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Saturday, December 21, 2019

Understanding the Source of Rising Atmospheric CO2

For the last time, increasing atmospheric CO2 is coming from fossil fuels, and not from volcanoes.

The concentration of CO2 in the atmosphere is rising rapidly.  Before widespread burning of coal, circa 1750, atmospheric CO2 was about 280 parts per million (ppm).  By 1955, global CO2 concentration had risen to 314 ppm.  Average global CO2 levels are now about 412 ppm, and are still rising at about 3 ppm per year. 

Industrial processes are able to change the composition of the earth’s atmosphere because there really isn’t very much atmosphere, and there isn’t very much CO2.  The atmosphere thins rapidly with altitude, so that about half of the atmosphere is less than 3 miles above the earth, and breathable atmosphere extends only about 6 miles above the earth.  Further, there isn’t very much CO2 in the atmosphere – about 400 ppm, or 0.04%.  Nevertheless, that small amount of CO2 is very effective at blocking thermal infrared radiation, which is why changing the CO2 concentration of the atmosphere has already had a significant impact on global climate. 

Figure 1.  There isn’t very much atmosphere, and there really isn't very much CO2.  The pie-slice of CO2 in the second figure is exaggerated three-fold for visibility.

A common myth that circulates on social media is that rising CO2 in the atmosphere is coming from volcanoes.   It isn't.  I already wrote one blog post about the origin of atmospheric CO2.  ( 

This blog post will present additional evidence that rising CO2 is of human origin.  The evidence is:
  • Declining oxygen concentration of the atmosphere
  • The quantity of missing oxygen
  • The location of declining oxygen concentration by hemisphere
  • Volumetric data for fossil fuel emissions, deforestation, and volcanism, compared to volumes of CO2 appearing in the atmosphere
  • The location of rising CO2 by hemisphere
  • Changing carbon isotopic composition of the atmosphere
  • The location of the declining carbon isotope measure (del C13) by hemisphere
  • The steady rise of atmospheric CO2, whereas volcanic eruptions are intermittent (although slow emissions from non-eruptive events, mid-ocean ridges and rifts also occur). 
Atmospheric CO2 is now also monitored by two orbiting carbon observatories (OCO), which directly measure CO2 concentrations in the atmosphere and connect rising atmospheric CO2 with points of origin.

The myth that volcanoes are responsible for human-caused atmospheric disruption has been propagated since the 1990s.  The book “Merchants of Doubt” provides a history of claims that volcanoes were responsible for destruction of stratospheric ozone, or for acid rain in the US and Canada.  Those claims were thoroughly debunked long ago.  Nevertheless, articles attributing rising CO2 to volcanoes still appear on climate-change denying websites, (e.g. James Edward Kamis’ 2018 post on ClimateChangeDispatch).

Let’s look at the evidence.

Fossil-Fuel Combustion
When fossil fuels are burned, atmospheric oxygen is converted to CO2.  Consequently, the oxygen concentration in the atmosphere falls.  If we quantify oxygen depletion in the atmosphere, we find that it validates the volumes of fossil fuel consumption reported by inventory methods (BP Statistical Review, CDIAC, EIA, etc.).  The volumes of CO2 determined by either method are approximately twice what is necessary to account for the observed rise in atmospheric CO2.  The remaining CO2 is dispersed into CO2 reservoirs in the oceans and biosphere.  A full accounting of the CO2 flows on earth can be found in the Global Carbon Project or Berkeley Earth websites. 

Simply stated, the depletion of atmospheric oxygen quantifies CO2 emissions from fossil fuels.  This volume of CO2 emssions more than accounts for the rise in atmospheric CO2.  There isn’t any room for a significant contribution from volcanoes without somehow getting rid of the CO2 from the combustion of fossil fuels in some as-of-yet unidentified carbon sink (which is unlikely to exist). 

Depletion of Atmospheric Oxygen
The amount of oxygen in the atmosphere is falling (although not enough to cause trouble for breathing).   Atmospheric oxygen is falling because oxygen is consumed by burning fossil fuels.  This would not occur if the source of rising CO2 was from volcanoes (Figure 2).  As seen in the bulk CO2 and Del C13 charts, there is a strong seasonal signal in the concentration of atmospheric oxygen, related to the growing season in each hemisphere.  The amplitude of the seasonal cycle is somewhat stronger in the Northern Hemisphere, due to the preponderance of temperate land-mass and agriculture. 
Figure 2.  The concentration of atmospheric oxygen is falling, due to combustion of fossil fuels.  The Per Meg (del O2/N2) can be roughly converted to ppm by multiplying by 0.2095, the fractional concentration of oxygen in the atmosphere.  A discussion of the Per Meg (del O2/N2) measure can be found on the Scripps Institute CO2 website FAQs.  The loss of 700 ppm of oxygen is a relatively small change because of the greater abundance of oxygen in the atmosphere as compared to CO2.  The percentage of oxygen in the atmosphere is about 20.95%; the percentage of CO2 in the atmosphere is about 0.04%.

