Mon. Nov 28th, 2022
Ars answers questions from a federal judge about climate change

Climate science has had its day in court before. For example, the Supreme Court ruled in 2007 that CO2 fits the definition of a pollutant under the Clean Air Act — a decision that forces the U.S. EPA to enact regulations to address climate change, regardless of the political wind. But on Tuesday, climate science literal have his day in court as a federal judge gets a five-hour tutorial he requested on the subject.

The case pits San Francisco and Oakland against BP, Chevron, ConocoPhillips, Exxon Mobil and Royal Dutch Shell. The cities allege that major oil companies were selling fossil fuels knowing their use would change the climate — and, critically, campaigning publicly to convince the public that they not change the climate. Since San Francisco and Oakland incur significant costs to build infrastructure to protect their cities from sea level rise, they want oil companies to foot the bill.

The case, which would obviously set a huge precedent if the cities were to win, already seems to have gone further than previous attempts. Other judges have filed lawsuits on the grounds that emissions must be regulated by the EPA and therefore the matter cannot be decided in a courtroom. But the specifics of the California case — the search for fossil fuel sellers rather than local fossil fuel users — convinced Judge William Alsup that it can go ahead.

Before the arguments get underway, though, Judge Alsup made a unique request: Both sides must present the facts of climate science themselves, in part by answering a list of his questions. In recent years, oil companies have publicly accepted the scientific consensus on global warming, so they are unlikely to present an opposing view in this case. But half of this “tutorial” will focus on the history of climate science, which the companies might label as more insecure to excuse their stance in the 1980s and 1990s.

As for Judge Alsup’s (surprisingly specific) questions about climate change, those are actually fundamental to science and pretty easy to answer.

Greenhouse go

Half of the judge’s questions are about how the greenhouse effect actually works. For example, he asks, “What is the molecular difference by which CO2 absorbs infrared radiation, but does not absorb oxygen and nitrogen?”

The term “greenhouse effect” is meant to evoke the basic result of the process rather than the actual physics involved. Greenhouses warm up by letting in sunlight and preventing heat energy and warm air from going out. The greenhouse effect of our atmosphere similarly allows sunlight (mainly in the visible light portion of the electromagnetic spectrum) to reach Earth’s surface to warm it, but absorb the infrared radiation our planet emits back to space.

You’ve probably come across this explanation before, perhaps along with an analogy of building a thicker blanket around the planet warming it. But how exactly does this work?

Skipping quantum mechanics, the simple fact is that gas molecules can only absorb (and emit) certain wavelengths of electromagnetic radiation. Carbon dioxide – a molecule made up of one carbon atom and two oxygen atoms connected in a line – can be vibrated by radiation of the correct wavelength. The atoms can quickly stretch back and forth like a runaway accordion, or they can bend out of line like the “boing” of a spring door stop when you brush against it.

A molecule of carbon dioxide can vibrate in a few different ways when excited by energy.
enlarge / A molecule of carbon dioxide can vibrate in a few different ways when excited by energy.

Oxygen and nitrogen (which make up about 99 percent of our air) are simpler dumbbell-shaped molecules composed of two identical atoms. That takes away the possibility of bending vibrations, while stretching the bond has no effect on the electric field (the atoms are identical). So these gases cannot interact with radiation in the infrared part of the spectrum.

CO2, along with the other gases we call greenhouse gases, happen to absorb infrared radiation but not solar radiation. If our planet had no atmosphere, there would be a simple balance between incoming and outgoing energy. Sunlight would heat up the Earth’s surface, which would then radiate an equivalent amount of energy as infrared radiation sent back into space. The addition of greenhouse gases changes this by absorbing outgoing infrared radiation, heating it up and then emitting infrared energy, both into space. and back to the Earth’s surface.

Earth's
enlarge / Earth’s “budget” of incoming and outgoing energy.

As the surface temperature rises, the planet emits even more infrared radiation, trying to give off heat. Eventually a new equilibrium is reached, where the outgoing energy is again equal to the incoming sunlight, but only after the temperature of the surface and the atmosphere has risen. Likewise, a blanket will warm you up in the winter, but it won’t raise your temperature incessantly to the point of catching you on fire.

while CO2 allows solar radiation to pass undisturbed, other gases interact with it. Ozone – that, as it is composed of three oxygen atoms, can do some vibrating quantum dance – absorbs ultraviolet radiation in sunlight. This not only acts as a planetary sunscreen, but also causes the ozone layer to heat up the stratosphere.

Water vapor is also a potent greenhouse gas, but it can form sunlight-reflecting clouds, meaning water vapor can cool or warm the Earth, depending on the situation. (Although the net effect of water vapor amplifies CO2-induced global warming2 instead of muting it.)

