In a recent FaceBook exchange, the question came up of why I object to the omission from most talk about AGW of the benefits from milder winters. I ended up sketching an approach to the question of whether increased mortality from hotter summers was more or less than decreased mortality from milder winters. It was a longer piece than I usually bother with on FaceBook, which suggested that it would be more appropriate here, so here, with some editing, it is.
I begin with a Lancet article that found that, globally, "cold-related deaths outnumbered heat-related deaths by a factor of nearly 20, overall." To figure out how summed deaths from heat and cold were changed by AGW so far, or estimate how they will be changed in the future, I need two more pieces of information.
1. As temperature rises, what is the relative rise in temperature of winters relative to the rise in temperature of summers. I don't have data on that and it surely varies from place to place, but the physics of greenhouse gas warming implies that it will tend to be larger in cold times than in hot, so I would expect that, on average, winters will get milder by more than summers get hotter. I picked up that point from something Freeman Dyson mentioned in The Scientist as Rebel, and so far as I can tell it is correct.
2. What is the marginal effect on mortality of changes in both highs and lows? What is the percentage increase in mortality due to heat if highs go up by one degree? What is the percentage decrease in mortality due to cold if lows go up by one degree? How do they compare?
So far as I know, data on that do not exist. So I start with the simplest assumption—that the marginal effects are the same. If so, raising both the high and the low by one degree will decrease mortality due to cold by almost twenty times as much as it increases mortality due to heat, as per the Lancet numbers. Since, as per my point 1 above, AGW will on average increase lows by more than it increases highs, a given increase in global temperature due to AGW should decrease mortality due to cold by more than twenty times the amount it increases mortality due to heat.
If the question is whether the net effect is an increase or decrease in total mortality, the argument implies that for the net to be an increase in mortality the marginal effect of higher highs has to be more than twenty times as great as of higher lows. I suppose that's possible but I can not see any reason to expect it. Perhaps someone reading this can point me at data on the marginal effect that would let me replace my guess with something better.
In my experience, news stories on global warming routinely cite figures on increased deaths from hotter summers, current or projected, but give no such figures for decreased deaths from milder winters.
P.S. The Physics
CO2 is a greenhouse gas. So is water vapor. The more of one greenhouse gas in the atmosphere, the less the effect of adding another–the combined effect, after all, cannot be to block more than a hundred percent of the long wave radiation coming up from the Earth. The warmer it is, ceteris paribus, the more water vapor is in the air. Hence the greenhouse effect tends to be less in warm times and places than in cold.
Your discussion of high and low temperatures reminds me of something I once surmised. This might relate indirectly to your subject.
Looking at the record high and low temperatures ever recorded at various locations on Earth, I was struck that the range of high temperatures was smaller than the range of low temperatures. The numbers were something like this (just guessing from memory):
-- Record high temperatures ranged maybe 50°F to 130°F (roughly 80° range). But most places seemed to have a record high temperature within a smaller maybe 20° range, maybe 95° to 115°F.
-- Record low temperatures ranged maybe -85°F to +55°F (roughly 140° range).
I guessed there must be some mechanism which moderates high temperatures more than low. But I don't know.
Humans occupy the habitable land between extreme warmth and extreme cold, and there are sunk costs associated with this habitable area. As the margins of habitability move closer to the poles, populations will migrate with it. But due to sunk costs associated with the marginally habitable areas of the world that are closer to the equator, you would expect a greater subset of the populations occupying these areas to fail to "move out of the way" in time. The marginally habitable areas that are closer to the poles, however, will only get more habitable over time. So sunk costs would cause extreme cold to be less of a problem in a GW scenario than in a scenario of no GW. I have no idea if this would make up the difference.
Regarding heat deaths. Global warming will extend the range of mosquitoes that carry malaria and other illnesses. Is that included in the mortality estimates?
Regarding greenhouse gasses. Water vapor forms clouds which reflect light before it can cause surface warming. Has that been factored in?
Your father is an American hero.
Im not going to comment on the heat vs cold deaths but i do have to correct your physics. The long wqve radiation is laready effectively completely blocked and it gets absorbed and re-emitted something like 14 times. Adding more greenhouse gasses makes the number of times this happens go up. CO2 and water also cover some different areas of that spectrum so the presence of both augments each other.
Each time the radiation is absorbed and re-emmited there is a few degrees of driving force required for the total upward heat flux to match the incoming light flux that reaches the ground. Think of it like a blanket. Each layer added on increases the ground temperature enough to drive the heat upward so the final layer can radiate the heat into space at the same rate it comes in. More greenhouse gasses will always increase the effect, but at a slowly reducing rate.
