ALEC Exposed: Warming Up to Climate Change

Evidence on CO2 and Global Warming I. Is it really getting warmer? A. YES. We are seeing more frequent highs, along with fewer lows. B. 1998 was the old all-time historic high temperature year. But 2009 was warmer than 1998, marking the warmest decade on record, while 2005 was warmer than 2009, and 2010 recently tied 2005 for warmest year in the modern historical record. C. One can plumb details about the temperature record endlessly. And that record is consistent with known phenomena, like temporary cooling from major volcanic eruptions and the scrubbing (or lack thereof) of SO2 from the smokestacks of coal-fired power plants, now particularly in China. D. But why is there a seasonal cycle for global CO2 level? Because there is more vegetation in the northern hemisphere. E. The radiative imbalance at the top of our atmosphere also shows conclusively that the Earth is warming. More is energy is coming to Earth than is leaving it. F. But didn't one model actually predict global cooling in the near future? Yes, and it was shown to be wrong. II. How do we know that CO2 is the main driver for global warming? Because CO2 is a catalytic greenhouse gas. A. How could CO2, a trace gas, constituting only 0.04% of our atmosphere, possibly be the main cause of global warming? Because, the main atmospheric gases, oxygen and nitrogen are clear there, while CO2 both absorbs and emits very strongly in the infrared. B. So, CO2 is a greenhouse gas. But isn't water vapor a more significant greenhouse gas? Yes, but water vapor is passive, while CO2 is the driving catalyst. More on that below. C. OK, warmer air can hold more water vapor, but is that actually happening? Yes. D. OK, CO2 is driving increased atmospheric water vapor. But won't increasing cloudiness mitigate global warming? According to recent evidence, apparently not. E. Meanwhile, some details about aerosol effects remain uncertain, but one must also assess the overall significance of these smaller influences. III. How do we know it's mainly humans who are increasing the CO2 that drives global warming? Simple calculations support it. More detailed global carbon inventories confirm it. A. One Back of the Envelope Calculation makes it pretty definite and it is entirely consistent with detailed global carbon inventories and calculated “airborne fraction”. B. Two other lines of evidence are consistent with humans driving most of the CO2 increase, the outgoing radiative spectrum (study this more closely) and changing C12/C13 isotope ratios. IV. Even if all the above is true, couldn't global warming still be due mainly to other causes? No. Other possible causes are inconsistent with the available evidence. A. Couldn't global warming be due mainly to increased solar luminosity? No. In fact, solar luminosity has been decreasing lately. B. Couldn't global warming be due mainly to solar orbital variations (Milankovitch cycles)? No. Milankovitch cycles take thousands of years. C. How about CO2 rising due to biogeochemical releases rather than anthropogenic causes? No. Biogeochemical changes also occur too slowly to explain the current rise rate. D. Isn't apparent global warming mainly due to natural variability? No. Filtering out all natural variability still leaves the global warming signal intact. E. How about fluctuations in the flux of cosmic rays as the principal cause of global warming? No. This claim has been thoroughly debunked. F. What about CO2 from volcanoes? Not significant. Contributions from human activity are at least 100 times larger. I. Is it really getting warmer? A. YES. We are seeing more frequent highs, along with fewer lows. According to a recent peer-reviewed article: http://europa.agu.org/?view=article&uri=/journals/gl/gl0923/2009GL040736/2009GL040736.xml&t=meehl "RELATIVE INCREASE OF RECORD HIGH MAXIMUM TEMPERATURES COMPARED RECORD LOW MINIMUM TEMPERATURES IN THE U.S.", by Gerald A. Meehl, National Center for Atmospheric Research, Boulder, Colorado, Claudia Tebaldi, Climate Central, Princeton, New Jersey, Guy Walton, The Weather Channel, Atlanta, Georgia, David Easterling, National Climatic Data Center, Asheville, North Carolina, and Larry McDaniel, National Center for Atmospheric Research, Boulder, Colorado "... current observed value of the ratio of daily record high maximum temperatures to record low minimum temperatures averaged across the U.S. is about two to one. This is because records that were declining uniformly earlier in the 20th century following a decay proportional to 1/n (n being the number of years since the beginning of record keeping) have been declining less slowly for record highs than record lows since the late 1970s. Model simulations of U.S. 20th century climate show a greater ratio of about four to one due to more uniform warming across the U.S. than in observations. Following an A1B emission scenario for the 21st century, the U.S. ratio of record high maximum to record low minimum temperatures is projected to continue to increase, with ratios of about 20 to 1 by mid-century, and roughly 50 to 1 by the end of the century." B. Also, 1998 was the old all-time historic high temperature year. But 2009 was warmer than 1998, marking the warmest decade on record, while 2005 was warmer than 2009, and 2010 recently tied 2005 for warmest year in