Story highlights Michael Mann: Findings from the National Climate Assessment underscore the serious and ever-growing threat of climate change

If we shift the discussion from whether climate change is occurring to how to reduce carbon pollution, we can work to keep global warming in check

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.

Michael Mann

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.

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