Oxygen Depletion by Hemisphere
Falling oxygen concentrations in the Northern Hemisphere lead falling oxygen in the Southern Hemisphere (Figure 3).  This is because 90% of fossil fuels are being burned in the Northern Hemisphere, consuming oxygen in the Northern Hemisphere.  Atmospheric mixing works to equilibrate oxygen concentrations, but continuing combustion of fossil fuels in the Northern Hemisphere keeps oxygen lower than in the Southern Hemisphere.

Figure 3.  Atmospheric oxygen recorded by Scripps Institute network of atmospheric observatories.   The seasonal cycle at each station was filtered with a 12-month rolling average.  The Northern Hemisphere leads the Southern Hemisphere in falling oxygen.

Oxygen – Carbon Stoichiometry
The number of molecules of oxygen disappearing from the atmosphere is a very close match to the number of carbon atoms burned in fossil fuels and deforestation (Figure 4).  There is a quantitative match, showing that for each atom of carbon burned, one molecule of oxygen disappears from the atmosphere, as C + 02 -> CO2.  The depletion of atmospheric oxygen, in stochiometric balance with human carbon combustion, validates the volume of CO2 released into the atmosphere by burning fossil fuels.  
Figure 4.  Moles of carbon burned by fossil fuels and deforestation annually, compared to atmospheric oxygen depletion in moles.   The close match confirms that volumes of CO2 released from fossil fuels and deforestation are responsible for rising atmospheric CO2.  
Moles of oxygen depletion can be calculated by converting “per meg” to ppm (oxygen/atmosphere) and assuming an initial volume of the total atmosphere of 1.81E+20 moles (various Internet sources).  Notes on the calculation are given in the Appendix, following References.

Volumetric Evidence
CO2 emissions from gas, oil, coal, cement, flaring, and deforestation are now about 40 gt per year, and forecast to go higher.   Estimates and measurements of volcanic CO2 emissions are far smaller than known volumes of CO2 from fossil fuels and deforestation (Figure 5).  Estimated volumes of volcanic CO2 include deep carbon emissions, and passive emissions from continental rifts and mid-ocean ridges.  Volcanic CO2 emissions are only about 1.8% of human CO2 emissions by volume.

Figure 5.  Annual Human CO2 Emissions by type and Volcanic CO2 Emissions, with EIA forecast to 2040.  Estimates of CO2 emissions from volcanic activity have been revised significantly higher since the 1990s, as CO2 emissions from deep volcanic source, continental rifts and mid-ocean ridges have been recognized and quantified.  Still, volcanic CO2 emissions are now estimated at about 700 million tonnes, compared to about 40 gigatonnes of CO2 from fossil fuels and deforestation.

Fraction of CO2 Emissions Which Remain in the Atmosphere
Only about 44% of human CO2 emissions remain in the atmosphere; the rest of the CO2 is absorbed by the oceans or taken up by plants.  Human CO2 emissions are more than twice what is necessary to account for rising atmospheric CO2.  Since volcanic CO2 emissions represent only 1.8% of human CO2 emissions, it is impossible for volcanoes to account for the large volume of CO2 now appearing in the atmosphere.  (Figure 6). 

Figure 6.  If all human CO2 emissions remained in the atmosphere, atmospheric CO2 concentrations would rise about twice as fast as what is observed (red line).  Actual average global CO2 is rising at a rate of about 44% of cumulative human CO2 emissions.  If only volcanic CO2 was entering the atmosphere, atmospheric CO2 would rise only negligibly, offset by the removal of carbon by natural processes.

Difference in CO2 between Northern and Southern Hemispheres, and
Comparison to Net CO2 Emissions from the Northern Hemisphere
About 90% of humans live in the northern hemisphere, and 90% of human CO2 emissions originate in the northern hemisphere.  Atmospheric CO2 concentrations in the northern hemisphere are consistently higher than CO2 concentrations in the southern hemisphere.   The amount of the difference is very close to the net CO2 emissions from fossil fuels in the northern hemisphere (Figure 7).  The close correspondence of net Northern Hemisphere CO2 emissions and the difference between Northern and Southern CO2 concentration is partly a coincidence between the mixing rate between the hemispheres and the reporting period for CO2 emissions.  However, the consistent fit is a clear proof that fossil fuel emissions in the Northern Hemisphere are principally responsible for rising CO2.  The largest volcanic eruptions of the past 60 years have been in the Southern Hemisphere, but these have made no impact on the record of atmospheric CO2.
Figure 7.  Northern and Southern Hemisphere CO2 concentrations, and net fossil-fuel emissions from the Northern Hemisphere.  Major volcanic eruptions, such as Mt. Pinatubo and Mt. Hunter in the Southern Hemisphere in 1991, are not observed as a difference in CO2 observations between the hemispheres. 

Carbon Isotope Ratios in Atmospheric CO2
Natural carbon mostly occurs in two isotopes: C12 and C13.  Plants and all fossil fuels (which derive from plants) are enriched in C12 by biological processes, giving fossil fuel emissions and deforestation a “lighter” isotopic signature (more C12) than the atmosphere.  The measure of carbon isotopic ratios is d C13/C12, typically called “del C13”.  Samples which are relatively enriched in “light” C12 have a negative del C13, while samples that are enriched in “heavy” C13 have a positive del C13.  A technical definition of del C13 is given at the bottom of the article, below the references.

