Editor's Note: (Michael E. Mann is Distinguished Professor of Atmospheric Science at Pennsylvania State University. His most recent book, with Tom Toles, is The Madhouse Effect: How Climate Change Denial Is Threatening Our Planet, Destroying Our Politics, and Driving Us Crazy (Columbia University Press, 2016). The views expressed in this commentary are solely those of the author.)
(CNN) With the news Tuesday that Syria has officially joined the Paris climate agreement, the United States, under President Trump, will stand as the lone dissenting country when diplomats gather in Germany this week to hammer out the details for implementing the accord.
Meanwhile, back at home, the Trump administration must now also confront the newly released US National Climate Assessment, a massive report assembled by hundreds of our nation's best scientists, led by the National Oceanic and Atmospheric Administration (NOAA). Unlike most science reports, which research the unknowns, the National Climate Assessment is dedicated to assessing the current body of existing science to establish what is known, and how well we know it. The report is the gold standard when it comes to what we know about climate change and its impact in the United States. Its findings underscore climate change's growing and catastrophic threat, including new science that indicates sea levels could rise potentially more than 6 feet by the end of the century -- if we continue down our fossil-fueled business-as-usual path.
Scientists like me spend most of our time researching and debating the "unknowns." The known just isn't that interesting. When it comes to climate change, experts agree (a) that it is occurring and (b) what's causing it -- greenhouse gas emissions, aka carbon pollution, mostly from smokestacks and tailpipes. Not surprisingly, then, the leading edge of science has long since moved on to more subtle questions like just how much sea level rise we could see by the end of the century, as well as exactly how quickly hurricanes are intensifying in our warming climate and precisely what role extreme drought and heat are playing in the unprecedented recent wildfires. As the latest science makes clear, uncertainty is not our friend. In the case of sea level rise, we are learning that ice sheets may be more vulnerable to near-term warming, yielding considerably more near-term melt and sea level rise than we had previously estimated.
The problem is that the Republicans who are currently in power in Washington, DC are stuck debating the knowns. They have grown more intransigent, raising questions that were literally answered decades ago. That predicament was most recently on display in testimony in front of the US Senate by Congressman Jim Bridenstine, a Republican politician from Oklahoma nominated by President Trump to lead NASA, one of our nation's premiere science agencies. When asked about the cause of climate change, Bridenstine could not even cite NASA's own science fingerprinting the role of greenhouse gases in driving warming. Instead he pointed to factors such as solar cycles (in reality, their impact is very small and if anything had a very modest cooling effect in recent decades that slightly offset global warming). When it comes to leading NASA, we must regretfully conclude that Bridenstine has The Wrong Stuff.
In this light, and with the United States now standing alone as a dissenter from the Paris accord, the timing of the US National Climate Assessment report could not be better.
The report concludes that "based on extensive evidence ... it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th Century." The report also concludes that "this period is now the warmest in the history of modern civilization" -- specifically, the warmest period over at least the past 1,700 years.
The report goes on to specify that not only are human activities the dominant cause of global warming, but that those activities are also most probably responsible for ALL of the warming observed over recent decades. The climate would most likely be cooling slightly, due to a downward trend in natural factors, were it not for the overwhelming influence of human activities warming the planet.
Sea level rise is a good example of the choices facing us. The National Climate Assessment reports that an extraordinarily rapid shift to a clean energy economy would limit sea level rise by 2100 to about 2 feet. Alternatively, if we continue down the business-as-usual path, sea level rise could exceed six feet by 2100.
In these projections you can see that, due to the delay in curbing carbon pollution, we are now facing sea level rise over the coming decades what will cost us tens of billions, if not more. Further delay that commits us to sea level rise of just six feet would, according to calculations released by the real estate firm Zillow based on a 2016 study, swallow about 1.9 million US homes -- about 2% of all US homes, worth a combined $882 billion -- by the end of the century.
Fortunately, the report also points out that we still have a choice. With significant reductions in carbon pollution, we can hold warming in check. But how we go about doing that is an open question. That's what policymakers in Washington should be arguing about.
Continuing to argue about what's causing the planet to warm is the moral equivalent of arguing over whether wood burns while a fire is climbing up out of the basement of your house. It's time Republicans stop arguing and got out the hoses instead.