Overview Studies - US Government

Climate Change Threatens ‘Things Americans Value Most,’ U.S. Assessment Says 1122

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:

1. It omitted paleoclimate data entirely, against which climate model output should be benchmarked.  The paleoclimate data shows much more warming and sea level rise from current greenhouse gas levels than most climate models do.

2. It greatly underestimates the amount of warming still to come from albedo changes (such as melting ice to yield darker water) and other changes (e.g., warming the deep ocean to equilibrium with the top of the atmosphere).

3. It omits current and especially future carbon emissions from permafrost, methane hydrates, peat fires, etc.

4. It says far too little about active methods for CO2 removal from ambient air.

5. It should discuss climate change effects on agriculture after mid-century and sea level rise after 2100.

6. It should enumerate and discuss tipping points more.

Chapter 1 - Overview & Findings - PDF, 12 pp

     Chapter 2 - Our Changing Climate - PDF, 49 pp

 Chapter 3 - Water - PDF, 44 pp

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

Section Map: Overviews