After decades of complacency, climate change is rearing its ugly head and people are taking notice. Political will, if not quite yet possible, is nigh, so it is time to make an overall climate assessment. Let’s see where we are, where we are going, and what we can do about it. Our global response to the crisis, politically, socially, and personally is likely to determine the ultimate trajectory we take. The reality of a run-away climate excursion is far too likely, far more devastating, and probably coming to all of us much sooner than we expect. Here is the story I tell.
Let’s start with what we know from climate history
Climate history, written in the ice cores, tells us that the climate likes to warm up much more quickly than it likes to cool down. We also know that CO2 levels and average temperatures are highly correlated. These two facts suggest that the earth climate system contains some positive feedback loops that link CO2 and temperature. Historically warming periods can be exceptionally rapid. About 11,000 years ago, the arctic temperature increased by about 10° C in just a few years at the transition from the Younger Dryas period. Humans for the last 10,000 years have lived in a relatively warm climate period. Moving to an even warmer climate is breaking new ground. Polar ice that has never melted in a million years has the potential to disappear this time around. As the poles melt, carbon that has been locked up for millennia in permafrosted boreal peat bogs and methane hydrates locked in cold northern oceans could escape into the atmosphere.
We lost our innocence on climate change in the mid 1980’s when the deep climate histories from the ice cores were revealed. Here are a few of the numbers. Typical temperature excursions from ice age to warm period are ~15° C in the arctic, 8° C in the antarctic. The CO2 concentration change corresponding to such a temperature change is about 75 ppm. We have already well-exceeded the maximum amplitude of the CO2 swings in the historic record. On the face of it, it seems difficult to see how we avoid even greater temperature excursions this time around. If you assume arctic heating is four times the global average and antarctic heating is about twice average warming, then the present 135 ppm over pre-industrial CO2 concentration would imply average warming of about 7°C already built-in to the atmosphere if this ratio was to hold for the present cycle. Of course climate sensitivity to CO2 has been studied and debated for some time. Generally, the number is expressed as the average global temperature increase induced by a doubling of CO2 concentration over the pre-industrial value (280 ppm), and conventional wisdom has that number as 3° C +/- 1.5° C. Physicists can calculate from physical principles involving Stefan’s radiation law, the absorption properties of CO2 and the radiation coming from the sun, that a doubling of CO2 will, on its own, generate a warming blanket that would be responsible for about 1.4°C of planetary warming. My naive analysis of the ice core graphs says that intrinsic sensitivity is 4°C/75ppm x 280ppm = 14.9° C for a doubling in CO2, which is clearly wrong. But it shows that this order-of-magnitude discrepancy between what the physics says and what climate history tells us is at the heart of climate uncertainty. There are arguments in the literature that say you cannot make a simple correlative extrapolation for the climate sensitivity because there are other forcings that contribute. I would argue that when you have strong positive feedback, as evidenced by the sawtooth waveforms especially during warming, then you are mostly seeing the natural response of the system rather than a response to the forcing function. Hence the crux of the uncertainty revolves around the magnitude of a variety of positive feedback effects. A review article C. Lorius et.al.1 on this subject recognized an overall feedback amplification of about ×3 giving 3°C to 4°C sensitivity to CO2 doubling, but did not consider the asymmetry in warming versus cooling which I see as significant. If you look at the slopes on the graphs above, the rising slopes are at least two or three times larger than the falling. If you accept Lorius et. al. net amplification of 3x over CO2‘s radiative forcing, in the near term the gain factor is much larger because of the heating/cooling asymmetry. Hence we could easily expect heating rates typical of 7° to 12° C per CO2 doubling in the near term. What is really saving us from near term disaster is that paleo-climate warming took thousands of years, so there is hope that in the short run somehow we can handle this for future generations. Although there are examples of very fast warming events in the northern hemisphere, in Antarctica the pace for climate warming is on the few-thousand-year scale rather than decade scale seen up north. This suggests that absent rapid changes from ice to blue water and accompanying changes in global circulation, the global climate control system has some inertia even in the presence of positive feedback mechanisms. But it also demonstrates its inexorable persistence. Maybe, although headed for >7° C temperature rise, if we are lucky, that increase will not happen on a rapid time scale and humans can get it together to do something about it. This, I think, is the naive hope for many of us.
