This is how the members of the Nobel Physics Prize committee summarize their decision for the two who developed the Earth's climate models and jointly won half of the 2020 Nobel Prize in Physics
An accessible explanation of the science behind the winning of the Nobel Prize in Physics by Syukuro Manaba from Princeton University and Klaus Hasselmann from the Max Planck Institute who perfected the climate models as published on the Nobel Prize website. Translation: Dr. Moshe Nachmani.
The greenhouse effect is essential to life But too much is not good either
Two hundred years ago, the French physicist Joseph Fourier studied the energy balance between the solar radiation reaching the ground and the radiation reflected from the ground. He understood the role of the atmosphere in this balance: on the surface of the earth, the radiation coming from the sun turns into reflected radiation - "dark heat" - which is absorbed by the atmosphere, and therefore causes its heating. The protective role of the atmosphere is now called the greenhouse effect. This name is derived from its resemblance to the glass panels in greenhouses, panels that allow the sun's rays to penetrate the contents and the heat to be trapped in the contents. However, the radiative processes in the atmosphere are much more complex.
The task that stood before Fourier remains - to examine the balance between the short-wave solar radiation coming towards our star and the long-wave infra-red radiation emitted from the surface of the earth. The details of this mechanism have been collected over the last two centuries by many good climate scientists. Contemporary models for describing the climate are increasingly powerful tools, not only for understanding the climate, but also for understanding the contribution of global warming for which humans are responsible.
These models are based on the laws of physics and developed from models that were used in the past for weather forecasting. Weather is described by meteorological indicators such as temperature, precipitation, wind or clouds, and is influenced by phenomena that occur both in the oceans and on land. Models for describing the climate are based on calculated statistical indices of the weather, such as average values, standard deviations, maximum and minimum measured values, etc. These indicators are not able to tell us what the weather will be like in Stockholm on December XNUMX next year, however, we can get some idea as to the average expected temperature or precipitation in Stockholm in December.
"Is the Earth warming? Yes. Is the reason the increasing amounts of greenhouse gases in the atmosphere? Yes. Can this be explained only by the natural factors? No. Are man-made emissions the cause of the temperature rise? Yes."
Determining the role of carbon dioxide
The greenhouse effect is essential for life on Earth. It controls the temperature because the greenhouse gases in the atmosphere - carbon dioxide, methane, water vapor and other gases - initially absorb the ground's infrared radiation and then release it, heating the surrounding air and the ground below.
Greenhouse gases actually make up only a small part of the Earth's dry atmosphere, which is mostly nitrogen and oxygen (99 percent by volume). Carbon dioxide makes up only 0.04 percent by volume. The most significant greenhouse gas is water vapor, but we cannot control the concentration of water vapor in the atmosphere, while we can control the levels of carbon dioxide.
The amount of water vapor in the atmosphere is closely dependent on temperature, a fact that causes a re-feeding mechanism. A greater amount of carbon dioxide in the atmosphere warms it more, a fact that allows a greater amount of water vapor to remain in the atmosphere, a fact that increases the greenhouse effect and causes the temperature to rise even more. If the carbon dioxide level drops, then some of the water vapor will condense and the temperature will drop.
A first and important part of this addition regarding the effect of carbon dioxide came from the Swedish researcher and Nobel laureate Svante Arrhenius. Completely coincidentally, it was precisely his colleague the meteorologist Nils Gustav Ekholm (Nils Ekholm) who in 1901 was the first to use the word 'greenhouse' as part of the description of the atmosphere's ability to store and emit heat.
Arrhenius understood the physics responsible for the greenhouse effect already at the end of the nineteenth century - that the emitted radiation is relative to the absolute temperature of the radiation body (T) to the fourth power (4T). The hotter the radiation source, the shorter the wavelengths of the radiation. The sun has a surface temperature of six thousand degrees Celsius and emits mainly rays in the wavelengths of visible light. The Earth, with a surface temperature of only about fifteen degrees Celsius, reflects radiation in the infrared range that is not visible to the naked eye. If the atmosphere did not absorb this radiation, then the surface temperature of the earth would only reach minus eighteen degrees.
Arrhenius was actually trying to understand what caused the recently discovered phenomenon of ice ages. He concluded that if the concentration of carbon dioxide in the atmosphere was half that, it would be enough for the Earth to enter a new ice age. And vice versa - doubling the amount of carbon dioxide will increase the temperature by five or six degrees Celsius, a result which, to some extent, is remarkably close to current estimates.
The pioneering model for the effect of carbon dioxide
In the XNUMXs, the Japanese atmospheric physicist Sokuro Manabe was one of the young and talented researchers in Tokyo who left Japan and continued his scientific career in the United States. The goal of Manaba's research, like that of Arrhenius some seventy years earlier, was to understand how high levels of carbon dioxide could cause higher temperatures. However, while Arrhenius focused on the radiation balance, in the sixties Manaba worked on the development of physical models that include the vertical transfer of air due to the convection effect, as well as the heat of the water vapor.
In order to take these calculations into account, he chose to reduce the model to one dimension - a vertical column, rising to a height of forty kilometers into the atmosphere. Even so, it took hundreds of expensive computational hours to test the model by changing the concentrations of the gases in the atmosphere. Oxygen and nitrogen had negligible effects on soil temperature, while carbon dioxide had a considerable effect: when the level of carbon dioxide doubled, the overall temperature rose by two degrees Celsius.
The Manaba climate model
Manabe's model verified that this warming was indeed due to the increased concentration of carbon dioxide, since it predicted rising temperatures near the ground while the upper part of the atmosphere became colder. If instead, changes in solar radiation were responsible for increasing the temperature, then the atmosphere as a whole (its lower and upper parts) would warm simultaneously.
