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Climate Hustle

Realistically What Might the Future Climate Look Like?

Posted on 31 August 2012 by dana1981

Robert Watson, former Chair of the Intergovernmental Panel on Climate Change (IPCC), recently made headlines by declaring that it is unlikely we will be able to limit global warming to the 2°C 'danger limit'.  This past April, the International Energy Agency similarly warned that we are rapidly running out of time to avoid blowing past 2°C global warming compared to late 19th Century temperatures.  The reason for their pessimism is illustrated in the 'ski slopes' graphic, which depicts how steep emissions cuts will have to be in order to give ourselves a good chance to stay below the 2°C target, given different peak emissions dates (Figure 1).

ski slopes

Figure 1: Three scenarios, each of which would limit the total global emission of carbon dioxide from fossil-fuel burning and industrial processes to 750 billion tonnes over the period 2010–2050.  Source: German Advisory Council on Global Change, WBGU (2009)

Clearly our CO2 emissions have not yet peaked - in fact they increased by 1 billion tonnes between 2010 and 2011 despite a continued global economic recession; therefore, the green curve is no longer an option.  There has also been little progress toward an international climate accord to replace the Kyoto Protocol, which suggests that the blue curve does not represent a likely scenario either - in order to achieve peak emissions in 2015 we would have to take serious steps to reduce emissions today, which we are not.  The red curve seems the most likely, but the required cuts are so steep that it is unlikely we will be able to achieve them, which means we are indeed likely to surpass the 2°C target.

Thus it is worth exploring the question, what would a world with >2°C global surface warming look like?

Global Warming Impacts

The 2007 IPCC Fourth Assessment Report (AR4) summarizes the magnitudes of impact of various degrees of warming here, and graphically in Figure 2, relative to ~1990 temperatures (~0.6°C above late 19th Century temperatures).

fig spm.2

Figure 2: Illustrative examples of global impacts projected for climate changes (and sea level and atmospheric carbon dioxide where relevant) associated with different amounts of increase in global average surface temperature in the 21st century. The black lines link impacts, dotted arrows indicate impacts continuing with increasing temperature. Entries are placed so that the left-hand side of the text indicates the approximate onset of a given impact. Quantitative entries for water stress and flooding represent the additional impacts of climate change relative to the conditions projected across the range of Special Report on Emissions Scenarios (SRES) scenarios. Adaptation to climate change is not included in these estimations. Confidence levels for all statements are high.  IPCC AR4 WGII Figure SPM.2.  Click the image for a larger version.

Some adverse impacts are expected even before we reach the 2°C limit, for example hundreds of millions of people being subjected to increased water stress, increasing drought at mid-latitudes (as we recently discussed here), increased coral bleaching, increased coastal damage from floods and storms, and increased morbidity and mortality from more frequent and intense heat waves (see here), floods, and droughts.  However, by and large these are impacts which we should be able to adapt to, at a cost, but without disastrous consequences.

Once we surpass the 2°C target, the impacts listed above are exacerbated, and some new impacts will occur.  Most corals will bleach, and widespread coral mortality is expected ~3°C above late 19th Century temperatures.  Up to 30% of global species will be at risk for extinction, and the figure could exceed 40% if we surpass 4°C, as we continue on the path toward the Earth's sixth mass extinction.  Coastal flooding will impact millions more people at ~2.5°C, and a number of adverse health effects are expected to continue rising along with temperatures.

Reasons for Concern

Smith et al. (2009) (on which the late great Stephen Schneider was a co-author) updated the IPCC impact assessment, arriving at similar conclusions.  For example,

"There is medium confidence that ~20–30% of known plant and animal species are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5 °C to 2.5 °C over 1980–1999"

"increases in drought, heat waves, and floods are projected in many regions and would have adverse impacts, including increased water stress, wildfire frequency, and flood risks (starting at less than 1 °C of additional warming above 1990 levels) and adverse health effects (slightly above 1 °C)"

