On Judgements, Speculation and Causation

In two recent articles, I explored how empirical scepticism can help in understanding the significance of extreme flooding events such as those recently experienced in Kentucky and Pakistan. In particular, I employed what I see as two of the central pillars of empirical scepticism:

  • To follow data and distrust judgement and speculation
  • To interrogate causal arguments

I discussed these strategies at length in my recent deconstruction of scepticism, but for the purposes of today, I need only extract the following passages. Firstly, with regard to following the data:

“Climate change may have its basis in science and data, but this basis has long since been overtaken by a plethora of theorizing and narrative that sometimes appears to have taken on a life of its own.”

And secondly, with regard to interrogating causal arguments:

“Basically, we are told that the event was virtually impossible without climate change, but very little is said regarding whether climate change on its own was enough…This problem of oversimplification is even more worrying once one starts to examine consequential damages whilst failing to take into account man-made failings such as those that exacerbate the impacts of floods and forest fires.”

These considerations led me to observe that a simplistic narrative was often evident in the reporting of flooding events and that the underlying science was often glossed over. Indeed, it was difficult to discern a strong scientific basis for the narratives if one concentrated purely upon the longer-term history of extreme precipitation events within the areas concerned. Furthermore, the simplistic narratives would often downplay or even completely overlook highly significant causative factors such as the massive deforestation of the Pakistani watershed.

I have chosen to return to this subject, however, as my previous articles themselves somewhat glossed over the underlying science. In particular, I failed to acknowledge the key role played by the recent intra-seasonal variability (ISV) observed in a number of monsoon regions, nor did I discuss the evidence cited for the link between global warming and an increase in extreme 5-day precipitation events.

Following the data

To follow the narrative and theorising presented by the media and politicians is easy enough because both are simple and consistent. Clarity, of course, is the main purpose since it enables the ‘correct’ thinking without introducing any troubling detail. So we have this with regard to the Pakistani floods:

“A monsoon on steroids”

UN Secretary-General António Guterres

“The rain was off the charts”

Pakistan’s climate change minister, Sherry Rehman

“Literally, one-third of Pakistan is underwater right now, which has exceeded every boundary, every norm we’ve seen in the past.”

Sherry Rehman, again

“The disaster has also highlighted the stark disparity between countries that are the largest contributors towards climate change and countries that bear the brunt of its impact. Pakistan produces less than 1% of global greenhouse gas emissions but its geography makes it extremely vulnerable to climate change.”

Pumza Fihlani, BBC News

That last quote is particularly relevant since it speaks to ‘climate injustice’, a particularly strong narrative used by those who look to receive massive financial compensation from the West, whilst playing down the extent to which their own governmental negligence has contributed to the disaster. This aspect of the narrative requires a clear and unequivocal science linking the floods to anthropogenic contributions to global warming. Consequently, you will find the science portrayed in very stark terms that leave no room for doubt:

“This year the country has been hit by the largest amount of rainfall in three decades – and it’s an irrefutable scientific fact of an overheating world that a warmer atmosphere holds more water, making downpours far more intense.”

Matt McGrath, BBC News

“The science linking climate change and more intense monsoons is quite simple. Global warming is making air and sea temperatures rise, leading to more evaporation. Warmer air can hold more moisture, making monsoon rainfall more intense.”

Georgina Rannard, BBC News

All of which would lead one to expect that a graph of Pakistan’s precipitation history would paint a picture of an increasingly volatile annual rainfall record, correlating with increasing temperatures. And yet it doesn’t:

Following this data seems to suggest that the simple narrative and theorizing must be missing out vital details. And indeed vital detail is missing, because it is only when one also considers intra-seasonal variability that a picture emerges which seems to reflect recently reported experience. Written with respect to neighbouring India, we have:

“Extremely heavy rainfall events over the last two monsoon periods may have led to a perception that India’s summer monsoon rainfall has increased, but it has in fact decreased by 6% over the past 60 years, say Indian government and international climate change assessments. The summer monsoon in 2021, though ‘normal’, was marked by a number of such localised extreme rainfall events and displayed variability in patterns of rainfall dispersal, both of which will only increase in future, these assessments warn.”

