The U. S. National Climate Assessment: Effects of Warming and Measures to Counteract Them

Summary. The Third U. S. National Climate Assessment, a federally mandated project, reports on the current status of global warming in the U. S. and its harmful effects on the population and the environment.  As a result of manmade emissions of greenhouse gases, damages resulting from harsh warming events and extreme weather events have been worse than in earlier periods.  They are projected to be become even more severe by the end of the present century in the absence of meaningful action to combat them. 

Mitigation and adaptation measures are available and need to be implemented to limit further warming and its harmful effects by 2100. 

Important procedures involved in combating further warming include risk assessment and evaluation, and iterative (cyclical) sequences of planning, decision-making and implementation of projects, coupled with critical analysis of steps in these processes along the way.  Applying the results of such analysis back to optimize the steps should be done repetitively in order to achieve desired goals.

 

Introduction.  The Third U. S. National Climate Assessment(NCA) was issued in May 2014 as mandated under the Global Change Research Act of 1990.  It discusses the man-made origins of contemporary global warming and the detrimental effects it is having on the U. S., presents projected future trends of warming and its effects, and discusses how the U. S. can embark on measures to combat these phenomena. Its tasks, however, do not include formulation of specific policies to address global warming.

An earlier post briefly presented important climatic changes observed around the world, as documented in the NCA.  It then rigorously developed the scientific findings that support the conclusions that a) humanity’s burning of fossil fuels (and deforestation activities) has caused, and continue to be responsible for, the increase by 40% of the atmospheric concentration of the greenhouse gas (GHG) carbon dioxide (CO₂) since the industrial revolution; and b) the increased CO₂ causes the global warming we are now experiencing.  This post summarizes some of the findings of the NCA on current and projected effects of global warming in the U. S., and how to address its damaging effects. 

This post and the earlier one are based on a Fact Sheet distributed by email by Bess Evans in the White House Office of Science and Technology Policy, and on the NCA Highlights (Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Highlights of Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program). 

Significance of the NCA.  The NCA was prepared by hundreds of scientists and experts, overseen by federal officials from thirteen departments and agencies (see the earlier post).  Its procedures assure that the results reflect the highest scientific standards and are presented in an objective, unbiased manner.

Effects of Global Warming Already Under Way.  The NCA presents the following graphic as one way of summarizing harmful effects already occurring worldwide as a result of global warming.

 

Ten atmospheric and environmental properties that are changing as a result of global warming already under way.  Upward white arrows show increasing trends, and downward black arrows show decreasing trends.

Source: Third National Climate Assessment; http://nca2014.globalchange.gov/.

 

 

Significant changes are occurring regionally in the U. S. and are projected to get worse as warming intensifies.  The NCA presented the summary table shown below to give examples of significant impacts; many more were described in the report.

 

Source: Third National Climate Assessment; http://nca2014.globalchange.gov/. 

 

 

The NCA finds important climatic extremes are occurring with higher frequency than in earlier times.  The number of heat waves in 2011 and 2012 was almost three times the long-term average.  Record heat reduced soil moisture drastically, such that in 2011 and 2012 severe drought impacted Oklahoma, Texas, Kansas, Arkansas and Missouri.  Elevated temperature in other regions increases the moisture content of the atmosphere.  This resulted in exceptionally heavy precipitation in the Northeast, Midwest, and upper Great Plains.  Heavy rainfall results in more, and more damaging, river flooding.  Coastal flooding has worsened, due to ocean storm surges which are made worse by higher average sea levels.

 

Projected future changes by the end of the 21^st century.  Under a favorable scenario of “substantial” reductions in worldwide emissions of GHGs, the continental U. S. is expected to experience temperature increases of 3-5ºF, varying by region, and much more in northern Alaska, by the last three decades of this century.  In a harsher scenario of “continued increases” in emissions, this increase ranges about 7-9ºF over most of the country, and much higher in most of Alaska.  In the “continued” scenario, the entire southern portion of the U. S. will have less precipitation, as will the northwest during summer, while the northern portion will have more. 

