So I was at work today, and with all the bad weather he had plenty of time to shout at the boss and another co-worker about global warming. It was a good 2-on-1 handicap match. “Talking” debates are not really my thing since no opportunities exist to check claims, reference sources, show graphs, etc that you could do in online/text correspondence, and so basically anything goes. Even totally wrong claims like “Volcanoes spit out more pollution than humans do.”
The boss and the co-worker were very skeptical. I’m not sure how scientific our exchange was– they spent most of the time trying to convince me I should be very cautious in trusting the general scientific community, and I spent most of the time telling them that they should trust physics, but no one budged. They’re intelligent group of folk (one trained in biology) but not really familiar with the climate science literature, so I tried to avoid ideas like “radiative forcings,” “water vapor feedback,” “stratospheric cooling,” and other concepts. So we didn’t really discuss “how CO2 influences climate” or even radiative feedbacks, and it probably was worthwhile as a philosophy of science talk if anything.
Still, I was troubled by a lot of misconceptions they had with terminology, and the basic way in which attribution of warming is (and is not) carried out. This is something that I’ve run into with other “dinner table” quality discussions. This post will be nothing interesting to those who have followed the issues, although many of us may lack experience talking to general people like our friends or co-workers who have not engaged in the back and forths of the “debate” or have studied documents by IPCC, National Academies, etc. Some concepts are:
1) Cycles: This follows the traditional “we’re in a cycle” line of thought. The justification was essentially that warmer and colder times happened before, and the co-worker reminded me of the ice core bubbles showing ups and downs in the past. I’m pretty sure she was talking about Milankovitch variations over the last million years. The term “cycles” in thrown around very loosely in these kind of discussions. So a few pointers
- The term “cycle” has a precise statistical meaning. Just because climate changed before doesn’t mean “it’s a cycle.” The sun has a very clear cycle of roughly 11 years corresponding to changes in solar output, day-night variations are a cycle, there is a seasonal cycle, but in fact true cycles which affect the climate of the planet are not very common. Milankovitch are probably quasi-cyclical, but also not relevant for modern global change. Long-term changes in plate tectonics, mountain uplift, and other geologic controls are not cycles.
- Cycles are real physical phenomena, and thus if they change the Earth’s climate they did it in some real way, which needs to be defined. Seasons for instance are caused by the tilt of the Earth and the motion around the sun, while day-night changes are caused by the Earth’s rotation. Just saying “it’s a cycle” is not very useful: does this cycle happen to deliver the Earth more solar output, what kind of fingerprints should it leave behind, how long is the cycle, etc?
- Humans are a new part of the equation. Life can influence the climate. Plants and other organisms took an entire deoxygenerated atmsophere and put oxygen into it making it suitable for the life we know today (which by the way is not a cycle). There should be nothing mystical about humans being able to change the climate, particularly as it’s easy to monitor changes in atmospheric chemistry through emissions.
- Timescale matters: Milankovitch cycles influence climate on timescales of thousands to hundreds of thousands of years. Day-night cycles influence people on timescales of many hours, while seasonal variations influence people on timescales of months.
- Forcings on climate need to be added, not replaced. Different things can change the climate. If multiple things are changing, then you need to add them up, not pick which ones you like. If the sun is going up and CO2 is going up, you can’t just say “it’s the sun” because you like “natural” stuff or you don’t like humans or you like big yellow balls of fire, or whatever else. The influence of CO2 is very well defined and can be calculated with high accuracy and thus no physical justification exists for ignoring it in modern or future global change
2) Self-Correcting mechansisms: My boss was convinced that even if it got warmer, the climate would fix itself. He was not necessarily referring to what some specialists would call “negative feedback” (some people invoke some cloud-albedo mechanism), and actually he bewildered me with some radical plate tectonics idea about warmer temperatures meaning more volcanic eruptions and a return to today’s climate (although that’s not actually what would happen). He told me an asteroid could hit the Earth, or whatever else that was beyond prediction. So, some points
- Asteroid impacts or more volcanic eruptions are not “self-correcting mechanisms.” They aren’t cycles either. They are completely random events, and various hypothetical examples could push the climate further or away from the current warming trajectory. Relying on them for prediction is obviously kind of strange. The Earth actually doesn’t care what the climate is, and so there is no tendency for it to be the pre-industrial climate. The concern is us, and current ecological structures.
- Again, timescale matters: The Earth has gone from climates without ice sheets and alligators roaming around in swamps in the present day arctic circle, and there have been climates where Earth was covered (or nearly covered) in ice. Some might call, say, the silicate weathering thermostat hypothesis to be a “self-correcting mechanism” although this is important on hundreds of thousands and millions of year scales. A key observation is that the climate can clearly change and stay in a new state on timescales which are far longer than we need to be worried about, and extra CO2 can influence climate for thousands of years after it is released. Because the surface boundary conditions and ice sheets will change, there’s also no reason why such “self-correcting mechanisms” should bring us back to this climate or anything which humans will be adapted nicely to.
