What is the National Climate Assessment? The Most Comprehensive Report on Climate Change in the United States

November 1, 2017 | 10:37 am
Rachel Licker
Principal Climate Scientist

The amount of scientific research and brainpower that goes into the National Climate Assessment is kind of astonishing. Scratch that. It’s really astonishing.

This report is on my mind because the first draft of the next version (the fourth National Climate Assessment, or, NCA4) and one of its associated technical reports (the State of the Carbon Cycle) are due to be released for public comment this fall. In addition, the final version of the Climate Science Special Report – billed as Volume 1 of the National Climate Assessment – is due to be released in November.

So far, these reports have proceeded according to plan and are slotted to provide the President, Congress, and the public with the best available science on climate change and its impacts on the United States.

The National Climate Assessment is mandated by Congress

Before I get back to how astonishingly comprehensive the National Climate Assessment is, the National Climate Assessment (NCA) is a report that an office in the White House called the U.S. Global Change Research Program (USGCRP) is required to prepare for the President and Congress every four years. In 1990, President George H.W. Bush signed the Global Change Research Act, which mandates that this report analyze human and naturally caused global changes, and analyze their effects on things like agriculture, energy production, and human health. This Act passed unanimously in the Senate.

The Climate Science Special Report – part of the NCA process – tells you how and why the Earth is changing

The Climate Science Special Report is like going to a doctor and being given a report of your vital signs. It has information on changes in things like the Earth’s temperature, extreme weather events, and sea level, as well as what is causing these changes. The NCA is like being told by a doctor what the symptoms of these changes in your vital signs are going to be like for your community and state (e.g. more sea level rise = chronic flooding along coasts).

The Climate Science Special Report and the NCA consolidate massive amounts of scientific research

Okay, back to the astonishing amount of science that is in the NCA. Take the Climate Science Special Report. Again, this is just one part of the NCA process. In the leaked draft of the Climate Science Special Report (the final version is due to be properly released to the public in November), the authors assess more than 1500 scientific studies and reports. 1500!

I can tell you first hand that publishing a single study in a credible journal is a major feat. First, there’s the time you spend conducting the research (this is oftentimes a multi-year process during which you get feedback from colleagues at conferences). When you have significant results, you write a paper about them. It is standard practice to solicit feedback on your paper from colleagues who have related expertise before you try and get it published. Then, you submit your paper to a journal, which sends your paper to experts in your field who judge whether it is a solid piece of work or not, and offer feedback on the ways that your study and paper can be improved. If your paper is accepted, you have to revise your work according to the feedback received. Then and only then does your paper see the light of day.

Multiply that process by 1500 and you can now get a sense for how much scientific research and knowledge the Climate Science Special Report is based on. Factor in all of the other components of the NCA process that rely on similar amounts of information (e.g. the aforementioned State of the Carbon Cycle Report and the full NCA itself), and you now have a sense for how astonishingly comprehensive the NCA is.

The NCA tells us what the state of the science is on climate change and its impacts for the United States

The experts involved in the NCA and its associated technical reports not only review massive volumes of scientific studies, they spend large amounts of time comparing their findings.

For any given topic, the experts systematically look at what studies found and how similar the results are, as well as how many studies have been carried out on the topic. The experts then use all of that information to carefully communicate exactly what science can tell us on any given topic. The findings in the NCA are thus not radical, but reflect careful assessments of large volumes of science. As a result, Americans have a place that they can rely on to learn what the state of the science is on climate change and its impacts.

The NCA is authored by hundreds of experts from across the country

In addition to the sheer volume of information contained in the Climate Science Special Report and the full NCA, the reports are also incredibly rigorous with respect to the number and breadth of experts involved and the amount of scrutiny the reports undergo.

More than 300 experts were involved in the third version of the NCA. 50 authors contributed to the forthcoming Climate Science Special Report.

The Climate Science Special Report, State of the Carbon Cycle, and the full NCA itself undergo extensive review and offer a platform for feedback from diverse perspectives. The full process is outlined here, but in a nutshell, the reports are open for review by technical experts from both within and outside of the government, the National Academy of Sciences, and the public alike. The previous NCA received 4161 unique comments in total. Report authors are required to respond to each comment submitted.

The NCA provides critical information on risks from climate change for decision makers

The NCA provides critical information on the impacts of climate change on well-being and the economy of the United States. However, it stops shorts of making policy recommendations – it leaves it up to decision-makers to decide what to do about the risks that the report identifies.

Because the NCA and associated technical reports are so comprehensive and rigorous, they offer an unparalleled starting point for decision-makers, our military, the private sector (the report is broken out by sector), and members of the public alike to both assess the risks that Americans are facing and consider solutions so that we can chart a prosperous and secure path forward.


Posted in: Climate Change

About the author

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Rachel Licker is principal climate scientist with the Climate & Energy Program at the Union of Concerned Scientists. In her role, she provides strategic thinking and technical and analytical expertise across the organization, analyzes new developments in climate science, and communicates climate science to policymakers, the public, and the media.