Two different takes on James Hansen

NYTimes: A Prophet of Doom Was Right About the Climate

Excerpt:

With the perspective of three decades, it is fair to ask: How right was his forecast?

The question defies a simple answer. In 1988, Dr. Hansen had to offer a prognostication not just about how the Earth would respond to greenhouse gases, but also about how much of those gases humans would choose to inject into the air.

He did what any cautious forecaster would do: He offered low, medium and high scenarios. The warming over the past 30 years has indeed fallen well within his upper and lower bounds.

One of Dr. Hansen’s scenarios, Scenario B, has turned out to be a reasonably close match for fossil-fuel emissions as they actually occurred. Yet we now know Scenario B predicted too much global warming, by something like 30 percent.

Two reasons for that stand out. One is that Dr. Hansen had assumed a continued increase in certain refrigerant gases that warm the climate. Those gases were ultimately brought under control by a global treaty, the Montreal Protocol — proof that scientific warnings, if taken seriously, can be acted upon at a worldwide scale. 

The bigger problem was that the computers he was using in the 1980s could not operate fast enough to give a realistic picture of the upper atmosphere; as a result, his model was most likely overestimating the Earth’s sensitivity to emissions. In the years since, computer modeling of the climate, though hardly perfect, has improved.

So while his temperature forecast was not flawless, in a larger sense, Dr. Hansen’s 1988 warning has turned out to be entirely on target. As emissions have soared, the planet has warmed relentlessly, just as he said it would; 1988 is not even in the top 20 warmest years now. Every year of this century has been hotter.

The ocean is rising, as Dr. Hansen predicted, and the pace seems to be accelerating. The great ice sheets in Greenland and Antarctica are dumping ever-rising volumes of water into the sea. Coastal flooding is increasing rapidly in the United States. The Arctic Ocean ice cap has shrunk drastically.

WSJ: Thirty Years On, How Well Do Global Warming Predictions Stand Up? James Hansen issued dire warnings in the summer of 1988. Today earth is only modestly warmer.

Excerpt:

Mr. Hansen’s testimony described three possible scenarios for the future of carbon dioxide emissions. He called Scenario A “business as usual,” as it maintained the accelerating emissions growth typical of the 1970s and ’80s. This scenario predicted the earth would warm 1 degree Celsius by 2018. Scenario B set emissions lower, rising at the same rate today as in 1988. Mr. Hansen called this outcome the “most plausible,” and predicted it would lead to about 0.7 degree of warming by this year. He added a final projection, Scenario C, which he deemed highly unlikely: constant emissions beginning in 2000. In that forecast, temperatures would rise a few tenths of a degree before flatlining after 2000.

Thirty years of data have been collected since Mr. Hansen outlined his scenarios—enough to determine which was closest to reality. And the winner is Scenario C. Global surface temperature has not increased significantly since 2000, discounting the larger-than-usual El Niño of 2015-16. Assessed by Mr. Hansen’s model, surface temperatures are behaving as if we had capped 18 years ago the carbon-dioxide emissions responsible for the enhanced greenhouse effect. But we didn’t. And it isn’t just Mr. Hansen who got it wrong. Models devised by the United Nations Intergovernmental Panel on Climate Change have, on average, predicted about twice as much warming as has been observed since global satellite temperature monitoring began 40 years ago. 

What about Mr. Hansen’s other claims? Outside the warming models, his only explicit claim in the testimony was that the late ’80s and ’90s would see “greater than average warming in the southeast U.S. and the Midwest.” No such spike has been measured in these regions.

As observed temperatures diverged over the years from his predictions, Mr. Hansen doubled down. In a 2007 case on auto emissions, he stated in his deposition that most of Greenland’s ice would soon melt, raising sea levels 23 feet over the course of 100 years. Subsequent research published in Nature magazine on the history of Greenland’s ice cap demonstrated this to be impossible. Much of Greenland’s surface melts every summer, meaning rapid melting might reasonably be expected to occur in a dramatically warming world. But not in the one we live in. The Nature study found only modest ice loss after 6,000 years of much warmer temperatures than human activity could ever sustain.

Several more of Mr. Hansen’s predictions can now be judged by history. Have hurricanes gotten stronger, as Mr. Hansen predicted in a 2016 study? No. Satellite data from 1970 onward shows no evidence of this in relation to global surface temperature. Have storms caused increasing amounts of damage in the U.S.? Data from the National Oceanic and Atmospheric Administration show no such increase in damage, measured as a percentage of gross domestic product. How about stronger tornadoes? The opposite may be true, as NOAA data offers some evidence of a decline. The list of what didn’t happen is long and tedious.

Comment: Why reading the NYTimes is worth the price ... just for the comedy value alone! Text of his testimony


Added: Another view