“Global warming is the greatest and most successful pseudoscientific fraud I have seen in my long life.” –Hal Lewis
The most valuable natural resources we have at our disposal during our brief lives are the following.
That’s right, the Earth and the Sun. And if we want life on Earth to continue as we know it, we have to avoid destroying our own natural environment. The big questions are whether we’re actually damaging it to the point of devastating destruction, and if so, what we need to do to fix it.
One of the things we’ve measured reasonably well — at, for instance, weather stations all across the world — is the global average temperature since the late 19th century. Have a look.
As the data shows in no uncertain terms, the world is — on average — getting warmer. And it’s doing so at a very fast rate: the global average temperature has increased by approximately one degree Celsius in the last century. Three years ago, the American Physical Society released this official statement on climate change:
Emissions of greenhouse gases from human activities are changing the atmosphere in ways that affect the Earth’s climate. Greenhouse gases include carbon dioxide as well as methane, nitrous oxide and other gases. They are emitted from fossil fuel combustion and a range of industrial and agricultural processes.
The evidence is incontrovertible: Global warming is occurring.
If no mitigating actions are taken, significant disruptions in the Earth’s physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now.
Because the complexity of the climate makes accurate prediction difficult, the APS urges an enhanced effort to understand the effects of human activity on the Earth’s climate, and to provide the technological options for meeting the climate challenge in the near and longer terms. The APS also urges governments, universities, national laboratories and its membership to support policies and actions that will reduce the emission of greenhouse gases.
There are a few people out there actively, vigorously, and loudly disputing this. Most recently, there’s a lot of hubbub over Hal Lewis‘s statements, such as my quote at the top, that cries of global warming are a hoax, and that there is a scientific fraud being perpetrated on the largest scale of all time. He recently resigned from the American Physical Society over their unwillingness to hold a Topical Group on Climate and Environment, and details his disgust here.
Other people have tried to explain why the science is sound, and I’m going to try to make it as simple as possible.
No, seriously, enough joking around. Let’s go directly to the science of what makes the Earth the temperature it is.
This is the Sun.
The Sun emits light. What form of light?
Well, visible light, but also ultraviolet and infrared light. Most of this light comes in through our (mostly) transparent atmosphere, and strikes (and gets absorbed by) the Earth’s surface. Without the Sun, the Earth would be about three degrees above absolute zero; thanks to the Sun, we’re more like 300 degrees above absolute zero.
But we don’t just sit around, absorbing the Sun’s energy and getting hotter and hotter. The Earth rotates, and during the night, it radiates this absorbed energy back into space. Although it doesn’t radiate visible light, the Earth radiates in the same way the Sun does: like a blackbody.
These two graphs look almost the same! The big differences are written along the axes. The Sun, of course, is much, much hotter and more energetic than the Earth! The Sun emits an intensity of light — in these units — that’s around 10,000,000 times that of Earth. The Earth, being so far away, only absorbs a tiny fraction of this light.
But, like we said, the Earth also radiates the energy absorbed during the day back into space at night. But it isn’t radiating visible light; the other main difference is the wavelength of light that the Earth emits; instead of visible light, this light is far into the infrared.
If this were all that were going on, the Earth would, on a year-to-year average, remain at the same temperature.
But if, hypothetically, if you fill the Earth’s atmosphere with gases that absorb the light the Earth emits, you will heat up the Earth. That’s what a greenhouse gas is, and the most abundant one on Earth is carbon dioxide, or CO2, which absorbs best at around four microns.
If we look at sunlight, we see that only a tiny, tiny fraction of the sunlight comes in at four microns, meaning that CO2 has a negligible effect on the energy coming in.
But what about the energy leaving?
We have to look at “Earthlight” for that, and wouldn’t you know it? A substantial fraction — somewhere around 1% of the total energy emitted by Earth — can get absorbed by the CO2 in our atmosphere.
What happens to that energy after the CO2 absorbs it?
It gets re-radiated back towards Earth, heating the planet up again!
In other words, the carbon dioxide acts like a two-way mirror, letting all the sunlight in, but reflecting the emitted heat back towards us! This last part — the reflection of the outgoing heat — raises our temperature, the same way reflected sunlight heats things up in a solar cooker.
That’s the principle behind global warming. Combine that with the observations that the Earth is getting warmer and the fact that we’ve added around 1,400 billion metric tons of CO2 to the atmosphere (thanks, stone1343) since the industrial revolution,
and you’ve got something that’s incredibly suggestive, logical, and quantifiable. Now we come to the question being thrown around by global warming deniers: Is it incontrovertibly, scientifically proven that the increase in CO2 causes global warming?
No, no it isn’t. But it’s unproven in the same way that all scientific theories are unproven; if you wait until every possible conceivable alternative has been explored, tested, and rejected, you will never conclude anything. In this case, where the Earth is at stake, it will likely be too late to undo the damage.
This isn’t just a scientific issue; it isn’t even an environmental, quality-of-life issue. We are doing a demonstrably destructive thing, by emitting the CO2 we are emitting into the atmosphere. If we don’t stop doing it, we will undoubtedly raise the Earth’s temperature, and it becomes a question only of “by how much?” And if you want to see the most catastrophic example of what carbon dioxide can do to a planet, look at the closest planet to us: Venus. We’re nowhere near that, yet, and I want it to stay that way.
And whether you’re a democrat, republican, independent, a global warming denier or a climate change advocate, or anything in between, you want the Earth to stay that way, too, whether you know it or not.