The Azimuth Project
Uncertainty in climate science (Rev #14)



Uncertainty in climate science is a complex issue, especially when scientists attempt to speak about it to the general public. To some folks, when scientists say that there is uncertainty in the data or predictions; this means that perhaps there is no problem - no real danger of a climate crisis - and that scientists are trying to hedge their bets by projecting a worst case scenario. Sadly, this is not the case, and the real truth is more nearly the opposite. If anything, the tendency has been for scientists to be timid of making dire projections, and perhaps a bit over-optimistic about how quickly climate fixes and sustainable practices can or will be implemented and adopted. This is one reason why we see the need for a Plan C, in case other plans fail to gain traction in time.

It is important for both the general public and scientists to recognize that the colloquial usage of the word ‘uncertainty’ and its use as a scientific term are different. What is worse; sometimes the way in which the word is being used is unclear, and this renders its meaning - or the proper interpretation - quite uncertain. This makes it a necessity for scientists to spell things out, to quantify their usage of the word uncertainty itself - so that the listener may understand that what a scientist is uncertain about, and the ways in which they are uncertain, are limited. That is; it must be made clear that while we are relatively certain environmental problems lie down the road - if we do nothing - we are unsure of how bad things will get, how soon they will get worse, and how much what we can do will help — perhaps unsure if even our best efforts will be enough to save humanity.


Uncertainty, in the general sense, is a way of describing what is not known, or quantifying the extent to which things cannot be accurately measured. For scientists, this term has a specific and limited meaning - as they are concerned with how to reduce errors in measurements and predictions as far as possible, and to quantify the remaining errors. However, the colloquial usage of the same word is that uncertainty sometimes implies doubt, mistrust, or suspicion. Thus; it is easy to be confused about uncertainty, especially when sometimes it is unclear which of its more precise meanings is intended by a given author or speaker. That is; people often have difficulty, because the intended meaning of the word ‘uncertainty’ is itself sometimes uncertain.

Ergo, it is necessary for people in Science who wish to help clean up the environment to be clear about what we mean, especially when using words like ‘uncertainty’ whose meaning among scientists is radically different from that of the general public. To be clear; we are not sowing doubt about the research of others, nor are we casting suspicion about the quality of their work, when we state that “There is uncertainty in the data they used.” However; it is easy to see how this type of comment could easily be misinterpreted, and seen as something other than a statement about the difficulty with measuring some phenomena. Since the same words could be seen as something more personal, it is best to avoid using the term ‘uncertainty’ in such an open-ended or ambiguous way.

Uncertainty is something we now understand is both practically and theoretically impossible to reduce to zero. For example; even if we go to the theoretical limit of measurement and observation, we cannot measure both the position and the momentum of a particle with ultimate precision at the same time, as per Heisenberg’s uncertainty principle. Any attempt to measure the momentum with greater precision interferes with or blurs the measurement of position, past a certain point - where the combination or product of the two uncertainties approaches Planck’s constant. And the same is true for measurements of position. So there is a certain absolute minimum uncertainty which cannot be reduced by any means.

Of course; actual inaccuracies of measurement seldom approach the theoretical limit, no matter how hard scientists try to get the errors to cancel each other out. And even with accurate instruments and careful calibration, there is always some estimation error or measurement error to deal with. Scientific data is normally presented with ‘error bars’ that bracket a result to show it is accurate within limits like + or - 0.1%. But in climate science, these problems are compounded by what can be called the chaotic element of all fluid flows in general, and therefore of all weather events and trends specifically. Simply put; the weather is unpredictable in the long term. More technically, the Lorenz attractor illustrates how paths of two points that are very close in the phase space of a physical system at one point in time can be seen to diverge later, even to the extent where they are on opposite sides of the figure. This is known colloquially as the Butterfly Effect.

Beyond this, there may be uncertainty about the mathematical models used to model the processes, events, or interactions we are trying to predict. Creating a mathematical model of a complex process means making approximations and simplifications and it can be hard to be sure that these are appropriate. If we choose the wrong equation, use too few terms in our approximations we will have inaccurate answers. But there is a further complication that lurks behind some commonly-used formulas. In many cases, the true equation - the one which accurately models the physics involved - is a non-linear one, and most non-linear equations are not analytically soluble. Sometimes limiting assumptions are made, to create a linear equation which we can solve and plug in actual numerical values. However, these equations are only valid within a limited region of the parameter space, and when scientists or engineers are unmindful of those limitations their predictions can fall apart. Also see the page on turbulence.

