State of the Carbon Cycle Report (SOCCR)

SOCCR2 Front Cover

 The Second State of the Carbon Cycle Report (SOCCR2) can be accessed via

Link to SOCCR2 metadata via the Global Change Information System (GCIS, 'an advanced, multifaceted bibliography, maintaining traceable provenance records of scientific information and providing access to the original data and research. The GCIS documents the cross-links among research papers, researchers, original data, and more and includes links back to authoritative sources for its information'):

The new State of the Carbon Cycle Report (SOCCR2) Website was released on Earth Day, April 22, 2019.



SOCCR2 back cover

 Second State of the Carbon Cycle Report (SOCCR2)

SOCCR2 can be accessed via

SOCCR2, Sustained Assessment report of the U.S. Global Change Research Program (USGCRP) was released on Friday November 23, 2018.

The SOCCR2 Report-in-Brief can be accessed here.

  • With over 200 contributing experts, this interagency Highly Influential Scientific Assessment was led by the Carbon Cycle Interagency Working Group (CCIWG) and U.S. Carbon Cycle Science Program under USGCRP auspices, and reviewed by 13 US Government agencies and departments, the U.S. National Academy of Sciences, and the general public.
  • This decadal interagency U.S. Government report involved diverse experts from multiple institutions over 3 years, producing over 6 drafts that collectively underwent over 6 rounds of formal reviews.
  • Incorporating 19 chapters distributed across four interconnected sections  (I. Synthesis, II. Human Dimensions of the Carbon Cycle, III. State of Air, Land, and Water, IV. Consequences and Ways Forward), SOCCR2 assesses the last decade of cross-sectoral carbon cycle advances across the U.S., Canada and Mexico, in the global context.
  • The 36-page SOCCR2 Report-in-Brief includes the Executive Summary and a plain language overview.
  • The 4th U.S. National Climate Assessment (NCA4) Vol. II was also released simultaneously.
  • SOCCR2 contributes to NCA4 Vol. II but is a stand-alone Sustained Assessment process report.
  • Individual chapter PDF links are provided below and can also be downloaded via

 Congratulations to the entire SOCCR2 team, whose commitment and hard work has been truly inspiring throughout this 3- years long process. Thanks to all of carbon cycle science colleagues and friends who helped in many ways, including in producing and sharing the science, tools and and knowledge assessed in SOCCR2.

 Please utilize, disseminate and amplify the SOCCR2 findings and information from using #SOCCR2.



Links to individual SOCCR2 PDFs

Download by sections of chapters (PDF files):

I. Synthesis

II. Human Dimensions of the Carbon Cycle

III. State of Air, Land, and Water

IV. Consequences and Ways Forward

Download indvidual chapters and appendices (PDF files) via or below:

Second State of the Carbon Cycle Report (Full Report)



Executive Summary

Section I: Synthesis (entire section here or individual chapters below)

Ch. 1: Overview of the Global Carbon Cycle

Ch. 2: The North American Carbon Budget

Section II: Human Dimensions of the Carbon Cycle (entire section here or individual chapters below)

Ch. 3: Energy Systems

Ch. 4: Understanding Urban Carbon Fluxes

Ch. 5: Agriculture

Ch. 6: Social Science Perspectives on Carbon

Ch. 7: Tribal Lands

Section III: State of Air, Land, and Water (entire section here or individual chapters below)

Ch. 8: Observations of Atmospheric Carbon Dioxide and Methane

Ch. 9: Forests

Ch. 10: Grasslands

Ch. 11: Arctic and Boreal Carbon

Ch. 12: Soils

Ch. 13: Terrestrial Wetlands

Ch. 14: Inland Waters

Ch. 15: Tidal Wetlands and Estauries

Ch. 16: Coastal Oceans and Continental Shelves

Section IV: Consequences and Ways Forward (entire section here or individual chapters below)

