Why We Need to Shoot for 1.5 C Even Though We Might Miss — Part 1

Each day, as individuals and as a global civilization, we decide how difficult our future will be. We do this, ultimately, by deciding whether we will burn fossil fuels, and whether or not we will emit carbon into the Earth’s atmosphere. The most liveable climate change scenario is the one where we emit the least carbon, where we first switch carbon emitting energy systems with renewables, and where we then learn how to draw carbon down from the atmosphere. In scientific parlance, this best case response to climate change is described as the RCP 2.6 emissions pathway.

(Shooting for 1.5 C Warming — Risk and Necessity.)

What is RCP 2.6? How do we define it?

We do this in many ways. By one measure, it roughly equates to an average of 490 ppm CO2 equivalent greenhouse gasses in the atmosphere over the course of the 21st Century. By another, it equals an added average radiative forcing at the top of the atmosphere of 2.6 watts per meter squared. By another, it roughly equals 1.5 C warming by 2100.

In short, it’s the best case that we could rationally hope for. A much more liveable world. But it is also a long shot. A heavy lift. One that will require great courage, moral fiber, innovation, and effort if we are to have any hope of achieving it.

In order to have a shot at hitting RCP 2.6 we’ve got to, as a global civilization, achieve net zero carbon emissions by 2050. What this means is that U.S. carbon emissions need to be net zero by 2035. And the world needs to quickly follow suit. That’s not going to be easy. But I think it’s doable, if we work hard and honestly and if we are lucky.

Ultimately, it’s something that we can’t not try to do and still be a good people. For in undertaking the path to 1.5 C we commit to the greatest rescue operation in the history of the planet and of humankind. And that’s what part 2 of this post series is about.

Hat tip to Greg


New Study Finds Clouds are Amplifying Human Warming

The mysterious clouds.

For decades, science has been unable to nail down how clouds might change with human warming of the climate. Sure, we knew that added water vapor through a heating-increased amplification of the rate of evaporation and precipitation would likely impact cloud formation. But how would those physical alterations impact climate? Would an added darkening of the Earth through increased cloud cover provide a cooling effect and slow down the rate of human-caused warming (also called a negative feedback)? Or would the added water vapor aloft, itself a powerful greenhouse gas, provide an extra boost to the human heating engine (also called an amplifying feedback)?

The mainstream climate models thus assumed a zero to slightly positive heat feedback from clouds and relied on decadal verification runs to help test for accuracy. A kind of backwards checking that excluded values from clouds due to a lack of needed information.


(From the global climate change perspective, some clouds are worse than others. The above image shows a thunderstorm set off by massive wildfires blazing through the permafrost zone near Great Slave Lake on August 5 of 2014. A pyrocumulonimbus cloud or, colloquially, a fire thunderstorm. Image source: NASA.)

Confusionists Take Advantage of Cloud Uncertainty

It was an uncertainty hanging in the very air above us. An uncertainty many climate confusionists used to sow doubt over a broad range of issues involving how sensitive the Earth is to the human heat forcing. They often argued, through this scientific dim spot, that climate sensitivity was, indeed, quite low and that we had very little to be concerned about regarding an immense dumping of heat trapping gasses into the atmosphere that is now at least 6 times faster than at any time in the deep history of life on Earth.

The shady clouds, in other words, would save us from ourselves.

Not so fast, said Dr. Andrew Dressler who in this paper and this paper recently defended consensus climate science from the cloudy claims of confusionists. Dressler, like mainstream climate science, assumed at least a small degree of positive feedback from changes to clouds and atmospheric water vapor loading. And his observational findings were consistent with an equilibrium climate sensitivity (ECS), or a one century rate of warming, in the range of 2.0 to 4.5 degrees Celsius for each doubling of CO2 (consistent with a multi-century warming [ESS] in the range of 4 to 9 C for each doubling of CO2 — or about a 6 C average).

New Study Finds Changes to Clouds are an Amplifying Feedback

But now, a new study has found that the picture is not quite so rosy as some claimed. The study, led by Dr. Kevin Trenberth, found that net changes to clouds and related additions of water vapor to the upper atmosphere is a positive or amplifying feedback to human caused warming. In other words, the way human heat alters clouds and the related hydrological cycle results in yet more heat being trapped by the Earth System.

This confirms Dr. Dressler’s work and raises a rather unpleasant question — if we have an added heat feedback from clouds under a regime of Earth Systems warming, then how strong is it?

Trenberth notes in an interview published today in The Guardian:

What we do find is that if one looks at tropospheric average temperature rather than surface temperature, then there is a much stronger relationship with energy flow at the top of the Earth’s atmosphere. We are able to find a water vapor signal that is clearly a positive feedback.

Climate Sensitivity Needle May Tilt Toward Upper Range of Estimates

This is somewhat unhappy news.