"climate change over the next century is likely to adversely affect hundreds of millions of people through increased coastal flooding after a further 2 °C warming from 1990 levels; reductions in water supplies (0.4 to 1.7 billion people affected with less than a 1 °C warming from 1990 levels); and increased health impacts (that are already being observed"

Smith et al. updated the 2001 IPCC report 'burning embers' diagram to reflect their findings (Figure 3).  On this figure, white regions indicate neutral or low impacts or risks, yellow indicates negative impacts for some systems or more significant risks, and red indicates substantial negative impacts or risks that are more widespread and/or severe.  They have grouped the various climate change consequences into 'reasons for concern' (RFCs), summarized below.

smith embers

Figure 3:  Risks from climate change, by reason for concern (RFC). Climate change consequences are plotted against increases in global mean temperature (°C) after 1990. Each column corresponds to a specific RFC and represents additional outcomes associated with increasing global mean temperature. The color scheme represents progressively increasing levels of risk and should not be interpreted as representing ‘‘dangerous anthropogenic interference,’’ which is a value judgment. The historical period 1900 to 2000 warmed by 0.6 °C and led to some impacts. It should be noted that this figure addresses only how risks change as global mean temperature increases, not how risks might change at different rates of warming. Furthermore, it does not address when impacts might be realized, nor does it account for the effects of different development pathways on vulnerability.

  • Risk to Unique and Threatened Systems addresses the potential for increased damage to or irreversible loss of unique and threatened systems, such as coral reefs, tropical glaciers, endangered species, unique ecosystems, biodiversity hotspots, small island states, and indigenous communities.
     
  • Risk of Extreme Weather Events tracks increases in extreme events with substantial consequences for societies and natural systems. Examples include increase in the frequency, intensity, or consequences of heat waves, floods, droughts, wildfires, or tropical cyclones.
     
  • Distribution of Impacts concerns disparities of impacts.  Some regions, countries, and populations face greater harm from climate change, whereas other regions, countries, or populations would be much less harmed—and some may benefit; the magnitude of harm can also vary within regions and across sectors and populations.
     
  • Aggregate Damages covers comprehensive measures of impacts. Impacts distributed across the globe can be aggregated into a single metric, such as monetary damages, lives affected, or lives lost. Aggregation techniques vary in their treatment of equity of outcomes, as well as treatment of impacts that are not easily quantified.
     
  • Risks of Large-Scale Discontinuities represents the likelihood that certain phenomena (sometimes called tipping points) would occur, any of which may be accompanied by very large impacts. These phenomena include the deglaciation (partial or complete) of the West Antarctic or Greenland ice sheets and major changes in some components of the Earth’s climate system, such as a substantial reduction or collapse of the North Atlantic Meridional Overturning Circulation.

All of these reasons for concern enter the red (substantial negative impact, high risk) region by 4°C.  Aggregate impacts are in the red region by 3°C, and some types of concerns are in the red region by 1°C.

For more details we also recommend Mark Lynas' book Six Degrees, which goes through the climate impacts from each subsequent degree of warming, based on a very thorough review of the scientific literature.  A brief review of the book by Eric Steig and summary of some key impacts is available here.  National Geographic also did a series of videos on the Six Degrees theme, which no longer seem to be available on their websites, but which can still be found on YouTube.

This is Why Reducing Emissions is Critical

We're not yet committed to surpassing 2°C global warming, but as Watson noted, we are quickly running out of time to realistically give ourselves a chance to stay below that 'danger limit'.  However, 2°C is not a do-or-die threshold.  Every bit of CO2 emissions we can reduce means that much avoided future warming, which means that much avoided climate change impacts.  As Lonnie Thompson noted, the more global warming we manage to mitigate, the less adaption and suffering we will be forced to cope with in the future.

Realistically, based on the current political climate (which we will explore in another post next week), limiting global warming to 2°C is probably the best we can do.  However, there is a big difference between 2°C and 3°C, between 3°C and 4°C, and anything greater than 4°C can probably accurately be described as catastrophic, since various tipping points are expected to be triggered at this level.  Right now, we are on track for the catastrophic consequences (widespread coral mortality, mass extinctions, hundreds of millions of people adversely impacted by droughts, floods, heat waves, etc.).  But we're not stuck on that track just yet, and we need to move ourselves as far off of it as possible by reducing our greenhouse gas emissions as soon and as much as possible.