Now lets look at where we are
The monitor on Mauna Loa in Hawaii has been gathering data since 1958 when it registered about 315 ppm CO2 in the atmosphere. Already in 1958 industrial fossil fuel use had added about 35 ppm above the 280 ppm baseline dating back thousands of years. Today we are at 413 ppm and growing faster. That is a change of 133 ppm from ancestral levels, or about x1.48 – not doubled yet. Keep in mind that with the sensitivity we found looking at ice core data above, the change in CO2 level that we have now would be consistent with a temperature increase in the antarctic of about 14° C and double that in the arctic regions.
Global temperatures have increased, but not nearly as dramatically as the present day CO2 level suggests is possible and coming. In the north, we find increases of 1° to 4.5° C with concentrated warming at the pole; in the south 0.5° to 2° C again warmer at the pole. Overall, the consensus is that the world has warmed a little more than 1° C. The potential heating I mention above is not nearly manifest yet. But what you can see from the graph of global average temperatures is that we are now an a fairly steady uptick. The train is rolling.
The northern hemisphere is much more reactive than the southern one to climate change, as born out by the Arctic and Antarctic Ice core data. Land under the Antarctic continent keeps the ice sheet stable and insulated from ocean waters, unlike the floating ice sheets in the Arctic ocean. Warming in the north melts the ice sheet, exposing more open water which efficiently absorbs solar radiation. This volatile effect is well underway in our current episode of climate heating. Relatively rapid changes in sea ice extent are evident. Recent years, this one included, are attempting to set records for the smallest patch of remaining sea ice. The graph below shows whats happening. The decreasing area in the 1980’s and 1990’s was not too significant, but by the 2000’s especially in the summer, the increase in blue water in the arctic is very significant and is likely a driver for some of the severe weather has become the norm in the last decade.
The moderating effect of the polar planetary ice cube is going away. The ice is not just decreasing in extent but in thickness as well. Total volume is dropping as more melts than is replenished year-on-year. The date for a totally ice-free summer is rapidly approaching.
Ice isn’t the only problem up north; we can’t forget the methane. Good data on methane levels started being collected in 1983. Methane levels are much lower than CO2 levels and methane has a half-life in the atmosphere of a dozen years or so, but the gas does about 30 times the greenhouse heating compared with CO2 so its a good idea to keep an eye on it. Methane was steadily increasing from ancestral levels (~680 ppb) until about 1999 when it leveled off for about ten years at about 1770 ppb. However in the last few years it has resumed it’s steady march upward, now at 1870 ppm and so being equivalent to about 32 ppm of CO2 warming potential.2 There is good and bad news about this. The good news is that the relatively short lifetime in the atmosphere of this gas means that there is hope to get rid of it by stopping leaks and preventing local emissions. To that end, there is a brand new satellite that gives data at much better resolution coming on line that will help in pinpointing the emission sources.3 The bad news is that the Arctic permafrost is collapsing in a dramatic fashion. Rather than gradually thawing, a few inches at a time, entire sections of ground are collapsing and turning to muck.4,5 Exactly how this is effecting the release of greenhouse gasses is not well understood because this is a brand new and unexpected phenomenon. An alternative explanation for the recent upturn in methane emissions is fracking.6 Production of natural gas increased greatly because of this technology that started coming on line around 2005, roughly the same time atmospheric methane started to rise again.
