PROVIDENCE, R.I. [Brown University] — Human activities are unequivocally warming the Earth’s atmosphere, oceans and continents and producing climatic extremes that are unprecedented on a scale of thousands of years, according to a newly released United Nations report on climate change.

The report, compiled by the Intergovernmental Panel on Climate Change (IPCC), concludes that emissions of CO₂ and other greenhouse gasses from activities like the burning of fossil fuels have caused global average temperature to rise by about 1.1 degrees Celsius since the year 1900. While sharp reductions in carbon emissions would eventually stall the warming trend, a further 1.5 degrees or more of warming over the next two decades is virtually assured by the emissions already in the atmosphere.

Such warming will cause more frequent and more severe heat waves while significantly altering precipitation patterns the world over, the report concludes. In already dry places, droughts are expected to become more severe. Meanwhile, precipitation in already wet places like the Indian subcontinent is expected to increase, leading to more frequent flooding. Significantly rising sea levels are expected to cause flooding in coastal areas all over the world.

Baylor Fox-Kemper, a professor in Brown’s Department of Earth, Environmental and Planetary Sciences, was a coordinating lead author for a chapter of the report focused on oceans, cryosphere and sea level change. Fox-Kemper says the latest findings are a sobering confirmation of what climate research has shown for years.

“In a lot of ways, this new report increases the confidence in what we’ve already known,” said Fox-Kemper, who is an expert in computer modeling of ocean dynamics. “We had access to a lot of new observations and new models that  made our story more precise than it’s ever been before. But in the broadest sense, that story hasn’t changed: Humans are warming the planet, and that warming is producing effects that we’re feeling today and that will only intensify in the coming decades and centuries. The more carbon we emit moving forward, the more severe those effects.”

The report was compiled by hundreds of scientists worldwide, drawing on more than 14,000 recent research studies. In an interview, Fox-Kemper discussed the findings and the work that went into them.   

What are some of the biggest takeaways from this report?

I think the approach that was taken is really important. The format we adopted looked at different warming scenarios: What happens at one degree of warming? What happens at two degrees or three degrees and so on? What we show is that if we stay under two degrees, the outcomes are vastly different than if we go to three, which are vastly different than if we go to four. That’s particularly true in terms of sea level, for example. If we stay under two degrees, we’re talking about 2 to 6 meters or so of sea level rise over the next 2,000 years. If we go up to four degrees, we’re talking about double-digit meters, which would be catastrophic. So to me, this speaks to the need to take action now to head off those catastrophic scenarios.

What are some of the key points covered in the chapter you worked on about oceans and ice?

Looking at sea level rise by 2100, we’re looking at one to two feet (0.28 to 0.55 meters) of sea level rise in the very low emissions scenario, and two to three feet (0.63 to 1.02 meters) in the very high emissions scenario. Those we can be quite confident about. There are also less confident scenarios. For example, if ice sheet changes we’re seeing in some locations in Greenland and Antarctica become widespread under very high emissions, up to six feet by the year 2100 and up to 50 feet by 2300 cannot be ruled out.

If we look a little closer into the future, to 2050, we show that the predicted sea level rise is not very sensitive to changes in emissions. In other words, the sea level rise we’re going to see in the next 30 years is a product of emissions that are already in the system. There we’re talking about 10 to 25 centimeters of sea level rise. That’s a lot when you consider that we’ve seen about 16 centimeters of sea level rise since 1900. So in the next 30 years, we’ll see as much rise as we saw over a century.

When we look further into the future we really see a huge difference between the high-emission and low-emission scenarios. Under the low emissions scenario, we’re looking at perhaps three meters of sea level rise. Under the high emissions scenario, we can’t rule out a rise of up to an almost unimaginable 15 meters. While we think that’s unlikely, we can’t rule it out.

In light of what you’ve learned, are you more or less optimistic about the future of the climate?

I’d say that I’m not quite as depressed now as I was when we were in the middle of doing the work. When we were in the thick of it, I think the outcomes were just too scary and I didn't think people were paying attention. But I think I’ve come around a little bit on that second part. I think that people are paying attention and want to do something about this. We’re seeing these wildfires, heatwaves, droughts and floods, and I think they’re getting people’s attention.

To me, one of the troubling things in the report is that even if we shut off our carbon emissions today, these scary climate effects won’t simply go away. The system doesn’t flush itself out that way. We’ll still have to deal with the effects of carbon we’ve already emitted, and the effects of what we’ve already done are significant.

But there is some cause for optimism. There are a lot of models in the report that look at what happens in the next 20 years if we dramatically curb emissions. They show that, while the carbon that’s been emitted already will still push temperatures up, that warming won’t necessarily go on for hundreds of years. They actually stabilize a little more quickly than you might think. So things will unfortunately get worse, but maybe not disastrously worse — if we take action. That said, there is enough fossil fuel in the ground to make things disastrous, so we need to be wary of that.  

How was the report compiled?

This is the IPCC’s Sixth Assessment Report from Working Group One, which is the physical science basis group. We don’t address impacts on humanity or strategies for mitigation; those other things are addressed by other working groups within IPCC. Our job is to assess the current state of the science. There are about 750 people involved in putting this together. For our chapter alone, there were roughly 60 people involved. It was an incredible amount of work over three years. Our chapter addressed around 15,000 reviewer comments, assessed more than 1,500 publications and developed over 400 draft chapter versions. I’ve never done anything like this. I thought writing a Ph.D. was hard. It’s not. This was hard.

What do you hope the report will accomplish?

The report is available to anyone who wants to look at it, and the hope is that will include all of our senators and members of Congress, as well as people in the White House. Policymakers are the intended audience. We also hope that all the CEOs of major corporations are taking a look. We want public services departments, mayors' offices and so on to take a look. Not just in the U.S. of course, but around the world. What they do with that information is not up to us; it’s up to them. But we hope they take notice.