Ch. 17: Biogeochemical Effects of Rising Atmospheric Carbon Dioxide

Ch. i18: Carbon Cycle Science in Support of Decision Making

Ch. 19: Future of the North American Carbon Cycle


Appendix A: Report Development Process

Appendix B: Information Quality in the Assessment

Appendix C: Selected Carbon Cycle Research Observations and Measurement Programs

Appendix D: Carbon Measurement Approaches and Accounting Frameworks

Appendix E: Fossil Fuel Emissions Estimates for North America

Appendix F: Acronyms, Abbreviations, and Units

Appendix G: Glossary

Major SOCCR2 milestones and planned next steps (as of September 2018, subject to change)


SOCCR2 Background

In 2015, the Carbon Cycle Interagency Working Group (CCIWG), via the U.S. Carbon Cycle Science Program, initiated plans for the Second State of the Carbon Cycle Report (SOCCR2) as a follow-up to the 1st SOCCR (2007) which was a Synthesis andl Assessment Product (SAP 2.2) of USGCRP, and as a product of the Sustained National Climate Assessment. Led by the CCIWG, under USCGRP auspices and with USDA as the administrative lead, this federal interagency report was published in the fall of 2018.

The focus of SOCCR-2 is on the scientific understanding of U.S. and North American carbon cycle stocks and fluxes, in the context of and interactions with global scale budgets and climate change impacts in managed and unmanaged systems.  Carbon stocks and fluxes in soils, water (including oceans), vegetation, aquatic-terrestrial interfaces (coastal/ estuaries/ wetlands), human settlements, agriculture, forestry etc. are included.

Relevant carbon management science perspectives and support tools for supporting decisions, as addressed in and related to the US Carbon Cycle Science Plan (2011) and U.S. National Climate Assessment, USGCRP 2012-2021 Strategic Plan and Global Change Research Act (GCRA) of 1990 will are included in this assessment.  In addition to identifying uncertainties, rising opportunities for improving measurements and projections in the carbon cycle are be identified.


Relevant Resources

Table of Contents and SOCCR2 team (Federal Steering Committee and Liaisons, chapter leads, science leads, contributors)  (updated Nov 23, 2018)

Report from the National Academy of Sciences Committee that reviewed the SOCCR-2 4th-order draft (March 2018)

Review editors and roles

2nd SOCCR2 Federal Register Notice: Federal Register Notice announcing Public Review of 4th Order Draft (November 8, 2017)

Request for Review Editors nominations

Presentation slides with background information (October 2017)

Prospectus (incl . draft Table of Contents)

Presentation slides from AGU 2016 (for info on report development process and leadership team composition)

All SOCCR2 team members - authors, leads, report credits (updated Nov 23, 2018)

All authors by chapters (as of March 23, 2017)

Presentation slides with SOCCR-2 updates (June 2017)

National Academy of Sciences, Engineering and Medicine Committee to Review the SOCCR2 Draft

 First SOCCR-2 Federal Register Notice (February 12, 2016)

  • 30-day Federal Register Notice (FRN) (released on February 12, 2016) by USDA-NIFA, on behalf of the CCIWG and USGCRP, is available here.
  • The PDF of the FRN is available here. The deadline for submission of nominations for contributors, technical input and comments on the draft prospectus was March 14, 2016.

National Climate Assessment and SOCCR-2 related resources:

Federal Register Notice: Public Comment on an Annotated Outline for the Fourth National Climate Assessment (July 2016)




SOCCR2 Public Engagement, Outreach, Updates


In addition to the above section, details on prior CCIWG-led SOCCR2 public engagement and outreach events and related opportunities can be accessed via the chronological list of public announcements below.

Please check, subscribe to @USCarbon and/or subscribe to Carbon News for updates.

April, 2019

 March, 2019

February, 2019

January, 2019

November, 2018

 SOCCR2 and NCA4 Released

September, 2018

June, 2018

April, 2018

March, 2018

January, 2018

December, 2017

A video documentary, townhalls, sessions and exciting interactions with the international geoscience science community....

A short public webinar outlining the process for SOCCR-2 development and the public comments submission procedure....

November, 2017

October, 2017

We are preparing for the Public Comment Period of the 2nd State of the Carbon Cycle Report Fourth-Order Draft.

August, 2017

July, 2017

We will be at the Ecological Society of America Meeting in Oregon and at the International Carbon Dioxide Conference in Switzerland....