Effects of changing climate are becoming more obvious and prevalent
How is the ~1° C increase we have so far impacting all of us? Is it just a nicer day at the beach? Unfortunately this is not the case. One thing we have seen over the last few years is larger and more frequent storms.NOAA compiles a list of Billion-Dollar disasters of all types. In the last two decades the frequency and cost of these events have increased dramatically. Severe storms are the billion-dollar disasters that have increased the most. Catastrophic flooding and fires have also become much more common.
The jet stream is driven in part by the temperature gradient between the pole and equator. With the arctic warming more than the equator the strength of the jet stream has diminished, allowing it to meander. This pushes hot weather north and cold weather south – leading to the unseasonable extremes that characterize present temperate-zone weather patterns. Some of the recent unseasonable winter storms, droughts, and fire activity can be attributed partially to this effect.
The figures above compare the jet stream in winter and summer for the norther and southern hemisphere. What you notice immediately is that the winter jet stream is much stronger than in the summer. The polar antarctic temperature gradient maintains an organized jet stream in the summer while in the north the jet stream disintegrates into turbulent tangled circulation. The archived maps and animations going back to 2015, never show very organized summer jet streams up north. This has always been the case, but it is possible to measure statistical changes the jet stream behavior over time.7,8 Troute et.al., attempts to compare shifts in jet stream location and variability by looking at local temperature changes in Britain and the Mediterranean using three centuries tree ring data as the proxy. They discover, indeed, an increase in inter-annual variability in the jet stream latitude that has increased in the late 20th century. They also note that some models suggest a general “waver” of the jet stream on sub-annual time scales but more rapid motion of the jet on daily time scales as the world heats up. What I see is a slowing down jet which becomes “frothy.” In the last few years, we’ve seen winter storms appearing in the eastern U.S. as the more organized winter jet begins to break up in the spring. In Europe it has been common for extreme heat waves to strike early in the summer. It is uncertain to me how this effect scales as the temperatures rise.
Sea surface temperatures are going up. The graphic below shows yearly averaged surface temperature anomaly over the last 40 years. At this point, no place has below normal temperatures — only hotter. Warm water in the Atlantic and Gulf of Mexico fuels hurricanes and tropical storms.
The yearly averages a decade apart show the inexorable trend accelerating. With virtually no place with below average sea temperatures, what used to be normal is now as cold as it gets. The Caspian and Black seas are gasping as the Mideast begins the march towards the inhospitable.
Writing today, July 10, 2019, looking at the CO emissions over Alaska reveals that the state is on fire. It is quite instructive to watch the world changing on a daily basis from the data brought to your screen by earth.nullschool. Spin the globe and see what is on fire today!
A few days later it is Siberia that is burning.
The problem is not only arctic heating, as can be seen with the fires in Brazil, here looking at particulates rather than CO. The Amazon basin is drying out producing an up-tick in fires, with similar conditions in southern equatorial Africa as well.
A lot of arctic carbon is entering the atmosphere, both from the melting permafrost and the rampant wildfires both up north and just south of the equator. This is exactly the evidence for the longer term carbon feedback, that spits more carbon into the atmosphere, which we need to avoid in order to be able to hope to get global heating under control. Once the carbon from these events is on same scale as the fossil carbon we are burning, then there is little hope of heading off the most extreme catastrophe.
The last two or three years have given us evidence that we are right on this precipice for the current heating event. Direct heating is accelerating as the ice caps are disappearing, and the real killer, arctic carbon, seems to be taking a big leap this year. It is hard to see how merely cutting our emissions to zero can stop this.
The oceans are the natural buffer for sucking up CO2. At the ocean surface there is chemical balance between CO2 in the air and HCO3– (bicarbonante) in the ocean surface waters. This process has gobbled up at least a quarter of all the extra CO2 mankind has added to the atmosphere. The result of this carbon sink is that the oceans are getting more acidic from this carbonation.
