finding 19.3 : key-message-19-3

The Southeast’s diverse natural systems, which provide many benefits to society, will be transformed by climate change (very likely, high confidence). Changing winter temperature extremes, wildfire patterns, sea levels, hurricanes, floods, droughts, and warming ocean temperatures are expected to redistribute species and greatly modify ecosystems (very likely, high confidence). As a result, the ecological resources that people depend on for livelihood, protection, and well-being are increasingly at risk, and future generations can expect to experience and interact with natural systems that are much different than those that we see today (very likely, high confidence).



This finding is from chapter 19 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

Prior to identifying critical issues for the Southeast assessment focuses for the Fourth National Climate Assessment (NCA4), the Chapter Lead (CL) contacted numerous professional colleagues representing various geographic areas (e.g., Florida, Louisiana, and South Carolina) for expert opinions on critical climate change related issues impacting the region, with a particular emphasis on emerging issues since the Third National Climate Assessment (NCA3) effort.7bdd9d20-6e83-40ab-8d50-68272c2b3dc9 Following those interviews, the CL concluded that the most pressing climate change issues to focus on for the NCA4 effort were extreme events, flooding (both from rainfall and sea level rise), wildfire, health issues, ecosystems, and adaptation actions. Authors with specific expertise in each of these areas were sought, and a draft outline built around these issues was developed. Further refinement of these focal areas occurred in conjunction with the public Regional Engagement Workshop, held on the campus of North Carolina State University in March 2017 and in six satellite locations across the Southeast region. The participants agreed that the identified issues were important and suggested the inclusion of several other topics, including impacts on coastal and rural areas and people, forests, and agriculture. Based on the subsequent authors’ meeting and input from NCA staff, the chapter outline and Key Messages were updated to reflect a risk-based framing in the context of a new set of Key Messages. The depth of discussion for any particular topic and Key Message is dependent on the availability of supporting literature and chapter length limitations.

Description of evidence base:

Winter temperature extremes, fire regimes, sea levels, hurricanes, rainfall extremes, drought extremes, and warming ocean temperatures greatly influence the distribution, abundance, and performance of species and ecosystems.

Winter air temperature extremes (for example, freezing and chilling events) constrain the northern limit of many tropical and subtropical species.9cef8d69-7596-480a-81b6-abd09ff1c1e3,fe86238e-eab4-4c02-a7dd-19bcd96a2613,59a8ba69-97e3-4a57-8625-45764b465463,30e64f09-40ad-4aa8-8a20-ecc203f91914,31446ba7-4409-483b-b467-ae773a9ba950,829784a1-9b0f-454b-8418-0acc7f6e4508,613c4c80-9df1-43a5-9990-5387092c74c8,fb5567e7-7296-4ea0-8749-76c74eae20d5,9b30cb39-2de7-468b-a292-d758d56c4aa3,0a8508df-df59-4080-89a2-52bfeaca47e0,01b0f914-7423-4f14-8ba9-84eb40e00ab9,ed8b17d0-d3f4-4fc8-bd1c-3034b4ea2599,28476a59-c86d-492e-aa97-ec61713f9775,2bc3a5f0-95b4-46c5-b4bb-6984f01bb3fa,e3f0f82a-4c3d-4c01-924e-5b396ab55f7d,64dedf01-8a9b-49ce-b494-410a386befbe,6b60f34d-c84f-4bdd-84a8-78ff37ea2b2e,ef49ecb5-1388-4e6c-bc78-ba94ea897c0c,04bcac75-caf7-452a-b1c8-de49f216c240,4ac9e33c-35e4-4d28-a720-da17cb3baa49,b61cb4f4-19bd-4342-8817-9b42e069afc7,959c3aa0-bdde-4ee9-9b39-2f1ee2eb079f,3a87a3e6-3e40-4a5d-8b61-2071f8cfadbe,44cdf44a-701f-4752-9980-cd02c4542d08,d01b509f-4eeb-44e9-ba26-e7d21b81e3eb,1c389f43-4f1a-4f94-a537-3538aa444497,4dfdd8ce-b51b-488f-ac53-0522b91111cd,da29fed3-0376-4167-95f1-90cd096a6ddd,43afbc10-9da8-467e-b65f-448599b05dd0 In the future, warmer winter temperatures are expected to facilitate the northward movement of cold-sensitive species, often at the expense of cold-tolerant species.30e64f09-40ad-4aa8-8a20-ecc203f91914,31446ba7-4409-483b-b467-ae773a9ba950,0a8508df-df59-4080-89a2-52bfeaca47e0,28476a59-c86d-492e-aa97-ec61713f9775,e3f0f82a-4c3d-4c01-924e-5b396ab55f7d,64dedf01-8a9b-49ce-b494-410a386befbe,6b60f34d-c84f-4bdd-84a8-78ff37ea2b2e,ef49ecb5-1388-4e6c-bc78-ba94ea897c0c,b61cb4f4-19bd-4342-8817-9b42e069afc7,44cdf44a-701f-4752-9980-cd02c4542d08,e4313895-fb80-4d31-906c-2fadb9da71de Certain ecosystems are located near thresholds where small changes in winter air temperature regimes can trigger comparatively large and abrupt landscape-scale ecological changes (i.e., ecological regime shifts).31446ba7-4409-483b-b467-ae773a9ba950,28476a59-c86d-492e-aa97-ec61713f9775,6b60f34d-c84f-4bdd-84a8-78ff37ea2b2e

