̽��ֱ�� of Cambridge - decision

Experiment evaluates the effect of human decisions on climate reconstructions

sc604 — Mon, 07 Jun 2021 09:21:35 +0000

̽��ֱ��experiment, designed and run by researchers from the ̽��ֱ�� of Cambridge, had multiple research groups from around the world use the same raw tree-ring data to reconstruct temperature changes over the past 2,000 years.

While each of the reconstructions clearly showed that recent warming due to anthropogenic climate change is unprecedented in the past two thousand years, there were notable differences in variance, amplitude and sensitivity, which can be attributed to decisions made by the researchers who built the individual reconstructions.

Professor Ulf Büntgen from the ̽��ֱ�� of Cambridge, who led the research, said that the results are “important for transparency and truth – we believe in our data, and we’re being open about the decisions that any climate scientist has to make when building a reconstruction or model.”

To improve the reliability of climate reconstructions, the researchers suggest that teams make multiple reconstructions at once so that they can be seen as an ensemble. ̽��ֱ��results are reported in the journal Nature Communications.

Information from tree rings is the main way that researchers reconstruct past climate conditions at annual resolutions: as distinctive as a fingerprint, the rings formed in trees outside the tropics are annually precise growth layers. Each ring can tell us something about what conditions were like in a particular growing season, and by combining data from many trees of different ages, scientists are able to reconstruct past climate conditions going back hundreds and even thousands of years.

Reconstructions of past climate conditions are useful as they can place current climate conditions or future projections in the context of past natural variability. ̽��ֱ��challenge with a climate reconstruction is that – absent a time machine – there is no way to confirm it is correct.

“While the information contained in tree rings remains constant, humans are the variables: they may use different techniques or choose a different subset of data to build their reconstruction,” said Büntgen, who is based at Cambridge’s Department of Geography, and is also affiliated with the CzechGlobe Centre in Brno, Czech Republic. “With any reconstruction, there’s a question of uncertainty ranges: how certain you are about a certain result. A lot of work has gone into trying to quantify uncertainties in a statistical way, but what hasn’t been studied is the role of decision-making.

“It’s not the case that there is one single truth – every decision we make is subjective to a greater or lesser extent. Scientists aren’t robots, and we don’t want them to be, but it’s important to learn where the decisions are made and how they affect the outcome.”

Büntgen and his colleagues devised an experiment to test how decision-making affects climate reconstructions. They sent raw tree ring data to 15 research groups around the world and asked them to use it to develop the best possible large-scale climate reconstruction for summer temperatures in the Northern hemisphere over past 2000 years.

“Everything else was up to them – it may sound trivial, but this sort of experiment had never been done before,” said Büntgen.

Each of the groups came up with a different reconstruction, based on the decisions they made along the way: the data they chose or the techniques they used. For example, one group may have used instrumental target data from June, July and August, while another may have only used the mean of July and August only.

̽��ֱ��main differences in the reconstructions were those of amplitude in the data: exactly how warm was the Medieval warming period, or how much cooler a particular summer was after a large volcanic eruption.

Büntgen stresses that each of the reconstructions showed the same overall trends: there were periods of warming in the 3^rd century, as well as between the 10^th and 12^th century; they all showed abrupt summer cooling following clusters of large volcanic eruptions in the 6^th, 15^th and 19^th century; and they all showed that the recent warming since the 20^th and 21^st century is unprecedented in the past 2000 years.

“You think if you have the start with the same data, you will end up with the same result, but climate reconstruction doesn’t work like that,” said Büntgen. “All the reconstructions point in the same direction, and none of the results oppose one another, but there are differences, which must be attributed to decision-making.”

So, how will we know whether to trust a particular climate reconstruction in future? In a time where experts are routinely challenged, or dismissed entirely, how can we be sure of what is true? One answer may be to note each point where a decision is made, consider the various options, and produce multiple reconstructions. This would of course mean more work for climate scientists, but it could be a valuable check to acknowledge how decisions affect outcomes.

Another way to make climate reconstructions more robust is for groups to collaborate and view all their reconstructions together, as an ensemble. “In almost any scientific field, you can point to a single study or result that tells you what to hear,” he said. “But when you look at the body of scientific evidence, with all its nuances and uncertainties, you get a clearer overall picture.”

