Libertarian writer Robert Tracinski’s recently wrote an article called “What It Would Take to Prove Global Warming” in which he challenged mainstream climate science on a number of issues. I was asked by a few people to give my thoughts on the article so I have written an informal response to several of the article’s claims below.
Picking up where the article gets substantive…
When I refer to “global warming,” and when Bailey and Adler refer to it, that term is a stand-in, not just for the trivial claim that average global temperatures are rising, but for “catastrophic anthropogenic global warming”: i.e., global temperatures are rising, it’s our fault, and we’re all gonna die.
Response: Tracinski starts of by creating a straw man argument that is easy for him to defeat. Serious scientists/policy experts do not tout the claim that “we’re all gonna die”. The important question is not whether or not “we’re all going to die”, the important question is whether or not it would be a net benefit to society and the environment if we regulate/reduce greenhouse gas emissions.
I’ve gone on record a long time ago sketching out what stages would be required to demonstrate that humans are causing rising global temperatures, never mind the much more dubious proposition that warmer weather is going to be a catastrophe. Let me elaborate on it here.
There are three main requirements.
1) A clear understanding of the temperature record.
The warmists don’t just have to show that temperatures are getting warmer, because variation is normal. That’s what makes “climate change” such an appallingly stupid euphemism. The climate is always changing. The environmentalists are the real climate-change “deniers” because they basically want global temperatures to maintain absolute stasis relative to 1970—not coincidentally the point at which environmentalists first began paying any attention to the issue.
Response: It may be generally true that “variation is normal” but the rate of warming that we have observed over the past century has been demonstrated to be outside the range of natural variability. Most of the natural climate changes that Earth has experienced in the past have occurred at rates much slower than the climate change we are currently experiencing. For example, it took 10,000 years for the earth to warm 9 degrees Fahrenheit when we came out of the last ice age. If humans decide to burn all remaining fossil fuels, we are looking at a similar magnitude of warming over 200-300 years instead of 10,000. It is the rate of climate change, not necessarily the magnitude that has people most concerned.
The bottom line is that climate does change with or without human actions but science has demonstrated that humans are the dominant cause of warming over the past century and this warming is occurring at a rate that is much faster than previous natural climate changes.
So to demonstrate human-caused global warming, we would have to have a long-term temperature record that allows us to isolate what the normal baseline is, so we know what natural variation looks like and we can identify any un-natural, man-made effect. A big part of the problem is that we only have accurate global thermometer measurements going back 135 years—a blink of an eye on the time-scales that are relevant to determining natural variation of temperature. Within that, we only have a few decades of warming that could conceivably be blamed on human emissions of carbon dioxide: a minor run up in temperatures from the 1970s to the late 1990s.
Response: Coincidentally, I just published a study that looks at natural variability in temperature over the past 1000 years and compares that to the magnitude of temperature change that we have experienced recently. In order to get estimates of variability of the past 1000 years you need temperatures proxies – things in the environment that co-vary with temperature like ice layer size, tree ring width, ocean sediment chemistry ect. There is definitely a great deal of uncertainty associated with estimating temperature from 1000 years ago, but all the available evidence suggests that the warming we have experienced over the past century is larger than what could be expected from natural variation.
Since then, warming has leveled off (despite strenuous attempts to pretend otherwise). I think it’s impossible to claim, on that basis, that we even know what natural temperature variation is, much less to demonstrate that we’ve deviated from it.
Response: 2014 was the warmest year in the instrumental record (see graph below). The rate of global warming varies from decade to decade because of a lot of factors but clearly the long-term trend is up.
Various environmentalist attempts to create a “hockey stick” that makes current temperatures look abnormal have been embarrassing failures, involving problems like an improper mixing of recent thermometer measurements with less accurate “proxy” measurements that estimate temperatures farther into the past. And they prove my point about warmists being believers in climate stasis. The hockey stick graphs all assume that global temperature have been basically flat for 2,000 or 10,000 years, so that minor recent warming looks like a radical departure. Who’s really denying climate change?
