Lots of people read the Clothesline Report, and they believe all kinds of things. Some are thoroughly convinced by climate science, and deeply alarmed about the consequences for their futures, their children and the earth. Some are more skeptical, or just uncertain. Some skeptics, to be sure, have questions that they probably don’t really want answered. But that’s generally not true of the questioning readers of the Clothesline. Here’s a sampling of questions I’ve recently been asked to address:
What about recent centuries when the climate has changed without the burning of fossil fuels (like the Medieval Warm Period and the Little Ice Age that followed it)?
Aren’t lots of scientists climate skeptics?
Since there’s so much carbon below the surface, wasn’t it once all in the atmosphere?
Since plants use CO2, isn’t more of it likely to make a greener world?
Didn’t I read somewhere that climate scientists had “cooked the books?”
I’ll get to all those things, even if it takes two or three posts. But first, let me set down a few things we actually know, beyond serious ongoing scientific debate.
Item #1: We know how much CO2 has been in the atmosphere for each of the last several hundred-thousand years.
Item #2: We know what the average global temperature was for each of those same years.
Item #3: We know that that global CO2 concentrations and global temperatures moved in lockstep for all those years.
Item #4: We know that CO2 works like a blanket in the atmosphere, keeping the earth at a suitable level of warmth for life.
Item #5: We know that global CO2 levels are increasing today to levels not seen on earth in over a million years.
Item # 6: We know that the burning of fossil fuels is the principal contributor to today’s increases in CO2.
Item #7: We know that today’s increasing CO2 concentrations are irreversible for centuries or millennia.
Really? We actually know those things, you ask? Well, yes, we do. Scientists seldom speak of knowing, preferring the language of likelihood and probability. But there are good reasons to speak in layman’s terms of knowing these things. Here’s why.
How do we know how much CO2 has been in the atmosphere for each of the last several hundred-thousand years?
Some will be surprised to hear that we actually have samples of the air for each of almost the last million years, left in little time capsules for us. Really. We don’t have to theorize or guess. We’ve got the air. Where? In Greenland and Antarctica, every year a new layer of snow blankets the prior year’s snow and ice. And with each successive year’s blanket, the layers below become compressed and stretched into thinner and thinner layers of solid ice, each one banded with distinctive summer and winter patterns. In Greenland, there are 450,000 years’ worth of ice layers, and the pile is more than two miles high; in Antarctica, more than 800,000 annual layers.
In recent decades, people have been drilling out cores of the ice, all the way to the bottom, in ice sheets all over the world – from the Andes to the Himalayas, and from pole to pole. What they get are miles of cylinders of ice, containing water, minerals and air bubbles untouched by anything since they were buried by subsequent snowfalls.
As you’ve guessed, they’re not doing this for fun. Rather, the ice cores contain the most fascinating information. When Mt. Pinatubo erupted in 1991, it spread a thin film of sulfur dioxide captured by the snow and ice, clearly visible in that year’s layer. Same for the Mt. Vesuvius eruption in AD 79. But all kinds of lesser events are also captured: When the Romans began smelting lead for plumbing in the centuries before Christ, sure enough, the ice caught them red-handed. When the fall of Rome put an end to lead smelting, you knew it from the ice.
But there’s more in the ice than water. Snow is mostly air, and even after eons of compression, the ice retains tiny bubbles of atmosphere captured from ancient times. Thanks to the ice cores, we can examine the air as it actually was over hundreds of thousands of years. And we can count the amount of CO2, among other things. Here’s what we know:
The jagged line that looks like a heart rate monitor is the level of CO2 in the atmosphere over the last 800,000 years, ranging from a low of 180 to a high of 280 parts per million. That is, it was in that range till the beginning of the Industrial Age, when humans began digging up coal to fire the engines of progress. Then came oil and gas, suburban commutes, SUVs and the like, and now we’re at 390 ppm, higher than any time on the chart by far, and growing.
How do we know what the average global temperature was for each of those same hundreds of thousands of years?
