Overview Studies - US Government

Draft 4th National Climate Assessment - 0817: 13 US agencies and many universities, PDF, 545 pp

Executive Summary, draft 4th National Climate Assessment - RTF, 39 KB

     This edition of the National Climate Assessment substantially remedies the problems noted below in the 3rd edition, but still leaves room for improvement.
This draft edition has been reviewed by the National Academy of Sciences and other simiar groups, but the White House has not yet signed off on it.  After the White House, it will be opened for public comment.
    Among other things, the report says “Evidence for a changing climate abounds, from the top of the atmosphere to the depths of the oceans.”
    “Many lines of evidence demonstrate that human activities, especially emissions of greenhouse (heat-trapping) gases, are primarily responsible for recent observed climate change….  There are no alternative explanations, and no natural cycles are found in the observational record that can explain the observed changes in climate. (Very high confidence)
    “Even if humans immediately stopped emitting greenhouse gases into the atmosphere, the world would still feel at least an additional 0.5°F (0.3°C) of warming over this century, compared with today.  The projected actual rise, scientists say, will be as much as 2°C.”

     "During the Pliocene, approximately 3 million years ago, long-term CO2 levels were similar to today’s, around 400 ppm….  [G]lobal mean temperature in the Pliocene was approximately 2° to 3.5°C (3.6° to 6.3°F) above preindustrial [1750], and sea level was somewhere between 20 ± 10 meters (66 ± 33 feet) higher than today.”
    “[A]bout 17-14.5 million years ago", Earth’s "proxy-estimated global mean temperature" was "8°C ± 2°C [14°F ± 4°F] warmer than preindustrial…  Geological proxies indicate CO2 concentrations of around 400 ppm ... suggesting that as yet unidentified feedbacks must be invoked to explain climate conditions.”
    About 125,000 years ago [the Emian interglacial period], with greenhouse gas concentrations similar to preindustrial [1750] levels, "global temperatures were … 1-2°C ... warmer than [1750] levels" and "sea levels were 6-9 meters higher than modern levels”.

     [Dr. Fry, this website’s author, says that the “unidentified feedbacks” from millions of years ago were largely albedo effects, changes in how much sunlight Earth reflects, much of it from less ice and snow, and probably more from reduced cloud cover and/or large-scale cloud structure changes, all multiplied by the greenhouse effect of more water vapor in a warmer atmosphere.]

Draft 3rd National Climate Assessment - Interagency 0113 - more than 1,000 pp

Almost all chapters are also available below.

(China completed its most recent (2nd) national climate assessment at the end of 2011, with similar conclusions.  A press summary is on the page: Summaries (mostly by the Press)

     Dr. Fry, in comments on the draft 3rd NCA, made several critiques:

     Representative Concentration Pathways (RCPs) are needed to interpret the graphs below it.  RCPs are newer scenarios than the IPCC used in 2007 (A2, B1, etc.)  Caveat: these appear not to include positive feedback loops, especially carbon emissions from thawing permafrost.

  Fossil fuel carbon emission pathways for the CO2 levels above: IPCC 5 Fig. TS-19.

    The inset graph relates RCP emission paths to ppm CO2 in the air.

     4 RCP emission paths are shown: in billion tonnes (Pg) of carbon per year.
    In RCP 2.6, net world CO2 emissions from fossil fuels peak ~2020, at ~10% higher than today's.  They fall below zero ~2075.  In this case, CO2 levels peak at ~450 ppm and fall to ~420 by 2100.  Relative to 1901-60, the US has already warmed 2°F.  We will warm 2°F more by ~2045, levelling off thereafter.

      In RCP 4.5, emissions peak ~2040, at 130% of today's, then fall to 60% of today's in 2080.  CO2 levels rise to ~540 ppm.  The US warms 4°F more by 2100.

   In RCP 6.0, they peak ~2080, double today's rate, by fall to 140% of today's by 2100.  CO2 levels rise to ~540 ppm by 2100 (and a good bit more after that).  The US warms 5.5°F (3°C) from today by 2100, and still more thereafter.  Hot!
    In RCP 8.5, emissions only slow by 2100, when they are triple today's rate.  CO2 levels rise to ~ 930 ppm by 2100 (then far higher).  The US warms 9.5°F from today by 2100, then far more.    

Dr. Fry: RCP 6.0 and esp. 8.5 would repeat conditions during the PETM 55 million years ago: an ice-free Earth, 10% less land, port cities under water, warm blood a disadvantage.  Human work capacity falls 60+%, as US heat stress exceeds Sahara / Amazon today.  See  Bio-Impacts page, bottom 0213.

     However, the world may be on track resembling RCP 2.6, a major change from the perspective 5-10 years ago.  China’s emissions have plateaued, near their peak, while emissions have been falling in Europe and the USA for more than a decade.  In 2021, Solar + wind + batteries are cheaper than coal and often natural gas for new power plants.  In the USA at least, they are also cheaper than continuing to operate coal-fired power plants.

  By 2100, the likeliest sea level rise seems to be 1-4 feet.
    But 0.66 to 6.6 feet is possible.

     If seas continue rising at the current rate, they will rise 1 foot by 2100, so 0.66 feet (0.1 meter) would be a deceleration.  6.6 feet is 2 meters.

     Chapter 2 - Our Changing Climate - PDF, 49 pp

2071-2099 Average, Less 1971-2000 Average - for 2 RCPs

Precipitation changes do not include evaporation changes.  Thus changes in soil moisture skew drier.

1991-2011 Average, Less 1901-1960 Average

      1971-2000 Baseline, versus 2041-70 and 2071-2100

 Chapter 3 - Water - PDF, 44 pp

   Chapter 16 - Northeast - PDF, 25 pp

     Chapter 17 - Southeast - PDF, 22 pp

     Chapter 18 - Midwest - PDF, 23 pp

     Chapter 19 - Great Plains - PDF, 21 pp

     Chapter 20 - Southwest - PDF, 25 pp

     Chapter 21 - Northwest - PDF, 27 pp

     Chapter 22 - Alaska - PDF, 23 pp

Chapter 23 - Hawaii & US Islands - PDF, 20 pp 

Figure 22.5: The Big Thaw

Caption: Projections for average annual ground temperature at 3.3-foot (one-meter) depth over time if emissions of heat-trapping gases continue to grow (higher emissions scenario, A2), and if they are substantially reduced (lower emissions scenario, B1). Blue shades represent areas below freezing (where permafrost is present at the surface), and yellow and red shades represent areas above freezing (permafrost-free at the surface) (Markon et al. 2012).

     Chapter 24 - Oceans - PDF, 22 pp

     Chapter 25 - Coastal Zones - PDF, 40 pp

     Chapter 27 - Mitigation - PDF, 22 pp

     Science Supplement Details - PDF, 55 pp

     Topics for Future Assessments - PDF, 2 pp.  Economics Analyses, National Security, Adaptation-Mitigation Interaction

     Frequently Asked Questions - PDF, 31 pp 

80% Renewables by 2050 - NREL 1012 - volume 1 - PDF, 286 pp

Section Map: Overviews