In the 1950s, the atmosphere had a del C13 value of about -7.5, reflecting a higher concentration of C12 than the oceans, which has a del C13 of about zero.  As mentioned above, fossil fuels are enriched in C12 with typical values in the range of -20 to -30.   Biogenic natural gas has been fractionated twice, and may have del C13 values ranging from -40 to -70.  Volcanic emissions have a heavier isotopic signature than the atmosphere, with a del C13 value of about -1 to -4.  

The isotopic composition of the atmosphere is steadily becoming lighter as CO2 concentrations rise.  This is only possible if the additional CO2 is from a source isotopically lighter than the atmosphere, not heavier.  Thus, fossil fuels, and not volcanoes or the oceans, are the source of rising CO2 (Figure 8).
Figure 8.  The Del C13 Carbon Isotopic Record of Atmospheric CO2, recorded by the Scripps Institute.  The record is marked by a strong seasonal cycle in the Northern Hemisphere.  During the Northern Hemisphere growing season C12 is preferentially taken out of the atmosphere by plants, and released back to the atmosphere in winter causing the seasonal cycle in the air.  Overall, the Del C13 index has fallen from -7.5 to -8.5 since 1977, showing an increasing prevalence of light C12 (characteristic of fossil fuels and deforestation) in the atmosphere.

After filtering the seasonal cycle, we see that the Northern Hemisphere leads the Southern Hemisphere in falling Del C13 isotope ratio (Figure 10).  This is because 90% of fossil fuel emissions occur in the Northern Hemisphere. The remaining wavy signal in the Del C13 record correlates to El Nino cycles (Figure 9), with a rapidly falling Del C13 ratio during El Nino events, and a slightly rising Del C13 ratio during La Nina events.  It is unclear whether the El Nino signal in the data is due to fractionation between atmosphere and ocean, changes in the uptake of carbon in the ocean, or related climate events. 
Figure 9.   The Del C13 carbon isotope record in atmospheric CO2, from Scripps Institute atmospheric observatories; the seasonal cycle was filtered with a 12-month rolling average.  Broadly, the Northern Hemisphere leads the Southern Hemisphere in falling Del C13, because 90% of CO2 emissions from fossil fuels occur in the Northern Hemisphere.  The residual long-wavelength signal relates to the El Nino/La Nina cycle. [See an earlier post: ]

Rate of Increase in Global Atmospheric CO2
Atmospheric CO2 is steadily rising around the globe.  Volcanic eruptions are intermittent; the largest eruption (Mt. Pinatubo) and the third-largest eruption (Mt. Hudson) of the past century both occurred in 1991, but there is no perceptible change in the rate of rising atmospheric CO2 (Figure 10).  Likewise, other large volcanic eruptions produced no perceptible impact over the period of detailed CO2 observations [Mount Agung (1963), Mt. St. Helens (1980), El Chichon (1982). Puyehue-Cordón Caulle (2011)].  Slow, *quiet*, emissions of CO2 also occur from non-eruptive events, mid-ocean ridges and onshore rifts, but these have been well quantified over the past 20 years, and do not contribute significant volumes of CO2 to the atmosphere.
Figure 10. Global atmospheric CO2.   This is my version of the Keeling Curve.  Data is from the Scripps Institute network of atmospheric observatories.  Cool colors indicate stations in the Northern Hemisphere. Warm colors show stations in the Southern Hemisphere. Atmospheric CO2 falls in the Northern Hemisphere summer, as carbon is taken up by plants, and rises in winter as the plants decay.  There is a strong seasonal cycle dominated by the Northern Hemisphere due to predominant location of temperate landmass and agriculture in the Northern Hemisphere.  Apart from the seasonal cycle, CO2 has risen steadily from about 314 ppm in 1955 to about 412 ppm today.

Orbiting Carbon Observatories and NASA CO2 Modeling
Two new NASA satellites, OCO2 & OCO3, now provide worldwide continuous CO2 monitoring.  Data gathered by these satellites will provide a detailed identification of the specific sources of CO2 across the entire globe. 

NASA also prepared a supercomputer simulation of atmospheric CO2, based on ground-based and aerial CO2 observations.  A video of the simulation can be seen on YouTube:
The simulation highlights major CO2 sources, in the eastern US, eastern China, industrial centers of central & eastern Europe, oilfields of western Siberia, and wildfires in the Amazon rainforests (Figures 11A and 11B).

Figures 11A and 11B.  Atmospheric CO2 Concentrations from NASA supercomputer simulations for the year 2006.  The location of CO2 sources is apparent from cities, industrial centers, and wildfires.

Rising CO2 concentrations are unquestionably from human sources, as a result of combustion of fossil fuels and deforestation.  There is volumetric, temporal, isotopic, geographic, stoichiometric evidence supporting human sources of rising atmospheric CO2.  There is no evidence that volcanoes make a significant contribution to rising CO2.

