# Correlation does not prove causation, but lack of correlation doesn’t disprove causation either.

IPCC AR5 WG1 Decadal variation in global temperature (IPCC)

UPDATE: After some feedback, I’ve added a bunch of graphs to the number lists below to help clarify.

What does it mean when someone says “correlation does not prove causation?” It’s a common phrase uttered by individuals who deny that climate change is happening, that it is dominated by the industrial emissions of greenhouse gases like carbon dioxide (CO2), and that the changes will be disruptive to both ecosystems and human society (aka industrial climate disruption, global warming, or climate change). In order to understand why these deniers of industrial climate disruption are wrong, we first have to understand what they’re talking about when they’re talking about correlation, causation, and the relationships between the two.

## What is correlation?

Correlation is a measurement of how related two different sets of numbers are to each other. Continue reading

# Climate Science for Everyone: How do scientists measure the temperature of the Earth?

Figure 1: Weather station (image credit: Blundells.org)

Before we answer the question in the title above, I’m first going to ask and answer a different question: how do you measure the temperature of a glass of water?

I’m guessing that most people will answer the question with some variation of “use a thermometer.” Stick a digital or glass thermometer into the cup, measure the digital reading or look at the colored bar inside the glass, and write down the number. Done, right?

Wrong.

We didn’t measure the temperature of the cup of water at all. We measured the temperature of the water that was next to the thermometer at a time just before we looked at the thermometer. But when we put the thermometer into the water, that act changed the temperature slightly as energy flowed between the thermometer and the water.

We can try again, of course. Let’s put the thermometer into the water again and let it sit for a little while, until we think that the probe and the temperature of the water have equalized, write down the number, and we’ve got it, right?

Nope, I’m afraid not. We’re still only measuring the temperature of the water that’s next to the thermometer. Continue reading

# Climate Science for Everyone: How much heat can the air and ocean store?

Let’s look at how much energy the oceans can store compared to the energy storage of the atmosphere.

One way to describe the amount of energy that something can store is called “specific heat.” This is essentially the amount of energy required to heat up a mass of a material by a certain temperature. In our case, we’ll use 1 kg heated by by 1 degree Celsius (1.8° F) because those are the international standards.

The specific heat of air is about 1158 J/(kg*C) while the specific heat of seawater is about 3850 J/(kg*C), where a Joule is a standard measurement of energy. We can see that air has a specific heat a little more than 3x smaller than that of water. But we know from our day-to-day experience that water is a lot denser than air is, and that will matter a great deal to our calculations. (For reference, one Joule is about the amount of energy you need to expend to lift one pound 9 inches.) Continue reading

# Climate Science for Everyone: heavy snows are expected in a warming world

There are people who say that heavy snowfall means that human-caused climate disruption must be wrong. This is a misunderstanding on their part. Fortunately, it’s quite simple to correct the misunderstanding.

You can live nearly anywhere and have personal experience of how hotter air has more water vapor in it. It always feels much more humid when it’s hot than when it’s cool. My personal experience with this was visiting Connecticut in late August, when it was 95 degrees out with unbearable humidity.

It’s also the case in the winter. There’s a reason why the Front Range of Colorado (where I live) gets more snow from an upslope flow than from any other weather condition – the warm air from the Gulf of Mexico has a lot of water vapor in it, and when that air cools down as it’s forced to higher (and colder) elevations by the Rocky Mountains, the excess water vapor freezes and falls as snow. Continue reading

# Climate Science for Everyone: Carbon dioxide increases in the air are mostly from burning coal, oil, and natural gas

Figure 1 – The carbon cycle

Over the last few decades, scientists have learned a lot about how life interacts with the air, land, and sea. And in the process, they’ve made observations that have demonstrated beyond any reasonable doubt that the increasing carbon dioxide in the air is from people burning coal, petroleum, and natural gas.

So how did the scientists put together all the pieces to make a complete conclusion? They started with an understanding of how plants use carbon during photosynthesis. That knowledge showed that the increased carbon dioxide in the air was from plants. Then they formulated some guesses as to where that much plant-based carbon dioxide could come from and, by process of elimination and careful accounting, determined that the source was human consumption of fossil fuels. Continue reading

# Climate Science for Everyone: How scientists measure the carbon dioxide in 800,000 year old air

Climate scientists who study the history of the Earth’s climate (also known as paleoclimatologists) know that modern carbon dioxide levels are at their highest level in the last 800,000 years. They tell us this because they’ve been able to measure the carbon dioxide in air that is actually 800,000 years old. So how do they do that?

Scientists know how much carbon dioxide was in the air hundreds of thousands of years ago because they actually have small samples of ancient air stored in glacial ice. To get a feel for how this works, consider the following examples. Continue reading

# Climate Science for Everyone: Why 3% annually is actually a lot of carbon dioxide

Atmospheric CO2 concentration data from ice core (blue, 1750-1975)
and direct atmospheric measurements (red, 1960-2010) vs. “compounding
interest” model described in post (purple). Click for a larger version.

In many ways, climate science is difficult. There’s a reason that the best climate models require some of the most powerful supercomputers in the world in order to run. But the most important concepts are easily understood by a non-expert with either a little mathematical skill or the ability to use some simple online tools. This is the inaugural post of a new series that seeks to illustrate how anyone and everyone can understand the most important concepts underlying climate science and the reality that is human-caused climate disruption.