First published JoNova; According to Oxford researcher Beatriz Monge-Sanz, brutal winter weather the USA, Britain and Europe have experienced recently were exacerbated by global warming.
Global warming may be behind an increase in the frequency and intensity of cold spells
Published: March 5, 2024 5.25am AEDT Beatriz Monge-Sanz Senior Researcher, Department of Physics, University of Oxford
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One less obvious consequence of global warming is also getting growing attention from scientists: a potential increase in the intensity and frequency of winter cold snaps in the northern hemisphere.
Some of the mechanisms that lead to their occurrence are strengthened by global warming. Key climate mechanisms, like exchanges of energy and air masses between different altitude ranges in the atmosphere, are evolving in ways expected to cause an increase in both the intensity and duration of cold snaps. These link to the behaviour of a region in the high atmosphere called the stratosphere.
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Global warming makes extreme weather more extreme, and scientific studies are starting to provide proof that this also applies to extreme winter cold spells. Developing the best possible modelling tools is essential to predict the evolution of extreme weather events in the coming years so that we can be better prepared for them.
In part 3 we discussed the relationship between changes in solar activity and climate changes. Exactly how solar changes affect climate is not understood. It isn’t the immediate change in radiation delivered to the Earth, since that is too small to have much of an effect. So, it must be how Earth’s climate system reacts to the changes. The observed impact of solar irradiance changes over the solar cycle on the climate is much larger than the change in delivered radiation can account for. A likely amplifying mechanism is Earth’s convection and atmospheric circulation system. This post examines that idea. It is yet another important idea that the IPCC and AR6 ignore and brush away as unimportant, vis-à-vis global warming.
The emphasis the IPCC places on global average surface temperature and the use of the phrase “global warming” suggests that atmospheric and oceanic circulation of thermal energy are not important in discussions of global climate change. Theodore Shepherd argues that global climate is driven by thermodynamics, and only regional climate is driven by convection and atmospheric circulation. He also admits that climate models are much less consistent in their predictions of precipitation than temperature, and that the difference is likely due to atmospheric circulation, which affects precipitation patterns more than temperature. Finally, he acknowledges that our understanding of atmospheric circulation is weak.
The IPCC makes much of the fact that the only way Earth gains thermal energy is through radiation that is absorbed by the atmosphere or the surface from outer space and the only way it loses energy is when radiation is emitted to outer space. This is true, but the apparent corollary that movement of thermal energy from one place to another on Earth’s surface makes no difference in the overall energy imbalance, is not true. Convection and circulation largely control the residence time of the energy within the climate system. When the average residence time is short, Earth cools, when the residence time is long, Earth warms.
To demonstrate this, we need to examine six critical areas of climate and geological research. The first is the areal distribution of incoming and outgoing radiation around the globe and the distribution of net radiation flux (incoming-outgoing radiation). Next, we will examine energy transport from the tropics, where there is a surplus of thermal energy, to the polar regions which have a deficit, or net loss of thermal energy to space. This thermal energy transport is called the “meridional transport” of energy. When meridional transport is strong, Earth cools, and when it is weak Earth warms. Figure 1 illustrates strong meridional flow in orange and weak (or “zonal”) flow in red.
Thirdly, tropical temperatures do not vary much over geological time because over the oceans they are limited to less than 30°C by evaporation. So-called “global warming” happens almost exclusively in the higher latitudes, not in the tropics. Fourth, we examine how the temperature difference between the equator and the poles forms a characteristic equator-to-pole temperature gradient. Fifth, the equator-to-pole temperature gradient today is relatively steep, suggesting the climate of today is unusually cold. Sixth, the temperature gradient powers meridional transport, the steeper it is, all else equal, the colder the Earth is.
Figure 1. Northern Hemisphere zonal flow (warming) in red and meridional flow (cooling) in orange. Source: (Keel, 2018).
While the temperature gradient powers meridional transport, meridional transport has many modulators, and the gradient is only one of them. It is unclear exactly how the temperature gradient and meridional transport interact, but clearly, they are the main drivers of global climate change at all time scales.
