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For 2016, Atmospheric CO2 Concentrations are Rising at the Fastest Rate Ever Seen

“The MMCO [Middle Miocene Climate Optimum] was ushered in by CO2 levels jumping abruptly from around 400ppm to 500 ppm, with global temperatures warming by about 4°C  and sea levels rising about 40m (130 feet) as the Antarctic ice sheet declined substantially and suddenly. ” — Skeptical Science

fossil-fuel-emissions

(Fossil fuel carbon emissions are about 100 times that of volcanoes during any given year. And so much heat trapping carbon dumped into the atmosphere is forcing the world’s climate to rapidly change. Image source: The Union of Concerned Scientists.)

Human beings have never seen atmospheric CO2 values that are so high as they are today. They significantly predate our species — even preceding our distant relative Australopithecus by about 7 million years. And weather and climate conditions to which we are not adapted — either as individuals or as a civilizations — are well on the way as atmospheric CO2 levels are ramping up into the lower range of those last seen during the Middle Miocene of 14-16 million years ago at 404 parts per million during 2016.

Record Rate of CO2 Increase for 2016

As we reported in November, 2016 is on track to see a record rate of atmospheric carbon dioxide (CO2) increase. A key heat-trapping gas, CO2 is the primary driver of the big temperature increases seen around the world recently. And with new figures out from NOAA for the month of November, we have a clearer picture than ever of just how unprecedented the jump will be.

For the first 11 months of the year, 2016 atmospheric carbon dioxide concentrations exceeded those of 2015 by an average of 3.45 parts per million. With no sign evident that the pace of increase has slackened — despite a transition to La Nina during the fall — it now appears that the world is set to experience a 3.3 to 3.5 part per million jump in the atmospheric CO2 measure for this year.

Carbon Dioxide Trend Mauna Loa

(Atmospheric carbon dioxide concentrations will rise by a record rate during 2016 to an annual average of around 404 parts per million. Levels during 2017 could peak at around 410 to 411 parts per million in April and May before averaging between 406 and 407 parts per million. Image source: NOAA.)

The past two record jumps were 2015 — with a 3.05 ppm annual increase and 1998 with a 2.93 ppm annual increase. But 2016 now appears set to exceed these two values by a pretty hefty margin.

More and More Toward the Middle Miocene Range of 400 to 500 Parts Per Million CO2

Such rapid rates of atmospheric carbon dioxide increase are primarily caused by global fossil fuel burning — which now produces an emission that is more than 100 times greater than all the volcanoes that erupt across the Earth during any given year. And recent reports have found that US automobile emissions alone equal the amount of carbon dioxide emitted by the Mount St. Helens eruption every three days. This is a heavy insult to the Earth’s climate system. One that is unprecedented for millions of years.

All this fossil fuel burning has largely helped to push atmospheric CO2 values for 2016 into an average range of 404 parts per million. This is 124 parts per million higher than the pre-industrial value of 280 parts per million. Meanwhile, peak monthly values during April-May of 2017 could strike as high as 410 to 411 parts per million.

calvert-middle-miocene-15-ma-embayment

(15 million years ago, atmospheric CO2 levels in the range of 400-500 parts per million produced Antarctic melt resulting in substantial sea level rise. The above image shows the estimated location of the U.S. eastern coastline at the time. Image source: Colorado Geosystems.)

These atmospheric concentrations are now roughly equivalent to the lower range CO2 levels of the Middle Miocene climate epoch of 14-16 million years ago. Meanwhile, atmospheric CO2 equivalent concentrations, which include other greenhouse gasses like methane, averaged 485 parts per million in 2015 and likely were around 490 parts per million during 2016. These CO2e values approach the upper Middle Miocene range.

During the Miocene of 14-16 million years ago, atmospheric CO2 levels, which had hovered around 400 parts per million for about 10 million years jumped higher due to volcanic activity. Global temperatures rose from about 2-3 C hotter than Holocene values to around 4 C hotter. Antarctic ice melted and seas which were around 60 feet higher than today lifted to around 130 feet above present day levels.

By continuing to burn fossil fuels, this is the climate context we enter more and more. It is why, for example, we are seeing so many impacts from expanding droughts, to declining ocean health, to more extreme weather, to rapidly destabilizing glaciers in Antarctica. And it is this burning along with a related warming of the Earth System that is causing atmospheric carbon values to jump so rapidly into ranges to which we are unaccustomed.