 

By 2100 the sea level is expected to rise 1 foot (substantial reductions) to 4 feet (continued increases) above the level of 2000.  (A tutorial on why sea level continues rising is given here.)  Over the continental U. S. summertime precipitation is projected to be 10-30% reduced in Texas, Oklahoma and neighboring regions, and Florida, and reduced even more over in the Pacific Northwest.  The NCA concludes for the remainder of this century “aggressive and sustained GHG emission reductions by the U. S. and by other nations would be needed to reduce global emissions to a level consistent with the lower [“substantial” reductions] scenario…”

 

Worsening warming will have widespread impacts on the American economic, social and natural environments.  Using the effects of Hurricane Katrina as an example, the NCA points out that extreme events can adversely affect interconnected facets of urban life in ways that worsen the effects of the calamity.  A second example is drawn from the Midwestern heat wave and drought of 2011-2012.  Agriculture suffered because water became less available than usual, since it was drawn to cool electricity generating plants called on to supply more electricity for air conditioning, rather than being available to operate irrigation pumps.

 

Coral reefs are already suffering destruction caused by higher ocean temperature and acidification due to increased dissolution of carbon dioxide, an acidic compound.

 

Warming adversely affects human health because it worsens air quality, increases heat stress and worsens the spread of food-borne, insect-borne and airborne diseases.  Additional stress from more intense heat waves will adversely impact mental health and physical wellbeing.  The NCA points out that measures to reduce GHG emissions will have “co-benefits” on health because of lower levels of particulates and sulfur dioxide as fossil fuel use is reduced.

 

About 80% of the U. S. population lives in cities and surrounding metropolitan areas.  This heightens our sensitivity to any extreme weather- or climate-related damage affecting our daily lives that may occur. 

 

As already noted, components of the various systems of the infrastructure are interconnected, so that disruption in one segment leads to loss of service in another.  Such systems include water supply and sewage treatment, electricity and fuel supplies, highways and train service for transportation, and the like.  Coping with disruptions in these systems by preventive adaptation will be costly; most coastal cities, and others further inland, are already at various stages of planning and implementing such strategies at local and regional levels.

 

Precipitation patterns and availability of water are projected to change considerably across the U. S.  Heavy precipitation events are increasing, even in regions with lower overall projected precipitation.  This can exacerbate flash flooding and river floods.  Increased drought conditions will put stress on water supplies, while sea level rise will affect coasts and adjacent aquifers.  Regionally, the Midwest and Southwest will experience lower precipitation, including reduced water from thawed snowpacks.  Water demand by 2060 will increase 25-50% or more across the Midwest and Great Plains, the Southeast, the Southwest and the Northwest coastal region.  The NCA emphasizes the interconnections among water resources, land use and provision of energy.  In the future these sectors will compete for availability and disposition of their respective resources in ways that may constrain use of each of them.

 

Agricultural productivity will be subjected to stress by the projected effects of global warming.  Agriculture currently produces crops valued at almost US$330 billion.  Compared to the last three decades of the last century, projections for the period 100 years later include a nationwide increase in the number of frost-free days which might benefit productivity and diversity; increased lengths of consecutive dry day periods by as much as 9-12 days or more, especially across the southern Midwest, the Southwest, and the Northwest; and increased occurrence of hot nights.  Both of the last two changes would adversely affect grain yields and increase stress on livestock.

 

The NCA presents overviews of adaptation strategies and mitigation measures, without espousing any particular proposal.  Adaptation relates to measures taken, either in response to a damaging event or in anticipation of a potential threat, to minimize their impacts.  In the absence of a national policy implementing adaptive measures, most activity is occurring at the state and local levels.  Significant barriers exist for adaptation, including political lethargy, reluctance to commit needed resources, and the difficulty of mobilizing action in the face of an indefinite and unpredictable future need.  Sharing of planning and execution experiences among locales should ease the way forward; to date most adaptation measures in the U. S. are in the planning stage.  In addition private corporations are implementing adaptation plans to protect business models and physical assets.