There are of course many people who believe that the planet will not warm as much, or that the impacts of the associated climate change will be as bad as the body of scientific evidence suggests.  That is certainly a possiblity, and we very much hope that their optimistic view is correct.  However, what we have presented here is the best summary of scientific evidence available, and it paints a very bleak picture if we fail to rapidly reduce our greenhouse gas emissions.

If we continue forward on our current path, catastrophe is not just a possible outcome, it is the most probable outcome.  And an intelligent risk management approach would involve taking steps to prevent a catastrophic scenario if it were a mere possibility, let alone the most probable outcome.  This is especially true since the most important component of the solution - carbon pricing - can be implemented at a relatively low cost, and a far lower cost than trying to adapt to the climate change consequences we have discussed here (Figure 4).

Figure 4:  Approximate costs of climate action (green) and inaction (red) in 2100 and 2200. Sources: German Institute for Economic Research and Watkiss et al. 2005

Climate contrarians will often mock 'CAGW' (catastrophic anthropogenic global warming), but the sad reality is that CAGW is looking more and more likely every day.  But it's critical that we don't give up, that we keep doing everything we can do to reduce our emissions as much as possible in order to avoid as many catastrophic consequences as possible, for the sake of future generations and all species on Earth.  The future climate will probably be much more challenging for life on Earth than today's, but we still can and must limit the damage.

Note: this post has been incorporated into the Advanced rebuttal to the myth "it's not bad."

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Comments 51 to 79 out of 79:

  1. Bostjan @50, Professor Shellnhuber does not claim that we are committed to an increase of temperature of 2.4 C above the pre-industrial average. Rather, he says that one of his colleagues believes that if anthropogenic aerosol forcings where removed, anthropogenic greenhouse forcings would be sufficient for a temperature increase to 2.4 C. He is careful to (twice) qualify this result as not yet proven.

    For what it is worth, total anthropogenic GHG forcing as of 2011 was 2.8 W/m^2, representing an equilibrium temperature increase of 2.1 C for the most likely value of climate sensitivity according to the IPCC AR4. It is certainly not clear, however, if, or when the total anthropogenic aerosol load will be reduced to zero so there is no contradiction in Professor Schellnhuber's talk.
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  2. I wold like to remind everyone here that the terms "catastrophy", "catastrophic", etc. already contain a value judgement. While most people coming to these pages are likely sharing similar values and are thus concerned about GW, many others are not, or not yet, as they do not share those values. While the denier community mocks the "C", the scientific community shies away from c-words as it is supposed to stay neutral on such judgements. Thus, leadership will have to come from others. As Bostjan pointed out, it will not come from politicians, as they want to be reelected, and not from the grass roots. That leaves NGOs, the media, and prominent individuals (such as Al Gore I guess). Thanks to SkS, they can find most of what they need here.
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  3. @Tom 51

    I can agree with your argument that it's human volcanoes that keep us nice and cool, and yes, who knows when – if ever - people will stop burning coal and oil. You're right also that Shellnhuber did say that it's Ramanathan who says we've already committed to 2.4 oC and he did say there are uncertainties about that. 2.1, 1.9, or even »just« 1.7 – that's really not that important. Now, I've listened to Ramanathan's lecture and it makes enough sense to be skeptical about the »budget«. With so many lives at stake I believe we have to take Ramanthan’s message seriously until he’s proven absolutely wrong and not vice versa.
    What worries me it's that small detail about the atmospheric lifetime of the GHG and aerosols. If humanity happened to achieve emission reductions as in Figure 1 (red curve seems more »plausible« to me), than we could expect a sharp drop in aerosols and a huge acceleration of warming. We saw that in the nineties here in Europe and I experienced it in my home town. When people started heating homes with gas and the Balkan wars destroyed most of the industry the sky became blue again and temperature skyrocketed. We would’ve cooked already if it wasn’t for a local factory which took care of us by spewing tones of TiO2 up the air every day.