Links:

NOAA Earth Systems Research Laboratory

Skeptical Science

2016 to See Record Rate of Atmospheric CO2 Increase

The Union of Concerned Scientists

US Auto Emissions Comparable to Mt. St. Helens Eruption Every Three Days

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Global CO2 to Reach Extremely Dangerous Peak Near 402 PPM for 2014, Methane Levels Ramp Ominously Higher

During 2014, human CO2 forcing continued its long march toward ever-more dangerous and climate-damaging levels. By the peak month of May, global CO2 had ranged well above the 400 parts per million threshold, catapulting Earth at raging velocity toward climate and atmospheric states not seen in at least 3 million years.

According to May readings from the Mauna Loa Observatory, the more volatile hourly measures jumped as high as 404 parts per million while daily and weekly averages tended to settle between 401.4 and 402.3 parts per million. Given these trends, overall CO2 levels for May of 2014 are likely to peak at near or just below the astronomical 402 ppm threshold.

Atmospheric CO2 Late May 2014

(Atmospheric CO2 levels measured by the Mauna Loa Observatory over the past two years. Peak values for 2012 hit near 397 ppm, peak for 2013 hit near 400 ppm, and peak for 2014 is likely to hit near 402 ppm. Image source: The Keeling Curve.)

CO2 levels near 400 parts per million are enough, according to our developed understanding of paleoclimates, to increase global temperatures by between 2 and 3 degrees Celsius, to melt Greenland, West Antarctica and a portion of East Antarctica, and to raise sea levels by 75 feet if sustained over a long term. According to recent glacial research, these very high levels, when combined with additional greenhouse gas forcing and concurrent ocean and atmospheric warming have already been enough to destabilize or push large portions of these major ice systems into irreversible collapse.

(A history of atmospheric carbon dioxide through early this year provided by CIRES and compared to the entire ice core record of the past 800,000 years. Video source: CIRES.)

36 Billion Tons of CO2 Emission per Year and Counting

Measured from peak to peak, the rate of atmospheric increase is likely near 2.5 to 3.0 parts per million per year over the two year period. Averages over the whole range of the past two years show increases on the order of 2.4 parts per million per year — a challenge to recent rates of increase near 2.2 parts per million a year since 2000.

Steadily ramping rates of atmospheric CO2 accumulation are driven by extreme global industrial, agricultural, and land-use emissions. According to the Global Carbon Project, 2013 saw total global CO2 emissions in the range of 36 billion metric tons. This emission was 2.1 percent higher than the 2012 level and about 60 percent higher than the 1990 level at around 22 billion metric tons of CO2. Such an extraordinary pace of emissions puts severe strain on both atmospheric carbon levels and on carbon sinks around the globe. The resulting risk of such a strong continued emission is that global sinks and stores may soon become sources (see methane monster below). An issue of amplifying feedbacks that grows ever more perilous with each passing year.

Rapidly Increasing CO2 Acting in Concert With Ramping Methane, other Greenhouse Gasses

Unfortunately, CO2 is not the only human emission forcing global temperatures rapidly higher. In addition, methane, nitrous oxide, and numerous other greenhouse gasses also make their way into the atmosphere each year through industrial sources. If we combine all these other greenhouse gasses, the total CO2 equivalent carbon emission is now at around 50 billion metric tons each year. A veritable mountain of greenhouse gasses dumped at a pace more than 150 times that of volcanic emissions each and every year.

Overall, the total greenhouse gas forcing from all these sources is now likely in the range of 481 parts per million of CO2 equivalent. This immense heat forcing, were it to remain in the atmosphere long-term, is enough to raise global temperatures by 3-4 C and to melt enough ice to raise sea levels by at least 120 feet. It is also enough, with only two more years of current emissions, to likely lock in an inevitable, irreversible and extraordinarily disruptive increase of 2 C in global temperatures for this century alone.

First Glimpses of the Methane Monster

The most potent and troubling of these additional greenhouse gasses is methane. Over the course of 20 years, methane is about 80 times as powerful a heat trapping gas as CO2 by volume. And though atmospheric methane levels are far less than comparable CO2 levels (at around 1.8 parts per million, or 1/3 the total atmospheric heat forcing of CO2), there is cause for serious concern.

