Climate Change Moves Firmly Into the Present: Blockbuster National Climate Assessment

Climate change, once considered an issue for a distant future, has moved firmly into the present,” begins a new 1,000+ page report on U.S. climate released May 6. The National Climate Assessment, issued every four years by NOAA, is an effort by more than 300 U.S. scientists to assess how the climate is changing in the U.S. The report was supervised and approved by a 60-member committee representing a cross section of American society, including representatives of two oil companies. “Summers are longer and hotter, and extended periods of unusual heat last longer than any living American has ever experienced,” the report continues. “Winters are generally shorter and warmer. Rain comes in heavier downpours. People are seeing changes in the length and severity of seasonal allergies, the plant varieties that thrive in their gardens, and the kinds of birds they see in any particular month in their neighborhoods.” The National Climate Assessment lists hotter heat waves, more intense droughts, coastal inundation due to rising seas, heavier downpours, melting of glaciers and permafrost, bigger wildfires, worsening air pollution, stronger storms, increased diseases transmitted by insects, food, and water, and threats to mental health, as being of particular concern for Americans. If you want a thorough understanding of how climate change is affecting and will affect the U.S., this highly readable document is a great one to read, and I plan to frequently reference it in the coming years. Coming on the heels of a major 3-part report released by the United Nations Intergovernmental Panel on Climate Change (IPCC) in September - April, the National Climate Assessment presents the same key themes: climate change is already having widespread impacts and will get much worse, but there are cost-effective measures we can take to adapt to it and help reduced it. “Climate change presents a major challenge for society,” the report warns. “There is mounting evidence that harm to the nation will increase substantially in the future unless global emissions of heat-trapping gases are greatly reduced.” What’s particularly handy about the NCA is that it is U.S.-specific, and discusses in great detail the specific impacts in eight different regions of the U.S.: Northeast, Southeast and Caribbean, Midwest, Great Plains, Southwest, Northwest, Alaska, and Hawaii and Pacific Islands. I present here a few highlights.

Wet areas will get wetter, and dry areas will get drier. To me, this is the key finding of the NCA. As shown in Figure 1 below, the water-rich will get richer, and the water-poor will get poorer. This pattern will increase the costs of both droughts and floods, and make it harder to grow crops, on average, when the nation-wide impact is considered.


Figure 1. Difference in precipitation (in percent) between the observed 1970 - 1999 period, and the 30-year period centered on 2084, as predicted by 15 climate models used to formulate the 2007 IPCC climate report. The models assumed a relatively high-emissions scenario (A2), though not as high as the path humanity is currently on. The results show a key prediction of the future for North America: wet areas are expected to get wetter, and dry areas are expected to get drier. The predicted summer dryness across the major grain-growing areas of the U.S. is of particular concern, since increases in dryness will make is harder to grow food. Image credit: NASA and NOAA.

Agriculture: “Climate disruptions to agriculture have been increasing and are projected to become more severe over this century. Some areas are already experiencing climate- related disruptions, particularly due to extreme weather events. While some U.S. regions and some types of agricultural production will be relatively resilient to climate change over the next 25 years or so, others will increasingly suffer from stresses due to extreme heat, drought, disease, and heavy downpours. From mid-century on, climate change is projected to have more negative impacts on crops and livestock across the country – a trend that could diminish the security of our food supply... Climate change effects on agriculture will have consequences for food security, both in the U.S. and globally, through changes in crop yields and food prices and effects on food processing, storage, transportation, and retailing. Adaptation measures can help delay and reduce some of these impacts.”

Water: “The Southwest, Great Plains, and Southeast are particularly vulnerable to changes in water supply and demand. Changes in precipitation and runoff, combined with changes in consumption and withdrawal, have reduced surface and groundwater supplies in many areas. These trends are expected to continue, increasing the likelihood of water shortages for many uses. Increasing flooding risk affects human safety and health, property, infrastructure, economies, and ecology in many basins across the United States.”

Heavy Downpours: “Heavy downpours are increasing nationally, especially over the last three to five decades. Largest increases are in the Midwest and Northeast. Increases in the frequency and intensity of extreme precipitation events are projected for all U.S. regions.”


Figure 2. Percent changes in the amount of precipitation falling in very heavy events (the heaviest 1%) from 1958 to 2012 for each region. There is a clear national trend toward a greater amount of precipitation being concentrated in very heavy events, particularly in the Northeast and Midwest. Image credit: NCA Overview, updated from Karl et al. 2009.

Extreme Weather: “There have been changes in some types of extreme weather events over the last several decades. Heat waves have become more frequent and intense, especially in the West. Cold waves have become less frequent and intense across the Nation. There have been regional trends in floods and droughts. Droughts in the Southwest and heat waves everywhere are projected to become more intense, and cold waves less intense everywhere.”

Hurricanes: “The intensity, frequency, and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have all increased since the early 1980s. The relative contributions of human and natural causes to these increases are still uncertain. Hurricane-associated storm intensity and rainfall rates are projected to increase as the climate continues to warm.”

Severe Storms: “Winter storms have increased in frequency and intensity since the 1950s, and their tracks have shifted northward over the United States. Other trends in severe storms, including the intensity and frequency of tornadoes, hail, and damaging thunderstorm winds, are uncertain and are being studied intensively.”

Oceans: “Ocean waters are becoming warmer and more acidic, broadly affecting ocean circulation, chemistry, ecosystems, and marine life. More acidic waters inhibit the formation of shells, skeletons, and coral reefs. Warmer waters harm coral reefs and alter the distribution, abundance, and productivity of many marine species. The rising temperature and changing chemistry of ocean water combine with other stresses, such as overfishing and coastal and marine pollution, to alter marine-based food production and harm fishing communities.” The NCA website has an impressive interactive graphic with a slider that allows one to see the impact of acidification on a pteropod’s shell.

The official roll-out of the NCA will occur at 2pm EDT May 6 from the White House, and will be webcast live at http:/www.whitehouse.gov/live. According to Andrew Freedman at Mashable, eight television meteorologists are slated to have rare one-on-one interviews about global warming with President Barack Obama on Tuesday, including Al Roker, co-anchor of NBC's Today Show; Ginger Zee, meteorologist on ABC's Good Morning America; John Morales, chief meteorologist of NBC 6 in Miami, Florida; and Jim Gandy, meteorologist of WLTX-TV in Columbia, South Carolina. President Obama also previously did an interview on climate change with a crew from Showtime's documentary series "Years of Living Dangerously”; the interview is scheduled to air sometime in the next few months.

Unlike the IPCC report, the U.S. National Climate Assessment is plainly written, easy-to-understand, and has an excellent web site with nice graphics, some of them interactive. I highly recommend perusing the Overview section of the NCA website to get a quick summary of their findings. They've also made available a collection of short videos.

I’ll have a new post on Thursday.

Jeff Masters