In summary, discussing annual or monthly global average surface temperature as if it represents global climate change is very misleading. Earth’s climate does not behave that way. It circulates excess energy from warmer areas with a strong greenhouse effect to colder areas that have a weak greenhouse effect. Deserts and the polar regions have a weaker greenhouse effect due to their lower humidity (water vapor is the strongest greenhouse gas) and can more easily send energy to space as a result. The speed of energy transport determines whether the world warms or cools. The world is not a static uniform object that simply receives energy from the Sun and evenly emits it back into space, with a minor delay caused by greenhouse gas emissions, which seems to be how the IPCC views and models our planet’s climate.
Areal distribution of energy
The tropics (roughly 30°N to 30°S) cover half of Earth’s surface. This is the region that contains the location where the Sun is directly overhead at noon. Half of the tropics, 25% of Earth’s surface, is in daylight at any given time, and this 25% of the surface receives 62% of the solar energy that strikes Earth. This, combined with a very large tropical greenhouse effect and a low albedo, creates an enormous surplus of energy in the tropics.
Figure 2. Net thermal energy flux at the top of the atmosphere by latitude. Vertical axis is in W/m2, positive numbers mean more incoming energy than outgoing, and negative values are a net loss of energy to space. After: (Randall, 2015, p. 13)
Because more energy is received in the tropics than is emitted to space, the excess energy must be transported elsewhere. To make the situation even more complicated, Earth has an axial tilt relative to the plane of its orbit around the Sun. The effect of this tilt is illustrated in figure 2, where the Northern Hemisphere winter net energy flux profile is shown as a heavy dashed line and the Northern Hemisphere summer profile is shown as a light dotted line. The yearly average is shown as a solid line. The X axis is the latitude, positive latitudes are north of the equator and negative are south.
Because Earth is closest to the Sun (perihelion) on January 4th, more total energy is delivered during the Northern Hemisphere winter. Figure 2 illustrates how complicated the task of regulating the surface temperature of Earth is. The point receiving the maximum energy input from the Sun is constantly moving. Besides this problem, the tropics have the strongest greenhouse effect in the lower troposphere as previously mentioned.
Meridional transport
In contrast to the tropics, the polar regions have the smallest greenhouse effect in the troposphere. This is especially true in the polar winter when the relative humidity is nearly zero due to the lack of sunlight and the low air temperature. This causes the air moving into the polar region to be warmer than the surface. The water under the polar ice is relatively warm (approximately -1.8°C) but it is insulated from the colder surface by ice. Thus, there is more radiant cooling to space from the polar air than from the surface because warmer bodies emit more radiation. In the dry polar regions, most radiation in the winter is from CO2, and adding more CO2 there means more radiation to space, which increases the rate of cooling, so we observe a reverse CO2-human-enhanced greenhouse effect during polar winters.
The transport of energy from the tropics to the poles (aka meridional transport) is very large, exceeding five petawatts, as illustrated in figure 3. In figure 3 the northward energy flow is positive and southward energy flow is negative.
Figure 3. The poleward transport of energy by the oceans and the atmosphere. Positive values are northward and negative values are southward. From (Randall, 2015, p. 15).
Figure 3 is an average over the year, it conceals very large differences during the year due to storms, Earth’s axial tilt, and changes in meridional transport.
Tropical temperature hardly varies
There is one more important point to make regarding surface temperature and incoming solar radiation. The tropical temperature is limited to about 30°C. As the ocean surface approaches 30°C, very rapid evaporation occurs and “deep convection” commences that drives lower density humid air very high (to an air pressure of about 200 hPa, or about 38,000 ft or 12 km) in the troposphere where it cools and forms clouds that shield the surface from the Sun. This deep convection also causes downdrafts of cool, dry air that work to cool the ocean surface.
The equator-to-pole temperature gradient
Because tropical temperatures are limited over the oceans and cannot exceed 30°C, the global energy balance forces global warming to occur at higher latitudes. Thus, a temperature gradient is created from the tropics to the poles that drives meridional transport. Since tropical temperatures do not change much, as the global average temperature decreases the temperature gradient increases in slope and as the average temperature increases, the gradient decreases. This is illustrated in figure 4, it is by Chris Scotese and colleagues.