For not only is the industrial emission of methane increasing, primarily through the use of very damaging hydraulic fracturing technologies (fracking), the global emission of methane from the Earth System also appears to be ramping higher. Over recent years, rapidly thawing permafrost and warming oceans both around the world and, particularly, in the Arctic show signs of venting an increasing volume of methane into the atmosphere from terrestrial sources. Though annual official tracking of total Arctic methane emissions at this point is practically non-existent, recent research allows for rational estimation.

Taking into account known emissions from permafrost and the East Siberian Arctic Shelf, and adding in expected emissions from the rest of the thawing Arctic, methane emissions for the entire region are likely around 40 teragrams per year, or about 7% of the global total. This emission is equivalent to that of a major industrial nation and initial indications are that it is growing.

Mauna Loa Methane 2007 to 2014

(Atmospheric methane increase since 2007 as measured at the Mauna Loa Observatory. Note the more rapid pace of increase from 2013 through the first quarter of 2014. Image source: NOAA/ESRL.)

The result of combined increases in the human methane emission and in the Earth System emission has been enough to continue to push global levels higher with Mauna Loa readings breaching the 1840 part per billion average by early 2014. What is even more troubling is that the Earth System methane store, composed of both permafrost methane and methane hydrate at the bottom of the world ocean system, is immense.

In total, more than 3,000 gigatons of carbon in the form of methane may be at risk to eventually hit the atmosphere as the Earth continues to warm under the current human forcing. A very large store that could easily multiply the current rate of Earth System methane release many times over. One that represents a clear and present danger for a potentially very powerful amplifying heat feedback to an equally extraordinary initial human forcing.

Links:

The Keeling Curve

NOAA/ESRL

What Does a World at 400 PPM CO2 Look Like Long-term?

Grim News From NASA: West Antarctica’s Entire Flank is Collapsing Toward the Southern Ocean

Global Carbon Budget 2013

A Faustian Bargain on the Short Road to Hell: Living in a World at 480 CO2e

Far Worse Than Being Beaten With a Hockey Stick: Michael Mann and Our Terrifying Greenhouse Gas Overburden

Beneath the Cracking, Melting Ice, Arctic Methane Monster Continues its Ominous Rumblings

CIRES

 

 

 

Far Worse than Being Beaten with a Hockey Stick: Michael Mann, Our Terrifying Greenhouse Gas Overburden and Heating the Earth by + 2 C by 2036

I’m going to say something that will probably seem completely outrageous. But I want you to think about it, because it’s true.

You, where-ever you are now, are living through the first stages of a disaster in which there is nowhere to run, nowhere to hide, and no safe place on Earth for you to go to avoid it. The disaster you are now living through is a greenhouse emergency and with each ounce of CO2, methane and other greenhouse gasses you, I, or the rest of us, pump into the air, that emergency grows in the vast potential of damage and harm that it will inflict over the coming years, decades and centuries. The emergency is now unavoidable and the only thing we can hope to do through rational action is to reduce the degree of harm both short and long term, to rapidly stop making the problem worse, and to put human ingenuity toward solving the problem rather than continuing to intensify it.

But damage, severe, deadly and terrifying is unleashed, in effect and already happening, with more on the way.

*    *    *    *    *

Manns-hockey-stick

(Michael Mann’s famous Hockey Stick graph showing Northern Hemisphere temperatures over the past 1,000 years. The influences of human warming become readily apparent from the late 19th to early 21rst centuries. But human greenhouse gas forcing has much greater degrees of warming in store.)

This week, Michael Mann wrote an excellent piece describing the immediacy of our current emergency in the Scientific American. In typical, just the facts, fashion, he laid out a series of truths relevant to the current greenhouse catastrophe. These facts were told in a plain manner and, yet, in a way that laid out the problem but didn’t even begin to open the book on what that problem meant in broader context.

Michael Mann is an amazing scientist who has his hand on the pulse of human-caused climate change. He is a kind of modern Galileo of climate science in that he has born the brunt of some of the most severe and asinine attacks for simply telling the truth and for revealing the nature of our world as it stands. But though Mann’s facts are both brutal and hard-hitting for those of us who constantly read the climate science, who wade through the literature and analyze each new report. By simply stating the facts and not telling us what they mean he is hitting us with a somewhat nerfed version of his ground-breaking Hockey Stick. A pounding that may seem brutal when compared to the comfortable nonsense put out by climate change deniers and fossil fuel apologists but one that is still not yet a full revelation.

