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.

15 Comments

  1. The most confident liars, as well as the most pathological, repeat their lies constantly. And as BBC, in this example, demonstrates so well, will openly state the counter evidence to their falsehood.

    Liked by 1 person

  2. Beth, Mark, Hunterson7

    Thank you for your feedback. I felt I needed to return to the subject because my previous articles (particularly the Pakistan one) lacked balance and depth. I hope I have put that right now but I suspect there is still a lot more that I have to learn before I can claim to have a reasonable grasp of the subject.

    Speaking of lack of balance and depth, you may have noticed that the Otto attribution study includes a full section on vulnerabilities. However, nowhere does it mention the effects of deforestation. In fact, the authors seemed much more interested in bemoaning the legacy of British colonialism in the form of outdated river management. Here is how they summarised:

    “In addition to the climatic hazard, the factors driving the devastating impacts for the 33 million people affected in Pakistan include the proximity of human settlements, infrastructure, and agricultural land to flood plains, limited ex-ante risk reduction capacity, an outdated river management system, underlying vulnerabilities driven by poverty, socioeconomic factors that disadvantage women, and ongoing political and economic instability.”

    In other words, anything but the elephant in the room.

    Liked by 1 person

  3. Once again the Clausius-Clapeyron effect is resorted to with the additional information that for every one degree Celsius increase the air temperature the air can absorb an additional 7% water vapour. It is argued that climate change will cause warmed air to absorb more water vapour and this in some undefined way causes more precipitation and extreme weather effects.

    This I have never understood. If temperature rise causes the atmosphere to absorb more water I would have thought that the increased capacity would have resulted in the atmosphere keeping more of its water rather than losing it to precipitation. It is true that if warmer air is cooled it may reach saturation and cause more precipitation. However if warmer air, when cooled, releases more precipitation, then summers should be associated with higher rainfalls than winters. Days with greater precipitation than nights. I don’t believe these are recognised relationships.

    I also half remember experiencing oppressively hot weather in India and being told that this was a result of a delayed Monsoon. This doesn’t seem to fit with the idea that hotter temperatures are associated with exceptional rainfall events.

    Someone with more physics and/or meteorological knowledge, please put me right.

    Like

  4. Alan,

    I believe it is a matter of water cycle amplification at the global scale. The article below sort of explains it and cites an interesting paper that suggests that measuring changes in oceanic salinity in different regions (the Salinity Contrast Index) could be a good way of tracking the changing patterns of evaporation and precipitation:

    https://usys.ethz.ch/en/news-events/news/archive/2020/09/new-study-of-ocean-salinity-finds-substantial-amplification-of-the-global-water-cycle.html#:~:text=Theory%20and%20models%20suggest%20that,precipitation%20is%20increasing%20as%20well.

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  5. John – from your link above –
    ““We show that the 0-​2000m salinity pattern has amplified by 1.6% and that at the surface by 7.5%. We also show that this increase is due to human influence, and that this anthropogenic signal has exceeded the natural background variability.””

    where do you find these papers?

    ps – “This study is a significant advance in the field”, said Michael Mann.

    it does sound a useful addition to our knowledge, but it’s used as expected.

    Like

  6. Interesting John, but this is not the way mention of the Clausius-Clapeyron effect is being used by most advocates of climate change. This makes the simple assumption that increased temperatures allows more water vapour to be held and thus (wrongly?) more rainfall is possible. Whereas the effect could also be interpreted to be that the increased temperatures at places where rainfall occurs means that more water vapour can be retained and so less rainfall will occur.

    If water cycle amplification is occurring, then some locations should be experiencing significantly more rainfall. One such place should be north-west Europe affected by successions of weather fronts that focus rainfall. With a significant increase in mid Atlantic salinity there should be an equally significant increase in rainfall amounts in warm periods. Can’t say I’ve noticed, especially this year.

    Isn’t it wonderful how the changes in salinity contrasts fit exactly the (unspecified) climate models and so prove human influences are to blame.

    Like

  7. ITV news last night had an item about droughts in Africa and the effect on the elephants. Very sad, but of course blamed on ‘climate change’.
    Two questions in my mind, firstly it was the worst drought for 40 years – so what caused the drought 40 years ago?
    Second, I thought ‘climate change’ caused floods! Make up your minds!

    Like

  8. Of course it’s much more likely that the drought is caused by a rare triple La nina and movement of the ITCZ.
    But ‘climate change’ is more newsworthy!