So, in order to understand what is going on, one has to focus upon the trends in intra-seasonal variability and how extreme precipitation events have featured in Pakistan’s rainfall history. Unfortunately, this is not as straightforward as one might hope, since Pakistan has a notoriously volatile rainfall history. It is one of those areas where an empirical sceptic would be particularly reluctant to theorize. Not so the attribution scientists, however.

Interrogating the causal arguments

Given the vulnerability of people affected, there is an understandable desire to explain recent events in terms of what we know about the climatology of the Indian subcontinent. However, the problem is that it is far from obvious that the recent ISV can be explained in terms of simple global thermodynamics, since regional atmospheric dynamics appear to be the more germane and these heavily reflect natural variabilities. According to a paper recently published in Nature:

“Accurate prediction of global land monsoon rainfall on a sub-seasonal (2–8 weeks) time scale has become a worldwide demand. Current forecasts of weekly-mean rainfall in most monsoon regions, however, have limited skills beyond two weeks, calling for a more profound understanding of monsoon intraseasonal variability (ISV)…The leading modes of HFISVs in Northern Hemisphere (NH) monsoons primarily originate from different convectively coupled equatorial waves, while from mid-latitude wave trains for Southern Hemisphere (SH) monsoons and East Asian (EA) monsoon. The Madden-Julian Oscillation (MJO) directly regulates LFISVs in Asian-Australian monsoon and affects American and African monsoons by exciting Kelvin waves and mid-latitude teleconnections. During the past four decades, the HF (LF) ISVs have considerably intensified over Asian (Asian-Australian) monsoon but weakened over American (SAM) monsoon. Sub-seasonal to seasonal (S2S) prediction models exhibit higher sub-seasonal prediction skills over AU, SA, and SAM monsoons that have larger LFISV contributions than other monsoons. These results suggest an urgent need to improve the simulation of convectively coupled equatorial waves and two-way interactions between regional monsoon ISVs and mid-latitude processes and between MJO and regional monsoons, especially under the global warming scenarios.

The fact is, whatever the attribution scientists say, it is currently beyond the skill of climate models to demonstrate how the regional ISV resulting from shifts in such atmospheric, dynamic coupling can be attributed to global changes in temperature. This problem was recognised by the recent Pakistani floods attribution study led by Friederike Otto:

“Many of the available state-of-the-art climate models struggle to simulate these rainfall characteristics. Those that pass our evaluation test generally show a much smaller change in likelihood and intensity of extreme rainfall than the trend we found in the observations. This discrepancy suggests that long-term variability, or processes that our evaluation may not capture, can play an important role, rendering it infeasible to quantify the overall role of human-induced climate change.”

That stopped the authors from making a confident attribution when the floods were viewed as a 60-day event. They were, however, still confident when it came to 5-day precipitation events:

“Looking at the future, for a climate 2 °C warmer than in preindustrial times, models suggest that rainfall intensity will significantly increase further, for the 5-day event, while the uncertainty remains very large for the 60-day monsoon rainfall.”

So where does the confidence come from when it comes to predicting how 5-day precipitation events are likely to change in both likelihood and severity under the influence of anthropogenic global warming? An explanation is given by the World Bank’s  Climate Change Knowledge Portal

“Extremes only occur in a conjunction of several preconditions. For example, extreme rainfall requires maximized (“potential”) moisture transport into the region, high temperatures (or large temperature gradients) and significant instability of the atmosphere. An alignment of these “ingredients” is relatively rare. Under climate change, however, some of these conditions might see a systematic increase in occurrence, which is particularly true for temperatures across the globe. If that one condition – higher temperatures – is more often fulfilled, then the chance for a combined occurrence can also increase. Warmer temperatures are especially important for precipitation because the Clausius-Clapeyron-Relationship dictates that for every 1ºC of increased air temperature, that air’s potential to carry moisture increases by 7%. Thus, the warmer the air, the much more moisture it “can” carry, and therefore if rain were to form, much more water could be tapped into.”