I will caveat what is a passionate interjection by simply saying that Michael Mann is one of my most beloved heroes. And so I will do my best to help him out by attempting to lend more potency to his already powerful message.

2 C by 2036 — Digging through the Ugly Guts of it

All that said, Michael Mann laid out some brutal, brutal facts in his Scientific American piece. Ones, that if you only take a few moments to think about are simply terrifying. For the simple truth is that the world has only a very, very slim hope of preventing a rapid warming to at least 2 C above 1880s levels in the near future and almost zero hope altogether of stopping such warming in the longer term.

The first set of figures Mann provides involves the current greenhouse gas forcing. Current CO2 levels are now at the very dangerous 400 parts per million threshold. Long term, and all by itself, this forcing is enough to raise global temperatures by between 2 and 3 degrees Celsius. But hold that thought you were just about to have, because we haven’t yet included all the other greenhouse gasses in that forcing.

Mann, in the supplemental material to his Scientific American paper, notes that the total forcing of all other greenhouse gasses currently in the atmosphere is about 20% of the total CO2 forcing. This gives us a total CO2 equivalent forcing of 480 ppm CO2e, which uncannily mirrors my own analysis here (the science may have under-counted a bit on the methane forcing, but this value is likely quite close to current reality for both the short and long term).

480 ppm CO2e is one hell of a forcing. It is nearly a 75% greater forcing than 1880s values and, all by itself, is enough to raise temperatures long-term by between 3.5 and 4.5 degrees Celsius.

And it is at this point that it becomes worthwhile talking a bit about different climate sensitivity measures. The measure I am using to determine this number is what is called the Earth Systems Sensitivity measure (ESS). It is the measure that describes long term warming once all the so called slow feedbacks like ice sheet response (think the giant glaciers of Greenland and West Antarctica) and environmental carbon release (think methane release from thawing tundra and sea bed clathrates) come into the equation. Mann, uses a shorter term estimate called Equilibrium Climate Sensitivity (ECS). It’s a measure that tracks the fast warming response time once the fast feedbacks such as water vapor response and sea ice response are taken into account. ECS warming, therefore, is about half of ESS warming. But the catch is that ECS hits you much sooner.

At 480 ppm CO2e, we can expect between 1.75 and 2.25 degrees C of warming from ECS. In essence, we’ve locked about 2 C worth of short term warming in now. And this is kind of a big deal. I’d call it a BFD, but that would be swearing. And if there is ever an occasion for swearing then it would be now. So deal with it.

Mann, in his article, takes note of the immediacy of the problem by simply stating that we hit 2 C of shorter term ECS warming once we hit 405 ppm CO2 (485 CO2e), in about two to three years. And it’s important for us to know that this is the kind of heat forcing that is now hanging over our heads. That there’s enough greenhouse gas loading in the atmosphere to push warming 2 C higher almost immediately and 4 C higher long term. And that, all by itself, is a disaster unlike anything humans have ever encountered.

Global Fossil Fuel Emission

(Global annual fossil fuel emission is currently tracking faster than the worst-case IPCC scenario. Aerosols mask some of the heating effect of this enormous emission, what James Hansen calls ‘a Faustian Bargain.’ Image source: Hansen Paper.)

But there is a wrinkle to this equation. One that Dr. James Hansen likes to call the Faustian Bargain. And that wrinkle involves human produced aerosols. For by burning coal, humans pump fine particles into the atmosphere that reflect sunlight thereby masking the total effect of the greenhouse gasses we have already put into the atmosphere. The nasty little trick here is that if you stop burning coal, the aerosols fall out in only a few years and you then end up with the full heat forcing. Even worse, continuing to burn coal produces prodigious volumes of CO2 while mining coal pumps volatile methane into the atmosphere. It’s like taking a kind of poison that will eventually kill you but makes you feel better as you’re taking it. Kind of like the greenhouse gas version of heroin.

