In 1971, a Princeton climatologist named Syukuro Manabe published a startling finding: based on the rising concentration of carbon dioxide in the atmosphere, Manabe predicted that by the year 2000 the global average temperature would rise 0.8 degrees Celsius over the 1900 baseline — a 0.57 degree increase over where things stood in 1970.
Manabe’s paper was one of the first projections of future global warming, and it turned out to be right on the money: by 2000, the observed global average temperature had risen by 0.54 degrees Celsius — just 0.03 degrees off Manabe’s figure.
Today Manabe won part of the Nobel prize in physics for the complicated modeling work undergirding that projection — groundbreaking at the time.
Manabe “led the development of physical models of the Earth’s climate and was the first person to explore the interaction between radiation balance and the vertical transport of air masses,” the Nobel Committee writes. “His work laid the foundation for the development of climate models.”
The relationship between CO2 and global temperature is taken for granted today — we’ve all seen Al Gore’s famous chart showing the correlation between the greenhouse gas and global temperature. But sussing out the precise nature of that relationship — going beyond correlation to demonstrate exactly how and why carbon dioxide heats up the planet — took decades of painstaking work. Manabe was at the forefront of that effort.
One of the complicating factors is that carbon dioxide has different effects at different layers of the atmosphere — it heats things up close to the ground, but actually cools things off higher up. To accurately predict how CO2 would affect global temperature you need to be able to account for all that variation in your model.
That’s what Manabe did. “Sixty years ago, computers were hundreds of thousands of times slower than they are now, so this model was relatively simple, but Manabe got the key features right,” the Nobel Committee writes. “You must always simplify, he says. You cannot compete with the complexity of nature – there is so much physics involved in every raindrop that it would never be possible to compute absolutely everything.”
Manabe’s work laid the foundation for today’s modern climate models. The latest of those, as summarized in this year’s IPCC report, predict that by 2100, the average global temperature will be nearly 3 degrees Celsius (5.4 degrees Fahrenheit) higher than it was prior to the twentieth century, or about 3 degrees Fahrenheit above what it is today. That would mean the end of the Arctic ice cap as we know it, bringing a total sea level rise of about 1.5 feet above the current level.
And that’s just the middle-of-the-road scenario. If countries fail to take action on carbon emissions the world could enter the 22nd century nearly 7 degrees (Fahrenheit) hotter than it is today. It’s hard to guess what such a world would look like, but the scientists studying these issues say we need to do everything in our power to not find out.