Previous Posts on Volcanic and Atmospheric CO2

Posts on Twitter on Volcanic CO2

External References:
Scripps Institute CO2 Home
Scripps Institute O2 Program

Boden, et al, 2013, Global and National Fossil-fuel CO2 Emissions, in Global Carbon Atlas

Burton et al, 2013,  Deep Carbon Emissions from Volcanoes
Discussion of CO2 flux from subaerial volcanic eruptions on page 332.
Total CO2 flux from volcanic sources:  637 mT per year, p. 341, table 6.
The eruption of Mt. Pinatubo in 1991 was the largest volcanic eruption since 1912.   That eruption produced ~50 Mt of CO2 (Gerlach et al. 2011).  Individual eruptions are dwarfed by the time-averaged continuous CO2 emissions from global volcanism.  The eruption of Mt. Pinatubo was equivalent to only 5 weeks of global subaerial volcanic emissions. 
The average volume of eruptive CO2 emissions over the past 300 years was only 0.1 cubic kilometers, which suggests an annual rate of about 1 million tonnes of CO2 annually (Crisp, 1984, cited in Burton).
CO2 consumption from continental silicate weathering was 515 Mt/yr, (Gaillardet et al., 1999, cited in Burton).
Metamorphism accounts for the release of about 300 million tonnes of CO2 annually.  (Mörner and Etiope, 2002, Carbon degassing from the lithosphere. Global Planet Change 33:185-203, cited in Burton). 

Lee et al, 2016, Massive and prolonged deep carbon emissions associated with continental rifting,  Nature Geoscience Letters, Jan.18, 2016. 
Paper accounts for additional CO2 emissions from East African Rift, potentially bringing natural world CO2 emissions to 708 mT, an increase of 11% from previous estimates.

Houghton, R.A. 2008. Carbon Flux to the Atmosphere from Land-Use Changes: 1850-2005. In TRENDS: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.

Marland, G., T.A. Boden, and R.J. Andres. 2008. Global, Regional, and National Fossil Fuel CO2 Emissions. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.

Erik Klemetti, 2015, Volcanic versus Anthropogenic Carbon Dioxide: An Addendum, WIRED website.

Pre-industrial atmospheric del C13 was about -6.5, and declined following industrialization, in correlation with rising atmospheric CO2.

Representative del C13 values from volcanism:
Del C13 :  -3.2
Del C13: -4.9 to -6.3
Del C13: Currently  -0.9 to -1.4; 1970s and 1980s ~ -4
Del C13: -6 to -10.  N.B.: These are samples of soil gases in a rift zone with known petroleum generation, and may be contaminated by thermogenic or biogenic CO2 deriving from petroleum sources.  
Faure, 1984, Principles of Isotope Geochemistry
Del C13: -2 to -6. 

Volcanoes and CO2
A good discussion of former and current estimates of CO2 emissions from volcanoes and fossil fuels.  Also, a good recap of errors made by certain commentators in creating and propagating the volcanic CO2 myth. 

Naomi Oreskes and Erik Conway, 2010, Merchants of Doubt.
A deeply researched book about right-wing scientists, funded by industry, working outside of their fields of expertise, tried to throw doubt on science that might result in regulations in the interest of public health or environmental protection.  The scientists involved were generally retired, had worked in military science and were given compensation or recognition in return for their efforts.  Among the false narratives they created was the idea that volcanoes were responsible for chlorine damage to stratospheric ozone, and that volcanoes were responsible for acid rain in the US and Canada.  Neither idea is correct.  The idea of blaming volcanoes for man-made atmospheric disruption has now been extended to CO2 and climate change.

Which emits more carbon dioxide: volcanoes or human activities?

The following are examples of deliberately misleading media articles about atmospheric CO2.
Volcano eruption WARNING: Intense volcanic CO2 activity 'drives GLOBAL EXTINCTION'
Article omits mention of fossil fuels entirely.

J.E. Kamis, 2018, Discovery Of Massive Volcanic CO2 Emissions Puts Damper On Global Warming Theory
This article contains false claims.  Notably, the article claims that:
“Natural volcanic and man-made CO2 emissions have the exact same and very distinctive carbon isotopic fingerprint.  It is therefore scientifically impossible to distinguish the difference between volcanic CO2 and human-induced CO2 from the burning of fossil fuels (see here).”
The reference provided ( directly contradicts the claim!  “In fact the global C13/C12 ratio has declined, which is very strong evidence the source of the CO2 increase has was C12 enriched, ie, derived from photosynthesis.  Therefore it is very strong evidence that it comes from the biosphere or fossil fuels, rather than from volcanoes or oceanic outgassing.”

Stoichiometry Calculations
Annual fossil fuel emissions are reported in tonnes of CO2 by CDIAC, the BP Annual Statistical Review of World Energy, and the EIA.  One tonnes of CO2 (1000 kg) contains 22,722 moles of CO2. 

Calculation Notes for atmosphere stoichiometry.  The Scripps pages on units and FAQs are helpful in understanding the use of the “per meg” unit, and conversion to ppm. 

“Per meg” units of oxygen reported by Scripps can be converted to ppm (oxygen/atmosphere) over small ranges by multiplying by 20.95%, the current oxygen fraction in air.  Parts per million (ppm) of oxygen can then be converted to moles by multiplying by the number of moles in the atmosphere (1.81E+20), from various Internet sources.