So the ghg heroin/coal has injected particles into the air that mask the total warming. And as a result we end up with a delayed effect with an extraordinarily severe hit at the end when we finally stop burning coal. Never stop burning coal and you end up reaching the same place eventually anyway. So it’s a rigged game that you either lose now or you lose in a far worse way later.

Mann wraps coal and other human aerosol emissions into his equation and, under business as usual, finds that we hit 2 C of ECS warming by 2036 as global CO2 levels approach 450 ppmv and global CO2e values approach 540 ppmv. At that point, were the aerosols to fall out we end up with an actual short term warming (ECS) response of 2.5 to 3 C and a long term response (ESS) of about 5 to 6 C. (Don’t believe me? Plug in the numbers for yourself in Mann’s climate model here.)

So ripping the bandaid off and looking at the nasty thing underneath, we find that even my earlier estimates were probably a bit too conservative and Mann, though we didn’t quite realize it at first, is hitting us very hard with his hockey stick.

What does a World That Warms So Rapidly to 2 C Look Like?

OK. That was rough. But what I am about to do is much worse. I’m going to take a look at actual effects of what, to this point, has simply been a clinical analysis of the numbers. I’m going to do my best to answer the question — what does a world rapidly warming by 2 C over the next 22 years look like?

Ugly. Even more ugly than the numbers, in fact.

First, let’s take a look at rates of evaporation and precipitation. We know that, based on past research, the hydrological cycle increases by about 6% for each degree Celsius of temperature increase. So far, with about .8 C worth of warming, we’ve had about a 5% increase in the hydrological cycle. What this means is that evaporation rates increase by 5% and precipitation events, on average, increase by about 5%. But because weather is uneven, what this does is radically increase the frequency and amplitude of extreme weather. Droughts are more frequent and more severe. Deluges are more frequent and more severe.

(Program in which top climate scientists explain how global warming increases the intensity of evaporation and precipitation all while causing dangerous changes to the Jet Stream.)

At 2 C warming we can change this loading from a 5% increase in the hydrological cycle of evaporation and precipitation to a 12% increase. You think the droughts and deluges are bad now? Just imagine what would happen if the driver of that intensity more than doubled. What do you end up with then?

Now let’s look at something that is directly related to extreme weather — sea ice loss. In the current world, about .8 C worth of warming has resulted in about 3.2 C worth of warming in the polar regions. And this warming has resulted in a massive and visible decline of sea ice in which end summer volume values are up to 80% less than those seen during the late 1970s. This loss of sea ice has had severe effects on the Northern Hemisphere Jet Stream, both pulling it more toward the pole and resulting in high amplitude Jet Stream waves and local severe intensification of storm tracks. At 2 C worth of global warming, the Arctic heats up by around 7 C and the result is extended periods of ice free conditions during the summer and fall that last for weeks and months.

stroeve-barret-p-10-plus-2012

(Actual rate of sea ice loss vs IPCC model predictions. The most recent record low value achieved in 2012 is indicated by the dot. Image source: Assessment of Arctic Sea Ice/UCAR Report.)

The impacts to the Northern Hemisphere Jet Stream are ever more severe as are the impacts to Greenland ice sheet melt. Under such a situation we rapidly get into a weather scenario where screaming temperature differentials between the North Atlantic near Greenland and the warming tropics generate storms the likes of which we have never seen. Add in a 12% boost to the hydrological cycle and we get the potential for what Dr. James Hansen describes as “frontal storms the size of continents with the intensity of hurricanes.”

Greenland melt itself is much faster under 2 C of added heat and the ice sheets are in dangerous and rapid destabilization. It’s possible that the kick will be enough to double, triple, quadruple or more the current pace of sea level rise. Half foot or more per decade sea level rise rapidly becomes possible.

All this severe weather, the intense rain, the powerful wind storms and the intense droughts aren’t kind to crops. IPCC projects a 2% net loss in crop yields each decade going forward. But this is likely to be the lower bound of a more realistic 2-10 percent figure. Modern agriculture is hit very, very hard in the context of a rapidly changing climate, increasing rates of moisture loss from soil and moisture delivery through brief and epically intense storms.

The rapid jump to 2 C is also enough to put at risk a growing list of horrors including rapid ocean stratification and anoxia (essentially initiating a mass die off in the oceans), large methane and additional CO2 release from carbon stores in the Arctic, and the unlocking of dangerous ancient microbes from thawing ice, microbes for which current plants and animals do not have adequate immune defenses.