the modern historical record. http://www.giss.nasa.gov/research/news/20100121/ http://www.noaanews.noaa.gov/stories2010/20100813_globalstats.html http://www.sciencenews.org/view/generic/id/68761/title/2010_ties_record_for_warmest_year_yet Moreover, extreme highs are occurring more and more frequently with each passing decade. http://www.skepticalscience.com/nasa-giss-what-global-warming-looks-like.html Indeed, below is a running 5 year average (to filter out more transient volcano/El Nino/La Nina effects). This is a satellite/surface data combination, pre-corrected for heat island effects), http://data.giss.nasa.gov/gistemp/graphs/Fig.A2.pdf It shows a fast rise from ~1975 by ~0.6 degs. C. Meanwhile CO2, the major atmospheric greenhouse gas, also rose during that period from 330 to 379 ppmv, ~1.7ppmv/year (parts per million by volume), accelerating lately to ~2+ ppmv/year. Since the beginning of the industrial era (~1850), CO2 levels have increased from ~280ppmv to 392ppmv (as of early 2011). Given collective human cultural inertia, little reason exists to believe that CO2 rise rates will drop below 1.7ppm/year w/i the next 30 - 40 years. If so, we may pass 450 ppmv by 2050. On a simplistic linear basis, this would yield an increase of 1.4 degs C (2.5 degs F) since 1975, or, to extrapolate further, an increase to 530ppmv with 3.0 degs C (5.0 degs F) of increase by 2100. However, such linear extrapolation neglects positive feedback from methane (~21 times stronger a greenhouse gas than CO2), thawing arctic peat bogs and sea floor clathrates, lowered arctic albedo from melting polar ice caps, increased water vapor (still the dominant greenhouse gas) due to air warmed initially by CO2. All of these would tend to accelerate the rise rate. C. One may also plumb details about the temperature record endlessly. And the record is consistent with known phenomena, like temporary cooling from major volcanic eruptions. E.g., correlation isn't causation, but the modest temperature drop from 1941 - 48 fits well with WWII economic devastation - with a 1 or 2 year lag. And the short 2009 temperature lull fits with Chinese factories slowing down in winter 2008, as consumers contemplated a global depression. Regarding volcano impacts, there was significant cooling for a year or two after Mt. Pinatubo blew up in 1991, minor cooling (becauseafter Mt. St. Helens in 1980, significant cooling after Agung in 1963. Bezymianny volcano blew up in 1956. Their impacts are fairly evident in the above temperature record. http://www.cru.uea.ac.uk/cru/info/volcano/ http://www.geo.umass.edu/faculty/bradley/bradley1988.pdf http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VCS-48DYWSR-1N&_user=10&_coverDate=08%2F31%2F1981&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1264558657&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=88cfe5cb793b03bb2f1ddba84a44daaa Also, the EPA mandated scrubbers on coal power plants in 1977 (Clean Air Act), which reduced SO2 emissions. Thus, we probably reduced acid rain while actually raising the global warming rate. Now, China emits much soot and isn't using scrubbers yet. This is very likely the reason why the warming rate has slowed down again lately. But on the whole, the smaller temperature increase from 1850 to 1975 vs. 1975 to 2005 for about the same increase in CO2, ~50ppmv, remains consistent with accelerated warming, as discussed above. D. But why is there a seasonal cycle for global CO2 level? Because there is more vegetation in the northern hemisphere. The global CO2 flux yields a small net balance between large intakes and exhausts, plants (especially land-based forest canopies) being the largest intake source. And plants both respire (exhaust CO2) and photosynthesize (take up CO2). But during their growing seasons, plants take up much more CO2 than they give off. However, there's more land mass for land-based flora to grow on in the northern than southern hemisphere. This means that global CO2 levels decrease during northern hemisphere summers. Conversely, they increase during northern hemisphere winters. This is exactly what you see on the above graph. Also, note that the ratio 392/280 implies a global CO2 level increase of 40% since around 1850. Yet, according to wikipedia, the major uptake sources still manage to sequester about 50% of our excess CO2 emissions on a year by year basis. http://en.wikipedia.org/wiki/Airborne_fraction E. The radiative imbalance at the top of our atmosphere also shows conclusively that the Earth is warming. More is energy is coming to Earth than is leaving it. More total radiation is coming down through the top of our atmosphere than is leaving Earth. Indeed, a 39.5% increase in CO2 levels since ~1850 has stimulated a net radiative imbalance of ~1.8 watts/per meter squared. This net radiative imbalance (more incoming than outgoing) means our planet must be warming, since no other way exists for Earth's heat to dissipate than via outgoing radiation. This imbalance is significant and has been ongoing for several decades. Moreover, the consensus from 13 different independent estimates (IPCC AR4 Table 9.3) is that doubling CO2 from current levels will yield 3.7 w/m^2 more net radiative imbalance than what we now already have, eventually initiating ~3 degs C more warming. So, CO2 increases seen thus far should