 

Mitigation refers to measures intended to reduce or minimize the emission of GHGs into the atmosphere.  In reducing further emissions, the NCA recognizes that the accumulated atmospheric concentration of GHGs is not reduced, but only stabilized at a new, higher level.  The “substantial” scenario used in the NCA would require reaching a peak emissions rate within 25 years, with reduced rates thereafter.  The NCA notes, however, that current emission trends are higher than required for this to occur, making the “substantial” scenario unattainable.  It recognizes that reforestation contributes importantly to mitigation, but realizes that this strategy may not be sustainable indefinitely. 

 

The NCA reports that the U. S. has no “comprehensive national climate legislation” in place, and that progress in the U. S. has been made as a result of regional and local efforts, and voluntary actions.  “Over the remainder of this century,” it states, “aggressive and sustained GHG emission reductions by the U.S. and by other nations will be needed to reduce global emissions to a level consistent with the [‘substantial’ scenario].”  While the NCA focuses on the U. S., this statement refers crucially to the important role that other nations, some with higher emissions than those of the U. S., must play in resolving the global warming issue.

 

The NCA summarizes possible measures available for mitigation, recognizing that it would be required significantly to decarbonize the global energy economy by 2100.  These include a) putting a price on carbon (i.e. on fossil fuels), b) regulating emission-producing activities, c) changing energy subsidy policies, and d) direct federal expenditures.  Other governmental policies include energy efficiency measures, migrating from burning fossil fuels to expansion of renewable energy sources, and lowering emission of non-CO₂ GHGs.

 

Making decisions to address global warming requires use of sophisticated analytical tools to assess risk and evaluate alternatives.  Several interacting factors are involved.  Assessing the likelihood of future damage, and valuation of likely harms, is critical in proceeding.  Interdisciplinary approaches to this undertaking are important, because making decisions involves not only scientific input, but also the frameworks used in the political and business world for program adoption in the face of incomplete knowledge.  For example, in an environment of limited resources, choices must be made about allocation of projects between mitigation of future emissions and adaptation to present and projected damages.  Public opinion is important, because such decisions cannot be sustained in the absence of support by stakeholders.  The NCA recommends an iterative process for proceeding, in which information and intermediate results are repeatedly subjected to assessment and evaluation in order to provide updated information on project development and implementation. 

 

Analysis

 

The National Climate Assessment is but one of many recent reports addressing global warming.  Another significant contribution was the Fifth Assessment Report issued by the United Nations-sponsored Intergovernmental Panel on Climate Change over the period from Sept. 2013 to April 2014.  These reports conclude that manmade emissions of GHGs supporting industrialization around the world cause higher long-term global average temperature, and its consequent harms and damages to society and the environment.  The NCA focuses on effects on the United States, whereas most other reports cover global effects broadly.

 

The NCA provides details on warming-related changes to weather patterns and their harmful social and economic effects already being felt, and projects even more severe future changes as emissions continue to accumulate and the global temperature continues to increase.  It enumerates various measures that can help mitigate future emissions, and notes that mitigation and adaptation strategies are closely interrelated.  The report points out that major, sustained efforts will be required in the U. S. and worldwide to reduce global GHG emissions sufficiently to keep additional warming low.

 

Importantly, it stresses the importance of risk analysis and interdisciplinary approaches that need to be invoked in order to combat global warming.  A significant aspect of this strategy should include repetitive cycles of planning, decision-making and action combined with assessment of interim processes and results.  The results obtained by weighing which processes work and which do not would provide useful inputs to the successive cycles of project development and implementation.

 

Finally, the NCA recognizes that global warming is truly a worldwide problem requiring global cooperation in arriving at an international agreement addressing both mitigation and adaptation.  GHGs, once emitted from a point source, are dispersed throughout the atmosphere around the world.  Accordingly, all source nations have to coalesce around the common objective of minimizing further emissions.

 

© 2014 Henry Auer