Skip to main content
U.S. flag

An official website of the United States government

How Abrupt Can Climate Change Be?

Right-click and save to download

Detailed Description

The United States faces the potential for abrupt climate change in the 21st century that could pose clear risks to society in terms of our ability to adapt.

USGS Associate Program Coordinator for the Office of Global Change John McGeehin discusses a new report on the potential for abrupt climate changes from global warming during this century.




Public Domain.


Abrupt Climate Change



Jessica Robertson:  Hello, and welcome to USGS CoreCast, I'm Jessica Robertson.

Today's CoreCast is the second of a three-part series on recent USGS slide reports on climate change, which were developed under the U.S. Climate Change Science Program. The report we will be discussing today focuses on the potential for abrupt changes from global warming this century.

I'd like to welcome and introduce you to our guest, USGS Associate Program Coordinator for the Office of Global Change, John McGeehin who was the USGS lead for this report. Thank you for joining us Jack.

First, can you provide us some background information and an overview of this report?

John McGeehin: Sure, Jessica. The report is entitled, "Abrupt Climate Change".

Abrupt climate change is defined as a large-scale change in the climate system that takes place over a few decades or less, persists or anticipated to persist for at least a few decades, and cause a substantial disruptions in human and natural systems. In particular, these changes can refer to temperature, precipitation patterns, ice sheet extent and sea level rise, to name a few.



The Abrupt Climate Change report is a synthesis and assessment product, or an SAP, but it's commissioned by the U.S. Climate Change Science Program or CCSP. There are 21 of these SAPs, covering a wide range of climate topics. The topics themselves are grouped according to the goals laid out in the CCSP strategic plan.

The SAP on abrupt climate change addresses goal three, which is to reduce uncertainty in projections on how the earth climate and environmental systems may change in the future.

Jessica Robertson:  And Jack, what specific issues did the report focus on, and why did you choose these topics?

John McGeehin: The report looks at four types of abrupt change that standout in the geologic records being so rapid and large in their impact that if they were to recur, they would pose clear risk to society's ability to adapt.

Those four topics are: abrupt changes in glaciers and ice sheets and the effect of those changes on sea level, abrupt changes to the hydrologic cycle particularly drought, abrupt changes to the Atlantic meridional overturning circulation or AMOC, as it's called. The AMOC is a critical component of global climate. It's characterized by the northward flow of warm salty water in the upper layers of the Atlantic Ocean.



And finally, abrupt release to the atmosphere of methane, a powerful greenhouse gas trapped in permafrost and in ocean sediments. 

Jessica Robertson:  Can you tell us what were the key findings of this report?

John McGeehin: Let's start with the more worrisome results. They come from the sections in the report on sea level rise from melting ice sheets and drought in the southwestern United States.

The Greenland and Antarctic ice sheets have been losing a significant amount of mass in recent years. Much of the mass loss from the ice sheets is being attributed to dynamic processes that are only now being understood.

For example, surface melt water can penetrate to the bed of an ice sheet and act as a lubricant that speeds up the flow of the glaciers exiting the ice sheets. Other processes that are being observed include ice sheet removal, ice front retreat and glacial on grounding that reduce the resistance of flow of these glaciers. All of these processes have the combined effect of hastening the flow melt water to the ocean and raising sea level.



Unfortunately, none of the processes I just mentioned are included in current climate models. Getting these dynamic processes into models is critical to improving the accuracy of sea level rise projections. The Intergovernmental Panel on Climate Change, or IPCC, 2007 report predicted 0.9 to 1.4 feet of sea level rise by the year of 2100. The authors of this report believe that these estimates will need to be rise substantially upwards if current rates have observed ice sheet melting continue.

The likeliness of increased in persistent drought in the southwestern United States is another worrisome key finding in this report. Future greenhouse gas warming is expected to influence precipitation patterns across broad regions globally. Particularly vulnerable is the southwestern portion of North America, including Mexico. The vast majority of climate models consider this part of this assessment indicate that subtropical drying will intensify and persist in the coming decades.

We know from studies of tree-rings that some prehistoric droughts in the United States have been much more persistent than those of the 19th and 20th century. These have been called mega droughts because they often last for several decades.