This is basically a return to the simplistic explanation offered at the head of this article – it’s all down to the Clausius-Clapeyron effect. All other things being equal, an increase in global temperature will lead to a higher incidence of extreme precipitation events of short duration, and any climate model will predict this if one is prepared to simplify matters by conditioning upon the remaining potential factors. There is nothing wrong in doing this but one should not immediately jump to the conclusion that the causation, thereby isolated, is the strongest of those in play. Increased global temperatures may be necessary to have experienced the recent Pakistani floods but they would not have been sufficient, and it may very well be that one of the other factors (e.g. instability of the atmosphere resulting from coupled natural cycles) was even more necessary and influential. Put another way, I am not sure that one can be confident regarding the attribution of 5-day precipitation events whilst remaining unconfident with respect to 60-day events, since I suspect that they are not entirely unrelated phenomena. Until regional climate models are developed sufficiently to support the asking of all relevant counterfactual questions, I fear this point will remain moot.

But floods are not just about rainfall

So far, I have concentrated upon the causation of extreme precipitation events, but flooding events are not entirely down to the level of rainfall. As with all risk, both threats and vulnerabilities have to be taken into account, and there are human factors that contribute to vulnerability. In the case of the Pakistani flooding these are many, but they have rarely featured prominently in the reporting. Even so, there was this to be found in the LA Times regarding the impact of Pakistan’s deforestation in the northern watershed:

“Deforestation played a tremendous role in aggravating the floods,” said Ghulam Akbar, director of the Pakistan Wetlands Program, an environment protection group funded by the United Nations and other international organizations. “Had there been good forests, as we used to have 25 years back, the impact of flooding would have been much less.”

“It was like doomsday,” said Fazl Raheem, a spry 70-year-old who lost his home, a guesthouse, his belongings and his poultry farm in the floods. Standing alongside the Chail River, he points to remnants of his property: a few jagged pieces of rebar jutting from the water and a mound of red bricks on the shore. “There wouldn’t be this amount of destruction if the trees were still here,” he said.

“The Indus would flood before, but the forests would slow down the water pressure,” Mohammed said. “But with the forests gone, the water flowed freely and destroyed our houses, our fields, our roads, everything. “Everyone was angry when the trees were cut, but what can a poor man do?”

Such assertions are all very well, but quantifying the impact is not so easy:

“The sheer scale of the current floods in Pakistan makes it difficult to talk about human responsibility, admits Saleem Ullah who works with the United Nations Development Program UNDP. ‘The intensity of the disaster was so much that the human role [e.g. the deforestation] would be not more than something like twenty, thirty percent’.”

The figure of twenty to thirty percent may seem modest but it has to be compared with the impact attributed to anthropogenic global warming in the recent Otto study:

“Due to these large uncertainties as well as the lack of structural diversity in the remaining models we refrain from quantifying the role of anthropogenic climate change. For the 60-day and the 5-day extreme rainfall, the majority of models do show an increase in likelihood (right panels in Figs. 13 & 14) and intensity (left panels in Figs. 13 & 14) that is potentially very large, with best estimates of a change in intensity of up to 30% for the large region (Fig. 13(left)) and up to 50% for the small region (Fig. 14(left)), respectively.”

So here we have a heavily caveated statement that alludes to ‘potentially’ very large changes in intensity that are, even so, in the same ballpark as those attributed to deforestation. And yet it is the AGW that is getting all of the headlines.

From scepticism to cynicism

If there is one message to be taken away from all of this it is that it is not easy to draw definitive conclusions based upon an extreme flooding event when the region concerned is notorious for extreme precipitation events and manifold self-inflicted vulnerabilities. Not only is the attribution of the precipitation event to global warming problematic (due to structural uncertainties in the models used), the attribution of the resulting flooding to the precipitation event can be blurred by hugely significant human factors. There is plenty for the empirical sceptic to be wary of, despite the confidence with which the political and scientific narratives are delivered.

When it comes to political commentary on flooding events, judgement can be found in abundance, and speculation based upon a simple causitive argument is an essential element that leaves the climate justice agenda front and centre. However, it is not only the empirical sceptic that remains to be convinced. I’ll leave you with the opinions of a resident from one of the worst affected areas in the Pakistani flooding:

“Our irrigation departments are not in touch with locals, our environmental protection agencies are not in touch with locals, and the Balochistan disaster management authority is currently the most useless institution in the country. And while climate change is important in water policy and government discourse, I think the federal and provincial governments place a lot of blame on climate change and use it as a scapegoat for their own incompetence.

I think there is a case to be answered there.

via Climate Scepticism


October 25, 2022 at 05:52AM

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