Modeling

The Most Common Skeptical Arguments About Climate Change (from the Grist articles: How to Talk to a Climate Skeptic – see site for images)


Kyoto is a big effort for almost nothing

Objection: The Kyoto treaty, even if fully implemented, would only save us about a tenth of a degree of future temperature rise many decades from now. What a waste of effort! You can see for yourself here at the Junk Science website.

Answer: There are three big problems with this claim.

First, it’s a red herring. The purpose of Kyoto is to establish international political and economic mechanisms for dealing with global warming, by taking the first tentative steps toward a difficult goal. You may as well time me walking to the sidewalk where I parked my car bicycle and then tell me at this rate I will never get home.

Second, Kyoto is a step-by-step process. The second phase (much less third, fourth, etc.) has not even been negotiated yet. How can anyone claim anything about how effective it is going to be? Junk Science and other sources of this propaganda are starting their dubious calculations from the assumption that Kyoto ends in 2012 when round one is over. That is just wrong.

Third, the temperature several decades from now is to a large extent already determined by the current energy imbalance, thanks to extra CO2 already in the atmosphere. Short of a complete cessation of emissions today, there is no foreseeable way to avoid the bulk of the warming “in the pipeline.” This is mostly due to the extreme thermal inertia of the oceans and therefore the climate system as a whole. It means that our actions today, or our inaction, will have consequences several decades hence.

Finally, I have a rather personal peeve with people who vociferously criticize any attempt at a solution and yet propose nothing in its place. You’d think if they were so sincerely concerned about how ineffective Kyoto will be (as, frankly, they should be), they would be agitating for more action rather than shrugging their shoulders and saying “I guess we should just sit it out.” It’s like a guy standing on the sidewalk watching all his neighbors fight a house fire, saying “you’ll never make it, you don’t have enough people.”

Shut up and help!


Why should the U.S. join Kyoto when China and India haven’t?

Objection: Why should the U.S. join Kyoto while India and China haven’t?

Answer: The U.S. puts out more CO2 than any other nation on earth, including China and India, by a large margin. Considering the relative populations (a billion-plus each for China and India versus 300 million in the U.S.), per capita emissions in the U.S. are many times larger. This has been true for the past 100-plus years of CO2 pollution.

For the U.S. to refuse to take any steps until India and China do the same is like the fattest man at the table, upon realizing the food is running out, demanding that the hungry people who just sat down cut back just as much as him, at the same time.

There is no morally sane assessment of the global warming problem that does not place a greater burden on the U.S., the worst polluter. Perhaps we should divide global emissions by global population and allocate carbon credits according to census data. Or, using a Kyoto 1990-levels approach, perhaps we should demand that all nations target the per-capita levels of the U.S. in the 1990s. If you live anywhere but inside U.S. borders, these proposals do not sound preposterous.

All that aside, it is simply untrue that China and India have not joined the Kyoto treaty. They have. They were simply not required to return to the third-world level of emissions they produced in 1990. What comes next for them has yet to be negotiated. Further, this framework of differing responsibilities and the acknowledgement of differing social needs was explicitly accepted in the UNFCCC treaty — which was ratified by the U.S.

The U.S. has already agreed that China and India should be held to different standards!

Paragraph 3:

Noting that the largest share of historical and current global emissions of greenhouse gases has originated in developed countries, that per capita emissions in developing countries are still relatively low and that the share of global emissions originating in developing countries will grow to meet their social and development needs …

Paragraph 6:

Acknowledging that the global nature of climate change calls for the widest possible cooperation by all countries and their participation in an effective and appropriate international response, in accordance with their common but differentiated responsibilities and respective capabilities and their social and economic conditions …

Clearly, the notion that it’s unfair to expect the largest historical polluters to make the greatest reductions is not only wrong, but it is a violation of an already signed and ratified treaty on the issue of global warming.

But now that the world’s biggest polluter has refused to make any sacrifices, what do you think China will have to say when renegotiations come around in 2012?


Climate change mitigation would lead to disaster

Objection: The kind of drastic actions required to mitigate global warming risk the destruction of the global economy and the deaths of potentially billions of people.

Answer: Is this supposed to mean the theory of anthropogenic global warming must be wrong? You can not come to a rational decision about the reality of a danger by considering how hard it might be to avoid. First things first: understand that the problem is real and present.

Once you acknowledge the necessity of addressing the problem, taking action suddenly become less daunting. There is no point in discussing the best solutions or the cost of those solutions with someone who does not yet acknowledge the problem.

But even if mitigating global warming would be harmful, given that famine, droughts, disease, loss of major coastal cities, and a tremendous mass extinction event are on the table as possible consequences of doing nothing, it may well be we are faced with a choice between the lesser of two evils. I challenge anyone to conclusively demonstrate that such catastrophes as listed above await us if we try to reduce fossil fuel use.

