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

The U. S. National Climate Assessment: Warming Is Due to Human Actions

Summary.  The U. S. government released its Third National Climate Assessment in May, 2014.  It shows that emissions from human use of fossil fuels since the industrial revolution began are reflected in increased carbon dioxide concentrations in the atmosphere, and that this is directly responsible for the increase in the long-term global average temperature.  This post summarizes these findings, affirming their validity beyond any credible scientific doubt.

A future post will consider the Assessment’s climate findings.  Warming has already had adverse effects across the U. S., including heat, drought, wildfires, changes in availability of water, floods, ocean storm surges, extreme weather and climate events and socioeconomic effects.  Worsening of these trends is foreseen during this century.

Introduction.  The Third National Climate Assessment (NCA) was issued May 6, 2014 as mandated under the Global Change Research Act of 1990 to “assist the nation and the world to understand, assess, predict, and respond to human-induced and natural processes of global change”.  Its tasks, however, do not include formulation of policies to address global warming.

Significance of the NCA.  The NCA was prepared by hundreds of scientists and experts, overseen by federal officials from thirteen departments and agencies (see Details at the end of this post).  Its procedures assure that the results reflect the highest scientific standards presented in an objective, unbiased manner.  Its importance lies also in its emphasis on observations and projections of climate in the U. S. by region and by the sector of ecological or economic activity.

This post and one to follow 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 ofClimate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, 148 pp.).  Here the scientific findings leading to the conclusion that global change arises from human activities are summarized.  A second post will present selected findings of the NCA drawn from the regions and segments mentioned above.  

The Earth is warming as a result of “human activities, predominantly the burning of fossil fuels” (NCA).  Carbon dioxide (CO₂) has been recognized as a greenhouse gas since at least the 19^th century.  Although it has been present in the atmosphere for geological time frames, the recent abrupt increase due to human use of fossil fuels has raised its concentration, and that of other man-made GHGs, higher than before these human activities began.  The incremental CO₂ raises average temperatures around the globe.  This has led to several effects identified in the NCA and shown in the following table:

Increasing Values or Amounts	Decreasing Values or Amounts
Primary Effects
Temperature Over Land
Sea Surface Temperature
Temperature Over Oceans
Air Temperature Near Earth’s Surface (Troposphere)
Ocean Heat Content
Consequent Effects
Water Vapor (Moisture Content of Air)	Sea Ice
	Snow Cover
	Glaciers and Ice Sheets

 

Strong Correlation between CO₂ and Global Temperature.  The NCA presents data showing a close correlation between rising atmospheric CO₂ concentration and global average temperature during the industrial era, shown in the graphic below.

Correlation between global temperature and CO₂ concentration from 1880 to 2012.  The thick black line gives the yearly CO₂ concentration in parts per million (volumes of CO₂ present in 1 million volumes of air) with values along the right vertical axis.  The ends of the blue and red lines show the temperature with values along the left vertical axis.  The horizontal line shows the average temperature across this time span.  The ends of the blue lines show the temperature values for years in which the temperature was below the average, and the ends of the red lines show the temperature values for years in which the temperature was above the average.

Source: NCA; www.nca2014.globalchange.gov.

 

The ends of the blue and red lines, ending at the average temperature value for each year, and the solid black line for annual CO₂ concentrations are highly correlated, suggesting a relationship between them. 

 

Emissions of CO₂ have risen sharply from zero since the beginning of the industrial revolution.  The sources of increasing atmospheric CO₂ from 1850 to the present are shown in the following graphic.

Annual rates of emission of CO₂ (evaluated on the basis of the carbon portion of the carbon dioxide molecule) from the three main fossil fuels, plus the production of cement from limestone.  The amounts shown represent about 80% of all human-derived carbon, with most of the remainder arising from human-induced deforestation.

Source: NCA (data from Boden et al. 2012); www.nca2014.globalchange.gov.

 

 

It is important to note that the time course for the annual rate of emission of C from burning fossil fuels in this graphic follows closely the time course for the annual values of atmospheric CO₂ concentration and annual temperature rise shown in the first graphic.   These data strongly suggest that the increased atmospheric concentration of CO₂ during industrial times originates from the burning of fossil fuels, and that the excess CO₂ causes the global temperature rise because of the greenhouse effect.

 

Burning fossil fuels is directly responsible for the increase in the concentration of atmospheric CO₂.  This conclusion is based on use of a distinctive molecular signature for CO₂, a physical property (the isotopic ratio of ¹³C to ¹²C in CO₂) which differs for CO₂ originating geologically in the atmosphere and CO₂ originating from burning fossil fuels.  The time course for this property, measured for the past 1,000 years, also follows the trends shown in the previous graphics.  Significantly, pronounced changes arise only during the industrial period, retracing the time courses shown above for temperature, atmospheric CO₂ and fossil fuel emissions.  The trend of values deviates from those for the first 800 years and curves strongly in the direction characterizing CO₂ originating from fossil fuels as the industrial revolution progresses (R. J.Francey et al., Tellus (1999), 51B, 170–193).   The researchers conclude “The overall [change in the isotopic ratio] during the last 1-2 centuries is attributed to anthropogenic [i.e., man-made] emissions”.  This result removes any credible basis for scientific doubt that the excess CO₂ in the atmosphere accumulating during the industrial period originates from burning fossil fuels.