How do we avoid this?

In short, it might not be possible to avoid some or even all of these effects. But we may as well try. And this is what trying would look like.

First, we would rapidly reduce human greenhouse gas emissions to near zero. As this happens, we would probably want a global fleet of aircraft that spray sulfate particles into the lower atmosphere to make up for the loss of aerosols once produced by coal plants. Finally, we would need an array of atmospheric carbon capture techniques including forest growth and cutting, then sequestration of the carbon stored by wood in lakes or in underground repositories, chemical atmospheric carbon capture, and carbon capture of biomass emissions.

For safety, we would need to eventually reduce CO2 to less than 350 ppm, methane to less than 1,000 ppb, and eliminate emissions from other greenhouse gasses. A very tall order that would require the sharing of resources, heroic sacrifices by every human being on this Earth, and a global coordination and cooperation of nations not yet before seen. Something that is possible in theory but has not yet been witnessed in practice. A test to see if humankind is mature enough to ensure its own survival and the continuation of life and diversity on the only world we know. A tall order, indeed, but one we must at least attempt.

Links:

Earth Will Cross Climate Danger Threshold by 2036

What does a World at 400 Parts per Million CO2 Look Like Long-Term?

One Scientist Argues 2036 Could be Point of No Return for Climate Disaster

A Faustian Bargain on the Short Road to Hell

Doubling Down on our Faustian Bargain

Dr. Jennifer Francis, Top Climate Scientists Explain How Global Warming Aps the Hydrological Cycle and Wrecks the Jet Stream to Unleash Extreme Weather

Assessment of Arctic Sea Ice/UCAR Report

 

A Faustian Bargain on the Short Road to Hell: Living in a World at 480 CO2e

On the highway to a smokestack hell, Faust met a devil who said to him:

“Give me all your tomorrows, all your children and all your children’s children, and I will make this one day, for you, a paradise.”

*    *    *    *    *

Understanding how much warming may be in store from all the CO2, methane, N2O and other greenhouse gasses humans have pumped into the atmosphere can be a bit problematic. First, definitions have tended to be confused due to the fact that equilibrium climate sensitivity measures (Charney) used to project warming for this century by the IPCC only take into account about half of long-term (slow feedback) warming should CO2 and other greenhouse gas levels remain high.

For example, equilibrium climate sensitivity measures show an effective rate of warming by about 3 degrees Celsius (C) for every doubling of CO2 from 1880 onward. By this measure, we get about 3 C worth of warming over this century once we hit 550 ppm CO2 and about 6 C worth of warming at levels around 1100 ppm. It is important to stress that these short term warming projections do not take into account long-term ‘slow’ feedbacks to a given rise of CO2 that are strong enough to double the ultimate temperature increase. This larger Earth Systems Sensitivity (ESS) measure is both observable in paleoclimate and in the various model runs that project a given level of atmospheric CO2 out through the centuries.

Fast Feedback vs Slow Feedback Climate Sensitivity

(Fast feedback equilibrium climate sensitivity over one century vs long term sensitivity over multiple centuries to a given greenhouse gas forcing. Note that approximately double the amount of warming occurs after ‘slow feedbacks’ like ice sheet response and environmental ghg emissions are taken into account. Image source: Leeds.)

So both paleoclimate and most model runs end up with a long term warming of about 6 C at 550 ppm CO2 and of about 12 C at 1100 ppm CO2.

It is here that we run into an additional difficulty. We don’t ultimately know how long, long-term will really be. We hope, and our climate models seem to support this hope, that such ‘long term’ warming from the so-called slow feedbacks like ice sheet albedo response and natural carbon emissions won’t appear in force this century. But given the stunning pace of human greenhouse gas build-up combined with a number of observed ‘slow feedback’ responses going on now, we don’t really know for certain. And there is some reason to believe that the ‘slow feedbacks’ might not be so slow after all.

In this context, the current level of CO2, at around 400 ppm, results in a warming this century of around 1 to 1.5 degrees Celsius (if the slow feedbacks are as slow as expected) and a long-term warming of about 2-3 degrees Celsius. And it is at this point where an already complex dynamic begins to break down, taking on a number of, yet more complex, factors.

