Two Huge Climate Messaging Errors
There has been and continues to be a long-standing problem with the way that methane is described as a greenhouse gas (GHG). The proper way to describe the strength of the various GHG’s using a pound of CO2 emitted (or a pound in the sky) as the benchmark would be to say A) How much heat is trapped while the gases are actually in the sky and then also B) How long each gas remains in the sky. Instead, the most commonly used standard is to use a 100-year interval after emission to compare the total warming caused by a pound of CO2 versus a pound of a different gas over the entirety of that period.
Carbon dioxide emitted now will remain largely in the sky (and a lot in the oceans) for many thousands of years. Some very powerful GHGs only last a few years because they break down in the sky. They vary a lot that way, and one can learn about many dozens of them here, courtesy of Wikipedia's "List of Refrigerants":
https://en.wikipedia.org/wiki/List_of_refrigerants
Look at the 100-year strength of a given chemical as a greenhouse gas ("net GWP, 100-yr" — compared to a pound of CO2) and at the estimated "Atmospheric Lifetime (years)". Those two numbers together can tell you a lot. If a GHG is rated at a net GWP (global warming potential) of 1000 but lasts only about 20 years, that means it's actually about 10,000 times stronger than CO2 while it's actually all still in the sky.
The average guess about the atmospheric lifetime of methane is 12 years, by which time nearly all of the methane which had leaked into the sky will have oxidized to CO2. Guesses about CO2’s atmospheric lifetime vary widely but for the sake of comparison with the other significant GHGs we can assume it’s infinite (apart from the major absorption into the ocean). So the correct way for us to talk about non-CO2 GHGs is to use two numbers, not one! One for how strong it is (while it's all still in the sky) and one for how long it lasts. Otherwise what's really going on is obscured by what is often a very misleading, single number.
In the List of Refrigerants we can see that methane is shown to have a net GWP of 28. This means that when averaged out over the first 100 years after it’s dumped into they sky that it is 28X stronger than a pound of CO2 that’s dumped into the sky at the same time. Whether they use ocean absorption of CO2 or not in their calculation I don’t know. Up until now, over 40% of the CO2 that we've together dumped into the sky has been absorbed by the oceans, which means that we're effectively carbonating them, i.e. to a degree we're turning then into a giant soda pop, lower the pH of the ocean, making it less alkaline, and in the process rapidly proceeding toward the literal dissolving of a huge fraction of all of the life forms of the ocean (corals, shellfish, diatoms, etc.).
We can calculate backward to estimate how strong a GHG methane really is by assuming a simple, straight line diminution of the methane over 12 years and assuming zero diminution of the CO2 over 100 years. Under those assumptions (which are at least pretty close to correct) the methane’s warming is the same as having 100% of it in the sky for 6 years followed by 94 years of having none. That means that while it’s actually fully still in the sky it’s 100 divided by 6 times stronger than the stated 28X. So that’s 16.67 x 28 = 466.76. Call it roughly 460 times stronger than CO2, per pound!
The figures we see over and over and over for how much stronger methane is at warming the planet compared with CO2 are based on either a 100-year comparison or a ~20-year comparison, usually the former. So we've been hearing numbers like 23X and 28X for the most part. But the truth about methane is that it’s roughly 460 times more powerful per pound as a greenhouse gas than CO2 and that it has a far shorter atmospheric lifetime of about 12 years.
People need to know this terrible truth about it. For one thing, the arctic sea ice is melting now, and that's a big-time emergency. So is the collapse of the floating ice sheet holding back the Thwaites Glacier in Antarctica. As prior methane emissions fade away to CO2 by oxidizing, becoming about one 460th as strong (while also gaining mass by replacing four light-weight hydrogen atoms with two 8-times heavier oxygen atoms) we are also replacing it with even more, fresh methane emissions which are greater in mass than what’s fading away, so this ferociously powerful GHG (by comparison to the super weak but very abundant CO2) is getting worse and worse for the climate. This does present us with a big opportunity for a quick fix by cutting methane leakage wherever we can, as a top climate priority. Refer to the 2021 book “Cut Super Climate Pollutants Now!”, written by close friends of mine for many of the details and the best overall climate strategy yet published. In the book, Durwood Zaelke uses the ~20 year comparison number.
