daniel Patrick Moynihan, then a Nixon aide:
As with so many of the more interesting environmental questions, we really don’t have very satisfactory measurements of the carbon dioxide problem. On the other hand, this very clearly is a problem, and, perhaps most particularly, is the one that can seize the imagination of persons normally indifferent to projects of apocalyptic change.
The process is a simple one. Carbon dioxide in the atmosphere has the effect of a pane of glass in a greenhouse. The CO2 content is normally in a stable cycle, but recently man has begun to introduce instability through the burning of fossil fuels. At the turn of the century several persons raised the question whether this would change the temperature of the atmosphere. Over the years the hypothesis has been refined, and more evidence has come along to support it. It is now pretty clearly agreed that the CO2 content will rise 25% by 2000. This could increase the average temperature near the Earth’s surface by 7 degrees Fahrenheit. This in turn could raise the level of the sea by 10 feet. Goodbye New York. Goodbye Washington, for that matter. We have no data on Seattle.
It is entirely possible that there will be countervailing effects. For example, an increase of dust in the atmosphere would tend to lower temperatures, and might offset the CO2 effect. Similarly, it is possible to conceive fairly mammoth man-made efforts to countervail the CO2 rise. (E.g., stop burning fossil fuels.)
We know now that the “7 degrees Fahrenheit,” thankfully, is a larger number than we’ve actually experienced. But we know that if we want to avoid the sea level rise — among other effects — that accompanies a continued temperature increase, we have to do something about this problem. And the first step, of course, is admitting that we have a problem.
I like this world, and I like trying to understand it. It’s what I do for a living, and it’s what climate scientists — for this world in particular — do for their living. It’s your world too. The only question left is, what are you going to do about it?