also yield ~1.8/3.7 x 3 = 1.45 degs C of total warming. But so far, we've only experienced slightly more than half that warming, mainly because more than 1/3rd of the excess heat went into the ocean, from where it will percolate slowly into our atmosphere over a span of decades. Moreover, several lines of evidence: a) CO2 increases, b) CO2 isotope ratios, c) net radiative imbalance at the top of our atmosphere, and d) airborne CO2 fraction, show that the Earth is warming, that added atmospheric CO2 is catalyzing that warming, and that human activity is mainly responsible for the warming since ~1850. F. But didn't one model actually predict global cooling in the near future? Yes, and it was shown to be wrong. From: http://www.realclimate.org/index.php/archives/2010/11/so-how-did-that-global-cooling-bet-work-out/#more-5345 about a paper from a few years back that predicted global cooling. So, how did that prediction work out? Two and a half years ago, a paper was published in Nature purporting to be a real prediction of how global temperatures would develop, based on a method for initializing the ocean state using temperature observations (Keenlyside et al, 2008) (K08). In the subsequent period, this paper has been highly cited, very often in a misleading way by contrarians (for instance, R. Lindzen misrepresents it on a regular basis). But what of the paper’s actual claims, how are they holding up? ...we can see clearly that while K08 projected 0.06ºC cooling, the temperature record from HadCRUT (which was the basis of the bet) shows 0.07ºC warming (using GISTEMP, it is 0.11ºC)." K08 was the model used in the above paper. But why did these modelers get it so wrong? "there is a simple explanation for such a temporary cooling in a model: an artifact known as ‘coupling shock’ (e.g. Rahmstorf 1995), which arises when the ocean is switched over from a forced to a coupled mode of operation, something that has no counterpart in the real world." II. How do we know that CO2 is the main driver for global warming? Because CO2 is a catalytic greenhouse gas. A. How could CO2, a trace gas, constituting only 0.04% of our atmosphere, possibly be the main cause of global warming? Because it absorbs and emits so strongly in the infrared. Scientists have known that CO2 is a powerful greenhouse gas for about 150 years. I.e., it has strong radiative infrared absorption/emission lines. However, the following describes how significant the greenhouse gas effect is on our planet. Epsilon, Earth's mean surface emissivity is ~0.97, nearly a black body (1.0). Sigma, a proportionality constant, is ~5.67 x 10^-8 watts per meter squared per temperature to the fourth power. Earth's mean surface temperature is ~ 288 degs Kelvin. Plugging this into the Planck gray body thermal emission formula: epsilon x sigma x temperature to the 4th power - yields ~390 watts per meter squared (w/m^2) of upwelling thermal radiation emitted by Earth's surface - quite consistent with all measurements. However, as verified by numerous satellite measurements, thermal radiation exiting the top of our atmosphere (TOA) is only ~240 W/m^2, versus the 390 W/m^2 emitted from the Earth's surface. This gap between 390 and 240 W/m^2 means that the greenhouse gases in our atmosphere (water vapor, CO2, methane, ozone, NO2, CFCs, PFCs in that order) are absorbing ~150 W/m^2 of the upwelling thermal radiation emitted from Earth's surface. This absorbed radiation then dissipates as heat. And this phenomenon is called the "atmospheric greenhouse effect". The ~150 W/m^2 of absorption is what keeps our planetary surface about 33 degs C warmer than it would otherwise be. And CO2 alone is responsible for ~ 14 - 25% of that warming. But as shown above, increased CO2 also acts to instigate warming, which then yields more water vapor and increases other greenhouse gases, which all then continue to amplify further warming. And here are some general references that explain more details about the atmospheric greenhouse gas effect: http://en.wikipedia.org/wiki/Greenhouse_gas#Greenhouse_effects_in_Earth.27s_atmosphere http://www.radix.net/~bobg/climate/halpern.trap.html Modern Climate Change by Thomas Karl and Kevin Trenberth (2003) available at http://stephenschneider.stanford.edu/Publications/PDF_Papers/worldweatherchanges.pdf B. CO2 is a greenhouse gas. But isn't water vapor a more significant greenhouse gas? Yes, but water vapor is passive. CO2 is the driver. On its own CO2 only accounts for 14 - 25% of the greenhouse gas effect. But the critical difference between CO2 and H2O is that atmospheric water vapor equilibrates very rapidly via the hydrologic cycle (evaporation/cloud condensation/rain-out). I.e., the hydrologic cycle produces large local humidity fluctuations over hours to weeks, but on global scales, that very rapid cycling means that global mean water vapor is quite sensitive to and rises rapidly with rising global mean temperature. So, water vapor will quickly increase to amplify any small temperature increase due to CO2. or any other cause. However, it takes decades to hundreds of years for increased water vapor to raise CO2 levels. This means, over decadal time scales, CO2 increases will drive water vapor increases, not vice versa. Indeed, water vapor amplifies the temperature-raising impact of anthropogenically induced