Obviously, this was before greenhouse gas warming. We don't know for sure how much of an effect greenhouse warming will have on drying, but as I indicated most models predict that it will increase drying in already dry regions.

If the model results are correct, then the southwestern United States may already be entering an abrupt period of increased drought that could last a decade or longer.

Jessica Robertson:  Well, those are certainly important issues.

And what other conclusions did you find?

John McGeehin: Well, Jessica, the key findings from these other topics are not as gloomy. Let's start with the Atlantic meridional overturning circulation or AMOC.

The AMOC is responsible for the transport of a substantial amount of heat from the tropics toward the North Atlantic where it impacts many aspects of the global climate system, including summer conditions over North America and Western Europe.

The AMOC is the reason you can have palm trees growing in southwestern Ireland. A concern is that global warming will cause the circulation system to abruptly slow down or collapse. Fortunately, the authors of this report find that a collapse or abrupt weakening of the AMOC is very unlikely in the 21st century.



However, it is very likely that the AMOC strength will decrease more gradually during this time, with a best guess estimate of 25 or 30 percent. Even with this weakening, it is very likely that the warming trend for the regions influenced by the AMOC will continue in response to increasing greenhouse gases.

Finally, we came to the methane chapter. Methane is a potent greenhouse gas; the second most important greenhouse gas that humans influence. CO2, being the first. Large concentrations of methane exist in solid form, locked away in ocean sediments and in permafrost.

A concern is that these concentrations may become unstable in the future because of warming temperatures that the methane will be released abruptly to the atmosphere. This report finds that an abrupt release of methane from hydrates this century is very unlikely.

However, it is likely that climate change will accelerate the pace of emissions from hydrates and wetlands. Current models suggest that wetland emissions to methane could double in the next century.

Jessica Robertson:  Now, Jack, can you expand on what this report tells us in terms of whether we should prepare for abrupt changes?



John McGeehin: Well, I think it is certainly in our best interest as a society to be prepared for the possibility of abrupt climate change. A big part of that preparation is having accurate climate projections at a useful scale for policy makers, land managers and the public.

As I mentioned earlier, this report corresponds to the CCSP goal of reducing uncertainties of projections about how the earth's climate may change in the future. Clearly, there are still uncertainties to overcome.

In each section of this report, there are recommendations for additional research aimed at further reducing uncertainties. The hope is that this report will help us to make informed decisions about where we go from here and what we need to do to prepare.

Jessica Robertson:  And what was the USGS role in this report and how do you draw these conclusions?

John McGeehin: The USGS was the lead agency in developing this report. We framed the study, organized the team of authors, arranged for peer and public reviews of the draft document, and ensured that the document met the federal government's information quality requirements.

The key findings, conclusions and recommendations made in the report were done by assessing the existing scientific literature on this topic. A particular focus was on a literature that came out since the IPCC report in 2007. Thirty-two scientists from federal and nonfederal institutions contributed to the report and it took two years to complete.



Jessica Robertson:  Thanks, Jack. Is there anything else you want to share with us?

John McGeehin: Yes, I would like to thank our partners at NOAA and the National Science Foundation for their help in planning and developing this SAP. Also, I would like to thank all of the authors of the report for their time and effort.

For the authors, the SAP was essentially a volunteer job, in addition to their regular jobs over the past couple of years. Finally, I would like to the peer and public reviewers for taking their time to comment on the report. It is a better document because of them.

This was a truly collaborative effort and I'm honored to have been a part of it.

Jessica Robertson:  Well, thank you for joining us today.

John McGeehin: My pleasure, Jessica.

Jessica Robertson:  And thank you to all of our listeners who joined us for this episode of CoreCast. Don't listen to our additional CoreCast on the other two USGS slide reports under the U.S. Climate Change Science Program.



Last week's episode focused on past climate change an variability in the Arctic and high latitudes, and next week's episode focuses on climate change impacts to ecosystems and resulting responses, including insect outbreaks, wildfire and forest dye bug which are not easily reversible.

If you would like to know more about this report and other CCSP products visit, The report discussed today is Synthesis and Assessment Product 3.4, Abrupt Climate Change.

As always, CoreCast is a product of the U.S. Geological Survey, Department of the Interior.



Related to this episode:

Show Transcript