Now, in terms of conservation and a global switch over to alternative fuels, the people who oppose doing this for climate change mitigation are forgetting something rather important. Fossil fuels are a non-renewable resource, and as such we have to make this global economic transformation regardless, whether now or a bit later. Many bright minds inside the industry think we are already at peak oil. So even if it turned out that climate mitigation was unnecessary, we would still be in a better place as a global society by making the coming switch sooner rather than later.

Seems like a win-win situation to me.


Hansen has been wrong before

Objection: In 1988, Hansen predicted dire warming over the next decade — and he was off by 300%. Why in the world should we listen to the same doom and gloom from him today?

Answer: While in some instances it is ignorant repetition of misinformation, at its source this story is a plain lie.

In 1988, James Hansen testified before the U.S. Senate on the danger of anthropogenic global warming. During that testimony he presented a graph — part of a paper published soon after. This graph had three lines on it, representing three scenarios based on three projections of future emissions and volcanism.

Line A was a temperature trend prediction based on rapid emissions growth and no large volcanic event; it was a steep climb through the year 2000 and beyond.

Line B was based on modest emissions growth and one large volcanic eruption in the mid 1990s.

Line C began along the same trajectory as Line B, and included the same volcanic eruption, but showed reductions in the growth of CO2 emission by the turn of the century — the result of hypothetical government controls.

As it happens, since Hansen’s testimony, emissions have grown at a modest rate and Mt. Pinatubo did in fact erupt, though in the early 1990s, not the middle. In other words, the Line B forcings scenario came remarkably close to predicting what actually came to pass.

Not coincidentally, the observed temperature trend has tracked closely with the Line B prediction as well.

Hansen was right on the money, and the models he used proved successful.

Unfortunately, when Patrick Michaels made his testimony before Congress in 1998, ten years later, he saw fit to erase the two lower lines, B and C, and show the Senators only Line A. He did so to make his testimony that Hansen’s predictions had been off by 300% believable. He lied by omission. This lie was picked up by Michael Crichton in his novel State of Fear (one of many omissions, confusions, and falsehood in that book — see here).

To my knowledge, Patrick Michaels has never owned up to his deception, either with an apology and retraction or with an explanation, and consequently the urban myth lives on to this day.

RabettRun has some more detail and illustrations here.


We can’t even predict the weather next week

Objection: Scientists can’t even predict the weather next week, so why should we believe what some climate model tells us about 100 years from now?

Answer: Climate and weather are very different things, and the level of predictability is comparably different.

Climate is defined as weather averaged over a period of time — generally around 30 years. This averaging smooths out the random and unpredictable behaviour of weather. Think of it as the difference between trying to predict the height of the fifth wave from now versus predicting the height of tomorrow’s high tide. The former is a challenge — to which your salty, wet sneakers will bear witness — but the latter is routine and reliable.

This is not to say it’s easy to predict climate changes. But seizing on meteorologists’ failures to cast doubt on a climate model’s 100-year projection is an argument of ignorance.


Chaotic systems are not predictable

Objection: Climate is an inherently chaotic system, and as such its behavior can not be predicted.

Answer: Firstly, let’s make sure we define climate: an average of weather patterns over some meaningful time period. We may thus discount the chaotic annual fluctuations of global mean temperature. That’s weather, and one or two anomalous years does not represent a climate shift.

Quite a few people believe that climate is a chaotic system, and maybe on some large-scale level it is. But it is not chaotic on anything approaching the time scales of which humans need to be mindful.

The notion that climate is chaotic tends to be taken as a given, with little supporting argument. Certainly the march of the seasons is nice and regular, determined directly by the orbital inclination of the earth. If a large volcanic eruption occurs, global temperature drops for a few years quite predictably. Diurnal cycles show the direct influence of insolation changes on the system.

Clearly, if you turn down the sun, the temperature drops. Clearly, if you throw a bunch of SO2 into the stratosphere, the temperature drops. Clearly, if you turn the surface completely white, the temperature drops. And clearly, if you double the amount of an important GHG in the atmosphere, the temperature rises.

What about longer timeframes, say, glacial/interglacial cycles? These are by no means perfectly regular, but they are far from random. They are also a broadly deterministic effect following from a known cause: orbital variations.

Granted, the data is quite chaotic on the multi-century time scale, though it clearly follows a 120Kyr cycle. But who’s to say that if we had enough data and understanding, these spikes and dips could not be thoroughly explained by solar influences, volcanic eruptions, greenhouse gas changes, ice sheet dynamics, etc.?

The ocean-atmosphere climate system is certainly a complex system, and capable of some surprising behaviours, but there is no evidence that it is chaotic in the formal sense.

I see no problem with speaking in a meaningful way about future expectations. Model outputs do produce specific year-to-year fluctuations — fluctuations that are not hindcasted well (that’s the weather, after all) — but nobody’s interested in knowing the exact temperature of any particular year. It is the decadal and century trends we want to anticipate.