CO2 increases (40% increase in total CO2 in 150 years) by roughly a factor of 3. Add other greenhouse gases, like methane, and that factor reaches 4. I.e., anthropogenic excess CO2 initiates a modest temperature rise that then catalyzes a much bigger rise due to other greenhouse gases. So, CO2 is THE global warming catalyst. Water vapor follows suit and amplifies the effects of CO2. Thus, the issue isn't whether water vapor accounts for more warming than CO2. It's whether water vapor or CO2 is the controlling factor. And also whether a complex system like our atmosphere can easily assimilate a new CO2 emissions source - namely us. As the wikipedia article on "airborne fraction" shows, the Earth is absorbing only about ~ half our excess CO2 emissions. The "water vapor is more significant a greenhouse gas than CO2" myth also ignores the finely tuned balance needed to maintain equilibrium in complex systems, which juggle many delicate balances, driven by nearly equal inputs and outputs. Even a small excess ( human CO2 contributions), if added too quickly, can disrupt a delicate balance between two large opposing fluxes, altering the basic state entirely. So, the bottom line is that CO2 is an amplifying catalyst, and that it drives water vapor increases exponentially with a CO2-initiated increase in global temperatures. Thus, a little CO2-induced initial warming initiates increased water vapor which, along with increases in the other greenhouse gases (methane, O3, etc.) induces even more warming. But over the short term (less than a few centuries) CO2 level remains the controlling factor, not water vapor. How is it that global atmospheric water vapor levels can increase with CO2-instigated temperature increases? Warmer oceans evaporate more water and warmed air holds more water in its vapor state. The extra water vapor absorbs more thermal radiation, further warming the air. The vapor level tends to rise exponentially with temperature, as the following example shows. How much more water can warmer air hold? If mean global surface temperature is T1 ~286.5 degs. Kelvin (56 degs F), what happens if temperature rises 3 degs. to T2 = 289.5 degs. K, a 1.05% increase? From the Magnus-Tetens relation for saturation vapor pressure (maximum amount of water vapor air can hold at a given temperature), e(T2)/e(T1) = exp(17.625 x T2/(T2 + 243.04) )/exp(17.625 x T1/(T1 +243.04) ) = 1.0467 , or 4.67% more water vapor for a 1.05% temperature increase, which is clearly supra-linear, as the exp stands for an exponential function of temperature ratios. This rough example neglects many mitigating factors: transport, convection, cloud condensation, rain-out, etc. However, consistent with basic thermodynamics, there is no common instance where intra-system negative feedback ever compensates fully for an initial forcing. Thus, once CO2 warms air initially, water vapor increases with temperature, begetting a non-linear positive feedback that induces more warming. Moreover, beyond the 20 - 30 year e-folding time for CO2-warming, current global temperatures still don't reflect most of the POSITIVE FEEDBACKS that loom for global warming. Arctic bogs and seafloor clathrates store thousands of times more methane than has been released thus far. http://www.nytimes.com/2010/03/05/science/earth/05methane.html?ref=science http://en.wikipedia.org/wiki/Clathrate_gun_hypothesis Nor has decreased polar albedo (increased solar rad absorptance) due to receding arctic sea ice quite reached a tipping point. And, though increased water vapor only increases its IR absorption logarithmically, the Magnus relation shows that atmospheric water vapor increases exponentially with temperature. Being mathematical inverses, an exponential tends to offset a logarithmic. Thus, the net impact of increased water vapor on temperature tends toward being linear, i.e., yet another POSITIVE FEEDBACK. C. OK, warmer air can hold more water vapor, but is that actually happening? Yes. The following peer-revie­­wed journal papers all confirm that, not just water vapor saturation level, but actual mean global atmospheri­­c water vapor content, is also rising with global warming. Note - most of these studies are data-, not model-base­­d. http://www.atmos.washington.edu/~qfu/Publications/jc.gettelman.2008.pdf http://www.nature.com/nature/journal/v449/n7163/full/nature06207.html. http://www.pnas.org/content/104/39/15248.full.pdf+html http://www.appmath.columbia.edu/users/sobel/Papers/wright_jcli_09_submitted.pdf http://www.sciencemag.org/cgi/content/abstract/310/5749/841 http://www.agu.org/pubs/crossref/2008/2008GL035333.shtml http://www.realclimate.org/index.php/archives/2005/11/busy-week-for-water-vapor/ along with Randall's work in the 2007 IPCC Again, these results are all consistent with water vapor being solely a passive positive feedback that merely amplifies the initial CO2-catalyzed warming. The only way water vapor wouldn't be a greenhouse amplifier is if its levels weren't rising with temperature. But all these recent publications show that it IS RISING to keep the relative humidity fairly constant as saturation levels keep rising with temperature. Also, the major climate models, which, rather than assuming some arbitrarily constant relative humidity, instead all compute water vapor levels from first principles, are also fully consistent with the results from the above papers. These are some of the main reasons why nearly all actively publishing climatologists agree that excess CO2 production by humans is the main driver for global warming. I.e., a poll by Doran and Zimmerman at Earth and Environmental Sciences, University of Illinois received replies from 3,146 of the 10,257 polled Earth scientists. 