National Climate Assessment (NCA): The Midwest

National Climate Assessment (NCA): The Midwest

Assessment Town Hall and the NCA

On February 12, 2013 I will be part of the rollout of the National Climate Assessment (NCA) at the Midwest Regional Town Hall. You can watch online, so here is the agenda if you are interested. The National Climate Assessment is in draft form and open for public comment through April 12.

What is the NCA? In the previous two blogs (last and next to last) I wrote about the need to bring the pieces of scientific research together into a body of connected knowledge. “Assessment” is the way that the scientific community formally pulls the pieces together. It is a snapshot in time of the state of the knowledge. Climate assessments are also a way to “translate” the science of climate change for use by policy makers and those engaged in adaptation and preparedness planning.

The national assessment is performed by people in the U.S., focuses on the U.S., and will stand as a definitive starting point for many applications for the next few years. It is similar in spirit to the assessments of the Intergovernmental Panel on Climate Change (IPCC); the IPCC assessments are, however, international and managed by the United Nations. Here is a link to the Executive Summary.

The national assessments of climate and climate change have been captured in the politics of climate change for the past 15 years. This assessment is a heroic and impressive effort, but from the beginning it has been conceived as just a beginning. There is a need to do this again and again. The climate is changing, and our knowledge is always increasing. Therefore, “A primary goal for the National Climate Assessment is to establish permanent assessment capacity both inside and outside of the federal government. Building on two previous National Climate Assessment Reports (2000 and 2009), the US Global Change Research Program has established the National Climate Assessment as an ongoing process that engages people and organizations across the country in creating and maintaining the information infrastructure needed to conduct sustained assessments that improve our country’s ability to understand, anticipate, and respond to climate change impacts and vulnerabilities.” (link)

Thinking about Weather and Climate and the NCA

Recently, I have been working on a climate adaptation plan for the Great Lakes Region. Snow and snow cover are important in the region for both ecosystems and people. Snow insulates the ground and modulates water supply, by storing water that melts into streams and reservoir during spring. One of the most difficult issues to describe in adaptation planning is what happens with snow. The natural intuition is that if it gets warmer, there is less snow. But the climate is warming. The surface air temperature of the Earth is increasing. The ocean is heating. Both of these facts suggest an increased amount of water in storms. With this increased water, if it is cold enough to snow, then there is likely to be a lot of snow. We see record blizzards 10 years apart.

We are at the start of a changing picture. Warm weather and rainstorms will increasingly follow these big snowstorms. This will cause rapid melting and winter flooding. This reduces how long the snow stays on the ground. There is another change that we expect with warmer weather – more ice. Ice storms occur when the temperature is close to freezing. As it gets warmer the transition line between snow and ice moves northward. Ice storms, especially in places where there have not been ice storms, are sources of enormous damage, bringing down tree limbs and utility lines. If you are an animal looking to graze, then ice is a different challenge from snow.

So we have this picture of it getting warmer, with bigger snowstorms, and more ice storms. We expect fundamental changes to the seasonal distribution of water, with less water available during the growing season, low stream flows in the late summer. Already, if we look at the last 30 years compared to the previous 30 years, we see this signal emerging (Figure 1). Decreases in snow and snow amount are marching up from the south (red arrow), and lake effect snow is increasing around the Great Lakes (blue circle).

This is the type of figure, which shows a consistent picture of warming world. We have two different 30-year figures – the standard length of time to define “climate.” We have measurements of snow. We see the intuitive decrease in snow marching up from the south. In the Great Lakes, which are dominated by local supplies of water, there is an increase in snow because it is warmer – less intuitive, but perfectly consistent. When observations line up, like this, with theory and predictions, we have increased confidence that we know what the future will hold.






Figure 1: Mean seasonal snowfall (inches) across the Midwest for a) 1961-1990 (left) and b) 1981-2010 (right) periods. Figures courtesy of Midwest Regional Climate Center.