Response: Many groups of professional scientists (who may or may not be “environmentalists”) have used different pieces of evidence to estimate how temperatures have changed over the past millennium (see graph below). It is absolutely false to say that these temperature estimates “assume that global temperatures have been basically flat”. These studies do not assume anything about how temperatures vary in the past. Any ‘flatness’ that these graphs show is a result, not an assumption of the studies. Also, all of these studies show that the warming of the 20th century is abnormal compared to natural variability.
And if you look at temperatures on the really big scale, we’re all just playing for time until the next ice age comes.
Response: Human caused increases in greenhouse gasses already guarantee that we will not be headed into an ice age any time in the next few millennia.
Assuming we can eventually compile a temperature record that is long enough and reliable enough to distinguish the effect of human activity from natural variation, we would also have to understand how human beings are causing this effect. Which leads us to the second big requirement.
Response: We already have temperature records long enough and reliable enough to distinguish the effect of human activity. Tracinski just doesn’t like the implications of these records so he assumes they must be wrong.
2) A full understanding of the underlying physical mechanisms.
We have to know what physical mechanisms determine global temperatures and how they interact. The glibbest thing said by environmentalists—and proof that the person who says it has no understanding of science—is that human-caused global warming is “basic physics” because we know carbon dioxide is a greenhouse gas. Carbon dioxide is a very weak greenhouse gas and there is no theory that claims it can cause runaway warming all on its own.
Response: No scientist that I know of claims that CO2 causes ‘runaway’ warming. However, basic physics does tell us that carbon dioxide is a greenhouse gas and that all else being equal, increasing CO2 will increase temperature. CO2 may be a relatively weak greenhouse gas compared to some others but humans are putting so much of it into the atmosphere (about 40 billion metric tones per year) that it still has a large effect.
The warmists’ theory requires feedback mechanisms that amplify the effect of carbon dioxide. Without that, there is no human-caused global warming. But those feedback mechanisms are dubious, unproven assumptions.
Response: There is still human-caused global warming with or without “feedback mechanisms”. However it is true that feedbacks amplify the impact of increasing CO2. For example, if you increase CO2, you warm the planet. This causes ice to melt which causes the planet to reflect less solar energy back to space. This results in more solar energy being absorbed which causes further warming. Feedback mechanisms have been studied expensively and we know a lot about them. They certainly are not “dubious, unproven assumptions”.
Basic questions about the “sensitivity” of the climate to carbon dioxide have never been answered. Even Bailey admits this.
In recent years, there has [been] a lot of back and forth between researchers trying to refine their estimates of climate sensitivity. At the low end, some researchers think that temperatures would increase a comparatively trivial 1.5 degrees Celsius; on the high end, some worry it could go as high as high 6 degrees Celsius…. In a 2014 article in Geophysical Research Letters, a group of researchers calculated that it would take another 20 years of temperature observations for us to be confident that climate sensitivity is on the low end and more than 50 years of data to confirm the high end of the projections.
Response: It is true that there is a wide range of possibilities for how much warming we expect for a given amount of CO2 increase.
Well, fine then. Is it okay if we wait? (No, it isn’t, and I’ll get to the implications of that in a few moments.)
And this leaves out the possibility that the climate’s sensitivity to carbon dioxide is even lower, that other mechanisms such as cloud-formation might serve to dampen temperature increases.
Response: This possibility is “left out” because there is no evidence that it is a real possibility worth considering.
Recently, I was amused at news that new science is debunking the “low sodium” diet fad of the past few decades. It turns out that “the low levels of salt recommended by the government might actually be dangerous” (which is not so amusing). This seems like a timely warning. Like the human body, the global climate is a hugely complicated system with a lot of factors that interact. We’re not even close to understanding it all, and having the government jump in and pick sides risks cementing a premature “consensus.”
Response: I agree that the climate is extremely complex and there is always the potential for surprises. But there is a difference between not knowing everything and knowing nothing. The vast majority of scientists who study this issue would say that we know enough about climate to be confident that humans are currently causing warming that is above and beyond natural climate variability.
The immense, untamed complexity of the climate is reflected in the poor performance of computerized climate models, which leads us to our last major hurdle in proving the theory of global warming.
3) The ability to make forecasting models with a track record of accurate predictions over the very long term.
We don’t know whether current warming departs from natural variation, nor have scientists proven the underlying mechanisms by which humans could cause such an increase.