Changing fire regimes are expected to have a large impact on natural systems. Fire has historically played an important role in the region, and ecological diversity in many southeastern natural systems is dependent upon fire.56b229a1-fc34-4010-9b6e-3ab94c77b49c,cfc7534a-a88e-47c0-bff4-47f7416ccc1e,52b8c0e6-00b2-42aa-9df5-6d46fe600b7d,4cf69f1f-d269-4a5d-8aae-cdd7cedec70f In the future, rising temperatures and increases in the duration and intensity of drought are expected to increase wildfire occurrence and also reduce the effectiveness of prescribed fire.de4a77df-03ba-4319-a13f-7fdefbb353a5,bb7efb4d-1cf9-4ce8-84e7-768910318053,54bc1048-87de-40b1-9f21-7482e2de3883,09848305-b2eb-4468-bab9-036dd20b9c2e

Hurricanes and rising sea levels are aspects of climate change that will have a tremendous effect on coastal ecosystems in the Southeast. Historically, coastal ecosystems in the region have adjusted to sea level rise via vertical and/or horizontal movement across the landscape.6c5f197a-cfe5-4433-9bce-2c53a1939f2d,7fb4916b-6576-4ceb-b3c0-dfb0ddbcc7be,36ca022b-b59b-405a-a575-f21196e2bfe1,3bffd087-0af7-47d7-8a00-a21f0fc63569 As sea levels rise in the future, some coastal ecosystems will be submerged and converted to open water, and some coastal ecosystems will move inland at the expense of upslope and upriver ecosystems.79a38ee0-fa95-411e-bb5d-48d0e34554cb,47e2e36b-27de-461f-8188-2d04216da2a5 Since coastal terrestrial and freshwater ecosystems are highly sensitive to increases in inundation and/or salinity, sea level rise will result in the comparatively rapid conversion of these systems to tidal saline habitats. In addition to sea level rise, climate change is expected to increase the impacts of hurricanes; the high winds, storm surges, inundation, and salts that accompany hurricanes will have large ecological impacts to terrestrial and freshwater ecosystems.babe9483-5a5a-4167-b004-9e80ab8f0db1,465fa644-f252-49a8-ae70-b1a8ca976c04

Climate change is expected to intensify the hydrologic cycle and increase the frequency and severity of extreme events. Extreme drought events are expected to become more frequent and severe. Drought and extreme heat can result in tree mortality and transform southeastern forested ecosystems.a073cf8e-8d74-4f11-bfe2-d3494b9bcc7a,878be8a3-989e-497d-af88-5417df6ab074,d8731246-25c1-4f5f-95ed-26eb14d03840,fc6e40e3-32d7-4d49-82c5-8fe3d9845886,57d6bbe1-4347-43e1-8727-de49161037bb,acd8431a-2d31-4bfd-b64f-905f7c066b74,298cdb3f-64e7-4ac9-814c-f8deefbf964b Drought can also affect aquatic and wetland ecosystems.989a57fc-3c12-4ed1-a80d-0c765a119a3f,77518d3d-0483-46e5-a6d6-8a57cd7b9969,f642c166-4880-4ce0-b798-d00f4ce73486,938aaf30-da39-4990-a2fb-30518482f772,0b46c942-55d2-4926-86d3-7afe04a29825,93f9d2a2-b3db-489d-9b0b-49a8a302d73a,3994dfa3-042a-41bc-b976-8e5a99ddba12 Extreme rainfall events are also expected to become more frequent and severe in the future. The prolonged inundation and lack of oxygen that result from extreme rainfall events can also result in mortality and large impacts to natural systems.f3efb037-04cf-442a-8d41-812d21f7a6c8 In combination, future increases in both extreme drought and extreme rainfall are expected to transform many southeastern ecosystems.

