How partisans distort debate on effects of climate change
Much in the news these days are lawsuits in many states accusing the major oil companies of suppressing what they knew about climate change and thereby behaving like the tobacco companies in hiding their knowledge on the nicotine addiction and lung damage that came from cigarettes. There are groups on both sides of this issue.
The groups who say the problem is very serious and the oil companies are evil, publish articles saying why, as do the groups saying climate change and its damages are minor. Examples of both appeared in The Chronicle’s Opinion page March 21, just as a federal judge, who is hearing a San Francisco case, had what I think is the first daylong judicial tutorial on the issues. Both pieces are typical, where each side cherry-picks the data to make its case. Here is the real story.
There is no doubt about the reality of the greenhouse effect. Most high school Advanced Placement physics courses teach about what is called “black body radiation.” You can use that to easily calculate what the temperature will be on planets in our solar system if there were no greenhouse effect. If you do it on Mars, the calculated surface temperature is about 60 degrees below zero Fahrenheit. Mars has almost no atmosphere and so no greenhouse effect, and its measured surface temperature is about 60 degrees below zero Fahrenheit.
Venus is closer to the sun and its no-greenhouse surface temperature should average about 110 degrees Fahrenheit. It has a very thick and dense atmosphere and its surface temperature is about 750 degrees Fahrenheit, about the same as the inside of a self-cleaning oven.
We, here on Earth, have the Goldilocks greenhouse effect. Without it, our surface temperature should be about 5 degrees below zero Fahrenheit. Instead, it is about 65 degrees Fahrenheit.
If someone tells you there is no greenhouse effect, then they are either lying or stupid or stand to make lots of money by ignoring it.
The next question should be: Is the greenhouse effect changing?
We know that the amount of greenhouse gas in our atmosphere is going up. We know that from measurements of gases trapped in bubbles of the Antarctic glaciers going back a million years. But this is a complicated story because, as the temperature changes, many things change.
For example, if carbon dioxide increases, the temperature will go up. But if the temperature goes up, there will be more water vapor in the atmosphere. Water vapor is a strong greenhouse gas, so the temperature will go up further. But, if water vapor increases, cloud cover increases. Clouds reflect incoming sun back into space and more clouds lower the temperature. Putting all this together, along with other effects such as heat absorption in the oceans, requires a model of how the greenhouse affects the real planet. There are many models.
Putting the story together is the job of the Intergovernmental Panel on Climate Change. Every five years or so, the IPCC commissions a new report. The newest is the Fifth Assessment, which came out in 2014. Each has four sections: the science basis, the impact analysis, mitigation possibilities, and the synthesis report. To come to a conclusion on what will happen by the end of this century, the IPCC needs an estimate of emissions and a model of how the emissions affect the average global temperature. They use a range of emission scenarios, and almost all of the peer-reviewed models of what happens when the temperature goes up.
This is where most partisans cheat their readers. They pretend that there is only one answer and then they cherry-pick one to make their case.
Here are a couple of examples. If you use the low-emission case, then the rise in sea level is between 1.0 and 1.9 feet. In the high-emission scenario, it is between 1.5 and 3 feet, and this is what the Union of Concerned Scientists used in its Chronicle Open Forum piece last week.
The Heartland Institute focuses on temperature change and, of course, because the institute doesn’t want anyone to believe it is a problem, it uses the lowest number; between 0.5 and 2.5 degrees Fahrenheit. The highend prediction is very much higher.
Things change as time passes. Emission scenarios will change as the world changes. The Fifth Assessment came out before China and India signed on to the Paris accord. Those nations signed on more because of the health effects of emissions than because of climate change, but as they cut back on coal use, greenhouse gas emissions will go down, and with that the estimates will go down as well. How much lower only time will tell.
I use the time it will take to reduce the uncertainty in the calculations from the various scenarios. It will take about 20 years for the measurement of global temperature rise to tell us if we are headed toward the lower or higher end of the region of uncertainty for each scenario.
Meantime, stay tuned for the latest news.