The strongest GHG of all is SF6, sulphur hexafluoride, which is about 23,000 times stronger per pound than CO2 and lasts for 1,200 years or so in the atmosphere — a remarkably wicked combination for total damage done over its lifetime. There are many GHG’s which are on the order of 10,000 times stronger per pound than CO2 (when in the sky), most of which only remains there for a few years to a few decades. You can see most of them in Wikipedia’s list, but not the ones that have never been used as refrigerants, thus showing that CO2 is a very, very weak GHG. Were it not, we’d all have been cooked by now. The fact that SF6 is 23,000 times stronger means that CO2 is only able to absorb something like 1 part in 23,000 or less of the IR radiation leaving Earth's surface! And yet there's so much of it in the sky already that the super-fragile planetary balance has been pretty well broken by things we've done, though the methane we've added to the sky is doing almost as much damage. There are also many, many other GHGs that we've added, including most notably nitrous oxide from using nitrogen-based fertilizer, HFC's, mostly from refrigeration uses, ground-level ozone in smog from burning fossil fuels, and soot, also from burning fossil fuels and wood, etc.
Letting people know the truth about methane instead of glossing over it, by oversimplifying it down to a single number instead of two numbers, hurts our vital point that it’s incredibly important to stop methane leakage any way we can ASAP. I find this to be a major strategic error of the entire climate-protecting community.
Another, more important error is to speak first about future sea level rise estimates for the year 2100, rather than first stating our best guess for what sea level rise will eventually amount to by the time it stops rising (under a given emissions scenario). That’s a difference between guesstimates of 2 to 8 feet and guesstimates of 35 to well over 100 feet, possibly even as much as 300 feet in the northern temperate latitudes (which would mean roughly 200 feet in the southern temperate latitudes on account of shifting of the planet’s center of gravity caused by the loss of the one- to two-mile-thick Antarctic ice) — in the event that we actually manage to melt all of the land ice on Earth, which is not beyond our capability. It’s largely irrelevant what sea level rise might be by 2100, save for the forthcoming, huge mitigation and budget planning problems. How much should we spend on a coastal highway? When should people stop investing in Miami real estate? For protecting the future of civilization we need to know what our past and future actions will ultimately have done with respect to wiping out coastal resources. On that front, the best science says we are likely to have already guaranteed an eventual rise of 65 feet (barring massive and rapid removal of CO2 from the sky). How’s that compared to frankly stupid warnings about 2 feet of rise? Two thirds of all our civilization is below 65 feet above sea level…. And essentially no one is teaching the public about this. This is catastrophically inept messaging. Two degrees Centigrade seems like a really tiny amount, but it's effect on sea level alone will be enough to mostly wipe out our entire civilization! Look at a good, online, topographic map of the world. Our cities are mostly at sea level. River deltas are all ultra-flat. Etc., etc.
I hope this helps clarify a thing or two. Try to find a coastal city anywhere on Earth that won't suffer devastating losses from 15 feet of sea level rise and you'll begin to understand why James Hansen at a climate conference in San Francisco a few years back was talking about a 15-foot rise as though larger rises would be hardly worth talking about because they would merely lead to even worse, slow-moving armageddons.
One more thing: The natural range of sea level on Earth since ice first began to form in Antarctica 34 million years ago is about 650 vertical feet. The last time land ice was at one of its higher extents of the Pleistocene (essentially the last 2 million years), that being about 15,000 years ago, sea level was 390 feet lower than today. And when all of the land ice is gone, the water all back in the sea, the waters are about 250 feet higher (again, 300 feet at our latitudes and about 200 feet at the latitudes of Melbourne, Auckland, and Capetown. From about 8,000 years ago until the middle of the 20th century, sea level was rock steady, probably not varying by more than a couple of inches! So humanity built our civilization on the presumption that sea level was a constant. It's not!!! Most of the best locations for cities start at zero feet above sea level. This is especially true when a city is built in or beside a river delta, as is incredibly common all around the world. Raising sea levels is simply a thing we cannot do. And yet we've already severely impacted and destabilized huge fractions of the world's major land ice masses. We can't wait another minute to attack this. The effects on our weather, fires, droughts, floods, heat waves and storms would be enough by themselves, even without the sea level locomotive that barreling toward us.
—Joseph Holmes