A plan to reverse global warming

kw: book reviews, nonfiction, climate change, compendia

The title of the book is Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming. It is edited by Paul Hawken, who founded and Executive Director of Project Drawdown. The Project has a large number of affiliated scientists and others who are working on numerous efforts that are at least "carbon neutral" and, it is hoped, able to actually take CO₂ back out of the atmosphere. He admits in his introduction that the plan he proposes is the "most comprehensive" because it is the only one. Fair enough. All other plans to date focus on mitigation, on slowing the increase of CO₂, and so forth.

It will take some doing for anyone to come up with a "more comprehensive" set of proposals. The book discusses 100, the top 100 from a pool of a few hundred. The top 80 are ranked according to expected reduction in greenhouse gases as "CO₂ equivalent"; for instance, methane is something like 30-40 times as effective as CO₂ is at trapping heat near the Earth's surface. So reducing a ton of methane is counted as about 40 tons of CO₂ equivalent. The other 20 ideas are gathered in a chapter titled "Coming Attractions", rather more speculative possible solutions that haven't been as thoroughly researched.

I was impressed with the scholarship and ingenuity that went into the chapters, including a half dozen essays on related subjects (so there are more than 100 chapters). But I looked for, and didn't find, one critical element. In the discussion of the history of the theory of greenhouse gases in the atmosphere, the early insight on human impact on the atmosphere, in 1831 by Alexander von Humboldt, is dwelt upon, but Svante Arrhenius, who quantified the effect in 1896, is not mentioned. Considering that the discussions of greenhouse effect, climate change, global warming, and a few similar and increasingly politicized terms, are based on mathematical analyses, the utter lack of even a fillip toward math dismayed me.

I remember learning of Arrhenius's work before I was a teenager, nearly 60 years ago. With the mathematical tools available to a ninth grader of the time, it wasn't hard to follow his reasoning, nor to reproduce his results. The tedium comes in adding up the effective ultraviolet/visible-versus-infrared spectra to determine an effective emissivity-temperature relationship for any particular gas. The concept is thus:

• There are "windows" in the spectrum of a gas, ranges of light wavelength that are transmitted with little or no hindrance.
• Conversely, there are "doors" in the spectrum, ranges of light wavelength that are absorbed by the gas and heat it up. It then radiates this heat as longer-wavelength infrared (IR).
• Ultraviolet (UV), visible (V), and near-IR (the shorter IR wavelengths) emitted by the Sun are little hindered by the atmosphere, and strike the ground, heating it.
• The warmed ground radiates mid- and far-IR (long to very long wavelength IR) upwards.
• Some of the re-radiated IR passes through "windows" of the various gases in the atmosphere, and so outward into space.
• Some instead hits one "door" or another, such that it heats the gas, which heats the rest of the atmosphere. Interestingly, nitrogen and oxygen, which make up 96-99% of the atmosphere, depending mainly on humidity, have spectra with very little in the way of "doors".
• Light that hits a "door" causes heating of the air, which then emits longer-wavelength IR (mostly far-IR) that is radiated in all directions. Simply put, half of it goes back down to increase the heating of the ground, and the other half goes up and out into space.
• The atmospheric temperature rises until the radiation passing upward through the "windows", and half of that which hit "doors", balances the radiation coming inward from the Sun. At that balancing temperature, total emissivity upward equals total emissivity downward, across all wavelengths.

That is the greenhouse effect. What gases cause the most greenhouse warming, that is, which gases have the biggest and thickest "doors"? Number 1 is water vapor! If Earth had no water at all, being as dry as the Moon, it would be 33°C (59°F) colder than it is (as the Moon is), with an average temperature near -18°C or 0°F. But Earth's atmosphere contains between 1% and 3% water vapor, which causes all this heating.

Although CO₂ is much less effective as a greenhouse gas than methane or nitrous oxide, it is much more abundant: a few hundred parts per million (ppm) versus 1.5-2 ppm for methane. The critical thing about CO₂ is that we can influence its abundance. We do so by burning stuff. Almost everything we burn for heating and creating energy such as electricity contains carbon. Coal is almost pure carbon; methane has the least, but is still 75% carbon by weight (and 25% hydrogen). But the heating value you get from a ton of methane versus a ton of coal means, kilowatt for kilowatt, it produces only about half the CO₂.

Since the year 1800, the amount of CO₂ in the atmosphere has risen from about 280 ppm to about 400 ppm. That has caused an average heating of Earth by about half a degree C, or close to 1°F. Note that the same climate scientists who compiled the various IPCC reports on global warming over the past 30 years differ quite a lot over whether it is half a degree, or one degree, or perhaps less than half. "Half a degree" is a sort of average of their opinions.

Here is a point I haven't read anywhere since about 1990: If we go far out on a limb and calculate the effect of CO₂ going way, way up, to perhaps 1% (where it affects our breathing reflex), and which is 10,000 ppm, the average temperature of the Earth would rise no more than 4°C (~7°F) above what it was in 1800 AD.

Now, 4 degrees is a large change, and would cause a lot of trouble. But it would not end human life on Earth...just human comfort! Because the #1 issue discussed in Drawdown, the factor that can reduce the greenhouse effect the most, is to eliminate refrigerants containing carbon! No A/C, folks, unless you want to return to using ammonia or CO₂ as a refrigerant. Ammonia is actually a great refrigerant, but it is so toxic that even a tiny leak could be catastrophic were it to leak into your house. Effective A/C using ammonia would have to be totally redesigned, to operate outdoors only, in a very well-ventilated area, creating chilled water that would be pumped through the indoor cooling system. More complexity, more cost, and just how rapidly do you think the world's slightly-less-affluent nations are likely to embrace it? CO₂ is a less efficient refrigerant, but at least it isn't toxic, though it can cause suffocation, so it still would have to be used in outdoors-only water-loop systems.

Before closing I need to address a typo and an unfamiliar concept. On page xiv in an introductory section, the author is discussing just what a gigaton is. After showing that it is the amount of water in 14,400,000 Olympic-size swimming pools, it is stated, "thirty-six billion gigatons is the amount of carbon dioxide emitted in 2016." The word "billion" needs to be omitted. It is either 36 GT or 36 billion tons, but not both! Secondly, the words "a billion acres" appear a few times, or various amounts such as half a billion or 1.5 billion acres, etc. To help us get our hands around it, one billion acres is about 2.7% of the land area of Earth. Since only a quarter of that land is arable, that comes to about 11% of land that can be farmed.

I like the ideas discussed in Drawdown; it's more practical and well-thought than most other writing I've seen on the subject. I hope the efforts of the Drawdown Project continue. These folks are more level-headed than most of the other loud voices in the climate arena.