Hence, the coral is dying and the shells of the shell-building phytoplankton that form the base of the chalk-building carbon-sequestering ocean organisms, the coccolithophores are dissolving. And that’s the rub. If the ocean burps, we all die. This process is outlined in a new paper by Rothman9 describing a mathematical model of an ocean carbon cycle characterized by internal feedback and limit cycles reminiscent of the ice sheet dynamics. The gist of the argument is that there is a chaotic equilibrium involving total dissolved inorganic carbon and carbonate ion concentration in the upper ocean layers. Various feedback mechanisms lead to natural fluctuations of these parameters on ~10,000 year time scales, and as long as perturbations to carbon injections are not too large, the system tends toward a quasi-stable equilibrium. However, with either a small excessive carbon injection over 10,000 year times scales, or with a larger short-duration carbon injection, the system will bifurcate to a “limit cycle” event that sends the ocean through a large swing of pH and dissolved carbon concentration. The cycle includes a burst of carbonate burial onto the ocean floor that is the key signature of this type of event in the geological record. Noteworthy is that these bursts of carbonate burial are correlated with several mass extinction events. This is not surprising because once sufficiently excited by the carbon injection, the limit cycle dynamic generates a very acid ocean, which rather than absorbing CO2 begins to spit it back out, further increasing greenhouse warming. Left hanging is whether the modern fossil carbon injection is enough to tip the scales and throw this dynamic into a limit cycle mode equivalent to those associated with previous mass extinctions. Rothman thinks we are within a factor of two of the amount of carbon released to the ocean/atmosphere system to trigger the full limit cycle excursion. Such an event would surely end humanity.
What time scale are we on?
The great Anthropocene experiment that humans are taking the world through is without precedent. Compared to the dramatic changes presented by the ice cores, the rates of change imposed by human incineration of fossil carbon is at least an order of magnitude faster. Humanity’s ability to cope with the changes in the climate depends very much on the speed with which they happen. Our dilemma is that humanity’s exponential growth has compressed most of the carbon injection into the atmosphere to just the last few most recent decades with maximum emissions still the current state of affairs. This is not a good place to be when we decide enough is enough.
Lets do the thought experiment about decadal versus millennial time scales. It is estimated that about 25% of the land area was covered in ice during the glacial maximum periods. This is about 37 x 106 sq km of ice, of which all but 15 x 106 sq km melted during the warming phase. Hence, during a 4000 year warming cycle, of order 5.5 x 103 sq km of new ground is appearing annually. If you look at the ice extent chart above, you can see that about 2 x 106 sq km of ice has gone missing over the last 50 years, about 40 x 103 sq km of ice per year. So we are burning through the ice an order of magnitude faster than ever before (although not quite fair because I’m comparing land ice with sea ice).
Similarly, the last full ice-age heating episode saw and increase in temperature of about 12°C over 4000 years, 0.003°C /year. Today we have seen about 1°C in 50 years, 0.02°C/year, again roughly an order of magnitude quicker.
We can argue that the basic processes during glacial warming events are in play today, but happening faster. The heating due the addition of greenhouse gasses in the atmosphere begins immediately as soon as the anomalous conditions appear, and can be characterized by a “climate sensitivity” for equilibrium heating eventually attained due to a CO2 doubling. But we know of feedback mechanisms that happen on much longer timescales that threaten to bring much more warming. Understanding the correct value for the climate sensitivity is important in order to predict future consequences. The IPCC considered this critical number to still have quite a bit of uncertainty, somewhere between 1.5°C and 4.5°C for doubling CO2. Goodwin looked at all this and notes that the “climate sensitivity” strongly depends upon the timescale over which it is invoked.9 On decade time scales he supports 2.4°C ±0.5°C for a doubling of CO2, but that grows to 2.9°C ± 0.6°C on the century time scale. This all somewhat begs the question – what does it mean for there to be an “equilibrium” CO2 concentration when the CO2 via its own heating effect, is causing even more CO2 in the atmosphere? What happens on the millennial time scale? (My naive number from the ice core data, 9.6°C, is far outside this range so lets just hope the climate scientists know what they are talking about.) Consensus has gather on the 3-4°C range for deep time. This is where the climate models to come into play and help us to get to the bottom of some of the effects we are seeing. I have avoided talking too much about models because they suffer the “over-fitting” problem. With enough free parameters – of which these models have plenty – you can get just about any result you are looking for. However used judiciously, models give insight, and with enough embedded physics and when calibrated to observations, they have useful predictive powers. Presently, many of the models do not have explicit carbon-on-carbon feedback, and for those that do model carbon feedback, the science is just not yet available to know what to expect. It is guess work about how much carbon will enter the atmosphere as things heat up, which is so worrying in the long run. Keep in mind that the long run seems to stop at 2100 in most model runs, barely a century into a multi-millennial epoch. Time is not on our side here. The deeper in time you look, the hotter things seem to get for the same initial forcing.