Figure 4 is based on a model created by making 100 maps of ancient Köppen climatic belts around the world, each map represents the estimated paleoclimate of a five-million-year period, so the maps cover the past 500 million years. Scotese’s studies are significant for two reasons. First, the surface temperature ranges over the oceans and any significant body of water are limited, and since most of Earth’s surface is water, this limits the global average temperature, regardless of the greenhouse gas concentration in the atmosphere. Secondly, his work shows that the global average temperature today is unusually cold.
Today is unusually cold
Scotese’s work suggests that the “normal” surface temperature for the Earth over the past 500 million years is about 19-20 degrees, thus our surface temperature today is well below normal for Earth. Today’s average temperatures, by latitude, are marked in figure 4 with small plus signs. They tend to fall between 14- and 15-degrees global average temperature.
The last column in figure 4 is the percentage of the time each gradient shown exists in his maps. Over half the time (59%) in Earth’s recent history the global average temperature was between 19 and 20°C.
Figure 4. The equator-to-pole temperature gradients for various global average temperatures (GAT). The average equatorial temperature is 26°C and polar temperatures vary from 8° to 23°. Today’s temperatures are shown with small plus signs. The percent of the past 540 million years with each gradient is in the last column. The most common global average temperature is about 19 – 20°C, some 4-5° warmer than today.
The current climate is unusual in Earth’s history, but it is unusually cold, not unusually hot. Scotese’s work is very well accepted in the geological community, yet it is ignored by the IPCC who prefer to proclaim current warming is unprecedented. In fact, although Chris Scotese is famous for his work on paleoclimate in the geological community, a search for his name in AR6 WGI comes up with nothing. In fact, his name is not referenced in any of the AR6 volumes, although his findings are relevant to all three.
Summary
Atmospheric circulation and convection do play a role in global climate change since they affect the speed and efficiency of meridional heat transport, which helps determine the equator-to-pole temperature gradient and the residence time of thermal energy in the climate system. Some would have us believe that global average temperature is only a function of thermodynamics and the global climate can be characterized by this quantity. Yet circulation patterns are very important in regional precipitation patterns, which are very poorly understood, and poorly represented in climate models.
Characterizing the global climate using the best modeled quantity (global average temperature) is not very scientific. The focus of our work should be on what we do not understand. As Shepherd states:
“Every aspect of climate change in which there is strong confidence … is based on thermodynamics. Circulation, on the other hand, is … governed by dynamics. Therefore, the earlier dichotomy can be re-stated as saying there is relatively high confidence in the thermodynamic aspects of climate change, and relatively low confidence in the dynamic aspects.”
Shepherd, 2014
In other words, if we treat Earth as a static and uniform thermodynamic body, we understand it. If we look at it as a real, dynamic planet with a circulating atmosphere and ocean, we don’t. A rather obvious point, and a part of the climate system that the CMIP models do not model well. This is acknowledged, regarding regional precipitation, in AR6.
In the next post, we will cover the sixth item in the list above, that the temperature gradient powers meridional transport. We will also cover the topic of storminess, that is extreme weather, is it increasing as the world gets warmer?
(Vinós, Climate of the Past, Present and Future, A Scientific Debate, 2nd Edition, 2022, p. 261), (Scotese, Song, Mills, & Meer, 2021), (Liang, Czaja, Graversen, & al., 2018), and (Barry, Craig, & Thuburn, 2002) ↑
(Wijngaarden & Happer, 2020) and (Pierrehumbert, 2011) ↑
The tropics are mostly covered by oceans and oceans absorb almost all incident solar radiation. Their albedo is small, meaning they reflect less energy than land or clouds. ↑
Net energy flux is just the incoming solar energy – the outgoing (to space) energy, averaged by latitude. ↑
A petawatt is 1015 Watts or a billion megawatts. ↑
A Köppen belt is a latitude band around the world that contains a set of diagnostic fossils and rocks that are characteristic of a climatic zone. For example, tropical rainforests have diagnostic fossils and rocks, as do deserts, temperate grasslands, and ice-covered polar regions. By dividing the world into diagnostic climatic zones, a pole-to-equator gradient can be constructed which can be translated into a global average temperature using Figure 4. See (Scotese, Song, Mills, & Meer, 2021) for more details. ↑
A recent article (Are Labour sleepwalking to energy disaster?) showed that the UK’s capacity of combined-cycle gas turbine generators (CCGTs) is declining, and that by 2030 will have fallen to 12 GW; it will disappear in the next decade.