    My local summer Tm from 1851 to 2012. Horizontal line marks 1988 when local industry collapsed. 2003 spike is clearly visible – that’ll be just an average summer by 2030s according to UK MetOffice.

    I really wouldn’t want to be offensive to anyone, but in this light, I find talking about the “budget” – and not mentioning any uncertainties associated with it - just music to Ms Merkel’s (and everyoneelse’s) ears. In the end we’ll happily accept sulfuric acid/TiO2 air-conditioning. Nobody will remember those “uncertainties” in calculations. The most important thing is that it’ll be good for GDP and everyone will be happy. So I’d suggest a short disclaimer for figure 1: “with massive GE effort”.
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    Moderator Response: [RH] Fixed image width that was breaking page format.
  4. @Kevin C - in place of CFLs, you might try some of the new LEDs. They're not cheap, so it makes economic sense to put them only where they'll be on many hours each day, but they provide a nicer light than the CFLs.

    Now if I can figure out the most economical way to get rid of our oil-fired furnace....
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  5. Estiben at 18:33 PM on 1 September, 2012, says, "...Minifarms are not as efficient, for one thing, and then there is the problem of distribution. If everyone is a farmer, who is going to deliver food to where it can't be grown?"

    This is a highly questionable statement. The most productive, sustainable way to grow food is manually. A small veg patch, run efficiently, can produce more weight of food per sq metre than any commercial operation, especially when the input of commercially-produced fertilisers, pesticides and use of fossil-fuel-powered machinery is taken into account.

    And that's also why the second half of your statement is invalid: if food is locally-produced, by as many people as possible, there is little or no transport involved. We should be doing everything to grow food as close as possible to where it's eaten.

    Even ignoring climate change, such a move will help avoid the negative impact of rising oil prices. A farmer without cheap oil is just a man leaning on his shovel.
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  6. John @55,

    Well said.

    I would also add to it: we (city dwellers/couch potatoes, which seems increasingly large portion of us) need to change our lifestyle and responsibility: learn to grow our food to support ourselves, rather than solely rely on a farmer. For example, do a tour of your vegie patch each afternoon which will also give you prescribed dose of physical excercise, rather than going to the gym and to the supermarket afterwards. Working in the garden can be both more interesting and healthoer than running on the treadmill in front of TV.

    If an average couch potato does not understand the environmental benefit of such lifestyle change, the financial & health self-benefit should be obvious.
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  7. @gws #52

    The development of the abbreviation 'CAGW' -- which is used almost exclusively by the denial lobby -- is interesting. I think 'CAGW' started to appear when a significant section of the fake sceptics realised that -- in spite of years of denying that CO2 is a greenhouse gas, that the planet is warming and that humans are causing it (and so many other memes) -- they would finally have to start secretly accepting the mounting evidence supporting the idea of AGW. At that point they had to rethink their denial and thus start to re-cast the 'debate' (as they saw it) into one of whether the outcome of climate change would be serious. Opposing 'CAGW' lets them continue denying and keeps their real agenda -- that we should do nothing about the problem.

    Of course, as we all know, just because those who switch to using 'CAGW' when commenting on posts -- thus demonstrating their underlying acceptance of 'AGW' -- will never go as far as to correct the more ill-informed fake sceptics who are still denying the unquestionable basics of climate science. They're just happy that doubt is being sown.
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  8. John Russell @55 Farm machinery doesn't have to be fossil fuel powered. But, yes, leaving out machinery, it would be more efficient to grow on a small scale. That's great, if you live where you can grow everything you want, or are willing to settle for what you can grow. I guess I could live without coffee and mangoes. Transport will still be needed, however. I don't think all the people in Arizona or the sub-Sahara can grow their own food locally, at least not without importing a lot of water.
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  9. @Estiben #58 writes... "Farm machinery doesn't have to be fossil fuel powered."

