Dr. James Hansen testifying before Congress in 1988
With the thirtieth anniversary of former NASA scientist Jim Hansen’s landmark testimony to Congress on the urgent need to address climate change, numerous articles marked the occasion by demonstrating that his 1988 predictions have proven to be accurate.
Inevitably, some writers seized the opportunity to revive long-debunked arguments in an attempt to cast doubt and confusion on the threat.
Perhaps the most misleading – and certainly the highest profile – was a June 21st op-ed in the Wall Street Journal written by Pat Michaels and Ryan Maue. Michaels is director of the Center for the Study of Science at the Cato Institute, a think tank financially linked to the fossil fuel industry. And Michaels has been found to have previously misled Congress by presenting a doctored graph of Hansen’s projections during public testimony before the House Small Business Committee.
Four decades of climate model projections have fared well
Their latest effort implies that U.S. climate policy is based on Hansen’s forecasts in 1988, and therefore we must “reconsider environmental policy” according to an evaluation of “how well his forecasts have done.”
In reality, climate policy is based on hundreds of years of collective research and an overwhelming amount of observational evidence gathered from all over the world.
Climate model development began as early as the 1950s, and projections from 1973 to 2013 (including Hansen’s 1988 paper) have been compared to observed temperatures by multiple institutions. All showed reasonably accurate surface temperature increases between 1970 and 2016, Hansen’s 1988 study included.
The largest uncertainties come not from lack of understanding of the climate system, but from unknown future human decisions. For example, if Hansen’s 1988 study had included the greenhouse gas emissions reductions that followed the Montreal Protocol Treaty – which took effect in 1989 and phased out ozone-depleting chemicals such as chlorofluorocarbons (CFCs) – the results from his “most likely” scenario would have matched projections by today’s more sophisticated models. Considering the lack of available data and computing power in 1988, this is incredibly impressive.
Predicting exactly what emissions path we’ll take is therefore a policy, and not science, question. Climate scientists work towards understanding how the climate will respond to a range of future emissions scenarios, and unless a particular emissions pathway comes to fruition, it is never expected that the climate model results will be exactly right even if the science is perfect.
However, even without accounting for the Montreal Protocol Treaty adjustment, Hansen predicted in his “most likely” scenario nearly 1 degree (C) of warming by 2016 with respect to a 1964-1983 average, and observations from the standard datasets by NASA and Cowtan and Way both show this amount of warming. On the other hand, Michaels and Maue’s piece misleads readers by inaccurately claiming that Hansen’s lowest projection was most accurate; a quick look at the data shows that this is not so.
The article goes a step further, inaccurately claiming that “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.” First, IPCC does not devise models themselves, but it collates, synthesizes, and standardizes model results from dozens of independent climate models worldwide. But the main problem with this claim is that it is based on comparisons of model results with satellite data that has since been found to have major calibration errors that underestimated temperature measurements. Correcting for the errors reveals that the models are very much in line with what we observe.
Another major flaw in the piece is that Hansen’s and the “IPCC’s” models “don’t consider more-precise measures of how aerosol emissions counter warming caused by greenhouse gases. Several newer climate models account for this trend and routinely project about half the warming predicted by U.N. models, placing their numbers much closer to observed temperatures. The most recent of these was published in April by Nic Lewis and Judith Curry in the Journal of Climate, a reliably mainstream journal.” Sophisticated climate models have long considered effects of aerosols, both directly and via cloud modifications. Lewis and Curry estimated a lower than average climate sensitivity not because of aerosols but because they selected a very low ocean heat uptake rate – a controversial choice among climate scientists; accounting for the latest ocean heat content data would have increased the climate sensitivity value to be on par with other model estimates. Further, their study used a version of a temperature dataset that didn’t include adjustments due to lack of coverage of the Arctic.
Temperature IS rising…
The authors of the opinion piece write that “Global surface temperature has not increased significantly since 2000, discounting the larger-than-usual El Niño of 2015-16.”
This is a tired canard that has been fully debunked elsewhere. This argument is based on flawed and cherry-picked data, and ignores the latest scientific understanding. First, when the flawed, underlying satellite data was corrected, it showed 140% faster warming since 1998 that was consistent with other datasets. Second, the data is cherry-picked to fit the authors’ argument; it is clearly unscientific to discount the El Niño of 2015-16, but not the common La Niñas that masked some of the warming, and not the El Niño of 1997-98 that makes the warming thereafter appear to “slow down.” Third, El Niño was found to play a very minor role in global temperature rise in 2015, which shattered previous records. While it played a relatively larger role in 2016, it is certainly not the cause of a century-long global temperature rise trend, and just amplifies warming when it occurs – in contrast to the La Niñas that mask warming when they occur.
Overall, five ground-based temperature datasets and two satellite datasets all from different scientific groups show rapid warming over the past 30 years that continues into the 21st century. The 2010s have been warmer than the 2000s, the 2000s were warmer than the 1990s, the 1990s were warmer than the 1980s, and the 1980s were warmer than the 1970s. And temperature changes are hardly the only indicator of a changing climate.
So the article’s central question – “Why should people world-wide pay drastic costs to cut emissions when the global temperature is acting as if those cuts have already been made?” is specious. Global temperature is not acting as if those cuts have been made. And basic physics known since the 1800s shows that the global temperature will continue on this path unless we cut emissions of greenhouse gases drastically.
In the U.S., we have also observed considerable warming. However, Michaels and Maue further tried to discredit Hansen by saying, without any evidence or source, “No such spike has been measured” in greater than average temperatures in the late ‘80s and ‘90s in the southeast U.S. and Midwest, as Hansen suggested in his 1988 paper. First, several states in these areas have seen higher than average temperature rise, including Florida, Michigan, Minnesota, and Wisconsin. Second, reading Hansen’s actual paper shows caveated language that there will be regional variations, and that there is a “tendency” for the southeast and central U.S. to be warmer than average. Hansen also fully acknowledges that major improvements are needed in our understanding of the climate system and our ability to predict change, especially the urgent need for more global measurements. For example, we didn’t know in 1988 important variability dynamics that have governed temperature change in these regions.
… and the planet IS reacting
The excess warmth has touched every continent and every ocean.
We’ve observed considerable melting of land ice, something that Hansen highlighted in a testimony during a 2007 case on auto emissions. However, the opinion piece didn’t quite accurately depict his sentiments, paraphrasing his words as “most of Greenland’s ice would soon melt, raising sea levels 23 feet over the course of 100 years.”
Rather, Hansen was referring to ice melt in Greenland and Antarctica, stated that “it is nearly certain that West Antarctica and/or Greenland would disintegrate at some point if global warming approaches 3°C,” and caveated his estimation of sea level rise as “his opinion” (and therefore implying this as not a scientifically robust finding). The authors cite “a Nature study that found only modest ice loss after 6,000 years of much warmer temperatures than human activity could ever sustain.” But the same study acknowledges a major rise in sea level during that time, which if not from Greenland, was from Antarctica.
As for climate-related extreme events that have been on the rise over the past 30 years, the opinion article claims that hurricanes have not gotten stronger, but observational evidence shows they have. The article claims that tornadoes have not gotten stronger, but that was never a mainstream theory, and observations have shown that tornadoes are clumping together causing more severe outbreaks.
Michaels and Maue finally conclude that the list of what has been predicted and didn’t happen “is long and tedious.” I’d like to see that list, because the sampling they provided is filled with inaccuracies and easily refuted.
Jim Hansen’s 1988 testimony is a landmark moment. No matter how the opponents of climate action try to sow doubt and confusion, the judgement of history is clear: Hansen was right.