Niels Bohr, who gets my vote for the greatest physicist in the 20th century, is reported to have said, “predictions are hard, especially about the future.” He was talking about predictions from the scientist’s point of view — the challenge of building enough knowledge to make a prediction and the effort to assemble the data and do the calculations. As I’m reading the latest report from the United Nations’s Intergovernmental Panel on Climate Change (IPCC), I find I’m thinking about another hard aspect of predictions — how to use them.
The IPCC released its first report in 1990. At that time, the link between carbon dioxide in the atmosphere and the temperature of the planet was already well established in the scientific literature. This first report tried to synthesize what scientists understood about how Earth’s temperature responds to carbon dioxide levels. A few years later, the second IPCC report said it bluntly (especially for scientists): “projections of future global mean temperature change and sea level rise confirm the potential for human activities to alter the Earth’s climate to an extent unprecedented in human history.”
Carbon dioxide concentrations in the atmosphere stood at 354 ppm when the first IPCC report was issued. They are now 412 ppm. The rise in carbon dioxide levels has pushed Earth’s temperature from 0.7 degrees Celsius (1.3 degrees Fahrenheit) above pre-industrial levels in 1990 to 1.3 degrees Celsius (2.3 degrees Fahrenheit) in 2020. This change was not only predictable — it was predicted by scientists and reported in the 1990 IPCC report.
The predictions in the IPCC reports are contingent on what society will do about carbon. The IPCC evaluates computer models run under low and high carbon dioxide emissions. The logic of using multiple scenarios allows them to highlight the costs and dangers of a high carbon dioxide world. They don’t make a prediction about what choices people and their governments are likely to make. Instead, the choice is up to us, and so far, we’ve been choosing the high carbon dioxide path.
Why did we choose this path? A lot has been written about the campaign to deny the science behind climate change. This has certainly been a factor. But I want to give us all a little bit of a break. I think a big factor, one that made climate denialism sticky, is that climate change has been discernible in data but not visible in most of our lives.
None of us experiences global mean temperature. We experience periods of heat and cold and all the stormy-noisiness of weather. It has been hard to distinguish events like storms and heat waves that have been juiced by climate change from ordinary bad luck that we humans have always experienced.
If the abstract nature of climate change excuses some of our lack of action to reduce carbon emissions, this summer should shatter that excuse. We are living in the world that was envisioned in past IPCC reports. Extreme heat waves like those that have rocked the U.S. West and extreme rain events that caused catastrophic floods in Europe and China are made worse by high carbon dioxide levels. The events we are seeing this summer were avoidable. They are consequences of the choices that we made since the first IPCC report.
A long time ago, in a galaxy far, far away from Bohr, the philosopher Yoda once said, “the greatest teacher, failure is.” While he wasn’t specifically talking about the challenges of acting on predictions (though he had a few), Yoda captures an essential truth — we learn by experience. Our pattern is that we don’t act until we begin to feel pain. Climate change is now part of our lived experience, and that experience is getting more painful. The latest IPCC report makes it clear that a high carbon future will move from painful to crushing.
It is not too late for us to act. We have the technology to reduce carbon emissions in time to limit warming to something close to 1.5 degrees Celsius. Keeping global temperatures close to this level would avoid many of the most dire predictions in the latest report. As Yoda also said, “Your path you must decide.”
Andrew Pershing is the director of Climate Science at Climate Central. He is an expert on how climate trends and events impact ecosystems and people and recently led the Oceans and Marine Resources chapter of the fourth U.S. National Climate Assessment. Follow him on Twitter: @Sci_Officer.