A Few Words about CO2 Carbon Isotopes
There are two stable isotopes of carbon, C13 and C12.  C12 is the more abundant isotope; the natural ratio of C12 to C13 is about 99 to 1.  The standard measure of carbon isotopes compares the C12/C13 isotope ratio of the sample in question to the C13/C12 ratio of a standard limestone, according to the expression:

d C13/C12 = ((C13/C12 sample/C13/C12 standard) – 1)*1000.

This expression, commonly termed “del 13”, amplifies small but meaningful differences in the isotopes, which are diagnostic of certain processes and occurrences of carbon.  The standard is a uniform Cretaceous limestone with a d 13 value defined as zero.   Positive values indicate a heavier composition, i.e., a greater concentration of C13 than the standard.  Negative values indicate a lighter composition, i.e., a smaller concentration of C13 than the standard.

Plants fractionate carbon, favoring the lighter isotope C12.  Anything derived from plants, including oil, gas, and coal (and algae, animals and people) carries a light (negative) d C13/C12 signature.  Limestone carries a d C13/C12 ratio near zero.  The atmosphere, in 1977, had a d C13/C12 ratio of about -7.5; it is currently about -8.3, reflecting the influence of fossil fuels.  Oceans have a slightly positive d C13/C12 ratio of dissolved inorganic carbon, although Northern Hemisphere waters show a negative ratio due to the greater use of fossil fuels in the Northern Hemisphere.  Fossil fuel CO2 emissions and CO2 emissions from deforestation carry a very light d C13/C12, often in the range of -25 to -28 (although biogenic natural gas, which is fractionated twice, can have del 13 value in the range of -40 to -70).  The distinctive isotopic signature of CO2 from fossil fuels and deforestation is useful in tracking the movement of carbon through the atmosphere and oceans.  

Saturday, July 20, 2019

Key References for Understanding Climate Change

Here are key references for understanding the cause and evidence for global warming and climate change. Also included are references for some of the consequences with a focus on Alaska.   Some of the references link to primary data (such as atmospheric data at Scripps); some assembly may be required.

CO2 Emissions
Boden, Marland & Andres, Global and National Fossil Fuel CO2, 2017
BP Statistical Review of World Energy (annual fossil fuel CO2 emissions, by nation & type)
U.S. Energy Information Agency, Data Tables, U.S. Energy Information Agency, Office of Energy Analysis, U.S. Department of Energy, Washington D.C. data tables, 2014
Houghton 2008 (CO2 emissions from land use changes)
Burton, 2013 (volcanic CO2 emissions)
Lee 2016 (volcanic CO2 emissions)
EIA World CO2 Emissions Forecast to 2050, International Energy Outlook 2017
Forecast CO2 Emissions by Region
ForecastCO2 Emissions by Fuel Type – select appropriate table.

Atmospheric CO2
Global CO2 and del C13 isotopes.
Global O2.  
Formerly available at CDIAC.

Heat Retention by Greenhouse Gases
Tyndall, 1861, 1872, cited in Arrhenius, 1906.
Arrhenius, 1896, On the Influence of Carbonic Acid in the Air upon the Temperature on the Ground
Arrhenius, 1906, The Probable Cause of Climate Fluctuations,%20final.pdf
NOAA Greenhouse Gas Index.  Page includes formulas for predictive calculation of radiative forcing as function of concentration, and a table for historical annual radiative forcing for major greenhouse gases.
IPPC 5th Assessment Report, Anthropogenic Effective Radiative Forcing history, pp 1404 – 1409.
Table includes historical radiative forcing for greenhouse gases, and negative radiative forcing for cooling anthropogenic emissions. 
Trenberth, et al, 2009, Earth’s Global Energy Budget. 
Ramaswamy, et al 2001, Radiative Forcing of Climate Change.

Ocean Heat Content

Melting Ice
National Snow and Ice Data Center
NASA Global Ice Viewer
Global Cryosphere Watch
Antarctic and Greenland
Gravity measure of Antarctic and Greenland Ice Loss
IMBIE: Ice Sheet Mass Balance Inter-Comparison Exercise
Antarctic and Greenland Ice-loss data preceding NASA GRACE mission.
NASA Ice-Bridge Project
Arctic Sea Ice
Polar Science Center
Chart with relative volume loss (km3) 1980 – 2018.
Sequential maps of Arctic sea ice extent and thickness.
Sea Ice Data Portal
NOAA Arctic Report Card
Continental Glaciers
World Glacier Monitoring Service
WGMS Global Glacier Change Bulletin 2013
Zemp et al, 2019, Global glacier mass changes and their contributions to sea-level rise from 1961 to 2016.
Pacific Marine Environment Laboratory, NOAA
UAF Geophysical Institute
Jorgenson, 2006, Abrupt Increase in Permafrost Degradation in Arctic Alaska
USGS, Alaska’s Thawing Permafrost

Warming Surface Temperature

General Climate Change
Climate Dashboard,
IPCC Fifth Climate Assessment, 2013
IPCC Fifth Climate Assessment 2013, Executive Summary, 2013
Fourth National Climate Assessment, Vol. I and II, 2014
Key findings of the 4th National Climate assessment, organized by topic and by region.
NASA Climate Change
JPL Satellite Data & Climate Models, Earth’s Energy Balance, Oceans & Ice, Carbon & Water
NOAA Climate Change
National Climate Data Center/NOAA
NOAA Sea Level Rise Viewer
European Space Agency Climate Work
World Meteorological Organization, Global Climate Observing System