Response: Just to reiterate the points above, we do know that the warming over the past century departs from what would have happened without human greenhouse gas inputs and scientists absolutely understand the underlying physical mechanisms.
But even if we did know these things, we would have to be able to forecast with reasonable accuracy how big the effect is going to be. A very small warming may not even be noticeable or may have mostly salutary effects, such as a slightly longer growing season, whereas the impact of a much larger warming is likely to cause greater disruption.
I should also point out that the “catastrophic” part of “catastrophic anthropogenic global warming” is a much larger question that is even harder to forecast. For example, global warming was supposed to lead to more hurricanes, which is why movie posters for Al Gore’s An Inconvenient Truth featured a hurricane emerging from an industrial smokestack. Then hurricane activity in the Atlantic promptly receded to historical lows.
Response: I essentially agree with this point. The science on the connection between human-caused climate change and any change in hurricanes is fiercely debated in the scientific community and I believe it was scientifically irresponsible for An Inconvenient Truth to use the hurricane in its logo.
It’s pretty clear that scientists aren’t any good yet at making global climate forecasts. Current temperatures are at or below the low range of all of the climate models. Nobody predicted the recent 17-year-long temperature plateau. And while they can come up with ad hoc explanations after the fact for why the data don’t match their models, the whole point of a forecast is to be able to get the right answer before the data comes in.
Response: On the decade-to-decade timescale there are a lot of factors other than CO2 that effect the global temperature. That means that CO2 can go up for a couple decades while global temperatures remain flat. It also means that CO2 could remain flat for a couple decades while global temperatures warm. However, on longer timescales (e.g., 100 years) CO2 has a much more dominant impact on global temperature. It is this long timescale that is most important for climate policy.
Given the abysmal record of climate forecasting, we should tell the warmists to go back and make a new set of predictions, then come back to us in 20 or 30 years and tell us how these predictions panned out. Then we’ll talk.
Response: I assume that Tracinski is against climate change mitigation policy because he fears that regulating greenhouse gas emissions will negatively impact the economy. If that is the case, then it would be fair to point out that economic models have a poor track record of correctly forecasting the future. Therefore, I think Tracinski has created an unfair double standard. He demands that climate models have the ability to perfectly forecast the future while simultaneously giving a pass to economic models.
The bottom line is that the future is hard to predict. The precise amount of warming that we will get for a given change in CO2 is hard to predict and the economic impact of climate change mitigation policies are hard to predict. Any serious appraisal of a CO2 mitigation policy would take into account the uncertainty of both and would not unfairly pretend that one side of the balance has no uncertainty.
Ah, but we’re not going to be allowed to wait. And that’s one of the things that is deeply unscientific about the global warming hysteria. The climate is a subject which, by its nature, requires detailed study of events that take many decades to unfold. It is a field in which the only way to gain knowledge is through extreme patience: gather painstaking, accurate data over a period of centuries, chug away at making predictions, figure out 20 years later that they failed, try to discover why they failed, then start over with a new set of predictions and wait another 20 years. It’s the kind of field where a conscientious professional plugs away so maybe in some future century those who follow after him will finally be able to figure it all out.
Response: The science of climatology has already been going through this process for a long time. The greenhouse effect was discovered in the 1820s, the first scientific paper written about CO2’s impact on global temperature came out in 1896, and the first major assessment report on human-caused climate change came out in 1979.
Yet this is the field that has suddenly been imbued with the Fierce Urgency of Now. We have to know now what the climate will do over the next 100 years, we have to decide now, we have to act now. So every rule of good science gets trampled down in the stampede. Which also explains the partisan gap on this issue, because we all know which side of the political debate stands to benefit from the stampede. And it’s not the right.
Response: The reason people feel that this issue is so urgent is because in order to stabilize global temperature (stabilize not bring temperatures back down to where they were) we would need to reduce CO2 emissions by ~80% from their current level. However, CO2 emissions are only growing exponentially. All reasonable policy/economic outlooks say that it would take decades to stabilize CO2 emissions and many more decades to bring CO2 emissions down to a level to where global temperatures would stop rising. Because of these huge time-lags, avoiding large global warming in the coming centuries requires that we begin to reduce greenhouse gas emissions now.