Last Friday the National Climate Assessment Report was quietly unveiled. It contained dire warnings about the consequences to the U.S. as a result of climate change.
President Trump, who once called climate change a hoax, said that he doesn't believe the findings of potentially devastating impacts. The President has since backed away from his assertion that climate change is a hoax, but apparently feels that the threat is overstated.
Let's review what we know to be true, what is understood about the greenhouse effect, and how models can be effectively used to make predictions. In a follow-up article, I will address a frequently overlooked tool for helping to address climate change.
Here are facts, accepted by almost everyone. I still encounter some people who don't accept them, but that doesn't change that these facts are demonstrated by multiple lines of evidence.
First, the atmospheric concentration of carbon dioxide has risen steadily since humans began to use large quantities of coal during the Industrial Revolution. The atmosphere has now reached levels of carbon dioxide that have never been seen in the history of human civilization.
Second, carbon dioxide is known to be a greenhouse gas. I will explain more about what this means in the next section.
Third, the average surface temperature of the earth is rising. That doesn't mean it's rising everywhere, and it doesn't mean the temperature rise is responsible for every significant weather event.
I live in Phoenix, and this summer it seemed that we broke new temperature records every week. The past two years have been two of the hottest on record in Phoenix, and that has been the case for many cities, and for the U.S. as a whole.
Fourth, the world's sea levels are rising. This is understandable because as water warms, it expands. And as the temperature increases, glaciers melt. Both factors add to the sea level, which has already risen by four to eight inches. This results in loss of coastline, and ultimately the loss of some islands.
Climate Change Science Made Simple
Now for a short primer on greenhouse gases.
The surface of the earth is warmed by visible solar radiation that passes through the earth’s atmosphere. As solar radiation causes surfaces to warm, energy is reemitted from those surfaces in the form of infrared radiation. Infrared radiation has longer wavelengths than the visible radiation from the sun, and it doesn't simply pass through the atmosphere.
The earth's atmosphere contains certain gases—water vapor, methane, and carbon dioxide, to name a few—that absorb the infrared radiation from the surface of the earth and radiate some of that energy back toward the earth.
Civilization likely only exists because of the greenhouse effect. Primarily because of the water vapor in the atmosphere (the most important greenhouse gas), the earth is about 60°F warmer than it would be without a greenhouse effect.
But, since greenhouse gases in the atmosphere are responsible for the greenhouse effect, it stands to reason that if the atmospheric concentration of those greenhouse gases increases, then so should the surface temperature of the earth.
So, there is a mechanism that explains why the temperature is increasing (rising greenhouse gases) and we have the actual observation that the temperature is increasing (and the supporting observation that sea levels are rising).
So far, this is pretty straightforward. None of what I have written thus far is controversial. So, why can't we all agree that there is a problem? There are multiple reasons, but let me focus on the simplest.
Even though we have an understanding of why rising carbon dioxide levels should impact the temperature, the ecosystem is complex. We have to rely on computer models to predict and project possible outcomes. When there are discrepancies between what the models predict and what is measured, critics seize on those discrepancies to cast doubt on climate science.
But speaking as someone who has developed and used computer models numerous times, this is how models are built and refined. You can build a model of a system (like a chemical reactor), but then you have to measure that model against reality.
For example, I can develop a model that may predict that the outlet concentration of a reactor should contain 10% methane. If the actual measurement in the outlet is 25% methane, I need to look at the assumptions of the model. I may need to revise equations that went into the model. Eventually, I will produce a model that matches what is actually observed.
But I am still not finished. I now have to do tests to further validate the model. I can change the temperature or pressure of the reactor, and see if the model can accurately predict the output under the new conditions. Over time, and through experimentation, I gain confidence in the model's ability to predict changes -- which is my ultimate objective.
This is the case with climate models. If a model incorrectly predicts a temperature, it may be that we simply don't fully understand some of the feedback loops. So, we revise and tweak the model until it better replicates reality. Then we can extrapolate into the future with a higher degree of confidence.
There is uncertainty in modeling, and that's seized upon by critics to overstate the uncertainty about the possible outcomes.
Make no mistake. The earth is warming. Some want to argue about how much of that impact is man-made, and how much is a function of natural fluctuations in the climate. But carbon dioxide concentrations are also climbing, and we know humans are responsible for that. So we know that humans are making at least some impact.
The bottom line is we are conducting an unprecedented experiment on the ecosystem, and we can say with a high degree of confidence that further warming is in store. Given the risks, we should use every tool in our arsenal to address this issue.
Date: Nov 30, 2018