Sea Level
Lambeck et al, 2014, Sea level and global ice volumes from the Last Glacial Maximum to the Holocene
R. Rohde, K. Fleming, Post-Glacial Sea Level
NASA Sea Level
Zemp et al, 2019, Global glacier mass changes and their contributions to sea-level rise from 1961 to 2016.
University of South Florida Satellite Oceanography Laboratory
Sea-Level Rise for the Coasts of California, Oregon, and Washington
Chambers et al, 2016, Evaluation of the Global Mean Sea Level Budget
between 1993 and 2014
French Space Agency, Satellite Altimetry Data website
NASA, New study finds sea level rise accelerating

Alaska and Arctic Climate Change
UAF Research
UAF International Arctic Research Center
Alaska Oceans Observing System
Arctic Research Consortium of the United States
Rick Thoman, at 2019 Weather and Climate Summit, (time marker 1:58 to 3:12)
Rick Thoman, A Century of Alaska Weather and Climate, Science for Alaska Lecture Series
Climatologists on Twitter:
Rick Thoman, IARC,
Brian Brettschneider, UAF,
Zach Labe, UC Irvine, Cornell,
Robert Rohde, Berkeley Earth,

Ocean and Food-Chain Stress
Seabird Die-off
Whale Deaths
Declining Humpback Migration and Calving
Seal Die-off
Krill and Mussel Die-off
Pink Salmon Die-off

Wednesday, June 27, 2018

Global Heat Budget #3 – Ice

This is the third in a series of posts about the global heat budget. 

Ice is melting around the world. 

Greenland’s ice cap is melting.  Antarctica’s ice cap is melting.  Arctic sea ice is melting. Continental glaciers are melting.  Arctic permafrost is melting.  The melting is happening at a rate that is readily visible to people who live near natural ice.  From decade to decade and year-to-year, glaciers are visibly retreating, and can be directly verified by the most casual observer.   

Melting ice is the second most important heat sink on the planet, after the ocean (albeit a distant second).  Melting ice accounts for about 3% of anthropogenic heat retained in the atmosphere.  Melting ice is the second most significant proof that human-caused climate change is happening.  Melting ice may be the most significant consequence of climate change in terms of costs and damage to humanity. 

The data is unambiguous and irrefutable.  The volumes of melted ice have been measured by a variety of methods, including high accuracy satellite measurements.  The heat required to warm and melt this volume of ice can be calculated and compared to the heat trapped in the atmosphere by greenhouse gases, and the rising heat content of the oceans.  The volume of meltwater entering the ocean can also be compared to measurements of rising sea level.   The rate of sea level rise is already 3 times the rate of the past 7500 years, and accelerating.  The observed volumes of melting ice and the measurement of rising sea level provide unambiguous proof that climate change is real. 

Ice on Greenland is melting.
Greenland covers an area one-fifth the size of Australia.  Almost all of Greenland is covered by ice, ranging between 1 and 2 miles of ice thick.  The Greenland Ice sheet contains more than 2.8 million cubic kilometers of ice.  That is enough to make sea level rise by 20 feet if it all melted.

NASA’s GRACE (Gravity Recovery and Climate Experiment) satellites have monitored the mass of the Greenland ice cap since 2002.  Gravity observations were supplemented by altimetry and radar data from overflights and satellites.  Other satellite observations include NASA’s early ICESat, and the ESA’s currently operating CryoSat2.

There is a strong seasonal signal in the history of ice loss from Greenland, with a slight build in ice mass during the Northern Hemisphere winter, and a stronger decline in the summer.  From 2002 to 2016, Greenland lost about 3900 gigatonnes of ice due to melting.  Each gigatonne is a little more than one cubic kilometer of ice by volume, and produces one cubic kilometer of fresh water when it melts.  Altimetry data show that most of the melting was concentrated near the coast, particularly on the western side.  Six feet to fourteen feet of ice has melted around the edges of the entire island. 

The GRACE satellite, designed for only a five-year life, actually worked for nearly fifteen years.  The last data was recorded in June 2017.  The replacement mission, GRACE Follow-On, is scheduled to be launched in five days, on May 19th, 2018.  

NASA’s IceBridge is an airborne project using laser altimetry and ice-penetrating radar data to measure the elevation, snow cover, and total thickness of Greenland and Antarctic ice.  IceBridge will provide data to connect and calibrate data from the new GRACE satellites.   IceBridge was originally designed to replace data from the ICESat satellite, which failed after seven years of service.  ICESat-2 is planned to be launched in September, 2018, to replace ICESat.

Ice on Antarctica is melting.
Antarctica is about seventeen times larger than Greenland, and nearly twice as large as Australia.  Ice covers 98% of the continent, to an average thickness of over a mile.  Antarctica holds about ten times the volume of ice as Greenland.  If all of the ice on Antarctica melted (which would require centuries to occur), it would raise sea level by about 200’, placing most of the world’s major cities and human habitation under water. 

The GRACE data for Antarctica is noisier than the data for Greenland and shows a weaker seasonal cycle.  It seems likely that the melting season over Antarctica is not (yet) as profound as over Greenland. 

