Why CO2 is a greenhouse gas

https://www.scientificamerican.com/article.cfm?id=why-carbon-dioxide-i s-greenhouse-gas

Here's a sampling of the Galileo Movement's facts and an assessment of how they stack up against the body of Earth and atmospheric science, based on an investigation by DailyClimate.org of several science sources.

Claim: CO2 is Nature's colorless, odorless, tasteless gas essential for all life on Earth. It's not toxic. It doesn't make land, water or air dirty or unsafe to use. It does not cause disease.

Claim: CO2 comprises less than 0.04 percent of the air.

Assessment: True but irrelevant in the global warming debate.

Nitrogen, oxygen and argon together make up close to 100 percent of the atmosphere. But all three are invisible to incoming "short-wave" radiation from the sun and outgoing "long-wave" radiation from the Earth's surface. They play no role in regulating the planet's atmospheric temperature.

But carbon dioxide and other trace gases in the atmosphere do absorb the outgoing long-wave radiation.

So while their concentrations are miniscule, their effect is anything but: If the atmosphere didn't have those trace amounts of greenhouse gases, New York City would be covered in ice sheets – not sweltering – on a typical summer afternoon. The globe's average temperature would be almost 60 degrees Fahrenheit lower.

Similarly, toxicity is not an issue in the climate change debate. Yes, crops need CO2. Breathing a little more of it while out on the links won't impair your golf game. But earlier findings that suggested higher CO2 levels could increase crop yields have been disproved by recent research showing that other nutrients are more often the limiting factor.

The relevant questions for climate science are how CO2 changes atmospheric temperatures and circulation and alters the oceans' chemistry and heat capacity.

Source: Scott Mandia, State University of New York, Suffolk http://www2.sunysuffolk.edu/mandias/global_warming/

Claim: CO2 stays in the air only five to seven years, possibly less than 12 months before Nature cycles it into plants, animals and oceans.

Claim: Of Earth's annual production of CO2, humans produce just 3 percent.

Assessment: True but misleading.

In this case, the claim confuses residence time of individual molecules in the air with the much longer perturbation to the whole system.

Carbon dioxide is continuously cycling among the earth, plants and animals, the atmosphere and the ocean's surface, with the deep ocean serving as a gigantic long-term reservoir.

Up until the last two centuries, this carbon cycle had been in close balance for the last 10,000 years. But society has pushed atmospheric carbon dioxide levels from 278 parts per million at the start of the industrial revolution to 392 parts per million today, a 40 percent increase.

What's more, the bulk – some 57 percent – of carbon emitted from tailpipes and smokestacks is not even in the atmosphere. It has cycled into the ocean, and scientists generally agree that most of our carbon emissions will ultimately come to a rest in its deepest depths. But that will take centuries. In the meantime, those extra CO2 molecules will slosh around from earth to atmosphere to upper ocean and back, absorbing energy, acidifying the seas and changing the planet in profound and potentially unwelcome ways. In other words, CO2 emitted today will still be impacting the planet for hundreds of years.

Claim: Measurements reveal that CO2 levels are a consequence of temperature, not the cause. Temperature drives CO2 levels.

Assessment: True before 1800. But false today.

Some 800,000 years' worth of ice core records indicate that temperature rises did drive an increase in CO2 levels. But that was before humans started digging up huge quantities fossil fuels and transferring all that sequestered carbon to the atmosphere.

It is worth noting, however, that even in the past CO2 had an impact on temperatures, given its role as a greenhouse gas.

It's also worth noting that ancient temperature and CO2-level changes happened over thousands of years. The Earth needed, for example, 5,000 years to bring atmospheric CO2 concentrations up 80 ppm after the last glacial period.

With the onset of industrialization, the tables turned. Humans have increased atmospheric CO2 levels almost 80 ppm in just 60 years. Now humans are the drivers of CO2 level, not temperature.

And what frightens climate scientists is that temperature hasn't caught up yet.

Claim: In every 85,000 molecules of air, just 33 are CO2. For every 33 molecules of CO2, 32 are from Nature and known to be essential to all life on Earth. How can one molecule of the same gas produced by humans be blamed for supposed imminent, irreversible, catastrophic global warming? It cannot.

Assessment: False.

Two hundred years ago, only 24 of those molecules would have been CO2. Today, 33 molecules are – a 40 percent rise of a key greenhouse gas.

The reference to "one molecule" is misleading: By talking ratios, the Galileo Movement obscures the staggering amount of carbon dioxide society has pumped into the air. In the last two centuries, society has dumped 220 billion tons of carbon dioxide into the atmosphere by burning fossil fuels. It added another 110 billion tons via deforestation and land-use changes.

The atmosphere weighs about 5 quadrillion tons, and carbon dioxide, despite our emissions, remains a small component of that. But it grows larger every year. The International Energy Agency expects annual global CO2 emissions from fossil fuels alone to top 40 billion tons a year by 2030.

The math gets complicated from here, but there is an enormous quantity of molecules in those 330 billon tons of CO2.