    Like

  9. Dfhunter,

    I think as sceptics it is important that we acknowledge the science for what it is. I have no issue with accepting that the Clausius-Clapeyron effect will lead to more intense precipitation, all other things being equal. And I accept that Otto and her colleagues were able to find a model within their ensemble that said AGW would have intensified the precipitation by 30% ‘for the large region’ (let’s leave my qualms regarding structural uncertainties and the statistical handling of ensemble outputs for another day). What I object to, however, is the portrayal that this effect, as attributed to AGW, could be used to fully explain what we saw in Pakistan this year. The actual excess rainfall was far beyond what Clausius-Clapeyron is able to explain. So when Otto said that the “fingerprints” of global warming could be clearly seen in the Pakistan floods, she is being somewhat disingenuous. Yes, the signs of AGW are there, but they have to be present to the extent that we can be sure its removal would bring the necessary relief to the people of Pakistan – because that is what the politicians are saying is at stake.

    I think ISV is the real issue as far as the science of monsoons is concerned, and the science that says that achieving net zero will address the ISV problem is far from settled. The best effort I’ve seen to date at putting the recent Pakistan ISV down to climate change is that offered by Fahad Saeed, one of the Otto study’s co-authors:

    “But other factors had the signature of climate change, Saeed said. A nasty heat wave in the region earlier in the summer — which was made 30 times more likely because of climate change — increased the differential between land and water temperatures. That differential determines how much moisture goes from the ocean to the monsoon and means more of it drops. And climate change seemed to slightly change the jet stream, storm tracks and where low pressure sits, bringing more rainfall for southern provinces than they usually get, Saeed said.”

    I think attributing slight shifts in jet streams, and positions of low pressure, down to AGW is a great deal more speculative than the Clausius-Clapeyron effect. Also, notice that he said “the differential between land and water temperatures…determines how much moisture goes from the ocean to the monsoon”, not the Clausius-Clapeyron effect.

    https://www.outlookindia.com/international/pakistan-floods-study-points-at-warming-manmade-reasons-that-worsened-the-deadly-deluge-news-223736

    Liked by 1 person

  10. Alan,

    I guess the point is that the driver for transferring water into the atmosphere (evaporation) is simpler to model than the drivers for its return. The reservoir in the sky will not return to ground until something precipitates it, and when this happens both the size of the reservoir and the mechanics of the precipitation will determine the intensity of rainfall. I think that the former rather than the latter receives the attention since it is easier to blame it on AGW.

    Like

  11. John,

    I too saw that report and I found it very sad and worrying. As always, I was also left unsure, given the long-term history of drought in the area and my lack of understanding of how natural variabilities play out. I guess all that really matters now is that my incertitude can be readily dismissed as ‘denial’. 😦

    Like

  12. H/T to Mark Hodgson for drawing my attention to the BBC’s latest attempt to cover the flooding in Nigeria. Although he posted his comment on another of my articles (A Closer Look at Pakistan’s Flooding), I think I have a point to make in the context of this thread.

    Here is what the BBC has to say about Nigeria’s rainfall:

    “With climate change expected to lead to even more rainfall in Nigeria…”

    https://www.bbc.co.uk/news/world-africa-63411446

    Here is what the World Bank has to say about Nigeria’s rainfall:

    “Observed rainfall patterns indicate that rainfall for the country over the past century declined by approximately 80 centimeters (cm).”

    Until the BBC starts to get its basic facts right, I will continue to read their environmental articles with increasing disdain. As with Pakistan, the real issue is one of variability. According to the World Bank:

    “In Nigeria, precipitation trends have a high degree of variability and the last several decades have observed a decrease in the predictability for seasonal rains across the country. Overall, rainfall has decreased incrementally across the country since the 1960s…The annual variation of rainfall, particularly in the northern parts, is large. This has resulted in climatic hazards, especially floods and droughts.”

    As with Pakistan, the challenge is to pin the increase in variability on climate change. Back to our BBC correspondent:

    “But in the past, when the floodwaters subsided, residents often returned to the sodden homes – a cycle that continues every year.”

    Like

  13. I forgot to provide a link to the World Bank report:

    Click to access 15918-WB_Nigeria%20Country%20Profile-WEB.pdf

    Also, to be fair to the BBC, I should point out that the CMIP5 ensemble projection is for an increase in annual precipitation for Nigeria, in stark contradiction to the global warming induced trend for the last 60 years. The BBC is going with the models, whilst I, as an empirical sceptic, prefer to go with the data.

    Liked by 1 person

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