Climate Change - Putting Scientific Debates in Context
A climate scientist will be giving a lecture at UCLA on May 3rd. Her name is Dr. Amy Clement, a professor at the University of Miami Rosenstiel School of Marine and Atmospheric Science. The lecture has been titled, "The Real Debate of Climate Science: Does the Ocean Matter for Climate?"
The summary for the upcoming lecture reads, "The media sometimes portrays the question of the human role in climate as a central debate in Climate Science, despite the strong scientific consensus that human emissions of greenhouse gases are affecting climate." This statement has been interpreted by some as meaning there is currently a debate among climate scientists as to whether or not humans are playing a role in changing the planet's climate.
This isn't what the statement says. Instead, it indicates that though it is clearly evident that human beings are having a discernible impact on global climate, with profound changes already underway, there are ongoing debates among academics regarding how we can gauge the severity of our impact on global climate and understand the consequences of the changes we're inducing.
To be able to answer these questions, we must first understand the extent naturally-driven processes might be having on climate change. Clearly over time there have been natural processes that have produced climate changes. No climate scientist debates this, and I explain this point in my blog, "Climate Change - A response to Dr. Linden's Letter to the POTUS".
Research attempting to determine the workings and influence of naturally-driven processes affecting climate, and the debates therein, should not be misconstrued as suggesting the current global warming trend is primarily naturally driven; the academic consensus is that it is not.
It is an unfortunate reality, but the public most often gets its information from poorly-informed exoheretics who cherry pick and misinterpret debates among academics, then make claims that simply aren't accurate.
This is exacerbated by the fact that most academic papers are not easily accessible to the public, and even if all of them were, they remain notoriously difficult for the average layperson (such as myself) to absorb. This is because they're written for an audience of academic peers who are assumed to already know the highly-technical jargon, and statistical information contained within.
I have the benefit of having free access to most academic papers. But most times I must read a paper more than once to absorb its information. This often entails a lot of research to understand what is meant by a single term or sentence in context of a bigger picture experts in the field already comprehend. As mentioned, papers are written for academic peers who are assumed to already have a robust background specific to the science and its latest findings.
Understanding natural variability in context of anthropogenically-accelerated climate change is an important factor to gauge, because that knowledge will greatly enhance both our predictive power, and our ability to intelligently respond to the global warming causing climate change.
For some, that last sentence might seem possibly redundant; "global warming causing climate change". Many exhoheretics claim the use of the term "global warming" has been supplanted in recent years with the term "climate change" as if some mistake were being covered up regarding climate data. This is a gross misunderstanding of the terms.
The fact is, carbon dioxide has been linked to affecting global temperatures since the 19th century (Arrhesius, 1896). This was later confirmed in papers published in the 1930s, and 1940s (ie. Callendar, 1938). By the mid-1950s, carbon dioxide's influence on global temperatures had become known as the Carbon Dioxide Theory of Climate Change (Plass, 1955). In the years that followed, that had shortened to "climate change", and has been a term used in academic circles for decades.
The term "global warming" simply describes the carbon-dioxide-driven retention of heat (global warming) by the atmosphere that is causing climate change. It really is that simple.
Understanding the extent to which natural variability has on climate change, first requires an understanding of the physical mechanisms that drive such variability. Of particular importance, is understanding the natural variation in the North Atlantic sea surface temperatures (SSTs) over time. This variability is known as the Atlantic Multidecadal Oscillation (AMO), and it's my guess that this will be a primary topic in the upcoming lecture hosted at UCLA.
An SST anomaly is any patch of surface water in the ocean whose temperature is either higher or lower than what is 'normal' for a particular region at a particular time during the year. Many anomalies are simply transient events, not part of a specific pattern or trend. Others are more meaningful. SST maps usually show anomalies as either yellow/orange/red areas (higher than normal temperature), or purple/blue areas (lower than normal temperature). In the North Atlantic, there are significant anomalies, and they oscillate over time, such that what was once a colder-than-average patch of surface water, later becomes warmer than average.
Generally speaking, the current anomalies of the North Atlantic (0 to 80 degrees north latitude) are a warmer-than-average stretch of water extending along the United States east coast & along the path of the Gulf Stream, as well as a colder-than-average patch of water in the North Atlantic subpolar gyre region (please see Fig. 1).
The AMO is important because it affects hurricane development and intensity (Ting et al., 2009). It also affects precipitation patterns & intensity, as well as changes in fish populations (Frajka-Williams et al, 2017) which in turn have effects on other niches either directly or indirectly dependent on those populations. Changes in fish populations can also affect the economic viability of fishing industries of countries around the North Atlantic basin.