It is the climate’s broadly deterministic responses to forcings that are of interest, and all evidence points to such determinism.

(The original article has a great deal of interesting discussion under it, for those with the stomach for talk of strange attractors, dynamical systems, and stochastic processes.)


We cannot trust unproven computer models

Objection: Why should we trust a bunch of contrived computer models that have never had a prediction confirmed? Talk to me in 100 years.

Answer: Given the absence of a few duplicate planets and some large time machines, we can’t test a 100-year temperature projection. Does that mean the models can’t be validated without waiting 100 years? No.

The climate is an extremely complex system. Our observations of it are by no means complete — even with regard to what’s going on today.

This is a shortcoming we need to work hard to correct, but it is also an opportunity for validating model predictions: Find a measurement we’ve never taken, see how the models say it should turn out, and then go take it and compare.

Still, there are global temperature predictions that have been validated. We can start with one of the pioneers in climate science. Over 100 years ago, in 1896, Svante Arrhenius predicted that human emissions of CO2 would warm the climate. Obviously he used a much simpler model than current Ocean Atmosphere Coupled Global Climate models, which run on super computers.

Arrhenius overestimated the climate’s sensitivity to CO2 by a factor of 2. At the same time, he hugely underestimated the degree of warming, assuming CO2 would rise very slowly (who could have predicted the emissions the future held?). Still, it was a pretty impressive early success for models.

Running the clock forward: in 1988, James Hansen of NASA GISS fame predicted [PDF] that temperature would climb over the next 12 years, with a possible brief episode of cooling in the event of a large volcanic eruption. He made this prediction in a landmark paper and before a Senate hearing, which marked the official “coming out” to the general public of anthropogenic global warming. Twelve years later, he was proven remarkably correct, requiring adjustment only for the timing difference between the simulated future volcanic eruption and the actual eruption of Mount Pinatubo.

And let’s face it, every year of increasing global mean temperature is one more year of success for the climate models. The acceleration of the rise is also playing out as predicted, though to be fair, decades will need to pass before such confirmation is inarguable.

Putting global surface temperatures aside, there are some other significant model predictions made and confirmed:

models predict that surface warming should be accompanied by cooling of the stratosphere, and this has indeed been observed;
models have long predicted warming of the lower, mid, and upper troposphere, even while satellite readings seemed to disagree — but it turns out the satellite analysis was full of errors and on correction, this warming has been observed;
models predict warming of ocean surface waters, as is now observed;
models predict an energy imbalance between incoming sunlight and outgoing infrared radiation, which has been detected;
models predict sharp and short-lived cooling of a few tenths of a degree in the event of large volcanic eruptions, and Mount Pinatubo confirmed this;
models predict an amplification of warming trends in the Arctic region, and this is indeed happening;
and finally, to get back to where we started, models predict continuing and accelerating warming of the surface, and so far they are correct.

It is only long-term predictions that need the passage of time to prove or disprove them, but we don’t have that time at our disposal. Action is required in the very near term. We must take the many successes of climate models as strong validation that their long-term predictions, which forecast dire consequences, are accurate.

If we seek even more confidence, there is another way to test a model’s predictive power over long time periods: hindcasting. By starting the model at some point in the past — say, the turn of the 20th century — and running it forward, feeding it confirmed observational data on GHG, aerosol, solar, volcanic, and albedo forcing, we can directly compare modeled behavior with the actual, observed course of events.

Of course, this has been done many times. Have a look at this page and judge for yourself how the models held up.

Would a prediction made in 1900 of temperature for year 2000 have been validated? Would politicians in 1900 have been wise to heed the warnings of science, had science had today’s climate models then?

Clearly, yes.


The models don’t have clouds

Objection: Clouds are a large negative feedback that will stop any drastic warming. The climate models don’t even take cloud effects into account.

Answer: All of the atmospheric global climate models used for the kind of climate projections synthesized by the IPCC take the effects of clouds into account. You can read a discussion about cloud processes and feedbacks in the IPCC TAR.

It is true, however, that clouds are one of the largest sources of uncertainty in the GCMs. They are complicated to model because they have both positive feedbacks, preventing surface heat from escaping back into space, and negative feedbacks, reflecting incoming sunlight before it can reach the surface. The precise balance of these opposing effects depends on time of day, time of year, altitude, size of the water droplets and/or ice particles, latitude, current air temperature, and size and shape.

On top of that, different types of clouds will interact, amplifying or mitigating one another’s effects as they coexist in different layers of the atmosphere. There are also latent heat considerations — water vapor condenses during cloud formation and precipitation events, and water droplets evaporate when clouds dissipate.

The ultimate contribution of clouds to global temperature trends is highly uncertain, but according to the best estimates is likely to be positive over the coming century. There is no indication anywhere that any kind of cloud processes will stop greenhouse-gas-driven warming, and this includes observations of the past as well as modeling experiments.