...for ensuring that all substantive public and the National Academy of Sciences review comments are appropriately addressed....

June, 2017

...third-order-draft transmitted to USGCRP member agency principals....

May, 2017

A new ad hoc Committee of the Academies will conduct an independent review of SOCCR-2.....

January, 2017

A new ad hoc committee of the Academies will conduct an independent review of the SOCCR-2 draft report, which will be available in early 2017....

December, 2016

Grants, opportunities and SOCCR-2 sessions and town halls in San Francisco in December 2016.....

June, 2016

The 2nd State of the Carbon Cycle Report (SOCCR-2): Assessing the Last Decades' Science of the Carbon Cycle across North America and Adjacent Oceans

February, 2016

Submit author nominations, technical input and comments on the draft prospectus.....

January, 2016

This 1-day public forum will present an opportunity for interested parties and stakeholders to provide individual input on proposed SOCCR-2 themes.

December, 2015

December 2015 AGU San Francisco sessions, February 2016 Washington DC Public Forum.....

October, 2015

... opportunities for the greater geophysical community to learn about and provide feedback on the 2nd State of the Carbon Cycle Report (SOCCR-2) that we are in the process of planning...

August, 2015

Participants learned about the USGCRP annual research prioritization process as well as partnerships and opportunities....

The US Carbon Cycle Science Program is organizing a special session 'Carbon Cycle Science at the Frontier of Global Change: A Coordinated Effort Among Federal Agencies'.....

June, 2015

Abstracts informing and related to this Special Scientific Assessment of the Current Status and Opportunities in carbon cycle science across terrestrial, atmospheric and oceanic systems are requested....

May, 2015

The CCIWG will meet with the CCSSG for individual input on carbon cycle science needs and opportunities......








Some background documents related to the earlier SOCCR, released in 2007, are available below.

State of the Carbon Cycle Report (SOCCR-1, published in 2007)

Color photo of front cover with white text on orange background and other photos

The carbon cycle chapter of the Strategic Plan for the U.S. Climate Change Science Program describes a vision to publish a series of government products on the status and trends of carbon emission and sequestration. The first of these reports, the State of the Carbon Cycle Report (SOCCR), was released by the US Climate Change Science Program (now the USGCRP) on November 13, 2007.

The 2003 Terms of Reference for the first SOCCR (2007), prepared by the Carbon Cycle Interagency Working Group and in consultation with the Carbon Cycle Scientific Steering Group, envisioned a report designed to provide accurate, unbiased, and policy-relevant scientific information concerning the carbon cycle to a broad range of stakeholders. The SOCCR Coordinating Team focused on (1) summarizing our knowledge of carbon cycle properties and changes relevant to the contributions of and impacts upon the U.S. and the rest of the world, and (2) providing scientific information for U.S. decision support focused on key issues for carbon management and policy. The report depends on results from comprehensive and informative programs, such as the North American Carbon Program and Ocean Carbon and Climate Change Program, and demands a global perspective, integrating information from studies on land and in the atmosphere and oceans around the world. The expected audience includes researchers, decision makers in the public and private sectors and the public. The Executive Summary is available here.


Background documents, prospectus, prior draft versions, review comments and responses from the first SOCCR (2007) are available here and below  (source:

SOCCR logo

Draft Versions of the SOCCR (2007) Report

March 2007 version of SOCCR/SAP 2.2, March 2007 revision of government review draft

Executive Summary

Entire Document

January 2007 version of SOCCR/SAP 2.2, government review draft

Executive Summary

Entire Document

September 2006 version of SOCCR/SAP 2.2, CCSP public review draft

Executive Summary

Entire Document

May 2006 version of SOCCR/SAP 2.2, submitted for technical/peer review

Entire Document

Review Comments and Responses

Public Review Commments and Authors' Responses

Technical Peer Review Commments and Authors' Responses


Draft Prospectus for Synthesis and Assessment Product (SAP) 2.2 (March 7, 2005)


Final Outline

The SOCCR Outline (as of November, 2004)

View the Responses to Comments Received on Outline through December 2005

Background Documents

About the SOCCR process

What is the Carbon Cycle?