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Nobel laureates made possible predictions on global warming and modern weather forecasting

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Like a climatologist myself, I was delighted to learn that Syukuro Manabe, Klaus Hasselmann and Giorgio Parisi were awarded the 2021 Nobel Prize in Physics. I first met Manabe when I was a graduate student in the early 1970s, I I was therefore particularly pleased that the award recognizes the profound importance of Manabe decades of work on creating climate models, as well as the application of these models to understand how increasing levels of greenhouse gases have led to global warming.

Climate and weather are influenced by many interconnected systems which all influence each other. (Femkemilene via WikimediaCommons /CC BY-SA)

How complicated is the weather and climate system?

The weather is what you see hour by hour and day by day. The weather only involves the atmosphere. The climate is the average weather over decades and is influenced by the oceans and land surfaces.

Weather and climate are complicated because they involve many different physical processes – from the movement of air to the flow of electromagnetic radiation, such as sunlight, to the condensation of water vapor – over a wide range of spatial and temporal scales.

The system is incredibly complex and interconnected. For example, a group of small thunderstorms can influence a weather system that spans a continent.

Prior to about 1955, meteorologists extrapolated future weather conditions from changes in previous days. They used simple but labor-intensive methods that were partly quantitative and partly based on experience.

Climate models take today’s data, break it up into smaller three-dimensional chunks, and run that data through complex calculations to predict the future. (NOAA via Wikimedia Commons)

The birth of climate models

In the late 1950s, it became possible to make forecasts by running weather models on emerging but rapidly improving digital computers. A weather model is a system of equations that expresses the physical laws that govern the weather. “Running” a weather model means solving equations on a computer, using today’s weather data to predict tomorrow’s weather.

Partly due to computer limitations, early weather models could only cover portions of the Earth – like North America, for example. But in the early 1960s, faster computers made it possible to create models representing the whole world atmosphere.

Manabe led the development of one of these models, creating an interconnected network of thousands of equations that could simulate climate and climate change.

With this model, Manabe and his colleagues were able to produce fairly realistic simulations of things such as jet streams and monsoons. Although modern weather forecasts and global climate models are much more powerful, they can be considered descendants of Manabe’s first model.

When Manabe began his work in the early 1960s, some scientists had already pointed out the possibility that an increase in atmospheric carbon dioxide could lead to global warming. In 1967, Manabe and his colleague Richard Wetherald used a simplified version of their climate model to perform the first quantitative study of the effects of increased carbon dioxide in the atmosphere. In addition to confirming that carbon dioxide increases global temperatures, they also found that the increased water vapor content in warmer air amplifies global warming because the water vapor itself is a greenhouse gas.

Syukuro Manabe was one of the first researchers to use climate models to study global warming.
(Bengt Nyman / Wikimedia Commons /CC BY)

Make predictions

Climate involves both the oceans and the atmosphere, but the first models did not unite the two. In 1969, Manabe and his fellow oceanographer Kirk Bryan built the first climate model for include both the oceans and the atmosphere.

On the basis of these advances, Manabe and Wetherald published in 1975 the results of a simulation of global warming using a global climate model. In this simulation, they doubled the mole fraction of carbon dioxide in the atmosphere from 300 parts per million volume to 600 parts per million volume and let the model calculate the numbers.

Almost 50 years ago they predicted global warming of the Earth’s surface, a much greater warming in the Arctic, a decrease in ice and snow cover, an increase in the global average rate of precipitation and a cooling of the stratosphere. During the 1980s, Manabe’s team also used their models to identify the possibility of increased drought in some mainland regions.

All these predictions have now come true.

Linking climate, weather and chaos

The work of fellow 2021 Nobel Laureates in Physics, Hasselman and Parisi, has followed Manabe’s early research and shows how large-scale interactions across the world give rise to the chaotic and difficult-to-predict behavior of the climate system on scales. from day to day.

Parisi studied the role of chaos in a wide variety of physical systems and showed that even chaotic systems behave in an orderly fashion. His mathematical theories are essential in producing more accurate representations of chaotic climate systems.

Hasselman filled another gap by helping to further link climate and weather. He showed that the highly variable and apparently random weather of the atmosphere becomes converted to much slower changing signals in the ocean. These slow, large-scale changes in the oceans in turn modulate the climate.

In combination, the work of Manabe, Hasselman and Parisi has enabled scientists to predict how the chaotic and coupled behavior of the atmosphere, oceans and land surfaces will change over time. While detailed long-range weather forecasts are not possible, humanity’s ability to understand this complicated system is an incredible feat. In my opinion, Manabe, Hasselman and Parisi are well deserving of the Nobel Prize in Physics.The conversation

This article is republished from The conversation under a Creative Commons license. Read it original article.


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