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Slight Climate Changes May Trigger Abrupt Ecosystem Responses

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This is the third and final installment of a three-part series on climate change. Slight changes in climate may cause abrupt changes in ecosystems that are not easily reversible. Some of these responses, including insect outbreaks, wildfire, and forest dieback, may adversely affect people as well as ecosystems and their plants and animals. USGS scientist Colleen Charles discusses a new report on the impacts of a warming world on ecosystems.

Previous Episodes: Arctic Heats Up More than Other Places (Ep. 82); How Abrupt Can Climate Change Be? (Ep. 84)




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Jessica Robertson:  Hello and welcome to USGS CoreCast, I'm Jessica Robertson.  Today's CoreCast is a third of a three part series on recent USGS-led reports developed under the U.S. Climate Change Science Program.  The report we will be discussing today focuses on how a warming world may impact ecosystems in North America. 

Slight changes in climate may trigger abrupt ecosystem responses that are not easily reversible.  Some of these responses include insect outbreaks, wildfire and forest dieback.  Today, I'd like to welcome and introduce you to our guest, USGS scientist Colleen Charles, who was the agency lead for this report.  Thank you for joining us today, Colleen.

Colleen Charles:  Thank you for having me, Jessica.

Jessica Robertson:  So first, can you provide us an overview of this report?

Colleen Charles:  Yes.  The title of this report is "Thresholds of Climate Change in Ecosystems".  And this report is a synthesis and overview of what is known to date about ecological thresholds. 


An ecological threshold is defined as a point at which there is an abrupt change within that ecosystem that generally produces large, persistent and potentially irreversible changes.  One of the biggest concerns is that once an ecological threshold is crossed, the ecosystem in question will most likely not return to its previous state. 

So the existence of thresholds are a key concern of scientists and natural resource managers.  This report addressing thresholds of climate change in ecosystems is one of 21 Synthesis and Assessment Products that were produced for the Climate Change Science Program.

Jessica Robertson:  And what did this report find in terms of weather thresholds will be crossed in response to climate change?

Colleen Charles:  This report does not predict where or when a threshold will be crossed.  In some ecosystems, we do know that we are approaching threshold conditions.  However, we still do not have all the information needed to identify when an ecosystem is going to cross a threshold.


In retrospect, by looking back at ecosystem conditions and reviewing existing literature, we can identify when thresholds have been crossed within an ecosystem.  This information helps us to identify changes that are occurring at a more rapid pace, especially in sensitive ecosystems.  And this also helps us to increase societal resilience or how society will respond to or work to mitigate thresholds and their effects.

Jessica Robertson:  Can you provide examples of what would happen if thresholds are crossed?

Colleen Charles:  Yes.  In some areas of the country, we are observing climate related threshold changes already.  In Alaska for example, slight increases in temperature has caused a number of effects such as earlier spring snow melt, reduction in sea ice coverage and warming of the permafrost. 

These effects have resulted in impacts to the ecosystems by causing dramatic changes to the wetlands, the Tundra, fisheries and the forest.  Not only are we seeing the forest drying out but we are also seeing an increase in insect outbreaks such as a spruce bark beetle.  This has resulted in forest die off which has also increased fire frequency.  Earlier snow melt and forest insect outbreaks and increased fire frequency are also being seen in other areas of the country.


A final example will be with coral reefs.  Coral reefs are not mobile, they cannot move to cooler water and they cannot move to an area with less environmental stress.  What we are experiencing now are more numerous events of increased sea surface temperature, which stresses corals, causing them to bleach and making them more vulnerable to disease and death.  So once a reef dies, it takes many years for corals to re-colonize it to become a living reef again.

Jessica Robertson:  And Colleen, can you elaborate on what exactly is an ecosystem.  What defines it?

Colleen Charles:  An ecosystem is a complete community of living organisms like plants and animals and microorganisms.  And the non living materials of their surroundings such as the soil, the rocks, the minerals, as well as the water sources and the local atmosphere.  Ecosystems also vary in size and complexity and they provide goods and services to society.


So the goods and services can be viewed as benefits that people obtain from the ecosystems.  And examples of goods and services are provisioning services such as food and water; regulating services such as flood, climate and disease control; cultural services such as spiritual and recreation; and supporting services such nutrient cycling and water cycling.  And all these systems and services supply wildlife habitat.  I think from these few examples that it helps us to realize how important it is to help define where a threshold in an ecosystem will occur.

Jessica Robertson:  Colleen, can you tell us what future research is needed to help us prepare for abrupt ecosystem changes in response to a changing climate?

Colleen Charles:  One of the recommendations that was drawn from this report is how to change our paradigm from managing ecosystems in a changing climate.  In addition to the research needed to answer these questions, we also need to be able to identify thresholds at an earlier stage.  We need to understand the ecosystem as a whole and how the different components interact and affect each other within that ecosystem to determine its diversity and the likelihood of a threshold being crossed.


In future research, we also need to consider that climate change is global in nature but it will manifest itself at different local and regional scales.  And therefore, we need to determine what can be managed and how it can be managed at various scales of ecosystems.

Jessica Robertson:  And is there anything else you want to share with us about this report?

Colleen Charles:  Yes, I would really like to thank our authors, the reviewers and our partners to making this report such a great success and that we look forward to working with our partners in addressing the research questions on thresholds of climate change in ecosystems.


Jessica Robertson:  Well, thank you for joining us today, Colleen.  And thank you to all of our listeners who joined us for this episode of CoreCast.  Don't forget to listen to our previous CoreCasts on the other two USGS led reports under the US Climate Change Science Program.  Those reports focus on past climate change and variability in the Arctic and high latitudes, as well as the potential for abrupt climate changes in the 21st century which pose clear risks to society in terms of our ability to adapt.

If you would like to know more about this report and other Synthesis and Assessment Products, visit  The report discussed today is "Synthesis and Assessment Product 4.2: Thresholds of Climate Change in Ecosystems." 

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

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