Not well understood: Organic surface carbon, grown from atmospheric CO2 in warm times, is trapped under glacial ice. As melting starts, the carbon enters the atmosphere as CH4 and CO2 to enhance the warming process. Yet the rate of warming is limited by the current average temperature and latitude of the ice line, the volume of organic carbon available at the melt line, and the melting rate in such a way that this natural process generates the multi-thousand year warming cycle we see in the ice cores. Not well modeled.
The poles are cold and relatively small. Could that be our salvation? Even if we melt all of the ice at the poles and thaw all of the permafrost, the land area effected is relatively small compared to the North American and Eurasian continents that were exposed as the glaciers retreated. I hope so.
With the rate of both global heating and the rate we are putting carbon into the atmosphere far faster than anything in the geological record, we really are in uncharted territory. Extraction rates for resources typical follow an S-curve shape where the maximum rate of extraction is close to the middle of the full-life process. Since we are still extracting carbon from the ground at record rates, we are probably near the middle of the life-extraction of carbon cycle. That would imply business-as-usual extraction of at least as much carbon again as we have already done, most of it coming in the next decade or two. Add to that the release of arctic and rain forest carbon from fires and melting permafrost, and we would most likely exceed the the carbon threshold that the oceans can tolerate without catastrophe.
Can we turn this all around?
Nature will take care of everything eventually. Once the earth heats up sufficiently, the radiative losses through our warming CO2 blanket will become as large as the input radiation from the sun and the earth will not get any warmer. In the shorter term, it appears to me that we are approaching the point where the earth is releasing as much carbon into the atmosphere as humans are by burning fossil fuels. This is the tipping point we are all worried about and it seems inevitable, especially seeing Siberia and Brazil burning this year. We will know for sure when this happens as the Mauna Loa CO2 graph kicks upward despite our best efforts to reduce emissions. We argued above that natural rates of emissions during prehistoric warming events were 10 times slower than the present cycle, and so we might expect that dramatically cutting anthropomorphic emissions would significantly slow even a run-away natural event. So don’t get me wrong — even if we are past the tipping point, we need to stop burning fossil carbon today! In the long run, we have to start pulling the carbon out of the air, but that is a lot harder than not putting it there in the first place. Eventually, the oceans could be our savior if we don’t tip them towards our extinction.
As we descend into climate chaos, there will be enormous pressure to “do something” about it. Geoengineering the planet to reduce the sun’s heating power by deflecting some of the light away by adding aerosols to the atmosphere is the most common suggestion. But ultimately that would almost guarantee our eventual extinction because there would be less reason to stop burning carbon and we would dig ourselves an even bigger hole. The softer varieties of geoengineering involve industrial scale methods to remove the carbon from the atmosphere. Among these technologies are biochar to sequester carbon in soils, and carbon-negative power generation methods.