 

Man-made CO₂ is responsible for global warming.  Climate models that simulate past global average temperature have been run for the cases that a) excess CO₂ originating from burning fossil fuels is omitted, and b) it is included.  The results are shown below.

 

Observed annual average global temperature changes from 1890 to 2010 (black line), and “hindcasts” from climate models shown as light green (models using natural factors only) and gray (models using both natural and human factors).   The change defined as 0ºF is a reference obtained from a temperature average over many of the years in the center of this period.

Source: NCA (data adapted from Huber and Knutti 2012); www.nca2014.globalchange.gov.

 

 

It is important to note that both models reproduce the long-term trend of observed temperature from 1890 to about 1970.  This validates the use of the models for “hindcasting” temperature from 1970 to the present.  The graphic shows, however, that after about 1970 only the climate models that include human factors, i.e., mankind’s use of fossil fuels and deforestation, reproduce the observed temperature data.  This shows unequivocally that the differential increase in global average temperature over the last several decades arises from the incremental addition of CO₂ to the atmosphere that comes from burning fossil fuels, and from deforestation. 

 

Summary.  The NCA Highlights have shown:

1.     Since 1880 the atmospheric concentration of CO₂ and the long-term average global temperature are highly correlated;

2.     Over the same time period emission of carbon (dioxide) into the atmosphere from burning fossil fuels and producing cement follows a strongly similar time course, suggesting that burning fossil fuels is a major contributor to the excess accumulation of atmospheric CO₂;

3.     In a report not included in the NCA Highlights Francey and coworkers analyze a particular physical property of atmospheric CO₂, showing unambiguously that the excess CO₂ appearing during the industrial revolution originates from fossil fuels; and

4.     Climate model “hindcasts” show that only by including contributions to atmospheric CO₂ from human factors can the global average temperature record from 1970 to the present be satisfactorily reproduced.

 

This sequence of results, rigorously and accurately collected by climate scientists over the past several decades, conclusively establishes the validity of the NCA Highlight statement:

“The majority of the warming at the global scale over the past 50 years can only be explained by the effects of human influences, especially the emissions from burning fossil fuels (coal, oil, and natural gas) and from deforestation.”

 

Conclusion

 

The NCA has been prepared by hundreds of scientists and other experts from the academic world, nonprofit organizations, government research facilities, private sector consultants, private corporations and foreign research facilities (see Details below).  Their work was overseen by federal experts drawn from thirteen U. S. federal agencies dealing with aspects of global change.  Their report was subjected to external review, which garnered several thousand comments.  These were accommodated in preparing the final document.  There can be no reasonable basis for doubting or dismissing the impartiality, cogency and veracity of the NCA’s findings.

 

The NCA Highlights state unequivocally that most of the warming of our planet observed over the last 50 years is due to the excess contributions of greenhouse gases to the atmosphere from human activities.

 

Most of the NCA details the effects of the warming of the planet on the U. S.  This will be examined in a coming post.

 

Details

 

Significance of the NCA.  The NCA was prepared under the supervision of a federal advisory committee whose members are drawn from every department and agency, thirteen in all, substantively involved in an aspect of global change science or policy.  The Assessment itself has been assembled by over 300 scientists and experts drawn from academic research settings, federal agencies and research facilities, state agencies, nongovernmental organizations, private consulting organizations, corporations and foreign research organizations.  The Assessment is based on citations to a large number of original research articles published in peer-reviewed journals, and other reports of comparable scientific validity.  A draft version was reviewed by others in federal agencies, the academic community, the public, and the National Academy of Sciences.  The final Assessment took 4,000 comments submitted by such groups into consideration.  Entry portals to the full document, in sections, are available here . 

 

The details of this process provide high assurance that the Assessment communicates the scientific basis of the various aspects of global change treated, without projecting particular points of view not supported by scientific findings.  While remedial approaches are discussed in broad terms, no particular policy position is espoused.

 

The importance of this Third NCA is that it is written almost entirely by American experts and emphasizes aspects of global change manifested in the United States.  (This is in distinction, for example, from the recent Fifth Assessment Report of the United Nations-sponsored Intergovernmental Panel on Climate Change, which addresses the issue at a global level.) 

 

The Third NCA is noteworthy for addressing first, separate results for eight geographic regions of the United States, and second, separate results for twelve climate-based and socioeconomic segments affected by global change.  This more refined approach is enabled, compared to earlier Assessments, because of the accumulation of more detailed, sophisticated information, as well as refinement and enhancements in computational treatment of climate change in the U. S. at the regional level and across various ecological and socioeconomic segments.  These improvements were not available earlier.  A second post will consider some of these aspects of the NCA.

 

© 2014 Henry Auer