    As an exercise, a few years ago, I estimated what weight of batteries an electric tractor would need to have the same capability as one diesel-powered. Using the then latest Li-ions the answer was 6 tonnes. I'll leave you to work out the additional cost.

    Anyway you look at it, once farming moves away from fossil fuels, the cost of food produced will sky-rocket.
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  10. John Russell, you're making an absolute statement after considering only one variable.

    What kind of charge duration did you assume? From the answer you came up with it seems like you assumed that this hypothetical electric tractor would need sufficient battery capacity to run as long as it could with a full tank of diesel. Yet those aren't guaranteed requirements.

    Consider advances in self-driving cars and then apply the concept to tractors. The only thing self-driving cars have not mastered is every possible unpredictable thing human drivers could do... a non-issue for a tractor in a field. Thus, there is no reason that an automated tractor could not be built with current technology. Which means it could run 24 hours a day. Which means it could have a smaller battery and stop to recharge as needed.

    OR advances in microwave power transmission or inductive charging could be applied and you could have a tractor that is continually charged with only an insignificantly tiny battery. OR ongoing advances in battery technology that significantly reduce cost and weight could be applied.

    Then there are other aspects of food price to consider. One of the major components is transport costs. Those go down when the transportation runs on electricity rather than gasoline... especially if some of the other technologies above are applied as well. If we get to self-driving electric trucks then nationwide shipping costs drop to a tiny fraction of current prices.

    So no, it isn't viable to say "Anyway you look at it". There are factors in play which could make 'electric farming' less expensive than current... and certainly less expensive than 'diesel farming' will eventually be as the price of oil continues to increase.

    All that said, there is also no reason farming couldn't continue using fossil fuels if mass transportation and power generation stopped doing so. If we only used fossil fuels for a few energy intensive industries like farming and air travel natural sinks would be able to absorb all of it AND some of the atmospheric excess each year.
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  11. It's funny, we're all looking for some SF techno fixes when there are so many carbon neutral technologies available.

    People used to plow and harvest with horses, cows and buffalos, in fact, in some parts of the world they still do.

    No batteries, no wars for resources... Just common sense!
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  12. @CBD You're completely right. But...

    Mine was a simple exercise. I took a tractor as it is today and worked out the weight of batteries required to give and it the same functionality and performance as diesel power provides.

    Are you aware that when, for instance, ploughing, a tractor has to be refuelled several times a day; and, when harvesting or silaging, a break for a recharge is not an option?

    I agree that sophisticated technologies might overcome these objections but given the slow uptake of GPS technology for automated field operations it's going to be a slow change. And I come back to my last point. The move from cheap fossil fuels is going to push the cost of food much higher.
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  13. It's funny, we're all looking for some SF techno fixes when there are so many carbon neutral technologies available.


    There was an old woman who swallowed a fly...
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  14. Just as a helpful point of comparison and ignoring a few peripheral but important issues of packaging etc. diesel yields some 45MJ/kg, just-within-view lithium/air rechargeable batteries ~9MJ/kg.

    Figuring in the Carnot cycle's annoying features, that puts batteries in shouting distance of diesel, ignoring logistical issues such as charging batteries versus refueling w/diesel, etc.
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  15. Doug Bostrom@64

    Just to be clear, 45MJ/kg is energy contained in the diesel fuel, but the diesel engine has a practical thermal efficiency of less than 50% (just a quick Wiki-loookup), so one should really compare the drive shaft-output in both cases.

    Nonetheless diesel still is more 'efficient', but not with that huge a difference.
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  16. Lanfear, right, which is why I mentioned the Carnot cycle, which is what brings batteries of any kind within the sphere of useful in comparison to caveman-style combustion and wretched castings full of thrashing parts.

    Getting to an apples-apples comparison is not easy but some choices are easy thanks to context. For my driving habit and addiction level an electric car is now easily feasible; I was about to plunk for a Leaf but now am dithering between that and a Focus. I'm one of a vast number of people who can now ponder over this choice and what a terrific thing that is.

    Tractors, not so easy.
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  17. Bostjan@61

    You are in principle correct about the animal-based farming.