Those same ice cores tell us much more than CO2 levels. The water also has a story to tell. As you know, not all water is plain old H2O. Some is “light water” (having an oxygen isotope containing one less electron), and some is “heavy water” (an isotope with a heavier molecular structure). As equatorial water vapors make their way toward the polar regions, the heavy water precipitates first, leaving the light water to fall last. In cool years, the heavy water is almost all gone before it reaches the polar ice sheets. In warm years, there’s much more heavy water in the polar snows. By measuring polar snow chemistry, we can know how cool or warm the trip from the Equator was that year.
If you look at the red line below, you’ll see how warm the atmosphere was over the last 400,000 years. Take a close look at the last ¼” on the right. See that nice flat warm bunch of red? That’s the last 10,000 years – the period of human civilization. No ice age, no sizzling heat. It’s been nice, right?
How do we know that that global CO2 concentrations and global temperatures moved in lockstep for all those years?
Well, the chart above shows – for one set of ice cores – what all the ice core analyses show. The temperature line and the CO2 line always move together. When the CO2 is high, so is the temperature. When it’s low, so is the temperature. This is always true, with one exception: the last hundred years (way over on the right), when humanity has been pouring CO2 into the air. CO2 has skyrocketed, but global temperature has only edged up — so far.
How do we know that CO2 works like a blanket in the atmosphere?
This is not disputed by anyone. It’s called the Greenhouse Effect, and it was discovered in 1824, subsequently measured and refined by many researchers. It’s a process by which thermal radiation from the earth into space is trapped by certain gases, called greenhouse gases (GHGs). Without them, the Earth would be a block of solid ice. Major GHGs are water vapor, CO2, methane, and ozone.
All GHGs have been increasing in recent years, but especially CO2. Notably, the earth has started warming markedly.
How do we know that global CO2 levels are increasing today beyond levels not seen on earth in over a million years?
The ice core records tell us a lot about CO2 levels over the years. But in 1958, researchers began measuring CO2 levels on a daily basis at a remote mountain station on the big island of Hawaii, far from pollutants and other local effects. Back then, CO2 concentrations had already increased from historical highs of 280 ppm to about 318 ppm. Since then the CO2 trajectory – called the Keeling Curve – has been invariably upward, accelerating with the passing of years as we burn more fossil fuels (see yellow line below). At last measure, the Keeling Curve stood at 393 ppm, 40% above the highest level in the last million years. And it’s accelerating, not slowing. To see more on the Keeling Curve, click here.)
How do we know that the burning of fossil fuels is the major contributor to the today’s increases in CO2?
Every year, the humanity pumps 9.2 billion metric tons of CO2 into the atmosphere from burning fossil fuels and from changes in land use. (This is not all that hard to measure, since detailed statistics are available for coal and oil production and consumption.) Of this, the oceans absorb 2.3 billion tons, and other factors such as plant growth absorb 2.8 billion tons. That leaves an additional 4.1 billion metric tons of CO2 in the atmosphere every year.
How do we know that new CO2 concentrations are irreversible for centuries or millennia?
The oceans and plant life absorb 5.1 billion metric tons of CO2 per year. But there are 814 billion tons of CO2 in the atmosphere today. And for the sake of illustration, even if we could stop burning every single fossil fuel immediately, it would take more than 50 years for these global forces to return CO2 levels to the million-year maximum levels.
So, that’s some of what we know. Not everyone who writes an internet blog knows this, but everyone who teaches at a research university does. They’ll fight like dogs on thousands of details and ramifications of all this, but this stuff is basic: CO2 is higher than it’s been in many hundreds of thousands of years, and global temperatures move with GHGs – notably with CO2. The main reason for the increase in GHGs is humanity and our exploding use of fossil fuels. While China has surpassed the U.S. in total GHG emissions, they’re nowhere near us in per capita emissions. And while it’s not all that hard to burn all this world-changing stuff into the atmosphere, once we do so, there’s no reversing what we’ve done for many generations.
Our grandchildren’s grandchildren will inherit what we do in the next decade, and there will be no changing things for lifetimes beyond theirs.
We believe many things. But these things, we know.
Thanks for reading, and may God bless you.
P.S. Next edition: What about disagreements among scientists? What about past climate changes before people burned coal and oil? Maybe all this CO2 will give us a more fertile world?