Carbon dioxide and other greenhouse gases (GHGs) are responsible for global warming, the long-term worldwide average warming experienced since the industrial revolution. GHGs arise from human use of fossil fuels for energy. Major emitters of GHGs include both industrialized countries and, in recent decades, developing countries as well. Higher global temperatures cause the extremes of hot and cold, and wet and dry, weather of recent years. This blog examines global warming and its effects.
See the Tabbed Pages for links to video tutorials, and a linked list of post titles grouped by topic.
This blog is expressly directed to readers who do not have strong training or backgrounds in science, with the intent of helping them grasp the underpinnings of this important issue. I'm going to present an ongoing series of posts that will develop various aspects of the science of global warming, its causes and possible methods for minimizing its advance and overcoming at least partially its detrimental effects.
Each post will begin with a capsule summary. It will then proceed with captioned sections to amplify and justify the statements and conclusions of the summary. I'll present images and tables where helpful to develop a point, since "a picture is worth a thousand words".
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
adaptation measures are available and need to be implemented to limit further
warming and its harmful effects by 2100.
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.
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
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).
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.
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
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.
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.
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.
changes by the end of the 21st 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]
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
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.
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.
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
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.
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
The NCA reports
that the U.
has no “comprehensive national climate legislation” in place, and that progress
in the U.
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
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
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.
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
Climate Assessment is but one of many recent reports addressing global
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
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.
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
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.