A Host of Extra Gasses No-One Really Talks About

At issue is the fact that humans have emitted a massive volume of additional greenhouse gas into the atmosphere. These gasses have grown in proportion and heating effect alongside the, admittedly larger and more significant, CO2 emission. And each has made their own additional contribution to human warming.

Some of these gasses, like methane, have been a typical part of natural atmospheres for millions of years. At times, methane concentrations are observed to have spiked to levels even higher than those seen today. But the periods during which such levels were apparent were also times of global crisis — the hothouse mass extinction events.

Methane Since 1984 MLO

(Atmospheric methane concentrations since 1984 as observed at the Mauna Loa Observatory. Image source: NOAA ESRL.)

But the other gasses: nitrous oxide, CFCs, HFCs, nitrogen triflouride, and a host of nearly 50 other industrial chemicals that contribute to warming were either never in the atmosphere before or were present at much lower levels than what is seen today. The result of this added pollution is yet more potential warming, in addition to a number of other difficult to deal with impacts. A pollution impact that is outside the context of past global crises and that puts current day greenhouse gas forcing at a critical and unstable level.

Methane levels alone have more than doubled since the start of the Industrial Revolution, rising from about 750 parts per billion to about 1835 parts per billion today. This value, depending on how it’s calculated over time, is equivalent to an additional CO2 forcing of between 22 and 110 parts per million. And though methane is the strongest non-CO2 warming agent, adding them all together can result in a value that is quite a bit higher than the base CO2 level would indicate.

Nitrous Oxide MLO

(Atmospheric nitrous oxide levels since 1997 as observed at the Mauna Loa Observatory. Image source: NOAA ESRL.)

In addition, on the negative side of the ledger, human fossil fuel burning (primarily coal) burning emits sulfur dioxide, other sulfates and various aerosols which, overall, create strong negative feedbacks in the climate system by reflecting incoming sunlight. The net result is a temporary suppression of a portion of human-caused warming. The reason this suppression is temporary is due to the fact that the sulfur dioxide and related sulfates rapidly wash out of the atmosphere. So if coal burning ceases, the reflective particles rapidly fall away and we readily come to witness the full strength of the human greenhouse gas emission.

Which brings us to the question — what is the full strength of the current human emission and how long will it last? There’s a term for this number: CO2e. In other words — the equivalent CO2 forcing of all greenhouse gasses added together.

Fortunately for our exploration, there’s been a bit of work done on just this subject. Last year, MIT’s Advanced Global Atmospheric Gasses Experiment issued a report describing model data that determined the current CO2 equivalent forcing from all of the more than 50 greenhouse contributing trace gasses in the atmosphere. And the results were somewhat disconcerting. As of June of 2013, that amount was equal to 478 parts per million CO2. Or a CO2e of 478 parts per million when all the other greenhouse gasses were added to the already high and rapidly rising levels of CO2. Adding in the current rate of CO2 rise, we end up with about 480 parts per million of CO2e from all greenhouse gasses by this year. So if we’re talking about the total burden of all greenhouse gasses and the one that will be with us through the long term, 480 is, unfortunately, the number we should be dealing with and not 400.

Aerosols and the Faustian Bargain

Unfortunately, to determine the current forcing one has to also take into account those pesky aerosols we mentioned above. And, luckily, we also have a reliable measure that provides the negative forcing or relative cooling effect of sulfur dioxide in the current atmosphere. As of 2013, the IPCC had found that sulfates and other effects due to aerosols provided a net negative forcing of about .8 Watts per meter squared or about 1/2 the positive forcing of CO2 which was, then, at around 390 ppmv (2011), about 1.68 Watts per meter squared. This approximate 1/2 value, when divided by the then observed rise in CO2 since 1880 gives us a rough equivalent negative forcing value of minus 55 parts per million CO2e.

ipcc_rad_forc_ar5

(IPCC AR5 Radiative Forcing Assessment. Image source: IPCC)

So subtracting out the net effect of sulfates and other aerosols brings us to a total net forcing from all factors related to human changes to the atmosphere of about 425 ppm CO2e. A rather disturbing final number both due to its departure over the current 400 ppm CO2 value and due to the fact that though most greenhouse gasses have atmospheric residence times of decades to centuries, the cooling sulfates would likely last for 1-2 years before falling out entirely. This means that once fossil emissions stop, we may as well just add +55 ppm CO2e to the current total.