- The paleoclimatic record, and even observations in the 20th century (like after the Pinatubo eruption) are incompatible with a very low sensitivity to change, and the geologic record provides a treasure chest of different climates. Thus there is no basis for claims that further heating will “correct itself” or bring us back to a state like today.
3) Projections vs. Predictions: As noted above, relying on asteroid impacts or alien invasions or worldwide viruses to knock out predictions of future global change is not very worthwhile, and it’s also meaningless to discount current projections because those things “could happen.”
The trajectory of future global change depends on climate sensitivity, but also on how human actions evolve in the future; the second one is purely up to us. For instance, whether we decide to stop all emissions today, or steady out CO2 slowly, or do nothing for 50 years and then stabilize are all different scenarios that have different repercussions for climate.
Therefore projection of future climate carries with it the assumption of various socio-economic scenarios (outlined in detail by SRES), something reasonable probably falls between the yellow line and the red line up there. This depends on how humans decide to clean up their act, or if we choose to do so at all. This is a different kind of uncertainty than how the climate actually responds to a given change in atmsopheric chemistry, which is why “a doubling of CO2” is often used as a better metric than “by 2100” or other date. As described in this paper emissions continue to grow from economic expansion and use. The world also doesn’t end in 2100, so choosing to do nothing will result in the high end of the above projections without stabilization at the turn of the next century, something a bit misleading with the green and purple line.
- How the past record ties into it: How the climate has changed before provides invaluable insight into how sensitive the system is to change, for testing our understanding of what forcing agents matters and on what timescales, etc. However, it is not very meaningful for the attribution of 20th century warming or projections of future global change. Humans are a new dimension in global climate, and thus our influence has to be evaluated accordingly. Just because forest fires occurred naturally in the past doesn’t mean an arson can’t start one today. Murderers don’t get off on the claim that “people always die anyway” and so humans shouldn’t get off the suspect list just because of how climate changed before, or because our measurements only go back a limited amount of time.
- Assessing spatio-temporal patterns of change: Attribution of climate change to a particular cause(s) is not a process-of-elimination approach. We don’t pick out of a hat, nor do we take a vote. Formal attribution doesn’t even depend on our ability to simulate the 20th century with models of greenhouse gas + natural forcing, and not natural forcings alone, and can even be accomplished when subtracting global mean trends (although this is interesting to stare at). Usually formal attribution involves comparing spatio-temporal patterns to a set of forcings (through models or theory) and allowing the amplitudes of various forcings to vary. Natural variations fail to account for the observed trends even with overinflated responses, something robust to various models, methods, or assumptions about internal variability. A key point is that no physically plausible way exists to systematically increase carbon dioxide in the air and not expect a warmer world.
- Assessment of future global change is not based on the increase of temperature over the last century.
The global mean temperature change is nearly 1 C over the last century.
This is not why we expect temperature to continue to rise…it has more to do with the fact that we expect greenhouse gases to continue to rise, and we know that the climate still has to “catch up to us” so heating in the pipeline will be realized. Even transient forcings like solar output going down or volcanic eruptions will eventually be outdone by the much longer-lived greenhouse gas influence.
- Science is done by scientists, so reading what scientists have to say about the subject is probably a good idea, at least before opining on the topic. Many people just don’t care all that much about the science (just as I know nothing about black holes or organic chemistry) and for such people the media or quick wikipedia searches will suffice, but then those people have to at least realize that they are not in a place to make judgment about the quality of research, just as I am in no posittion to disagree with an astrophysicist about black holes. It makes no sense. If you think the scientists are bending the truth after a good amount of research is conducted, it’s your perogative (although much of the underlying data and physics can be validated for people really interested), but for those really interested there’s very good reports from the IPCC, from the recent Copenhagen climate conference as well as various pieces by the National Academies of Science, USCCP, as well as the hundreds of peer-reviewed documents available in journals, “.edu” resources, etc. The studies and data coming out analyzing climate change are done by research groups at universities, organizations like NASA, NOAA, etc. There is thus no need to rely on Al Gore (or Rush Limbaugh!!) for information, and such spokespeople do not directly contribute to the research in the field. Some blogs, random “.com” websites, etc may be good, although you probably won’t be able to tell the difference if you don’t familiarize yourself with the original research first.
- I think many people are unaware of the breadth and depth of the scientific literature on climate change, and the overwhelming amount of research conducted by the scientific community. The first estimates of the influence of CO2 change was done in 1896, and the field has evolved tremendouly over the last century, with many of the key aspects known well before any of the researchers today were born. This is not one of those things which is open to public preference or opinion, and it involves a great deal of complexities which cannot be understood through quick google searches.
Update– July 8: I’ve messed around with the wording of things for clarity.