Temperature oscillations have become more extreme in post-industrial times, particularly since the mid-20th century. This has scientists alarmed given the fact the AMO affects weather and climate in the North Atlantic basin, which in turn impacts global weather and climate patterns.
Ocean water circulates on a global scale; after all, it's a global ocean (with several different regional names). Surface water is driven by wind, veering slightly to the right of wind direction in the northern hemisphere due drag and the Coriolis effect. But deep water is driven by water density differences.
Water density is most affected by two things: one is temperature, and the other is salinity. Insofar as temperature is concerned, warmer water is less dense than relatively cooler water, with maximum density being reach at a cold 4 degrees Celsius. Temperature most affects water density. A secondary, yet substantial influence on ocean-water density is salinity. Higher salinity causes higher density, and vice versa. Below is a generalized picture of the global ocean conveyor circulation; driven by both wind and water density differences (please see Fig. 2).
The North Atlantic portion of the global ocean circulation conveyor system is circled in yellow (please see Fig. 3). That portion of the global conveyor is called the Atlantic Meridional Overturning Circulation (AMOC or sometimes simply MOC). A key feature of the AMOC is the warm equatorial surface water it transports northward towards Europe. About 100 million cubic meters of water flows northward every second, carrying with it about 300 million kilowatt hours of heat energy. That heat is released to the atmosphere at those higher latitudes, and this affects regional climate. This northward arm of warm surface water is called the Gulf Stream, and it's a critical part of the AMOC.
As heat from the Gulf Stream is released to the atmosphere, the water cools, thereby increasing the surface waters' density and causing it to sink. This sinking action occurs in the region between Iceland, Greenland, and Norway to the tune of about 17 million cubic meters of water per second. [UPDATE: A recent study has shown it to be between Greenland, and Scotland (Lozier et al., 2019).] Not only does this take dissolved carbon dioxide from the atmosphere down with it (a carbon sink), it acts to push the entire conveyor system with the Gulf Stream being the tail end of it.
I want to reiterate that the sinking water pushes the conveyor (including the Gulf Stream). Popular YouTube channels like Kurzgesagt, with millions of subscribers teach this wrong. Claiming the sinking water of the AMOC "pulls" the Gulf Stream northward. It is not pulled. Water has no tensile strength, and therefore cannot be pulled without defying the laws of physics. The water is being pushed by the sinking action near Greenland/Iceland/Norway.
To understand this, we must look at the entire conveyor, not just the AMOC and its Gulf Stream. I've made this diagram to illustrate the push in simple terms:
Once the water sinks, it migrates southward and produces the global conveyor.
While the AMO is experiencing more extreme variability, the AMOC is experiencing a record slow-down (Caesare et al., 2018). The conveyor system is stalling because surface waters in the North Atlantic are warming and becoming too light to sink. High resolution climate model simulations show a strong correlation between increasing carbon dioxide and a weakening AMOC (Caesar et al., 2018).
There is no debate over whether or not global warming is causing the stall. The debate is over whether or not this is caused by the warming of the polar ocean by meltwater and warm polar air, or if it's due to the tropical portions of the AMOC getting too warm and being unable to cool enough to sink once arriving in the North Atlantic. Either way, both models require global warming to occur. The effect remains the same; water is no longer sinking at the rate it once did, and if it doesn't sink at the same rate, it doesn't push with the same force, and the entire thermohaline circulation gets thrown out of wack.
12,000 years ago, Earth's climate was considerably cooler. Though debate is ongoing as to what triggered that colder climate, one hypothesis suggests the culprit was a slowdown of the AMOC (Eisenman et al., 2009). However, no consensus as to what triggered the colder conditions back then has been reached (Broecker, 2006), and the hypothesis that it was a slowdown of the AMOC continue to be debated. At any rate, this might be why some exoheretics say we can expect a "moderate ice age"; a claim made by a member of the American Meteorological Society who included me in his group email.
A little known fact, however, is that we're already in an ice age, and have been for the past 2.58 million years. It's called the Modern Ice Age, or Quaternary Glaciation. Ice ages invariably last millions of years, and are global in scale, and therefore are never "moderate".
What the individual might have meant, was 'glacial period'. Ice ages are punctuated by glacial and interglacial periods; cold and warm stretches of time within an ice age. We're in an interglacial period now, and have been warming into it for over 10,000 years. Problem is, that warming has accelerated quite blatantly since the Industrial Revolution, and even more so since the mid-20th century, coinciding with increases in atmospheric carbon dioxide with an isotopic anthropogenic fingerprint written all over it. As far as a slowdown of the AMOC leading to a glacial period.. I've yet to see any peer-reviewed papers suggesting this outcome, though perhaps I'm wrong about this.
