In 1981 James Hansen and colleagues published research in the prestigious peer-reviewed journal Science titled “Climate Impact of Increasing Atmospheric Carbon Dioxide.” They discussed the result of basic physics, that carbon dioxide in the air inhibits Earth cooling off, thus heating the planet. They also reported the results of computer simulations of Earth’s climate in a world with ever-increasing CO2.
In that research they stated some of the more notable results, both for the long term (if we double the amount of CO2 in the air), and some of the changes expected by the year 2010 if CO2 kept increasing the way it had been (because of our burning fossil fuels). These include:
Doubling the atmosphere’s CO2 would raise Earth’s overall temperature by 2.8°C (5°F). By 2010, Earth’s temperature would rise about 0.4°C (0.7°F). The Arctic will warm considerably faster than the globe as a whole. There will be a reduction of sea ice in the Arctic. There’s a chance we might see the opening of the fabled “Northwest passage” during late summer.
Naturally one wonders, how did things turn out?
First on the list is climate sensitivity, the global warming we expect from a doubling of atmospheric CO2. We don’t know how accurate the 1981 result is, because climate sensitivity is still one of the more troubling uncertainties of climate science, but modern estimates put it somewhere in the range of 2 to 4.5°C (3.6 to 8.1°F). The width of that range testifies to just how uncertain we are about this, but all plausible values are a serious threat to mankind.
It’s also important to emphasize that when it comes to climate sensitivity, uncertainty is not your friend. In fact the opposite is true: uncertainty is your enemy. We’ll be extremely lucky if sensitivity is only 2°C (3.6°F) because that will only be a lot of trouble. But if sensitivity is on the high side — if doubling CO2 (which we’re on track to do before this century is complete) raises global average temperature by 4.5°C (8.1°F) — then we are way beyond serious trouble. The consequences of that kind of global warming would be apocalyptic. That’s not exaggeration or “alarmism,” it’s just the truth.
How much has Earth actually warmed since 1980, when the paper was written (although it was published in 1981)? Here’s the annual average global temperature each year from 1970 through 2016 (data from NASA, and the 2016 value is incomplete because the year isn’t over yet):
The values for 1980 and 2010 are circled in red. The difference — an estimate of the warming since then — is 0.44°C (0.79°F), very close to (in fact a little higher than) their estimate of 0.4°C.
An even better estimate is one which removes the influence of random year-to-year fluctuations. We can do so by fitting a straight line to the data, to estimate the underlying trend, which gives this:
The values for 1980 and 2010 are circled in red. Their difference is 0.55°C (0.99°F), more than 35% higher than the projected increase from Hansen et al. in 1981.
They also predicted that the Arctic would warm faster than the planet as a whole. NASA also reports the temperature for various regions of the Earth, and here’s a comparison of the warming since 1970 for the globe as a whole in blue, to that for the Arctic (in this case, the Earth north of latitude 64°N) in red:
The Arctic has indeed warmed faster than the global average, by a lot. Since 1970, it has warmed nearly three times as fast.
What about their projected decline of Arctic sea ice? Here’s the annual average extent of Arctic sea ice since we started observing with satellites in the late 1970s (data from the National Snow and Ice Data Center, with a trend line in red):
Finally, what about the Northwest passage? There is no single specific “Northwest passage,” it’s a generic term for crossing between the Atlantic and the Pacific oceans by sailing over the northern part of North America. It has been attempted many times, and was finally accomplished when Roald Amundsen reached Alaska via that route in 1906. But by no means was it smooth sailing; departing in 1903 it took him three years, including winters being frozen into the ice.
What is really meant, in practical terms, is just that smooth sailing which would enable passenger and cargo ships to make the journey — without having to take three years to do it. Because of global warming, it has already happened. On this very day, a cruise ship called “Crystal Serenity” is departing Alaska with over 1,000 passengers, bound for New York with a scheduled passage by Greenland. It has real risks, and I wish them a safe journey, but there’s also no getting around the fact that the prediction that we might see the Northwest passage actually practical during summer is no longer a dream or a slogan, it’s a reality.
The upshot of all this is that, 35 years after the fact, the expectations expressed in Hansen et al.‘s 1981 paper have come to pass. They’re all things that, frankly, could not have happened without real, significant climate change. Actually predicting them, without a good reason to expect unnatural climate change, would have been lunacy. But predicted they were, and more important they have come to pass. And those who tell you that all computer simulations of climate are utterly useless are either more than three decades out of date, or are spinning a web of lies.
Global warming and its dangers isn’t a “hoax invented by the Chinese.” It’s a threat. We’ve been warned, for decades now, and it’s time for us to act.
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