Scientists warned the US president about global warming 50 years ago today

Dana Nuccitelli, from The Guardian

Fifty years ago today, as the American Association for the Advancement of Science highlighted, US president Lyndon Johnson’s science advisory committee sent him a report entitled Restoring the Quality of Our Environment. The introduction to the report noted: "Pollutants have altered on a global scale the carbon dioxide content of the air and the lead concentrations in ocean waters and human populations."

The report included a section on atmospheric carbon dioxide and climate change, written by prominent climate scientists Roger Revelle, Wallace Broecker, Charles Keeling, Harmon Craig, and J Smagorisnky. Reviewing the document today, one can’t help but be struck by how well these scientists understood the mechanisms of Earth’s climate change 50 years ago.

The report noted that within a few years, climate models would be able to reasonably project future global surface temperature changes. In 1974, one of its authors, Wallace Broecker did just that in a paper titled Climatic Change: Are We on the Brink of a Pronounced Global Warming?.

You can read the details about this paper and Broecker’s modeling here and in my book Climatology versus Pseudoscience. His model only included the effects of carbon dioxide and his best estimates of natural climate cycles. It didn’t include the warming effects of other greenhouse gases, or the cooling effects of human aerosol pollution, but fortunately for Broecker those two effects have roughly canceled each other out over the past 40 years.

Broecker’s model predicted the global warming anticipated by 2015 both from carbon pollution alone, and when including his best estimate of natural climate cycles. In the figure below, the carbon-caused warming is shown in blue, and in combination with natural cycles (which Broecker turns out not to have represented very accurately) in green, as compared to the observed global surface temperatures from NOAA in red. As you can see, the climate model predictions from over 40 years ago turned out to be remarkably accurate.Twitter Wallace Broecker’s 1974 climate model global warming predictions vs NOAA observations. 

The 1965 report also debunked a number of myths that climate contrarians continue to repeat to this day. For example, the first section of the climate chapter is titled Carbon Dioxide from Fossil Fuels – the Invisible Pollutant. Although the US supreme court ruled that carbon dioxide is a pollutant in alandmark 2007 case, many contrarians object to this description. Nevertheless, climate scientists realized a half century ago that human carbon emissions qualify as pollution due to the dangers they pose via climate change.

The report noted that although carbon dioxide is an invisible “trace gas” – meaning it comprises a small percentage of the Earth’s atmosphere as a whole – it can nevertheless have significant impacts on the climate at these seemingly low levels. As the scientists wrote: "Only about one two-thousandth of the atmosphere and one ten-thousandth of the ocean are carbon dioxide. Yet to living creatures, these small fractions are of vital importance … Within a few short centuries, we are returning to the air a significant part of the carbon that was slowly extracted by plants and buried in the sediments during half a billion years."

Contrarians today often repeat the myths that because carbon dioxide is invisibleand only a trace gas, it can’t possibly cause significant climate change. This report demonstrates that scientists understood the greenhouse effect better 50 years ago than these contrarians do today.

The report documented the several different lines of evidence that prove the increase in atmospheric carbon dioxide is entirely human-caused, concluding: "We can conclude with fair assurance that at the present time, fossil fuels are the only source of CO2 being added to the ocean-atmosphere-biosphere system."

This is yet another fact understood by climate scientists 50 years ago that some contrarians, including a few favorite contrarian climate scientists like Roy Spencer and Judith Curry, continue to cast doubt upon to this day.

The report also projected how much the atmospheric carbon dioxide level would increase in the following decades.: "Based on projected world energy requirements, the United Nations Department of Economic and Social Affairs (1956) has estimated an amount of fossil fuel combustion by the year 2000 that with our assumed partitions would give about a 25 percent increase in atmospheric CO2, compared to the amount present during the 19th Century."

A 25% increase from pre-industrial levels would result in about 350 ppm of carbon dioxide in the atmosphere. The United Nations underestimated the growth in fossil fuel combustion, because the actual carbon dioxide level in 2000 was 370 ppm.

In addition to rising temperatures, the report discussed a variety of “other possible effects of an increase in atmospheric carbon dioxide”, including melting of the Antarctic ice cap, rise of sea level, warming of sea water, increased acidity of fresh waters (which also applies to the danger of ocean acidification, global warming’s evil twin), and an increase in plant photosynthesis.

These climate scientists warned President Johnson in 1965 not just of the dangers associated with human-caused global warming, but also that we might eventually have to consider geoengineering the climate to offset that warming and the risks that we’re causing by inadvertently running a dangerous experiment with the Earth’s climate. "Through his worldwide industrial civilization, Man is unwittingly conducting a vast geophysical experiment. Within a few generation s he is burning the fossil fuels that slowly accumulated in the earth over the past 500 million years … The climatic changes that may be produced by the increased CO2 content could be deleterious from the point of view of human beings. The possibilities of deliberately bringing about countervailing climatic changes therefore need to be thoroughly explored."

Fifty years later, the impending Paris international climate negotiations represent our last chance to heed the expert counsel about the dangers posed by human-caused climate change before we’re fully committed to the deleterious consequences that climate scientists have been warning us about for a half century. 

That’s why more than 1,500 academics from around the world have signed an open letter asking world leaders and delegates at Paris to take vigorous action now in order to avoid a future of catastrophic global warming.