As with Greenland, the Antarctic ice sheet has been monitored by NASA’s Grace and ICESat satellites, and the IceBridge aerial observation program.  Earlier observations were integrated by the European Space Agency’s IMBIE (ice sheet mass balance comparison exercise) to provide the ice balance record from 1992 to 2010.  The chart showing both IMBIE data and GRACE data is shown below.  From 1994 through 2017, at least 2450 gigatonnes of ice on Antarctica melted.

I should note that gravity methods will not detect ice loss on the portions of the ice sheet that are floating (and more susceptible to ice loss).  Ice floating on water will have the same net density as ice-free water.  So, altimetry methods must be combined with gravity methods for a full determination of ice loss on Antarctica.  The East Antarctic (Filchner-Ronne) and West Antarctic (Ross) ice shelves are approximately 900,000 square kilometers in area.  Dozens of smaller ice shelves also exist.  The actual loss of ice from Antarctica may be greater than 2450 gigatonnes, because losses from these floating ice shelves are not detected by gravity. 

While melting of floating ice shelves is difficult to observe, it is also true that the melting of floating ice will not cause sea level to rise, at least as a first-order consequence.  The same buoyancy of ice shelves that makes sea-ice loss invisible to gravity detection means that sea level does not change when a volume of ice is converted to water.  Melting ice shelves matter to the earth’s heat budget, but not (directly) to sea level. 

The rate of future ice loss in Antarctica depends on feedback mechanisms.  The principle feedback mechanism is the restraining force that ice shelves exert on flowing glaciers.  Ice shelves impede the flow of ice from the continent and into the ocean; when those shelves melt, the rate of ice loss will accelerate.  The timing and amount of acceleration are unpredictable, so the best estimates of future sea level rise are uncertain on the high end.  We are fairly certain about the minimum expected sea level rise, but the maximum possible sea level rise is very uncertain.

Antarctic Sea Ice
For many years, Antarctic sea ice was not subject to the declines seen in Arctic sea ice (seen in the next section).  This was often referenced in commentaries on climate-change deniers’ web sites.  In recent years, Antarctic sea ice has declined, but it is likely to continue to show an irregular response to climate change.  The reason is simple.  Antarctic sea ice is regularly replenished by calving from Antarctic glaciers and ice shelves.  Anyone with tour-boat experience in Alaska knows that sea ice actually increases following calving events.  So, with a huge reservoir of ice in the Antarctic ice cap, Antarctic sea ice is likely to fluctuate, but not disappear, as the mother-lode of ice continues to flow and break apart, feeding the sea ice around the continent.

 Arctic Sea Ice
Arctic Sea Ice is melting.
In contrast to Antarctica, the Arctic has no mother-lode of ice feeding the polar sea ice.  The sea ice freezes and melts in a seasonal cycle.  For the past forty years, each cycle has ended with less ice, on average, than the previous cycle.  The loss of ice has accelerated over that period.   There was about 250,000 square miles less sea ice in the 1990s than during the 1980s.   From the 1990s to the 2000s, the decadal average showed a loss of about 500,000 square miles of sea ice.  The annual data from the current decade suggests an even greater rate of loss. 

Area is not the only measure of sea ice.  Some sea ice persists through multiple seasons, gaining thickness from season to season.  However, against the background rate of general melting, less and less ice persists from season to season, and the overall thickness of Arctic sea ice is also declining.   Between 1984 and 2016, 94% of the sea ice more than four years old had disappeared.
Image by M Tschudi and S. Stewart of the University of Colorado, and W. Meier and J. Stroeve of NSIDC.

Some researchers have attributed 30 percent to 50 percent of the loss of Arctic sea ice to natural variability, and 50 to 70 percent to anthropogenic influences, including direct warming by greenhouse gases, and the second-order influence of atmospheric circulation patterns. 

Overall, Arctic sea ice has declined by 12,000 cubic kilometers since 1980.   As noted in the section about Antarctica, there is no sea level impact due to the melting of floating ice, but there is an impact on the earth’s heat budget. 

The loss of sea ice in some of the peripheral seas of the Arctic Ocean (Chukchi Sea, Bering Sea, Barents Sea, and others) is more evident.  
Image Credit, Rick Thoman, National Weather Service, Fairbanks

Continental Glaciers
Continental glaciers are melting. 
People who live near glaciers are well aware of the historical and current melting of glaciers.  In Alaska and Western Canada, popular glaciers often have signposts or old photographs showing the earlier extent of the glaciers.  Some examples are the Columbia Ice Field in Alberta between Banff and Jasper National Parks, and in Alaska, Root Glacier near Kennecott mine, Exit Glacier near Seward, Portage Glacier and associated glaciers near Anchorage, and the many tidewater glaciers along the Alaskan coast, including Glacier Bay near Juneau, College Fjord near Valdez, the glaciers of Kenai Fjords National Park, and Columbia Glacier near Valdez.  Glaciers are in retreat, on a scale which is noticeable from year to year and dramatic over the course of decades. 