A final point is that since water is condensable it only stays in the atmosphere on the order of days. The initial increase from CO2 can cause more water to evaporate which adds more greenhouses gasses. This is one of the primary amplifying effects. (If there is increased cloud cover this may partially offset it, but can't completely or there would be no increased water vapour to make the clouds)
Change is scary and so if the climate changes, the assumption is that the scariest stuff will happen disproportionately to the poorest brownest people, who have the fewest resources with which to adapt. People arguing for C-AGW want to signal how much they care about the poor brown people and want to protect them from change.
Like I've said, the whole global warming argument seems to be a kind of pressure valve for the pent-up conservative impulses of people who otherwise would shrink in horror at the notion of being conservative about anything. What's really happening and what the actual effects might be are of secondary, maybe tertiary importance.
Another issue with milder climates closer to the poles might be reduced sunlight exposure. As more people move further from the equator, even if they enjoy milder temperatures, their exposure to sunlight is reduced. This might decrease skin cancer rates, but I would expect higher rates of other types of cancers and cardiovascular disease (the NIH published some work which showed that exposure to sunlight and proximity to the equator has a lot more health benefits than costs - in terms of disease and mortality). This is just an example that there are so many factors involved that it is (nearly) impossible to do a real cost-benefit analysis of changing temperatures.
The USDA Hardiness Zones (useful for growing crops) are based on low temperatures rather than high temperatures. Thus, a place without "real" summer like San Francisco is being judged on the mildness of its winter and is comparable in ranking to central Florida. I assume some data about mortality due to milder winters can be extrapolated if taking this map (using data by county?) into account.
One of the reasons for decreasing temperate variation at higher temperatures is that the final outflow of heat from earth (thermal radiation) varies with temperature to the fourth(!) power. ie, realizing a degree in difference between temperature at equator and poles will require a progressively larger energy input differential the hotter it gets. That is of course only one of many factors that go into this complex equilibrium; but without an dominant dynamic of this nature, there would not have been forests at the poles in the past; or we should have seen water-boiling conditions at the equator at the same time. Speaking of water; the strongly nonlinear increase of water vapor pressure with temperature is another such equalizing factor.
Related to that, 'too much fresh water' is really a very niche, and relatively easily mitigated concern, in the big scheme of things. Draught is much more of a drag on the human condition than river floods. Deserts do not exists by virtue of an excess of radiation influx (the tropics have more, and they are not known for their lack of ability to sustain life), but by virtue of a lack of water. All the deserts currently on the planet didn't use to be there when the planet was just a few degrees warmer on average. If only those poles wernt so cold, soaking up those precious fresh water molecules liberated by what limited radiation falls on the ocean surface...
Much like the benefits of warmer winters, you never see the prospect of getting rid of the worlds deserts mentioned a lot.
David Friedman, do you have any comment on Scott the psychiatrist's banning of me and Homo Iracundus? I consider the banning of the latter to be 100.00% purely politically motivated. As we were the two first and most persuasive responders to his nonsensical first anti-Trump post, and this banning took days after we posted our relevant comments, the evidence for these bans as being purely politically motivated rises. Jill and TheWorst have both engaged in much worse insults than I (not to even speak of the good Homo Iracundus) and have not been banned. I consider this a move in a negative direction for SSC, and as a capitulation to left-wing trolls who have the time to troll against "right-wingers", but refuse to listen to any reason or to refute any evidence these "right-wingers" present themselves. This is either a sign of weakness or deliberate subversion.
@Richard O Hammer
High surface temperatures increase the rate of evaporation at the surface. This evaporisation traps heat (sometimes called the latent heat). The vapour rises in the atmosphere until it condenses again, releasing the latent heat of evaporisation, which has effectively been lifted high into the atmosphere, cooling the surface and becoming closer to being radiated into space, which will cool the planet. Overall this water evaporisation / condensation cycle is a system of negative feedback, damping high surface temperatures, by a mechanism which is a lot like the way refrigerators work.
Thank you for that explanation.
You cost benefit analysis would be accurate except you forgot to account for the increase of Vitamin D through increased sun exposure and increased use of sunscreen in your cost benefit analysis of climate change. jk
I think you may have a finger on one of the concerns I have with the AGW crowd: no consideration is ever given to mitigating factors. The only things they report are potential catastrophes, and in the worst possible light.
For instance, the current temperatures are well within the predicted range by the original IPCC report as the margin of error actually allows for (from memory) something like a degree and a half of cooling, given how wide the margin was. The news media and the invested politicians all insisted that the high end of the margin of error was right.
Those of us who have been at the very least skeptical of AGW call this 'ratchet reporting'.
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