Saturday marks two years since President Trump announced he would pull the U.S. out of the Paris Climate Agreement, and the scientific case for acting to slash planet-warming emissions of greenhouse gases has only grown stronger since then.
The big picture: Climate science is now more clear than ever about the damage climate change is already causing, whether it be via sea level rise, heat waves or epic deluges. Scientists tell Axios they now have:
- More confidence in the observed amounts of global warming, showing the planet has been heating up faster than previously thought.
- More confidence in tying various (though not all) types of extreme weather events to climate change.
- Clear evidence that virtually all of the observed warming since 1950 is due to human activities.
- Robust data showing that limiting global warming to the Paris targets of 1.5°C or 2°C would have significant, tangible benefits.
In addition, estimates of ocean heat warming have been revised upward in recent years, according to Zeke Hausfather of Berkeley Earth. At least 90% of added heat is going into our oceans.
“Over the past two years we’ve learned that key impacts of climate change, like the melting of ice, the rise in sea level and the increase in devastating weather extremes, are playing out faster than our models projected just a few years ago," Michael Mann of Penn State University tells Axios.
Between the lines: A study published last week projected that unchecked growth in greenhouse gas emissions could cause global sea levels to rise by an average of 3.6 feet by 2100.
- This compares to just 2.3 feet if warming is limited to 2°C, or 3.6°F, above preindustrial levels, co-author Robert Kopp tells Axios.
The difference between business as usual and meeting the Paris temperature target by 2100 is especially clear when modeling the worst-case scenarios.
- For example, Kopp says that there would be a 1-in-20 chance of 7.8 feet of sea level rise under unchecked emissions. Such rapid and extensive sea level rise could imperil coastal megacities worldwide within the next few decades.
- This would drop, though, to a 1-in-20 chance of 4.1 feet of sea level rise in a 2°C world.
Studies also show that limiting the amount of warming decreases the likelihood that we'll trigger climate change tipping points, such as the loss of the West Antarctic ice sheet.
But, but, but: Emissions are heading in the wrong direction, having hit a record high in 2018.
"As long as emissions are unconstrained, our situation is getting worse. At this point, we're rapidly running out of runway. Rapid mitigation will be politically challenging, as will be the required levels of adaptation. If we do neither of those, then we'll be left to suffer through the unabated impacts of climate change. It will not be pretty."— Andrew Dessler of Texas A&M University