76 of 79 climatologists who "listed climate science as their area of expertise and also have published more than 50% of their recent peer-reviewed papers on the subject of climate change" believe that mean global temperatures have risen compared to pre-1800s levels. 75 of 77 believe human activity is a significant factor in changing mean global temperatures. Among all respondents, 90% agreed that temperatures have risen compared to pre-1800 levels, and 82% agreed that humans significantly influence global temperatures. In 2007 Harris randomly surveyed 489 members of the American Meteorological Society or American Geophysical Union. 97% agreed that global temperatures have increased during the past 100 years; only 5% believe human activity does not contribute to greenhouse warming. 84% believed that global climate change poses a moderate to very great danger." There are NO scientific organizations of national or international standing that still reject the basic findings of human influence on recent climate change. The following science organizations regard global warming as real and mostly man-made: The science Academies of: Australia, Belgium, Brazil, Canada, China, France, Germany, India, Indonesia, Ireland, Italy, Japan, Malaysia, New Zealand, Russia, South Africa, Sweden, United Kingdom, and the USA. Also, the European Academy of Sciences and Arts U.S. National Research Council American Association for the Advancement of Science American Chemical Society American Institute of Physics American Physical Society European Science Foundation Federation of Australian Scientific and Technological Societies American Geophysical Union European Federation of Geologists European Geosciences Union Geological Society of America Geological Society of Australia International Union of Geodesy and Geophysics National Association of Geoscience Teachers American Meteorological Society Australian Meteorological and Oceanographic Society Canadian Foundation for Climate and Atmospheric Sciences Canadian Meteorological and Oceanographic Society Royal Meteorological Society (UK) World Meteorological Organization American Quaternary Association (paleoclimatologists) International Union for Quaternary Research (paleoclimatologists) Society of American Foresters American Astronomical Society American Statistical Association Even the American Institute of Petroleum Geologists changed their tune in 2009. "In the last century growth in human populations has increased energy use. This has contributed additional carbon dioxide (CO2) and other gases to the atmosphere. Although the AAPG membership is divided on the degree of influence that anthropogenic CO2 has on recent and potential global temperature increases, the AAPG believes that expansion of scientific climate research into the basic controls on climate is important. This research should be undertaken by appropriate federal agencies." Here are some web sites where such views can be verified directly. http://www.ucsusa.org/global_warming/ http://www.giss.nasa.gov/research/features/pliocene/page2.html http://www.aip.org/history/climate/links.htm National Oceanic and Atmospheric Administration http://www.ncdc.noaa.gov/oa/climate/globalwarming.html National Academy of Sciences http://books.nap.edu/collections/global_warming/index.html State of the Canadian Cryosphere http://www.socc.ca/cms/en/socc/permafrost/currentPermafrost.aspx Environmental Protection Agency http://epa.gov/climatechange/index.html The Royal Society of the UK http://royalsociety.org/Climate-Science-Statement/ American Geophysical Union http://www.agu.org/sci_pol/positions/climate_change2008.shtml American Meteorological Society http://www.ametsoc.org/policy/climatechangeresearch_2003.html American Institute of Physics http://www.aip.org/gov/policy12.html National Center for Atmospheric Research http://eo.ucar.edu/basics/cc_1.html American Meteorological Society http://www.ametsoc.org/policy/jointacademies.html Canadian Meteorological and Oceanographic Society http://www.cmos.ca/climatechangepole.html http://arctic.atmos.uiuc.edu/cryosphere/ Australian climate data http://www.bom.gov.au/climate/data/weather-data.shtml D. OK, CO2 is driving increased atmospheric water vapor. But won't increasing cloudiness mitigate global warming? According to recent evidence, apparently not. Net heaters or coolers? Yes, cloud feedback has been a big uncertainty. From the most prestigious journal in science, SCIENCE, Dec. 10, 2010 "... analyzing the top-of-atmosphere radiation budget from March 2000 to February 2010. Over this period, the short-term cloud feedback had a magnitude of 0.54 ± 0.74 (2σ) watts per square meter per kelvin, meaning that it is likely positive." http://www.sciencemag.org/content/330/6010/1523.abstract?sid=3ac80d72-18dc-48b8-be9f-0cfbc23633f5 'The work is the most detailed look at how clouds affect climate — one of the biggest scientific unknowns in how much global warming to expect (SN: 12/4/10, p. 24). Some researchers have suggested that clouds might cool the planet, but the study supports the opposite idea.... “This is really the first quantitative test of the total cloud feedback in climate models,” says Andrew Dessler, an atmospheric scientist at Texas A&M University in College Station. “The results suggest that our understanding of the cloud feedback, and the simulation of the cloud feedback by models, is actually quite good.”' http://www.sciencenews.org/view/generic/id/67324/title/Clouds_warm_things_up' Indeed, Dessler showed earlier that total tropospheric water vapor is rising with warming initiated by rising CO2, thus contributing to the warming, as water vapor is itself a major greenhouse gas. http://mls.jpl.nasa.gov/joe/Minschwaner_2004.pdf E. Meanwhile, some details about aerosol effects remain uncertain, but one must also assess the overall significance of these smaller influences. I.e, total aerosol seems a modest cooling agent, but black carbon (soot, mainly from fossil fuel power plants, ag burning, and primitive cook stoves) is a net warmer, with amounts and geographic/size distributions not well quantified - YET. Aerosol injection height also matters. Cooling is greater for aerosols reaching the stratosphere, as residence time gets stretched. So, a few really big volcanic eruptions impact global temperatures for a year or two at a time. But Mt. Pinatubo in 1991 was our last really big stratospheric aerosol injection, while Mt. St. Helens wasn't, as it blasted diagonally, not straight up. To view science properly, we must assess diminishing impacts for zeroth, 1st, or 2nd order effects. Total atmospheric greenhouse gases warm Earth's surface by ~33 degs. C, absorbing ~150 W/m^2 of the ~390 W/m^2 in surface radiative emissions. Thus, only ~240 W/m^2 actually exits the top of our atmosphere (TOA). That's the Zeroth (grossest) order. Water vapor is the main greenhouse gas. Its IR absorption spectrum somewhat overlaps CO2. Given that and the near-saturation of some lines, increased water vapor, due to a CO2-increase-induced temperature rise yields a logarithmic (less-than-linear), impact on the TOA radiative budget. Yet, water vapor also increases exponentially with temperature. Exponentials and logarithmics are mathematical inverses - multiplying them yields a linear product. Thus, water vapor amplifies CO2 rise-induced increases in global mean temperature roughly linearly. Given little overlap/saturation for methane, O3, CFCs, PFCs, SF6, because they're still at trace levels, they also amplify the CO2 effect roughly linearly. By itself, CO2 is only 14-25% of the total greenhouse gas effect. Thus, CO2's increase and its amplification by water vapor and trace greenhouse gases remains roughly linear. This is the 1st order effect. The above is well-known. Though future cloud coverage, esp. high vs. low clouds, aerosol and soot levels, etc., remain somewhat uncertain, these are 2nd order effects. I.e., they can't swamp the Zeroth and 1st order - YET. But possible increased cloud coverage may eventually curtail runaway global warming. We don't know. III. How do we know it's mainly humans who are increasing the CO2 that drives global warming? Simple calculations support it. More detailed global carbon inventories confirm it. A. One Back of the Envelope Calculation makes it pretty definite. "~" means roughly. "ppmv" means parts per million by volume. Humans induce ~35 Billion Tons of EXTRA CO2/year. CO2 is rising at ~2.2 ppmv/year. CO2 is a "greenhouse gas", which BY DEFINITION means it absorbs outgoing thermal radiation emitted by Earth's surface, converting it to heat. Earth's radius = ~6,370 kms. Scale Height of the atmosphere (height if it were all at sea level pressure) ~8 km. Sea Level Air Density: ~1.29 kg per cubic meter So, the mass of atmosphere is: 4pi x 6,370,000m2 x 8,000m x 1.29 kg/m3 = ~5.26 quadrillion metric tons. How much of that is CO2? At a current 392 ppmv, it's (392/1,000,000) x 5.26 quadrillion tons = ~2.06 trillion tons. So, 1 ppm of CO2 is 2.06T/392 = 5.26 billion tons. But by volume 1 ppmv of CO2 is 44/29 (relative molecular weights CO2 vs. air) x 5.26 = 8 billion tons. So, humans add 35/8 = ~4.4ppmv of CO2 annually. But CO2 is rising at ~2.2ppmv. Thus, Earth absorbs only ~ half the anthropogenic CO2, consistent with more detailed carbon inventories, http://en.wikipedia.org/wiki/Airborne_fraction For humans not to be increasing CO2, Earth would have to absorb most anthropogenic CO2, but little CO2 from significant but otherwise unknown sources. There is no plausible physical mechanism for that to be happening. Ergo, humans are increasing atmospheric CO2 A.1 By the way, how do we know that humans are producing about 35 billion tons of excess CO2 per year? Americans emit ~20% of global CO2, ~21% via auto exhaust, 40% for home heat/light/appliances, the rest for industrial/commercial, transport, etc. Americans drive an average 12k miles/year at ~17.1mpg. 12,000 miles/17.1mpg = ~700gls of gas/year, or ~a tank per week. Gasoline weighs ~6 lbs/gl. So, we burn ~6 x 700 = ~4,200 lbs of gasoline/year. Gasoline is mostly iso-octane - C8H18 (C=12, H=1, so mol. wt. = 114); heptane is C7H16 (mol. wt. = 100). So, 89 octane yields an average mol. wt., of ~113. Burning a molecule of it yields ~7.9 molecules of CO2 (O=16; ergo, mol. wt. 7.9 x 44 = 348). So, a U.S. auto emits ~(348/113) x 4,200 = ~12,930 lbs or ~ 5.9 metric tons of CO2/year. If 21% of total, then each American emits ~5.9/0.21 = ~28 metric tons of CO2/year. We have ~240 million U.S. cars/trucks. So, we make ~28 x 240 million = 6.7 billion tons of CO2/year, ~20% of the global total. That yields 6.7/0.20 = ~33.6 billion tons of CO2 globally/year. Add billions for fires + global deforestation and there's more than 35 billion tons. Wikipedia cites more detailed global carbon inventories that totaled about 31.8 billion tons from fossil fuel combustion in 2008. http://lgmacweb.env.uea.ac.uk/lequere/co2/carbon_budget.htm B. There are also two other lines of evidence consistent with humans driving most of the CO2 increase – the outgoing radiation spectrum and the changing C12/C13 isotope ratio. The claim is consistent with changing atmospheric carbon isotope ratios and changing outgoing thermal radiation spectra (www.nature.com/nature/journal/v410/n6826/abs/410355a0.html ). That is, land-based plants take up less C13, the radioisotope of normal C12 carbon. Since fossil fuels derive from plant decay, they both have about 2% lower C13/C12 ratios than the atmosphere. So, burning fossil fuels lowers atmospheric C13/C12 ratio. C13/C12 tree ring ratios reflect changing atmospheric ratios. Our atmosphere now displays the lowest C13/C12 ratio in 10,000 years, and its rapid decline started ~1850, when humans began burning fossil fuels in earnest. Thus, no theory, other than that anthropogenic CO2 is raising atmospheric CO2 levels, fits the available evidence. Stuiver, M., Burk, R. L. and Quay, P. D. 1984. 13C/12C ratios and the transfer of biospheric carbon to the atmosphere. J. Geophys. Res. 89, 11,731-11,748. Francey, R.J., Allison, C.E., Etheridge, D.M., Trudinger, C.M., Enting, I.G., Leuenberger, M., Langenfelds, R.L., Michel, E., Steele, L.P., 1999. A 1000-year high precision record of d13Cin atmospheric CO2. Tellus 51B, 170–193. Quay, P.D., B. Tilbrook, C.S. Wong. Oceanic uptake of fossil fuel CO2: carbon-13 evidence. Science 256 (1992), 74-79 IV. Even if all the above is true, couldn't global warming still be due mainly to other causes? No. Other possible causes are not consistent with the available evidence. A. Couldn't global warming be due mainly to increased solar luminosity? No. In fact, solar luminosity has been decreasing lately. from NATURE, 2006, "Variations in solar luminosity and their effect on the Earth’s climate P. Foukal1, C. Fro¨hlich2, H. Spruit3 & T. M. L. Wigley4 Variations in the Sun’s total energy output (luminosity) are caused by changing dark (sunspot) and bright structures on the solar disk during the 11-year sunspot cycle. The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years. In this Review, we show that detailed analysis of these small output variations has greatly advanced our understanding of solar luminosity change, and this new understanding indicates that brightening of the Sun is unlikely to have had a significant influence on global warming since the seventeenth century." http://www.mpa-garching.mpg.de/mpa/publications/preprints/pp2006/MPA2001.pdf Or "Solar Activity over the Last 1150 Years: Does it Correlate with Climate?" I.G. Usoskin, M. Schussler, S.K. Solanki, and K. Mursula "Note that the most recent warming, since around 1975, has not been considered in the above correlations. During these last 30 years, the solar total irradiance, solar UV irradiance, and cosmic ray flux has not shown any significant secular trend, so that at least this most recent warming episode must have another source. www.mps.mp.de/dokumente/publikationen/solanki/c153.pdf Even Scafetta and West, 2006 say: http://www.acrim.com/Reference%20Files/Sun%20&%20Global%20Warming_GRL_2006.pdf "since 1975 global warming has occurred much faster than could be reasonably expected from the sun alone." Note that Scafetta is the researcher that global warming deniers often like to quote because he once incorrectly assessed a supposed discrepancy between ACRIM and PMOD satellite data to suggest a larger solar contribution than actually exists. This discrepancy was corrected by Krivova, Solanki, and Wenzler 2009. www.agu.org/pubs/crossref/2009/2009GL040707.shtml Thus solar fluctuations as a major cause of for global warming has been thoroughly refuted. No legitimate climate scientist takes that notion seriously nowadays. But don't forget that, since 1850, when humans began burning fossil fuels in earnest, CO2 levels have risen 39.5%. And as shown above, CO2 is a known greenhouse gas, which means by definition that it traps radiation emitted by the Earth's surface and converts that to heat.” B. Couldn't global warming be due mainly to solar orbital variations (Milankovitch cycles)? No. Milankovitch cycles are far too slow. The present phenomenon of global warming is occurring over a period of a few hundred years, while Milankovitch-type solar orbital variations occur over time scales of tens of thousands of years. For example, the next ice age is not slated to occur until around 50,000 AD. http://www.sciencemag.org/content/297/5585/1287.summary http://campus.udayton.edu/~physics/rjb/PHY399Winter2007/Berger%20-%20Long%20Interglacial.pdf http://www.nature.com/ngeo/journal/v3/n5/full/ngeo828.html How about increased