We are reliant on CCGTs to cover times when intermittent, renewable output is low, and to ensure grid stability. We will therefore need to build more CCGTs, but this is an attractive option, since CCGT plants are cheap and quick to build. There was one noteworthy addition to the CCGT fleet in 2023: Keadby 2. Its performance is remarkable, boasting an efficiency of 63% – compared to the 46% of the retiring CCGTs. It was cheap and quick to build (see Table 1). The carbon dioxide emissions of the old CCGT fleet was 365 g/kWh but ‘Keadby’ CCGTs could decrease that to 260 g/kWh – 30% lower. Keadby 2 has great flexibility in the fuel it can burn. There will be changes in output power and efficiency between different fuels, but it can burn gas from offshore gas fields or fracked gas. It can also burn syngas which can be extracted from UK coal, increasing our fuel security. Replacing old CCGTs with higher efficiency ones has other advantages. The existing site can be reused, including the operational, secure connection to the electricity grid. Building 30 GW of CCGTs on existing sites would cost less than £15bn. There are further benefits of reusing the CCGT sites. The cooling water system will be in place and only has to be reworked for the new plant. The small team that managed and operated the old CCGT can move across to the new. There will already be road access to the site capable of handling heavy loads. The photographs below show how much simpler construction of the power station was compared to an offshore wind turbine. Contrast the delivery of the single Siemens SGT5-9000 590 MW gas-turbine for Keadby 2 with the installation methods of one wind-turbine (perhaps 8–10 MW) offshore. Cut our carbon dioxide emissions by improving efficiency? The last hundred years has seen a remarkable change in the way electrical energy is produced and distributed. Most generation was coal-fired up to 1960, but the stations increased in size and the operating temperature, to a point where the standard installation was a 660-MW steam turbine. By the same year, electricity was delivered over a UK-wide transmission and distribution grid designed to reduce transmission losses and to create multiple paths to secure supply. The world’s first nuclear generator opened in 1956. Our first CCGT power station opened in 1996, opening the way to large-scale generation from gas plants with higher efficiencies than coal-fired station. This progression produced two important benefits: by 2000 the price of electricity had fallen from 25p/kWh in 1921 to 2.2p kWh – a ratio of nearly 12:1. Carbon dioxide emissions from generation fell from 3,500g/kWh to 520g/kWh – a ratio of nearly 7:1. The benefits of improved generation efficiency. Emissions of CO2 decrease and prices fall…until renewables arrive. From 2005 there has been a steady addition of renewable generation: 15 GW onshore wind turbines, 15 GW offshore, and 13 GW solar, and even 2.6 GW of wood-burning. The introduction of renewables from 2005 to 2023 reduced carbon dioxide emissions to 200g/kWh – halving the 2005 level. Over the same period, however, electricity prices rose to 32p/kWh – a factor of nearly nine. Domestic electricity prices have never been this high before. This is almost the highest price for electricity in Europe. The price rise tracks declining coal and gas generation and increasing solar and wind generation between 2015 and 2024 (bar the intervention of the Ukraine war in the last few years) . Most renewable generation is from wind. Its production is variable: over the last four years it has has varied from 29 to 32.5% of nameplate capacity. It is very intermittent: in 2021 the production for May to August was only 19% of nameplate capacity; over that same period, most of Europe was also experiencing low wind speeds. Solar generation is only significant between April and October. We have relied on our CCGT generators to cover these shortcomings and to ensure the security of our grid, but it is now reaching the point where most of the remaining capacity will be retired by 2035, and all of it by 2040. The surge of renewable generation construction has trebled household electricity bills treble since 2010. There is no cheap, emission-free solution that will mitigate the intermittency of this generation. A 10–15-year programme of building modern CCGTs would do much to reduce costs to all consumers, and at the same time make meaningful reductions in the UK’s carbon dioxide emissions (Table 2). This could reduce costs and provide a low-emissions solution to the intermittency of our renewable generators. This proposal would make no call to expand the national grid, saving ~£50 billion to 2030, per-unit emissions would continue to fall (by 60g/kWh), and prices would fall. Capell Aris is a retired power systems engineer, and the author of several papers for Net Zero Watch and the Global Warming Policy Foundation.
