DETROIT – Last weekend’s article about how global warming has impacted heat waves generated more than a little interest…to the tune of hundreds of comments on the Local 4's Facebook page. That is why I am taking this opportunity to answer some of your questions, and respond to comments.
The most frequent comment was about how the current warming is part of some natural cycle.
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First and foremost, yes, there have been cycles of planetary warming. In fact, Michigan was once covered by an ocean! If you ever find a Petoskey stone up north, it is a fossil of coral that lived in that ocean long before the dinosaurs even existed.
However, scientists know why all of the previous warmings occurred, and all of them were caused by astronomical changes (changes in Earth’s orbit, rotation, or axis tilt). None of that has happened this time.
There are three main things that determine a planet’s average temperature: how close it is to its star, its surface albedo (color), and the composition of its atmosphere.
The only thing that has changed over the past 100 to 200 years is that humans have changed the composition of our planet’s atmosphere. It may sound hard to believe, but human activity has done exactly that.
Heat is basically energy coming in minus energy going out. The gases we have added to our atmosphere are preventing some of the heat from going back out into space, resulting in a warming of the climate.
The next most frequent comment I received involved the length of our temperature record, stating that we don’t have a long enough record to actually know what our climate is doing.
First of all, climate scientists have a record of not only Earth’s temperatures, but also its atmospheric composition, dating back well over 800,000 years (I believe they have now extended the record to two million years ago). This aspect of climate science is called paleoclimatology. How is this possible? From ice cores. You see, in the Arctic and Antarctic, snow falls every winter on top of the previous winter’s snow, year after year after year.
Eventually, the weight of that snow crushes the snow down below, and it turns into ice…and in that ice are bubbles of air. Air that existed thousands and millions of years ago. Scientists have drilled very deep into that ice pack and extracted cylindrical cores dating back well over 800,000 years.
They keep those cores frozen, and carefully extract the air from inside those bubbles, and not only determine the composition of our planet’s atmosphere way back then, but also Earth’s relative temperature (by tracing the amount of deuterium, an isotope of hydrogen).
So, we actually have a record of our planet’s atmospheric composition and temperature going back a very long time, and during that time atmospheric carbon dioxide never exceeded 300 parts per million. Over the past (only) 100 to 200 years, the industrialization of society exponentially grew that number to 414 parts per million. That’s thirty-eight percent higher than the previous known highest amount. And it’s still rising due to human activity. And, as explained above, the increase in gases like carbon dioxide in our atmosphere causes warming.
So even though the instrumental temperature record started in the 1800s, this is why the climate change historical context I discuss is accurate.
Another set of comments stated that scientists have flip-flopped, so we can’t believe them, citing a magazine cover story from the 1970s.
Back in the 1970s, we had a couple of very harsh winters. I remember them vividly, standing at the morning bus stop waiting for the bus to take me to Andover High School. Those were bitter cold mornings…my sharpest memory is that six or seven minutes after sitting in the warm bus, my fingers and toes started stinging as they thawed. And this happened often. So Time magazine did a 1977 cover story about the harsh winter weather. And that article did not mention anything about global cooling. Now, Time magazine is not a scientific journal, and the reality is that most scientists who were researching earth’s climate at that time did not think we were heading into another ice age.
One commenter tried to turn the warming climate into a big positive, stating that a longer growing season and longer “tourism season” is a “win-win.”
Here are the facts on that. Yes, growing seasons are getting longer. But no, that’s not a good thing because the earlier blooming of our fruit trees, for example, puts those blossoms at risk if there’s a killing frost, and that has happened very dramatically at least twice in the past 20 years, when unusual early season warmth got the cherry blossoms (and others) blooming in March or early April, with a following freeze killing the majority of Michigan’s tart cherry crop.
Maybe you don’t care about cherries. But you do care about your allergies, and a longer growing season means a longer allergy season. In fact, since 1970, the growing season here in southeast Michigan has increased by an average of 27.2 days. That’s nearly an additional month of allergies. How does that make you feel? But wait, there’s more. The increase in atmospheric carbon dioxide is increasing the amount of pollen produced by each plant. That’s right: plants are now emitting more pollen than they used to. At the current rate of increasing carbon dioxide, the amount of pollen produced will increase 62% by the year 2060. If you are an allergy sufferer, then the longer growing season and higher pollen production is very, very bad news for you.
As for the longer tourism season, warmer winters actually mean that our winter tourism season in many years will be shorter – and winter tourism is a nice part of Michigan’s economic picture. So that would actually decrease tourism, because a longer warm season won’t necessarily mean more warm weather tourism to offset the decrease in winter tourism.
One comment stated that I am ignoring some of the very cold weather we had this past winter.
Let’s talk about why we sometimes have extreme cold, even in a warming world. One of the earliest global warming predictions was that higher latitudes would warm faster than the rest of the world…and that is exactly what is happening.
Now, let’s talk about the jet stream, which is that band of strongest wind aloft. The jet stream is a result of the difference in temperature between northern and southern latitudes. Since the northern latitudes are warming faster than the southern latitudes, that temperature contrast between the two is weakening, and recent research suggests that the jet stream is also weakening as a result.
We are now seeing bigger peaks and valleys in the jet stream, and those deep valleys in winter bring polar air farther southward.
So, while extreme heat events are increasing and extreme cold events are decreasing, that doesn’t mean that we don’t see extreme cold anymore (such as at the end of January 2019), and some of those events can be quite noteworthy.
Finally, I have also strongly communicated the wintry aspects of climate change…I don’t just focus on heat. For example, I have said many times that Detroit has seen six of its eleven all-time snowiest winters since 1980. That’s because the warming climate is evaporating more ocean water into the atmosphere, which winter storms then turn into more snowfall.
One commenter stated that ice caps are expanding and the Amazon rainforest is flourishing like never before…a sign that the planet is not warming.
It’s just the opposite, in fact. The polar ice caps are shrinking, and human clear-cutting of the Amazon rainforest is diminishing its size. Those rainforests take a lot of carbon dioxide out of the atmosphere, and by reducing their size we also increase the amount of carbon dioxide in the air. So when I say that humans have changed the composition of our atmosphere, this is a legitimate part of the story.
Another comment implied that solar activity is the cause of Earth’s current warming. I’ve asked climate scientists about this, and they’ve ruled out solar activity as having any meaningful impact on our planet’s current warming.
One comment stated that “people” are not saying that the earth is not warming, but that people are not agreeing on how much and why.
I don’t communicate information from just “people.” I only communicate information from the world’s climate scientists, and an overwhelming majority of them agree that earth is warming at a very unusual rate, and that the proximate cause is the change in our planet’s atmospheric composition due to human activity.
People can disagree upon whatever they want. However, if the comment was referring to climate scientists, then that is incorrect: most of them agree about this. In fact, depending upon which study you cite, either 94% or 97% of the world’s climate scientists agree based upon their published research.