Greg Rau is a researcher at U.C. Santa Cruz and LLNL who’s work I keep bumping into when looking for carbon mitigation solutions, most of which involve the ocean. Take, for instance, the Ocean Thermal Energy Conversion (OTEC) system that uses deep ocean thermal temperature gradients to generate power, and with Greg’s modifications, sequester CO2 and de-acidify and cool the ocean surface layer.12 Or check out a general approach to generating negative-CO2-emission hydrogen fuel from renewable energy sources much more efficiently compared to biomass approaches.13 Rau’s key insight is that methods which enhances the earth’s natural weathering processes which bring carbonate into the oceans can be used to our advantage to repair the damage we have done with acidification from CO2. These are very hopeful technologies. If the true cost of carbon pollution was included in our fuels and electricity, you could not stop these type of plants from being built.
Naturally, at the end of the day we come to political will. We are so close to the path for eventual extinction at this point that it seems inconceivable that there will not be 100’s of millions of lives lost as planet earth tries to shake us off. The ultimate danger is that humanity loses control of our climate destiny. Once the consequences of climate change are so severe that our productive surplus is eliminated, it will be much harder to muster the resources to build the infrastructure needed to remove carbon from the atmosphere. That we must cease emissions now, that we must cease the growth in the numbers of humanity, that we must clean up our planet from chemical toxins and pesticides that are killing the foundation of all life, these are all urgent actions that cry out for leadership beyond the individual.
One cannot forget the Tragedy of the Commons, where individual self interest resulted in behaviors that harmed everyone. The commons is now our entire Earth and the potential tragedy is the extinction of humanity and most other life on the planet, and yet still in the short term any individual will see the need to drive their cars and run their air conditioners in the cheapest way possible. The right-wing solution to the “commons problem” was to privatize the land so that ownership would beget stewardship. But our atmosphere resists boundaries and ownership. We are only left with the other solution to the “commons problem” which is cooperation and regulation of our shared common resources. These very old ideas of a “commons” and of a “public trust” to ensure their accessibility to all is being tested in the case of Juliana vs. the United States, the climate kids asserting their rights to a future with the commons intact. In a civilized society that actually functioned by the rule of law, this case could propel us in the right direction. I wish we lived is such a society.
This week Greta Thunberg spoke to the United Nations, imploring the assembled nations to finally act to limit emissions. The impact of this young climate activist on world climate awareness cannot be overstated. I will leave you with her image, since it is the movement that she has inspired that has given me the most hope.
- 2019). Very strong atmospheric methane growth in the 4 years 2014–2017: Implications for the Paris Agreement. Global Biogeochemical Cycles, 33, 318– 342. DOI:10.1029/2018GB006009 , , , , , , et al. (
- Hu, H., Landgraf, J., Detmers, R.,Borsdorff, T., Aan de Brugh, J.,Aben, I., et al. (2018). Toward global mapping of methane with TROPOMI: First results and intersatellite comparison to GOSAT. Geophysical Research Letters,45, 3682–3689. DOI:10.1002/2018GL077259
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- Katey Walter Anthony et al. 21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes, Nature Communications (2018). DOI: 10.1038/s41467-018-05738-9
- Howarth, R. W.: Ideas and perspectives: is shale gas a major driver of recent increase in global atmospheric methane?, Biogeosciences, 16, 3033–3046, https://doi.org/10.5194/bg-16-3033-2019, 2019.
- Historical trends in the jet streams, Geophys. Res. Lett., 35, L08803, ( 2008) doi:10.1029/2008GL033614 , and ,
- Trouet, V., F. Babst, and M. Meko. 2018. Recent enhanced high-summer North Atlantic Jet variability emerges from three-century context. Nature Communications, 9(1), 180. doi: 10.1038/s41467-017-02699-3
Characteristic disruptions of an excitable carbon cycle,
- IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535
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- Rau, Greg H., Jim R. Baird, Negative-CO2-emissions ocean thermal energy conversion,
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- Rau, Greg H., Willauer, Heather D., Ren, Zhiyong Jason, The global potential for converting renewable electricity to negative-CO2-emissions hydrogen, Nature Climate Change, 8, pages 621–625 (2018). DOI:10.1038/s41558-018-0203-0