To be fair, it is not only scientists who suffer from a blindness about deterministic predictions. The desire to make predictions sometimes trumps reason, and this is a problem on Wall Street and Main Street, to every bit as great a degree as in any laboratory. Nor could climate scientists make a case for the need to clean up our act, unless they are able to make some predictions about what will happen if we do nothing to prevent environmental disasters from ending humanity’s time on planet Earth. But part of what climate scientists are faced with is the need to inform the public that the climate is a complex and often chaotic system which defies any easy prediction through deterministic models, while assuring the public that they are relatively certain we do face an impending environmental crisis, unless some swift action is taken to prevent that outcome.


Michael D. Lemonick’s Scientific American article Climate Heretic - Why can’t we have a civil conversation about climate? illustrates the problems climate scientists face when trying to deal with the issues surrounding predictive and scientific uncertainty, which center on how the story of climate change and the climate science community are presented to the public. The disparity between scientific and public perception has put climate researcher Judith Curry in the center of a controversy, because she is relatively unique among her colleagues by actively engaging climate change skeptics. She has drawn criticism from colleagues by not showing unwavering support for the official consensus, and for sharing her feelings about just how uncertain the future is with the general public. As explained above, even scientists are susceptible to the lure of predictability and the dangers of hidden uncertainties. The Scientific American editors make the following points in summary.

  • If people and governments are going to take serious action to reduce carbon emissions, the time pretty much has to be now, because any delay will make efforts to stave off major changes more difficult and expensive to achieve.
  • In the wake of “Climategate” and attacks on policy makers, the public is more confused than ever about what to think, particularly when it comes to talk of uncertainty in climate science.
  • Climate policy is stalled.The public needs to understand that scientific uncertainty is not the same thing as ignorance, but rather it is a discipline for quantifying what is unknown.
  • Climate scientists need to do a better job of communicating uncertainty to the public and responding to criticism from outsiders.

So it is clear there is a reason for some doubt, or reasons not to trust predictions blindly. We must be clear though, that this does not mean that we should necessarily doubt the likelihood of dire consequences - if no action is taken to clean up the environment further, or to institute sustainable practices, policies, and patterns for growth which allow for a livable future for humans. Even if some of the climate change which could threaten humanity is the result of natural cycles of the Earth and Sun - over which we have no control - it is equally true that our fate hangs in the balance and depends greatly on what human beings do over the next 10-15 years. To the extent that we do nothing consequential during that time; the fate of humanity is potentially sealed, as even heroic changes in the way we live may not save us later, should we wait until then to act.


The topic of uncertainty is the home of questions. And Climate Science is rife with uncertainties. It is healthy to have questions and to ask questions. Both average people and scientists must be willing to ask questions, and to entertain questions, in order for progress to be made. Furthermore; the topic of climate change is perhaps the one subject for which all questions should be allowed or allowable, rather than one which requires a closed consensus - open only to debate among the experts. To the extent that the public participates in the process of climate change; they need to know what scientists are discussing and that there are things non-scientists can and should do to help fix things. We can all do something. But we must continue to ask questions and to respond to people who have questions. If ever there was a topic which requires a multi-disciplinary approach to solve known problems, that topic is Climate Science. This is perhaps the only thing about climate science that is relatively certain.

Specific questions that remain open include

  • How much of an environmental problem is there now?
  • How bad will future environmental crises or catastrophes get?
  • How soon will catastrophic effects be noticeable, or have they already begun?
  • How much good will our efforts accomplish, or how much more do we have to do - before those efforts will make a difference?
  • Can we damage the natural environment beyond it limits, or will Nature find ways to bounce back regardless (though perhaps without humans)?
  • Can we ever hope to restore and repair the natural environment, and make it livable for humans and animals again, if we do damage it beyond its own ability to heal?

Also see

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