Spinning climate data to fit a policy agenda undermines public faith in science.
Public trust in many mainstream publications continues to consistently decline. Part of the reason for this seems to be that media outlets cater more and more to the ideological tastes of specific groups, sacrificing their credibility to a wider audience in the process. I have criticized the New York Times, for example, for exaggerating the impacts of climate change, but this type of criticism may be in vain if they are covering climate exactly how their audience wants them to. It is in a media environment like this, however, that we desperately need reputable sources of scientific information. Sources that will avoid the same temptation to cater to their audiences and prioritize dispassionate reporting of facts instead. Nature magazine has a reputation as one of the most reliable sources of information on earth. Their publication has a section of peer-reviewed articles as well as softer sections dedicated to science news and the like. I have criticized the landscape surrounding high-impact peer-reviewed scientific studies published in places like Nature, but I won’t elaborate on that here. Here, I want to bring attention to Nature’s science news section. Sadly, this section now appears to be engaged in similar levels of spin on climate information as outlets like The New York Times. Two recent articles serve to illustrate the point. The first is titled: Surge in extreme forest fires fuels global emissions. Climate change and human activities have led to more frequent and intense forest blazes over the past two decades. The second is titled: Climate change is also a health crisis—these graphics explain why…Rising temperatures increase the spread of infectious diseases, claim lives, and drive food insecurity. Between these two news articles, we have four claims: one on wildfires, one on infectious disease, one on deaths, and one on food security. Let’s scrutinize each claim one by one. Are wildfires and their carbon emissions increasing? The title and subtitle of the first article conveys the impression that global wildfire activity is increasing, which in turn increases CO2 emissions from wildfires. This idea is also communicated several times in the text of the article (emphasis added): “Global forest fires emitted 33.9 billion tonnes of carbon dioxide between 2001 and 2022…Driving the emissions spike was the growing frequency of extreme forest-fire events.” “Xu and her colleagues found that the growth in emissions had been mostly fuelled by an uptick in infernos on the edge of rainforests between latitudes of 5 and 20º S and in boreal forests above 45º N.” “The increased numbers of forest fires was partially driven by the frequent heatwaves and droughts caused by climate change” The article also goes on to raise the concern of a self-reinforcing feedback loop:“In turn, the CO2 emitted by forest fires contributes to global warming, creating a feedback loop between the two.” There are, of course, many positive and negative feedback loops in the climate system (i.e., responses to warming that either amplify or counteract the initial warming). The relative sizes of these feedback loops are systematically documented in synthesis reports like those from the Intergovernmental Panel on Climate Change. According to the IPCC, the CO2 feedback associated with fires is very small relative to other feedbacks. To put it in perspective, it is only about three percent as large as the water vapor feedback (as the atmosphere warms, it can “hold” more water vapor, which is a greenhouse gas, that further enhances warming). Thus, a self-perpetuating cycle of warming leading to more fires and more CO2 emissions is not exactly at the top of our list of concerns. Second, and more importantly, despite what is communicated in the article, global CO2 emissions from wildfires are not actually increasing! The Nature article covers a recent non-peer-reviewed report by the Chinese Academy of Sciences that contains one figure on changes in wildfire CO2 emissions over time (with emissions separated by region): This figure does not indicate an increase in global emissions over the study period (2001-2022). Independently, the most well-known estimate of CO2 emissions from wildfires comes from the Copernicus Atmosphere Monitoring Service (CAMS), Global Fire Assimilation System (GFAS). This estimate shows a decrease in global wildfire carbon emissions over its record (dating back to 2003): This reduction in carbon emissions is also in line with a long–term observed decrease in the annual amount of global land area burned by wildfires: Since all these numbers seem to contradict what is communicated in the Nature article, I emailed the author to get some clarification. She told me that: “Based on my interview with Xu Wenru, a co-author (of the Chinese Academy of Sciences report), extreme forest fires became more frequent over the past 22 years in areas prone to forest fires (on the edge of rainforests between 5 and 20º S and in boreal forests above 45º N), and their CO2 emissions increased rapidly.” But this amounts to saying that CO2 emissions from wildfires are increasing…where CO2 emissions from wildfires are increasing. And it completely leaves out the important context that global CO2 emissions from wildfires are decreasing. Full post
Iowa Climate Science Education 