Short Course: Global Warming
1. It is widely considered that over 350 ppm (parts per million) is a threshold that ushers in the worse parts of global warming, ie. Ice sheets melting, extreme weather conditions (kinda like the futures market - higher highs, lower lows, when it rains it pours sorta thing)
2. Global warming does not preclude the absence of prolonged times of colder than normal weather. (We have the elements for global warming, ie Greenhouse Gases, built up in our atmosphere. However, we must remember that our star, The Sun, is what dictates all the weather on Earth. Our Sun has cycles, like seasons on Earth, but it's cylcles are in hundreds and thousands of years, and they are magnetic, not seasonal. Currently, our sun is in a cycle where the magnetism, for what ever reason, is not as strong. Because of that, it is not "putting out" as much solar radiation as it does when it is more magnetically active. You have heard me talking about this for some time. We are supposed to be at Solar Maximum, where the Sun is extremely active with sunspots and a high level of solar activity. It's not. It's one of the least active solar maximums recorded. Which is also why I've been talking about a cooler than normal summer in the Norther tier of states.)
3. Weather Extremes. Warmer global temperatures allow for more water vapor in the atmosphere, which in turn allows for more precipitation (when and where it does fall), which accounts for the number of big rain events (100 year, 500 year, even thousand year events) being recorded.
The longer course - I include excepts of some of that below. Global warming is here. Don't be fooled into thinking that because we are going though a cooler than normal time frame, that it doesn't exist. Our knowledge of the Sun and it's long term effects have come mainly from borings in the Greenland ice sheets, and observations over the last 100 or so years - a time span that is nothing in the grand scheme of things. The "Little Ice Age" in Europe took 50 years to play out. (1650 - 1700) We could be entering (or in) that phase of the Sun now. The fact is - we don't know. China has the longest written record of life on this Earth - is this part of the reason they have been on a 'buying binge'. Again, I don't know. What I do know, is the Sun is less active than I would expect, and I think it's already effecting our temperatures in the northern latitudes.
Jen
CO2 in our atmoshpere:
On March 12, 2014, NOAA MLO recorded the first daily average above 400 ppm since Spring 2013.
399.47ppm
Atmospheric CO2 for March 2014
Preliminary monthly average as of April 2, 2014
(Mauna Loa Observatory: Scripps CO2 Program)
NOTE: On May 10, 2013, NOAA & Scripps first reported daily averages that temporarily reached 400 ppm.
Target Atmospheric CO2: Where Should Humanity Aim?
James Hansen*,1,2, Makiko Sato1,2, Pushker Kharecha1,2, David Beerling3, Robert Berner4,
Valerie Masson-Delmotte5, Mark Pagani4, Maureen Raymo6, Dana L. Royer7 and James C. Zachos8
1NASA/Goddard Institute for Space Studies, New York, NY 10025, USA
2Columbia University Earth Institute, New York, NY 10027, USA
3Dept. Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
4Dept. Geology and Geophysics, Yale University, New Haven, CT 06520-8109, USA
5Lab. Des Sciences du Climat et l’Environnement/Institut Pierre Simon Laplace, CEA-CNRS-Universite de
Versailles Saint-Quentin en Yvelines, CE Saclay, 91191, Gif-sur-Yvette, France
6Dept. Earth Sciences, Boston University, Boston, MA 02215, USA
7Dept. Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459-0139, USA
8Earth & Planetary Sciences Dept., University of California, Santa Cruz, Santa Cruz, CA 95064, USA
Abstract: Paleoclimate data show that climate sensitivity is ~3°C for doubled CO2, including only
fast feedback processes. Equilibrium sensitivity, including slower surface albedo feedbacks, is
~6°C for doubled CO2 for the range of climate states between glacial conditions and ice-free
Antarctica. Decreasing CO2 was the main cause of a cooling trend that began 50 million years ago,
the planet being nearly ice-free until CO2 fell to 450 ± 100 ppm; barring prompt policy changes,
that critical level will be passed, in the opposite direction, within decades. If humanity wishes to
preserve a planet similar to that on which civilization developed and to which life on Earth is
adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be
reduced from its current 385 ppm to at most 350 ppm, but likely less than that. The largest
uncertainty in the target arises from possible changes of non-CO2 forcings. An initial 350 ppm
CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting
agricultural and forestry practices that sequester carbon. If the present overshoot of this target CO2
is not brief, there is a possibility of seeding irreversible catastrophic effects.
Keywords: climate change, climate sensitivity, global warming
1. INTRODUCTION
Human activities are altering Earth’s atmospheric composition. Concern about global
warming due to long-lived human-made greenhouse gases (GHGs) led to the United Nations
Framework Convention on Climate Change [1] with the objective of stabilizing GHGs in the
atmosphere at a level preventing “dangerous anthropogenic interference with the climate
system.”
The Intergovernmental Panel on Climate Change [IPCC, 2] and others [3] used several
“reasons for concern” to estimate that global warming of more than 2-3°C may be dangerous.
The European Union adopted 2°C above pre-industrial global temperature as a goal to limit
human-made warming [4]. Hansen et al. [5] argued for a limit of 1°C global warming (relative to
2000, 1.7°C relative to pre-industrial time), aiming to avoid practically irreversible ice sheet and
species loss. This 1°C limit, with nominal climate sensitivity of ¾°C per W/m2 and plausible
control of other GHGs [6], implies maximum CO2 ~ 450 ppm [5].
Our current analysis suggests that humanity must aim for an even lower level of GHGs.
Paleoclimate data and ongoing global changes indicate that ‘slow’ climate feedback processes
not included in most climate models, such as ice sheet disintegration, vegetation migration, and
GHG release from soils, tundra or ocean sediments, may begin to come into play on time scales
*Address correspondence to this author at NASA/Goddard Institute for Space Studies, New York, NY
10025, USA; E-mail: jhansen@giss.nasa.gov