Sixty years ago, computers were hundreds of thousands of times slower than today, so this model was quite simple, but Manaba was right about the important features. You always have to judge things, he says. It is impossible to compete with the complexity of nature - so many laws of physics are associated with each drop of rain that it will never be possible to really calculate everything. The insights gained from the one-dimensional model led to the development of a three-dimensional climate model, which Manaba published in 1975; It was just another milestone on the path to understanding the secrets of the climate.
The weather is chaotic
About ten years after the publication of Manaba, Klaus Hasselmann was able to link together weather with climate by finding a way that stacked on the rapid and chaotic changes in weather that were too difficult to calculate. Our planet has wide variations in its weather since the sun's radiation is very unevenly distributed, both geographically and temporally. Our Earth is spherical, so less solar radiation reaches the higher places than lower on the equator. Not only that, but the Earth's axis of rotation is tilted, a fact that causes seasonal changes in the radiation reaching the ground. The density differences between warmer and colder air cause an increased transfer of heat between different heights, between sea and land, between larger and lower air masses, factors that drive the weather on our planet.
As we all know, formulating reliable weather forecasts more than ten days ahead is a serious challenge. Two hundred years ago, the French scientist Pierre-Simon Laplace remarked that if we only knew the position and speed of all the particles in the universe, it would be possible to calculate both what happened and what might happen in our world. Basically, this may be the truth; Newton's laws of motion, which also describe air convection in the atmosphere, are completely deterministic - they are not random.
However, nothing could be more wrong when it comes to the weather. This is in light of the fact that, partially and practically, it is impossible to be accurate enough to calculate the air temperature, pressure, humidity or wind conditions for each and every point in the atmosphere. In addition, the equations are not linear - small changes in the initial values can give rise to a completely different weather system. Based on the question of whether the flapping of a butterfly's wings in Brazil can cause a tornado in Texas, the phenomenon was called the "butterfly effect". In fact, the intention is that it is impossible to make long-term weather forecasts - the weather is chaotic; This discovery was made in the sixties by the American meteorologist Edward Lorenz, who laid the foundation for today's chaos theory.
The logic behind noisy data
How can we produce reliable models of climate several decades or centuries into the future, even though weather is a classic example of a chaotic system? In 1980, Klaus Hasselmann demonstrated how changing and chaotic weather phenomena can be described as rapidly changing noise, that is, developing long-term climate forecasts on a solid scientific basis. Moreover, he developed methods for detecting human influence on the observed global temperature. As a young PhD student in physics in Hamburg, Germany, in the 1958s, Hasselmann worked on fluid dynamics, then began developing observations and theoretical models of ocean waves and currents. He moved to California and continued in the field of oceanography, where he worked with his colleague Charles David Keeling, a legendary researcher who, back in XNUMX, began the longest series of atmospheric carbon dioxide measurements in Hawaii. Obtaining a climate model from noisy weather data can be demonstrated by describing the running of a stray dog: the dog runs, back and forth, side to side and around its owner's feet. How can you use dog tracking to see if you are walking or standing still? Or if you walk fast or slow? The dog's tracks are like the changes in the weather, and the owner's walk beside the dog is the calculated climate. Is it even possible to draw conclusions about long-term climate trends using noisy and chaotic weather data?
Another difficulty lies in the fact that the changes that affect the climate change radically over time - they can be fast, such as in wind strength and air temperature, or very slow, such as
Ice glaciers are melting, and the oceans are warming. For example, a uniform heating of only one degree Celsius can last thousands of years for the ocean, but only a few weeks for the atmosphere. The ingenious idea of the researchers was to include the rapid changes in the weather into the calculations as noise, and show how this noise affects the climate. Hasselman developed a random and probabilistic (stochastic) climate model, which means that change is embedded into the model. His inspiration came from Albert Einstein's theory called 'Brownian motion', also called 'random motion'. Using this model, Hasselman demonstrated that a rapidly changing atmosphere can actually cause slow changes in the ocean.
to notice traces of human influence
Once the model for climate change was complete, Hasselman developed methods for detecting human influence on the climate system. He found that the models, alongside the observations and theoretical considerations, include within them appropriate information regarding the properties of noise and signals. For example, changes in solar radiation, volcanic particles or levels of greenhouse gases leave unique signals, fingerprints, that can be separated and distinguished. This fingerprinting method can also be applied to measure the impact humanity has on the climate system. Hasselman, it turned out, found the way to further investigate the climatic changes, which demonstrated traces of the human influence on the climate using a large number of independent observations.
Climate models have become more and more accurate as the processes involved in the complex interrelationships of the climate are mapped more precisely, also thanks to satellite measurements and observations of the weather. The models clearly show an accelerating greenhouse effect; Since the mid-nineteenth century the levels of carbon dioxide in the atmosphere have increased by forty percent. The Earth's atmosphere has never contained such a large amount of carbon dioxide in hundreds of thousands of years. Accordingly, temperature measurements have shown that the world has warmed by one degree Celsius during the last hundred and fifty years.
Socorro Manaba and Klaus Hasselmann contributed the greatest benefit to humanity, in the spirit of Alfred Nobel, by providing a solid physical basis for our understanding of the Earth's climate. Now we can no longer say we didn't know - the climate models are unequivocal.
- Is the Earth warming? Yes.
- Is the reason the increasing amounts of greenhouse gases in the atmosphere? Yes.
- Can this be explained only by the natural factors? No.
- Are man-made emissions the cause of the temperature rise? Yes.
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One response
Another proof that carbon dioxide warms the earth can be seen in the link
https://www.youtube.com/watch?v=5KUIVUJ9xb8