Regardless, one thing we can all be certain of, is that a continued slowdown of the AMOC will dramatically alter climate conditions; at least around the North Atlantic basin. And it's expected to slow further with continued global warming (Caesar et al., 2018).
So far, a colder due to a slow down in the AMOC doesn't seem to be the path we're on. Low sub-polar sea surface temperatures have been shown to favor air pressure distribution regimes that act to channel warm air northward into Europe (Ibid.). The 2015 European heat wave has been linked to the cold patch of surface water in the North Atlantic (Duchez, 2016). (Because I'm trying to get this blog post up this evening, I haven't had time to search for papers linking anomalous SSTs to the cold weather in the New England states, but I suspect such papers exist.)
Warming summers in Europe aren't all. A slow down of the AMOC coincides with changing patterns of sea surface temperatures which have been linked to above-average sea level rise along the U.S. east coast (Sallenger et al., 2012) and (Ezer, 2015), as well as harsher drought conditions across the Sahel (Defrance, 2017).
If I'm not mistaken, the UK has experienced an unusually high-frequency of heat waves in recent years, and I'd be curious to know if any of them have been linked to sea surface temperature anomalies in the North Atlantic. Certainly increased storminess is a possibility; a difficult-to-avoid outcome from injecting heat and moisture into a region.
The observed variability of North Atlantic sea surface temperatures (the AMO) has two notable features: 1) a cold patch of surface water in the subpolar gyre region, and 2) extreme warming of surface water along the U.S. east coast and Gulf Stream (please see Figure 4).
The cold patch in the North Atlantic has been linked to the weakening AMOC since the mid-20th century, and particularly since 1970 (Rahmstorf, 2015). The cold patch also shows up in computer simulations wherein the AMOC is slowed down (Olson et al., 2017).
Rahmstorf (2015) links the slowdown to global-warming-caused melting of the Greenland ice sheet. He notes that the slowdown since 1975 is unprecedented in the past 1,000 years as evidenced from the AMOC index derived from ocean measurements, coral-based proxies (nitrogen-15), hemispheric temperature differences, and sea surface temperatures.
The publicly available 2018 peer-reviewed paper, "Observed Fingerprint of a weakening Atlantic Ocean overturning circulation", suggests the observed cold patch in the North Atlantic sub-polar gyre region is "due to reduced heat transport, and warming in the Gulf Stream region due to a northward shift of the Gulf Stream as a result of pronounced weakening of the AMOC since the mid-20th century" (Ibid.).
This paper has improved the AMO-index used by climate scientists such as Dr. Clement to show that the AMOC slowdown appears to be at a record low, which is claimed to be consistent with record-low sea surface temperatures sub-polar North Atlantic.
What this paper, Dr. Clement's papers, and nearly all peer-reviewed papers in climate science consistently state, is that there remains a need to better understand to what extent natural variations in the AMO, and the AMOC may be having on the observed changes we're witnessing.
This often gets misinterpreted by exoheretics as meaning they don't know enough to be making claims that climate change due to global warming is anthropogenically driven. Nothing could be farther from the truth. Papers consistently point towards the anthropogenic influence as the primary culprit with extensive evidenced-back research.
The issue is with the fact that there is still a dire need to fully understand natural factors' contributions, because without that knowledge, predictive capabilities go out the window. That's the part the media ignores (I suspect); as though mentioning this need to understand natural variability and influence might somehow undermine the consensus that the accelerated rate of global warming is human induced.
This just exposes media ignorance, and makes media-interpreted climate science seem dishonest. The science, by nature is never dishonest. Peer-review prevents it. Climate scientists consistently make the point in their papers that there is a need to determine if there is a contribution by natural processes, and if so, the scope of those processes' influence.
Consider such papers as those by Bakker et al. (2017), or Laepple and Huybers (2014), which look at past climate changes in the prehistoric past to get a better understanding of natural influencers. (I talk about naturally-induced climate change in my blog post, "Climate Change - A Response to Dr. Lindzen's Letter to the POTUS".) Both papers speak in context, yet both papers have been cherry picked and used as climate skeptic ammunition in non-academic blogospheres.
I'll be the first to admit, peer-reviewed papers are not easy reading. At least not for me. Much of the laity who claim to have read the papers, actually only read their abstracts (wrongly), and their conclusions (also wrongly), and then write entire blogs, articles, or forum posts about what they think the papers said; oftentimes not citing the papers they claim to understand.