Another question from Judge Alsup is a fairly common one: “Apart from CO2what happens to the collective heat from exhaust pipes, engine radiators and all other heat from the combustion of fossil fuels?”

Since it’s been called “global warming,” it’s tempting to wonder if the heat we produce is as important as these invisible and abstract greenhouse gases. However, it doesn’t take a lot of math to find the answer. The total energy used by humans is currently close to 20 terawatts. Assuming it all ends up being converted to waste heat, that’s: would come out about 0.04 watts per square meter of the Earth’s surface. The total amount of energy added to our climate by human activities, meanwhile, was estimated at 2.3 watts per square meter in the latest report from the Intergovernmental Panel on Climate Change.

So the heat coming out of your car’s exhaust is not the concern. The carbon dioxide is.

Modified Carbon

Judge Alsup’s questions also concern contributors to the CO2 increase we measured. Besides simply asking the root cause of that rise, he asks how much CO2 is exhaled by humans and why don’t plants just take all the extra CO . have converted2 in oxygen.

These are questions about the carbon cycle — the many interconnected processes through which carbon changes shape and moves through Earth’s atmosphere, oceans, terrestrial ecosystems and even rocks. When all these processes are in equilibrium (which was basically the case before the industrial revolution), the amount of CO2 in the atmosphere remains stable. When we started extracting fossil fuels from the ground and burning them into CO2 on a large scale, the carbon cycle was no longer in equilibrium.

There are multiple ways to determine the cause of rising CO. to find out2. First, there is simple accounting. Researchers are working hard to estimate how much CO2 is released by human activities and then compare it to measured changes in the atmosphere, oceans and land ecosystems. For example, in 2016, human activities were estimated to have released about 11.2 billion tons of carbon, of which the ocean and terrestrial ecosystems absorb about 5.3 billion tons. (Dissolving CO2 in the oceans there is no free lunch – it changes the pH of seawater and threatens marine ecosystems.) The rest corresponds to the increase in atmospheric CO2.

This accounting can be informed by the isotopes of carbon in atmospheric CO. to analyse2-which can be carbon-12, carbon-13 or carbon-14. Since the dawn of the industrial revolution, the relative proportions of these isotopes in the atmosphere have changed in a way that can only be explained by throwing tons upon tons of carbon-12-dominated fossil fuel CO.2 in the air.

Judge Alsup’s guess that plants CO. have to record2 from the atmosphere is a good one. Indeed, life has our impact on atmospheric CO. diminished2 by taking some of it. But photosynthetic growth is limited by much more than just the availability of CO2 (things like water and nutrients are important); otherwise, plants would just use all the CO. consume2 in the atmosphere.

However, the judge is wrong when he questions whether human respiration is a major source of CO. could be2. Unless your diet is full of coal, the carbon you exhale eventually comes from plants (even if you ate the cow that ate the plants), and plants just borrowed that carbon from atmospheric CO2. So you can breathe the atmospheric CO. don’t raise2 any more than your gas station’s “take a penny, drop a penny” container can increase the number of coins in circulation.

Who? Wedunnit, huh.

Judge Alsup’s questions also relate to past ice age cycles in climate and the dominant source of our current warming trend – why did the climate change in the past and why is it changing today?

The rhythmic ice ages of the last few million years have been dominated by slowly changing cycles in the Earth’s orbit around the sun, which sometimes conspire to bring stronger sunlight to the great ice sheets of the Northern Hemisphere. Shrinking ice sheets changed the carbon cycle in a way that reduced atmospheric CO. elevated2further warming the planet.

Those orbital cycles are far too slow to explain what we’ve seen over the past 150 years, and data shows sunlight hasn’t gotten stronger. When you compare all the factors that could potentially warm or cool the Earth, it becomes abundantly clear that one factor explains most of modern warming: our greenhouse gas emissions.

Add warming (positive) and cooling (negative) factors.  The sun provides some short-term motion and volcanoes have brief, sharp cooling effects, but the warming influence of carbon dioxide and other greenhouse gases dominates.
enlarge / Add warming (positive) and cooling (negative) factors. The sun causes some short-term movements and volcanoes have brief, sharp cooling effects, but the warming influence of carbon dioxide and other greenhouse gases dominates.

While there may be some differences in what the two sides in the case present, there is very little room to dance around these basic facts. As a non-expert, Judge Alsup has asked reasonable questions that should provide him with a rudimentary understanding of climate science. However, due to this hearing, we are still a long way from knowing whether this concept actually plays a role in the case.

By akfire1

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