Reference:
Ulf Büntgen et al. ' ̽��ֱ��influence of decision-making in tree ring-based climate reconstructions.’ Nature Communications (2021). DOI: 10.1038/s41467-021-23627-6

̽��ֱ��first double-blind experiment analysing the role of human decision-making in climate reconstructions has found that it can lead to substantially different results.

Scientists aren’t robots, and we don’t want them to be, but it’s important to learn where the decisions are made and how they affect the outcome

Ulf Büntgen

Hrafn Óskarsson

Subfossil trees preserved in Iceland

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̽��ֱ��price of a happy ending can be bad decision-making, say researchers

fpjl2 — Wed, 10 Jun 2015 13:09:51 +0000

New research using high-speed gambling experiments shows that, for most of us, the last experience we’ve had can be the defining one when it comes to taking a decision, coming at the expense of other experiences we’ve accumulated further back in time.

̽��ֱ��study, published today in the journal Proceedings of the Royal Society B, supports the idea that the ‘banker’s fallacy’ - focusing on immediate growth at the expense of longer-term stability that would produce better results - is intuitive in the way many of us make quick decisions.

People's natural inclination towards a ‘happy ending’ means that we often ascribe greater value to experiences than they are worth, say researchers. We end up overvaluing experiences with a final uptick over those that taper at the last minute, despite being of equal or even lesser overall value, and making our next moves on that basis.

Writing in the journal, they use the analogy of a three-course dinner: it has mediocre starter, a fine main, and an excellent dessert. This will be viewed much more favourably - and have much more weight in any future decision - than the inverse: an excellent starter and ending with a mediocre dessert, despite the fact that overall both experiences share equal value.

Researchers say that the computational demand to try and factor in all experiences equally would be vast, so our brain constantly updates its internal ‘logbook’ as we go, with each new experience being condensed and then ranked against the previous few for context. Then, a new experience only has to be judged against the running total.

However, a ‘temporal markdown’ comes into play, meaning that the further back an experience, even if still quite recent, the less weight it carries in the next decision despite its relevant value; the most immediate experiences carry much more weight in decision-making than they should - meaning a recent ‘happy ending’ has a hugely disproportionate influence, say researchers.

They say that a wealth of information and experience “leaks” as a result of this cognitive mechanism, leading to false and delusional beliefs that cause wrong-headed and often short-term decision-making despite historical experience that should convince us of the contrary.

Yet a small number of those tested (nine of the 41 participants) were able to maintain an almost perfect capacity to recall previous experience accurately, without the markdown of past experiences, and make solid long-term decisions as a result - almost as if they were “looking down on time” said lead author Dr Martin Vestergaard.

“Most people we tested fall foul of the ‘banker’s fallacy’, and make poor short-term decisions as a result. This may be because they struggle to access historical experience, or give it the correct value, but we also think they become overly impressed with the moment to moment fluctuation of experiences,” said Vestergaard, from Cambridge ̽��ֱ��’s Department of Physiology, Development and Neuroscience.

“While the majority of participants made decisions based only on very or most recent events, a minority were able to maintain a seemingly perfect ability - at least within the parameters of the experiment - to see time on an equal footing, unconstrained by the myopia inherent in the decision-making of most,” he said.

“ ̽��ֱ��next stages of our research will be to use imaging techniques to look at whether this ability is linked to certain parts of the brain, or perhaps social conditioning such as age and education.”

Vestergaard did question age and occupation for the initial study, and found no correlation between those who are older, or who have a more or less technical occupation, with this panoptical ability to flatten time, but says the current sample size is too small to draw conclusions.

̽��ֱ��experiment involved participants trying to accumulate money by gambling between two sets of gold coins of varying sizes at high reactions times so participants were forced to go on memory and instinct.

Research using gambling techniques shows that even very recent experiences carry a ‘temporal markdown’ so that those more immediate carry disproportionate weight in decision-making, meaning that a ‘happy ending’ can wildly skew what we think we should do next over what experience would tell us.

A minority were able to maintain a seemingly perfect ability - at least within the parameters of the experiment - to see time on an equal footing

Martin Vestergaard

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̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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