Take for instance Caesar et al. (2018). It discusses the slowdown of the AMOC and its relation to the AMO. It shows a strong correlation in high-resolution climate models between increasing atmospheric carbon dioxide and the AMOC slowdown. It suggests that "...the AMOC decline since the 1950s is very likely to be largely anthropogenic...", and follows up by saying "...long-term natural variations cannot be ruled out entirely".
A climate scientist will read those statements and see them for what they say; that the changes we see are very likely human induced, but we need to know to what extent natural variations have in the long term. "...largely anthropogenic" doesn't mean entirely anthropogenic. It means the primary driver is anthropogenic, but it rightly suggests there may be natural contributions as well. Hence the reason they cannot be "entirely" ruled out.
An ideologue might interpret the Caesar et al. paper as saying, "...we think it could be human induced, but it might not be, but it sure seems like it is. Actually, to be honest, we just don't know for sure. In fact, we don't know anything really. We need to get better day jobs."
See the difference?
I suspect Dr. Clement will discuss all this in her lecture at UCLA this week.
Another thing the laity tends to get confused about, is when climate research presents an observation without an explanation discussing how or why exactly the observation reported exists. They think presenting an observation without explanation is either dishonest or superfluous. This exposes their naivete. Let's take the recent paper by Caesar et al. (2018) again as an example:
The paper discusses a strong correlation between increasing atmospheric carbon dioxide and the slowdown of the AMOC. However it doesn't explain why this correlation exists in the high-resolution climate model simulations they ran. This doesn't mean the observation is without merit. In science, observations must first be made before research can be conducted to explain them. Patterns and correlations between things are observed, recorded, and presented before they're explained. That's how things generally work, though in particle physics things are often explained before they're observed. But that's another story.
At any rate, understanding natural influence on climate is just as important as understanding anthropogenic influence, despite the consensus that the anthropogenic influence is the primary driver. We need to understand both if we're to have any predictive power. Especially since there exists a bit of irony in the fact that increased heat leads to increased volatility and therefore decreased predictability.
There is also a need to understand the primary physical mechanisms driving the AMO; a key focus of Dr. Clement's research as far as I'm aware. I suspect Dr. Clement will discuss this need to understand the physical mechanisms driving the AMO in her lecture. Especially since it is widely assumed outside of academic circles that it's driving mechanisms are fully understood. I think even Wikipedia makes this claim, though that site updates every second, so I could be wrong now.
Contrary to popular belief, there is no scientific consensus as to what drives the AMO. Generally speaking, there are two competing ideas: 1) The AMO results from ocean circulation displacing warmer tropical currents northward in the Atlantic basin. Or, 2) Atmospheric circulation delivers the heat that warms the northern Atlantic surface waters. Conventional wisdom has assumed option 1. Dr. Clement's work suggests option 2.
This debate in climate science is real, and important, but certainly has nothing to do with exoheretic claims that such a debate "proves" climate scientists don't know enough to be making claims about climate change. Debates in science don't suggest confusion among scientists. Again, such an assumption only serves to expose exoheretic naivete.
Also, while there may be debate over the societal impacts changes in climate will have, there remains one thing that seems to be eluding most folks; and that is that people live where the climate supports them. Any change in climate will be catastrophic because people will be left without a climatic support base. People can't pick up and move to more hospitable climates as easily as it might seem on paper. National borders, family, jobs, and a myriad of other factors have tremedous limiting power on our ability to relocate to more hospitable latitudes.
Some may think technology will help them adapt, but technology in the grand scheme of things is a crutch, and won't do much good in a world where energy demands are ever increasing. For example, our need to stay comfortable during hot summer months has and will continue to lead to widespread power outtages. And as far as "green energy" goes, there is no such animal. That will require a blog post of its own to explain, but logic states that if we want to be more efficient with our use of energy, we ought to first start by using less of it. More efficient tech is a bandaid that gets ripped off by Jevons paradox over time.
If we look at human history, we'll see that climate change has caused cultures to go extinct (ie. Anasazi, Mohenjo Daro, Sumeria, etc.), not to mention the fact that climate changes in the fossil record are accompanied by mass extinctions. These aren't coincidental.
Nature rarely operates linearly. One thing tends to trigger another, and that trigger can either establish a negative feedback loop, or a positive one, or nothing at all. Unfortunately, evidence points towards global warming triggering a positive feedback (ie. methane release from melting permafrost). An analogy a friend of mine uses is: change one tooth in one gear of a clock, and the whole system adjusts to tell time differently.
I have a hunch the upcoming lecture at UCLA will cover aspects of what we've discussed here.
Thanks all for taking the time to read this thoughtfully.