This warmth masking factor of human coal emissions was described by James Hansen as a kind of Faustian bargain in which current burning of the dirty fuel provides temporary respite to warming at the cost of even more rapid future temperature increases. And it is just this devil’s deal in which we are now entangled.

425 CO2e: A Dangerous Interim

So it is likely that current atmospheric forcing, including all greenhouse gasses and all human sulfates, is probably at around 425 ppm CO2e. And since the residence times of these gasses are decades to millennium, while Earth Systems feedbacks appear to be enough to maintain high methane levels indefinitely, we should probably view this as an interim figure when considering how much short and long-term warming is likely locked in.

In the short term, using equilibrium climate sensitivity measures, we are likely to end up with between 1.2 and 1.8 C warming over the course of this century even if all greenhouse gas levels, along with sulfate levels, were to remain stable and if the slow feedbacks move along at the expected pace. Meanwhile, long-term warming of between 2.4 and 3.6 C would be expected if all atmospheric gas levels were to stabilize.

But unless an ongoing regime of sulfate aerosol spraying of the stratosphere were put into place, the sulfates would, predictably, fall out once human emissions stopped. And that rapidly brings us back to the 480 ppm CO2e number.

480 CO2e: What is Probably Locked in Long-Term

Looking at the more permanent 480 CO2e value, the fact begins to sink in that we are already well on the way to extreme climate difficulties. For 480 CO2e, without the reflective aerosols, means that the world probably ends up warming by between 1.8 and 2.3 C before the slow feedbacks kick in and between 3.5 and 4.5 C long-term. At these levels, major ice sheet destabilization and melt is eventually likely to result in between 50 and 140 feet of sea level rise with the only remaining glaciers in the end confined to central and eastern Antarctica.

The only saving grace to a cold turkey cessation of emissions now is that most of the worst amplifying feedbacks are likely to be kept in check and thus prevent rapidly accelerated warming and climate destabilization. The extra 1.7 to 2.2 C worth of long-term warming likely comes from a combination of albedo loss, permafrost thaw and related ghg release keeping currently high levels high long-term, and, perhaps, a methane belch in the 1-50 gigaton range that spikes atmospheric levels.

I say likely to be kept in check… but we have to also consider that there is a low, but not out of the question, risk of setting off a kind of mini-runaway that generates warming far beyond the expected range and pushes climates to a hothouse state not seen since the PETM or Permian extinction events. There is little evidence for such an event in response to current climate forcings in the models at this time, but we have a number of scientists, including Peter Wadhams, Natalia Shakhova, and Igor Simeletov, who have raised the possibility, based on their observations of Arctic sea ice and carbon stores, that just such an event could be in the offing. Unfortunately, without more in-depth research into the potential pace of release of current carbon stores (permafrost, forest, clathrate, ocean) we don’t have a scientific oracle that provides a comfortable certainty on this key issue.

It’s worth noting that this best possible future, where the risk of a mini-runaway in warming to PETM or Permian levels remains low, probably won’t happen as business as usual fossil fuel emissions continue unabated with no sign of being rationally held in check. Under the current regime, a CO2e of about 550 ppm, enough to warm the Earth between 5-6 C long term, is locked in within 25-30 years. A climate state that pushes the risk of a mini-runaway to moderate. Meanwhile, levels that would almost certainly set off a Permian or PETM type, anoxic ocean, extinction event, at around 800 ppm CO2e, become possible under BAU by 2060-2080.

The situation is, therefore, once again worse than expected…

Links:

400 PPM CO2? Add in Other Gasses and It’s 478 CO2e

Earth Systems Sensitivity

Leeds Climate Sensitivity

Jules Charney (bio)

NOAA ESRL

Radiative Forcing Links:

Real Climate: Radiative Forcing

The Advanced Global Atmospheric Gasses Experiment

NOAA: Radiative Forcing of Non-Greenhouse Gasses

IPCC: Initial Radiative Forcing Assessment

Non-CO2 Greenhouse Gasses: Scientific Understanding, Control and Implementation

CDIAC: Recent Greenhouse Gas Concentrations and Analysis

IPCC AR4 Appendix/Glossary

Nitrous Oxide and Climate Change

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