How do we know climate change is human-caused?

It’s a question I get asked a lot: how do we know humans caused climate change? Especially since our earth is KNOWN for cycles of heating and warming. Instead of responding with an entire essay to individual people in the comments of my content, I thought a nice succinct blog post I can send them would work well and be a good resource for others as well.

So, let’s dive in

Let’s first establish one thing: weather does not equal climate or vice versa. You can watch this full video here for the long explanation, but here is the short version:

Weather is the events that happen each day and is different in different parts of the world and changes in the span of minutes, hours, days, and weeks.

The climate is the average weather pattern in a given place over several decades. Different regions have different climates and global climates refer to the average of allllll regional climates.

Now, what is climate change?

Climate change refers to long-term shifts in temperatures and other weather patterns such as precipitation (or lack thereof), temperature, and so forth. These changes can be natural such as variations in the solar cycle, or unnatural such as the effects of human actions.

We’ve already established that our earth’s climate is constantly changing and has for millions of years without the influence of humans. Let’s take a look at this chart from the Utah Geological Survey. As you can see, the earth has naturally cooled and heated over its lifetime. So how do we know that what we’re seeing now is not natural?

Over the past few decades, scientists have seen and recorded extremely high levels of CO2, carbon dioxide, which is a heat-trapping gas responsible for most of the warming we have seen in recent years. As you can see from this chart from the Union of Concerned Scientists, there is always some level of CO2 in our atmosphere that is considered normal. But take a look at the huge spike that has occurred since the industrial revolution.

What causes CO2 in the first place?

Carbon dioxide is a byproduct of normal cell function when it is breathed out of a body which is why there is always a level of CO2 in the atmosphere. But, it is also produced when fossil fuels are burned or from decaying vegetation. Pockets of oil and coal are carbon stores that have been storing CO2 for millennia or longer. So, when we burn them, that stored carbon gets released and causes heat to be trapped in our atmosphere.

But it’s not just CO2…

Methane: an atmospheric gas that comes from natural and man-made sources. It comes from plant-matter breakdown in wetlands but also from landfills and livestock. Methane is 80x more potent than CO2 and you can learn more about why food waste in landfills is so devastating here.

Nitrous Oxide: another potent greenhouse gas produced by farming and it is released during commercial and organic fertilizer production and use. It also comes from burning fossil fuels and has increased by 18% in the last 100 years.

Chlorofluorocarbons (AKA CFCs): CFCs do NOT exist in nature and are entirely man-made and used as refrigerants, solvents, and propellants.

Water Vapor: what?? Water is causing climate change? Yes, it’s a nasty cycle. These GHGs are accelerating the warmth which is accelerating the evaporation of our oceans which means there is more water vapor in our atmosphere. While water vapor isn’t causing climate change alone, it amplifies climate change already in motion and increases the more and more the earth warms. You see how this is just a painful cycle.

How is this our fault?

I think Nasa puts it best, so you can just read verbatim what they say on the topic:

“Over the last century, burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO2). This increase happens because the coal or oil burning process combines carbon with oxygen in the air to make CO2. To a lesser extent, the clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases.

The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels by nearly 50% since 1750. This increase is due to human activities because scientists can see a distinctive isotopic fingerprint in the atmosphere.

In its Sixth Assessment Report, the Intergovernmental Panel on Climate Change, composed of scientific experts from countries all over the world, concluded that it is unequivocal (without a doubt) that the increase of CO2, methane, and nitrous oxide in the atmosphere over the industrial era is the result of human activities and that human influence is the principal driver of many changes observed across the atmosphere, ocean, cryosphere, and biosphere.”

Is climate change caused by the sun?

As we talked about before, sometimes solar irradiance can cause the climate to fluctuate, but scientists agree that what we are seeing now cannot be explained by the sun, which often people think is what is causing our current uptick in global temperature. The sun has an 11-year solar cycle. Studies have shown that variations in the sun’s patterns have indeed changed the climate. But take a look at this chart:

While at the beginning of the industrial revolution, it looks like the solar irradiance matched the global temperature, in 2020, it does not. In fact, they are opposite one another. So, it can be ruled extremely unlikely that the sun is to blame for our current warming.

But, aren’t we coming out of an Ice Age? Of course, it’s warming!

Okay, maybe you’re still caught up on the fact that we are coming out of an ice age (it’s a long game, people, it takes millions of years)…how do we know that the warming we’re seeing isn’t just the natural warming of coming out of an ice age?

Scientists at NASA have studied 800,000 years of data covering 8 ice ages and warming periods. The end of the last ice age was 11,700 years ago which marks the beginning of human civilization and our modern climate. Here’s another great chart that shows ice age norms from the last 8 cycles and where we are today:

Could it be an insane natural outlier? I’m no climate scientist, but NASA scientists agree that the spike is clearly a result of human activities from the mid-1800s to the present day and is continuing at an unprecedented rate that has never been seen before.

Scientists have been studying CO2 effects on the earth since the mid-1800s. They’ve seen how it affects tree rings, coral reefs, rocks, and more. This evidence reveals that our current levels of warming are happening 10x faster than the average rate of any heating period we’ve seen before. CO2 rates are increasing around 250x faster than they did from any natural source during any other ice age. It’s clear this is manmade.

Why is the margin of 2 degrees Celsius a bad thing?

I get it, 2 degrees Celsius of average change sounds like nothing. A change that much in weather wouldn’t even warrant me putting on a coat. But, from some perspective, the difference between an Ice Age and an interglacial period (where we are right now) is only 3-8 degrees Celsius. That is why keeping it under 2 degrees is so vital.

Usually, I have a sort of call to action, a “what can we do now” action item. But today, I don’t. Today’s post is simply educational, a one-stop shop for all of this valuable information.

I hope that you enjoyed it, learned something, and will share it with people in your lives who still don’t have a grasp on climate change. There’s no shame, we aren’t taught this in school and the media often tries to put climate change on the back burner. But, it’s time for action. We ALL need to learn about it and care for our planet and our future. If not your own future, the future of your children, grandchildren, great-grandchildren, and more to come.

And remember that our small actions make a big difference in the long run :)

Emma

Busting common climate change myths…how do we know climate change is man-made?