What it means is that the Earth System is at least as sensitive as climate models suggest. But, even worse, there is a chance that the Earth System may be closer to the upper range of climate sensitivity estimates. It means that accumulation of heat in the atmosphere, in glaciers and in the ocean may happen somewhat faster than consensus models predict and that geophysical changes may, consequently, be greater and more catastrophic.

Whether model simulation of climate sensitivity will need to be altered has not, as yet, been determined. The study is now very new and it will take some time for the more recent data to wash out in the model projections.

But what can be plainly stated is that fossil fuel industry funded voices of false comfort have again been proven dreadfully wrong and that there is some risk that the situation may be even more dangerous than current science anticipates. As such, there is absolutely no reason for further delays in policy action and a very rapid draw-down to zero human carbon emissions.


Climate Variability and Relationships Between Top of Atmosphere Radiation and Temperatures on Earth

Changes in Water Vapor and Clouds are Amplifying Global Warming

A Determination of the Cloud Feedback from Climate Variations Over the Past Decade

Clouds and The Earth’s Energy Budget


Hat Tip to TodaysGuestIs

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 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…


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

Earth Systems Sensitivity

Leeds Climate Sensitivity

Jules Charney (bio)


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

Worldwide CO2 Levels at 394.4 ppm in Early November, Likely to Hit 402 ppm by May, 2014

CO2 November 2013, Six Month

(Global CO2 measurements over the past six months. Small dots – daily values. Large dots – weekly values. Blue line – smoothed trend. Image source: The Keeling Curve)

After hitting a new record high above 400 ppm during the latter weeks of May, 2013, CO2 followed seasonal trends by falling to a new record high low of around 393.5 ppm in early October. By early November of 2013, CO2 had rocketed back to 394.4 ppm and, if current trends continue, will likely touch 402 ppm or higher by May of 2014.

Over the past few years, worldwide CO2 values have risen by an average of around 2 parts per million each year. But in 2013, the trend line steepened, with values increasing by about 3 ppm between 2012 and 2013. Should the new, more rapid, pace hold through 2014, maximum CO2 values for that year will reach between 402 and 403 parts per million by late May.

In context with the known geological record, the current pace of CO2 increase is far faster than anything previously observed. Past major warming events, at most, hosted a yearly CO2 increase of around .35 ppm. The most recent rate of 2 ppm per year, on average, is about six times as fast. A yearly increase of 3 ppm is nearly eight times this total.

It’s worth considering this amazing fact: human emissions are more rapid now than anytime in the geological past. Nothing, not the PETM, not the great flood basalts of the Permian, exceeded the current rate of human burning. And those great past events, many coinciding with the worst mass extinctions, were 1/6th to 1/8th the pace of what humans are doing now. Our CO2 injection machinery is more powerful, by far, than even the most terrible forces ever produced by nature.

This screaming pace of CO2 increase is leading to a series of unprecedented and damaging climate, weather, and Earth systems changes. Changes we are just beginning to understand. At the very least, we have projected ourselves into climate territory not seen in the last 3.6 million years — the last time CO2 levels were as high as they are bound to be over the next ten years. And that’s if we are somehow able to halt global CO2 emissions soon. If human emissions continue to increase as they have over the past decades, by mid century, we could be looking at atmospheric CO2 levels not seen in the past 15 to 30 million years. By the end of this century, we could achieve an atmospheric state not seen in at least 55 million years.

A Little Heat Age Every Six Years

It is not just the scale of the change, creating levels of CO2 not seen since ages in the Earth’s deep past, it is the pace of this change which is so immense and dangerous. According to the most recent IPCC draft report, the current increase in CO2 levels is causing an increased heat forcing of .16 watts per meter squared at the top of the atmosphere every six years. By comparison, the grand solar minimum experienced during the Little Ice Age had a negative forcing of around .15 watts per meter squared. So we now have the equivalent to a Little Ice Age, but on the side of hot, being pumped into the Earth’s atmosphere every six years. And should the sun cool to another grand minimum, it would take only about six years of current human emissions to overwhelm its cooling effect.

Should we hope to see a continued progress of human civilizations this extraordinarily rapid and dangerous pace of human CO2 emissions is an issue that must be addressed immediately. We have likely already created a serious and devastating string of events that will continue to unfold and worsen over the coming decades and centuries. Some, we have already seen, but these are the earlier, more mild, outliers, the events we locked in 20, 30, 50 years ago. So the force of events 20 years, 30 years, 50 years from now will be proportionately worse.

Continued emissions and further increases, under such a scenario, is not a survivable option. If we are to continue, to have any hope for future progress, we need to halt this mad pace of emissions as soon as possible.


The Keeling Curve

IPCC Working Group 1 Draft Report


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