photosynthesis? Again, insufficient http://www.atmos.umd.edu/~haifee/research/clivar04_c4mip_poster.pdf C. How about CO2 rising due to biogeochemical releases rather than anthropogenic causes? No. Biogeochemical changes also occur too slowly to explain the current rise rate. It is true that, as a result of rising temperatures, CO2 gets released to the atmosphere from both weathering rocks and the oceans on time scales of several hundreds of years or longer. So, this explains in some pre-human era cases, as shown by the 800K year EPICA and 400K year Vostok ice core records, why temperatures rose before CO2 levels rose. But in the anthropogenic era, CO2 is rising much more rapidly than during most geological eras, due mostly to fossil fuel combustion and also partly due to human-induced global deforestation. However, even if one were to examine the 400k year Vostok record, as one can readily do, the so-called "800 year lag" between rising temperature and rising CO2 appears to be rather questionable, at least in that particular data set. I.e., did CO2 increases lag temperature increases by ~800 years during past (pre-human) global warming periods? To assess this question, one can pull the 400k year Vostok Antarctic ice core graph into MS Word. http://www.en.wikipedia.org/wiki/File:Vostok-ice-core-petit.png , which is taken from http://www.ncdc.noaa.gov/paleo/icecore/antarctica/vostok/vostok_data.html Set the page to landscape/legal. Stretch the graph to full screen for maximum time resolution (~260 years at 1600 pixels). Check each lag by aligning the vertical ruler tool against each CO2/temperature start and peak. For the 4 warming eras matching or exceeding current temperatures (what we want to check), the one can see that: 305-340,000 BC. Start and peak of temperature rise lagged start and peak of CO2 rise. 230-245,000 BC. Start of temp rise lagged CO2 rise. Temp peak coincided with CO2 peak. 110-140,000 BC. Start of temp rise lagged start of CO2 rise. CO2 peak slightly lagged temp peak. now - 15,000 BC. Start of temp rise lagged start of CO2 rise. CO2 and temperature haven't peaked yet. So, CO2 lagged temperature just once at seven critical points. Five of six display the opposite lag. Again, the scientific consensus is that orbital variations tens of thousands of years long initiate ice ages and we're in another extended warming period. But current CO2 exceeds all prior Vostok data by a huge 100 ppm, with another +250ppm looming. So, anthropogenic CO2 puts us in uncharted territory. D. Isn't apparent global warming mainly due to natural variability? No. Filtering out all natural variability still leaves the global warming signal intact. Researchers have carefully studied this possibility and have managed to rule it out. However, when longer term "natural" variability was filtered from the observed temperatures, what was left was steadily accelerating warming throughout the 20th Century and longer. http://deepeco.ucsd.edu/~george/publications/09_long-term_variability.pdf www.skepticalscience.com/climate-shift-synchronized-chaos.htm Note that the 2009 Swanson et al. paper was authored by the same group that climate skeptics like to cite (Tsonis and Swanson, 2007) as evidence against man-made global warming. F. How about fluctuations in the flux of cosmic rays as the principal cause of global warming? No. This claim has been thoroughly refuted. This appears to be a claim entirely without merit, according to all verifiable data. http://rspa.royalsocietypublishing.org/content/466/2114/303.full http://stephenschneider.stanford.edu/Publications/PDF_Papers/Laut2003.pdf http://eprints.whiterose.ac.uk/4060/1/brownb1.pdf= F. What about CO2 from volcanoes? Not significant. Contributions from human activity are at least 100 times larger. The volcanic contribution to contemporary global warming is nearly nil. http://www.newscientist.com/article/dn11638-climate-myths-human-cosub2sub-emissions-are-too-tiny-to-matter.html CO2 from land-based volcanoes is less than 1% of human contributions. Also from http://www.scientificamerican.com/article.cfm?id=how-do-volcanoes-affect-w "...volcanic eruptions produce about 110 million tons of CO2 each year." - about 0.3% of CO2 from human activities. Summarized the U.S. Geological Service... http://volcanoes.usgs.gov/hazards/gas/climate.php "The half dozen or so published estimates of the global CO2 emission rate for all degassing subaerial and submarine volcanoes lie in a range from 132 million (minimum) to 378 million (maximum) metric tons per year (Gerlach, 1991; Varekamp et al., 1992; Allard, 1992; Sano and Williams, 1996; Marty and Tolstikhin, 1998; Kerrick, 2001). If estimate medians and author-preferred estimates of these studies are used to lessen the influence of outlier estimates, the range is restricted to about 150-270 million metric tons of CO2 per year. The current anthropoge­nic CO2 emission rate of some 36,300-mil­lion metric tons of CO2 per year is about 100 to 300 times larger than these estimated ranges for global volcanic CO2 emissions.­" Rather, the main impact of major volcanic eruptions, like Pinatubo - 1991, Agung - 1963, Bezymianny - 1956 is global cooling, via stratosphe­ric injection of aerosolize­d sulfates. http://en.­wikipedia.­org/wiki/C­limate_cha­nge#Volcan­ism http://ear­thobservat­ory.nasa.g­ov/Feature­s/Volcano/