Obama speaks on global warming: What you need to know to be certain that global warming is real

President Obama is speaking at the unprecedented UN Climate Conference today. It’s great to see a US President taking a stand on the great issue of our time, but inevitably the Glenn Beck crowd will be out with the usual talking points. “It’s been cooling since 1998!” (It hasn’t.) “Climate change is natural!” (Not this time.) You may even hear these arguments from your friends. So I thought it would be helpful to outline the case for global warming, and explain why it’s so bulletproof.

Surprisingly, it can be hard to argue back to climate change deniers, because anyone who cares enough to actually defend the position that global warming is not real has likely spent time amassing an array of talking points to muddy the waters - talking points that have been repeated and reinforced by Beck, Jim Inhofe, and others. It's nearly impossible to prepare for all of them; some will likely stump you, and some sound so scientific that doubt may even begin to creep into your mind.

Don't let it. The problem with climate change denial arguments is not only that they're wrong, but that they are plain illogical – climate deniers suffer from a cognitive bias called the “Dunning-Kruger effect,” a lack of self-awareness that prevents them from seeing their errors, so don’t let their false confidence fool you. Thus, you don't have to understand the complex science of climatology to speak intelligently on global warming - as long as you know four key facts and have a basic grasp of logical reasoning, you can make a bulletproof case that no skeptic can answer.

None of the evidence here is new, but it's helpful to put it together this way to show how simple the case for global warming really is. So here we go...

FACTS

When I say "fact," I mean it in the scientific sense, "that which is observed." These are the raw observations that no research scientist disputes.

Fact #1: Global temperatures have risen by about 0.8 degrees C (1.4 degrees F) since records began, with the ten warmest years on record all occurring from 1997-2008. This is not disputed.

Fact #2: CO2 is a greenhouse gas; a basic physical property of CO2, repeatedly measured and confirmed since the 1890s, is that it absorbs and emits infrared (heat) radiation, so CO2 in the atmosphere traps heat from the sun. This is undisputed.

Fact #3: CO2's concentration in the atmosphere has risen by 35% since the Industrial Revolution, and is now at its highest level in at least 450,000 years (measured in bubbles of air trapped in ice cores). CO2 measured at the Mauna Loa observatory in Hawaii shows an uninterrupted increase since records began in 1959. This is undisputed.

Fact #4: The amount of extra CO2 in the atmosphere matches almost exactly with the amount released from fossil fuels (minus the amount that would be taken up by natural carbon sinks). That sounds like a big claim, but miners, drillers, factories, and utilities are, after all, businesses who keep careful records of the fuel they burn, so it's relatively easy to measure. So we know with 100% certainty that the extra CO2 comes from human emissions. This is undisputed.

(If you need further proof, the CO2 released from fossil fuels contains only one isotope of carbon, C-12, because the radioactive C-13 and C-14 atoms found in "natural" CO2 have, in fossil fuels, all decayed over millions of years; sure enough, as you’d expect if the extra CO2 was coming from fossil fuels, the concentration of "natural" C-13 and C-14 is steadily declining.)

So we know for certain that humans are adding significant amounts of CO2 to the atmosphere, that CO2 is a heat-trapping greenhouse gas, and that temperatures are rising. The logic is inescapable. If you’re a lawyer in a monkey trial, to logically prove that humans are NOT causing the observed increase in temperatures, you would need to prove both of two things:

First, you need to show how it could be possible to pump more of a known greenhouse gas into the atmosphere WITHOUT temperatures increasing. How can the earth absorb more energy from the sun without its temperature rising?

Second, if CO2 is not causing the observed warming, you need to show what IS. Long-term global temperature change is only caused by an external forcing that causes either more energy to come in from the sun, or less energy to escape back into space; absent a forcing, there’s no temperature change. We know that temperatures are rising, so if it's not the greenhouse effect causing that increase, what is?

The first question regards the sensitivity of the earth's climate to changes in CO2, which requires a scientific background I don't have. If you're interested in learning more, check here and here.

The second is easier to deal with, as long as you can read a graph. The most common alternative to greenhouse gases is the sun. Solar activity, the argument goes, is correlated with past climate changes; therefore, the sun must account for the global warming we see today. The problem is, solar activity has decreased since the 1970s, just as global temperatures have risen the most. So while the sun may have caused PAST climate changes, it cannot be causing TODAY’S.

Remember, a climate skeptic must answer BOTH claims to have a credible point.

But what about the evidence FOR global warming—is there a smoking gun? Well, there are several, but here’s one that involves no complex calculations, correlations, or models. As it turns out, greenhouse gas-induced warming has a telltale signature, based on how different layers of the atmosphere heat up. If you imagine the earth and its atmosphere as a person covered by several blankets, there are two ways the person can get warmer: either more heat comes in from the outside (i.e. you turn up the heat in the room), or less heat escapes through the blanket (i.e. you throw another blanket on). If you crank the heat up, the extra heat passes through all the blankets, heating them all up. But if you throw another blanket on, you trap more heat in the lower layers, and the top blanket doesn’t warm up much.

That’s basically how the atmosphere works. If the increase in global temperatures were due to more energy coming INTO the earth (i.e. the sun was getting hotter), you would expect to see warming of ALL layers of the atmosphere. But if warming were caused by greenhouse gases trapping more heat, you’d expect to see warming of only the lower layers of the atmosphere where the heat was being trapped. When you look at the data, what we actually see is that while the lower atmosphere (the troposphere) is warming, the upper atmosphere (the stratosphere) is actually COOLING. That’s the smoking gun, proof that global warming is definitively caused by extra greenhouse gases, which we know to be from human activity.

Questions? Think I’m an idiot? Leave a comment and I’ll respond or send you a link to the appropriate source.