Warming ocean temperatures due to climate change are expected to have a large effect on marine and coastal ecosystems.cfdaea11-95e2-4789-914b-74901b2f26b0,91134a9b-6dde-4607-bc9f-6301da1e1800,4c1d952b-234b-4f64-8757-d94e3565b067 Many species are sensitive to small changes in ocean temperature; hence, the distribution and abundance of marine organisms are expected to be greatly altered by increasing ocean temperatures. For example, the distribution of tropical herbivorous fish has been expanding in response to warmer waters, which has resulted in the tropicalization of some temperate marine ecosystems and decreases in the cover of valuable macroalgal plant communities.e4313895-fb80-4d31-906c-2fadb9da71de A decrease in the growth of sea turtles in the West Atlantic has been linked to higher ocean temperatures.6a37fde2-5a4b-470e-b14b-304ca956b4b6 The impacts to coral reef ecosystems have been and are expected to be particularly dire. Coral reef mortality in the Florida Keys and across the globe has been very high in recent decades, due in part to warming ocean temperatures, nutrient enrichment, overfishing, and coastal development.b09adbe5-6a17-4d3c-ab96-b3d9e306af67,41a1d67f-e2ba-4cb0-857f-8fce73368301,1ea5ba53-3e63-45ad-ae18-ce49750ea571,78e5de17-2746-4800-8c79-082715ff4e37,4ee62705-7f16-4bd9-871b-cd103d8439fa Coral elevation and volume in the Florida Keys have been declining in recent decades,5c1b02bb-0002-4f57-9a64-68a8d0539cfa and present-day temperatures in the region are already close to bleaching thresholds; hence, it is likely that many of the remaining coral reefs in the Southeast will be lost in the coming decades.bd3dbfa7-8dc4-4442-9cf2-14f583dc4a36,c3eee222-c3b5-4e90-a034-5e90f96c2687 In addition to warming temperatures, accelerated ocean acidification is also expected to contribute to coral reef mortality and decline.e684169c-60a2-4c78-a724-36fb93fb385a,7ab1d9e1-75a1-48c5-8d85-02258496f919

New information and remaining uncertainties:

In the Southeast, winter temperature extremes, fire regimes, sea level fluctuations, hurricanes, extreme rainfall, and extreme drought all play critical roles and greatly influence the distribution, structure, and function of species and ecosystems. Changing climatic conditions (particularly, changes in the frequency and severity of climate extremes) are, however, difficult to replicate via experimental manipulations; hence, ecological responses to future climate regimes have not been fully quantified for all species and ecosystems. Natural ecosystems are complex and governed by many interacting biotic and abiotic processes. Although it is possible to make general predictions of climate change effects, specific future ecological transformations can be difficult to predict, especially given the number of interacting and changing biotic and abiotic factors in any specific location. Uncertainties in the range of potential future changes in multiple and concurrent facets of climate and land-use change also affect our ability to predict changes to natural systems.

Assessment of confidence based on evidence:

There is high confidence that climate change (e.g., changing winter temperatures extremes, changing fire regimes, rising sea levels and hurricanes, warming ocean temperatures, and more extreme rainfall and drought) will very likely affect natural systems in the Southeast region. These climatic drivers play critical roles and greatly influence the distribution, structure, and functioning of ecosystems; hence, changes in these climatic drivers will transform ecosystems in the region and greatly alter the distribution and abundance of species.

Provenance
This finding was derived from scenario rcp_8_5

References :

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