The UN Glacier Monitoring Service and its predecessor organizations have measured the melting of continental glaciers, other than Greenland & Antarctica.  WGMS issued major reports in 2008 and 2015; each report shows overwhelming evidence of melting of glaciers worldwide.  WGMS includes data on about 100,000 glaciers, with digital outlines of about 62,000 glaciers; data on glacier fluctuation includes over 35,000 length observations for nearly 2000 glaciers (as of 2008).  Detailed mass balance observations are conducted on a smaller number of reference glaciers (including the most volumetrically significant glaciers).  Data from reference glaciers are extrapolated to other glaciers on the basis of regional association, altitude and latitude.

At any given time, a small number of glaciers are growing, due to natural fluctuations of snowfall, warmth, and air circulation. But the great majority of glaciers worldwide are melting. 

Annoyingly, the WGMS does not report summary ice loss in terms of cubic kilometers or gigatonnes.  Glacial Mass Balance is reported in terms of meters of water equivalent, a vertical measure of average ice melted.  Volumes of melted ice can be calculated from the reported total area of glaciers under study.  Those volumes can then be used for purposes of understanding the global heat budget and sea level rise. 

Sea Level
The earth entered a period of cyclic ice ages about 3 million years ago.  The last 600,000 years have been characterized by ice age cycles of about 100,000 years, apparently triggered by variations in earth’s orbit.  The influence of the orbital cycles is enhanced by feedback mechanisms, including CO2 and the reflectivity of ice.  The peak of the last glacial cycle occurred only about 20,000 years ago, and remnants of ice may have persisted in Ontario until about 8,000 years ago.

Deglaciation following the last ice age was mostly complete by 8000 years ago.  We know this from studies of sea level and sediment cores.  Sea level rose by about 80 meters between 14,000 years ago and 8000 years ago, an average rate of 1.3 cm/year.  From 7500 years ago to the 20th century, sea level rose only 5 meters, a rate of 0.07 cm/year.   Through the 20th century, sea level rose at about 0.2 cm/year, a significant increase over the background rate.  Satellite data over the past 25 years shows that sea level rise has accelerated to 0.35 cm/year, five times the rate of sea level rise for the past 7500 years.  This is a clear indication that global warming from human greenhouse gases is contributing to melting ice.
Additional heat retained by greenhouse gases will result in a faster rate of melting ice, and higher sea level rise.  Current forecasts of sea level rise range from about 2 feet to 8 feet by the end of the century.  Sea level rise of only 4 to 6 feet would seriously damage some coastal communities around the world, including the inundation of barrier island and low-island communities.

Heat Budget

From 2003 to 2016, greenhouse gases retained 1.6 x 1023 joules of heat in the atmosphere, according to tables of radiative forcing published by NOAA (  This figure for anthropogenic heat does not include the effect of cooling or warming aerosols, primary heat from fossil fuels and deforestation, or other minor sources of heat.  Estimates for some of these other anthropogenic disturbances are found in the IPCC 5 report, but only through the year 2011.

We have good estimates of the cumulative ice lost from Antarctica, Greenland, Arctic sea-ice and Continental Glaciers from 2003 to 2016, due to high-quality satellite observations.  About 10,400 gigatonnes of ice was lost over that period.  The heat required to warm (+10 C) and melt that volume of ice is 3.7 x 1021 joules, or about 2.3% of the total heat retained by greenhouse gases.  The allocation of heat to warm the ice by 10 degrees C was to reflect heating of an equivalent amount of ice, which has not yet melted.  Average temperatures of -10 C from core-holes in Greenland and Antarctica were taken as the ambient temperature of ice before melting. 

Considering that about 2.9% of the earth’s surface is covered by ice, this seems like a reasonable distribution of greenhouse heat which is going to warm and melt ice.  Looking forward, if a higher percentage of heat goes towards melting ice, sea level will necessarily rise faster.  Possible reasons for faster melting of ice could be more rapid ice flow from Antarctica and Greenland.  This might occur as the base of the ice is lubricated by meltwater, or when restraining ice shelves are lost around Antarctica.


Antarctica and Greenland
NASA GRACE Ice Mass, Antarctica and Greenland

Grace Data
Wiese, D. N., D.-N. Yuan, C. Boening, F. W. Landerer, and M. M. Watkins (2017) Antarctica Mass Variability Time Series Version 1 from JPL GRACE Mascon CRI Filtered. Ver. 1, PO.DAAC, CA, USA. Dataset accessed [2017-06-07] at

IMBIE:  Ice Sheet Mass Balance Inter-Comparison Exercise
Integrated Methods Measuring Ice Mass

Arctic Sea Ice
Arctic Sea Ice Volume
Chart with relative volume loss (km3) to 1980. 

Charts of Arctic Sea Ice Extent by Month

Image of declining multi-year Arctic Sea Ice.  Image by M Tschudi and S. Stewart of the University of Colorado, and W. Meier and J. Stroeve of NSIDC.

Arctic Sea Ice
Multi-year ice grows up to 4 meters thick, while single-year ice is 2 meters thick at most.

the area covered by Arctic sea ice at least four years old has decreased from 1,860,000 square kilometres in September 1984 to 110,000 square kilometres in September 2016.

Continental Glaciers
World Glacier Monitoring Service bi-annual update, 2015

Volume estimate for Glaciers and Ice sheets (other than Antarctica and Greenland.