    However please take into consideration the population size that this animal-based technology did, and still does support in some parts of the world today. You will notice that it could not, and will not support the current population of 7+ Gperson primarily due to the ratio of animals needed to replace a single farm engine such as a plowing tractor.

    On a tangent, there is/was an interesting opening sequel in James Burke's Connections-series called 'The Trigger Effect'.
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  18. Lanfear.

    Speaking of animal-based technologies, it would be a travesty if we didn't tip our hats to a true artist with a poignant message.
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  19. Does the unexpectedly fast loss of cryosphere albedo mean IPCC AR4's temperature projections are too low?
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  20. @Lanfear67
    Can you be more specific why you think it'd be impossible to feed 7+ population with working animals? I was quite skeptical about it, needed almost a year to get used to it, but now it looks ok. It's not really my idea - my professor asked me during an exam what I thouhgt about it.

    Regarding how many oxen you need to do the work of a tractor: I'm not sure if this is the right question to ask. I'd start with the area of land available and then ask what the production capacity of it is. How much primary photosynthetic production will go to feed the animals on the farm, how much will be taken as produce and how much will be fed back to soil directly, and if this division is sustainable?

    Does anyone have any idea how the emissions from animals compared with diesel?
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  21. Bostjan, the carbon comong from livestock is primarily derived from plants and is all part of the normal carbon cycle. Diesel fuel contains carbon that was locked away for millions of years and is then rapidly and massively reinjected in the atmopshere, so the 2 do not compare.
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  22. Mark-US@69

    AR4 predictions for temperature changes are outdated. Now even skeptics are using it to prove that nothing is going on and that if it happens it'll only be in 2100.
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  23. @Philippe
    Thanks for that, but I was thinking about warming effect of methane that's much higher compared to CO2. So even though it's not of fossil origin it may have even stronger warming effect on a short term scale than using diesel tractors.
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  24. @Bostjan #70

    Having discussed with colleagues for many years the question of substituting draught animals for fossil-fuelled machinery, it would appear that if we went back to say, oxen (which are generally thought to be more efficient than horses), around 25% of available land would be taken up in growing the necessary fodder to enable production of arable crops for human consumption on the remaining land. This ratio is based on historical records confirmed by calculations.

    As things stand, replacing fossil fuels in agriculture doesn't seem so viable in the short term while ever world population continues to grow.

    As I've said before, any way you look at it, we can expect some significant rises in food prices in the near future.
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  25. Bostjan - "Does anyone have any idea how the emissions from animals compared with diesel?"

    Horses, being animals, are carbon neutral aside from the energy needed to produce their feed.

    Their major emissions problem is discussed in From Horse Power to Horsepower, namely... manure. In 1894 the Times of London estimated that by 1950 every street in New York city would be buried nine feet deep in horse manure - they were just running out of places to put it, of uses to put it to. There simply was no use (not even fertilizer) for that much manure. And the quality of life for city horses (not to mention the difficulty of pulling dead horses from the streets) was rather too horrible to contemplate.

    The problem early in the 20th century was (for a while, at least) solved by fossil fueled vehicles, whose emission was gaseous and did not need shoveling. Of course, now we're paying the price for those emissions, and perhaps electric, biofuel, or other options are better choices for the future.

    The amount of horse manure deposited by sufficient horses to replace diesel powered vehicles for 7 billion people is more than staggering. And not just from an olfactory point of view.
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  26. Bostjan Kovacec at #70.

    Given that humans are estimated to co-opt around 40% of net primary productivity (NPP), with a range* of 20-55%, it should be apparent that there's little room to replace the current use of fossil-fueled machinery with additional horse-power, ox-power, donkey-power, buffalo-power, elephant-power, insert-alternative-beast-power.

    Those extra animals would be in addition to the current working stock, and even though they're grazers rather than carnivores they'd still need additional tapping of PP co-option for their fueling. This would place an extraordinary burden on the remaining portion of the biosphere's PP that's not currently co-opted, and quite frankly I think that the estimation of co-option of humanly-useful PP is in fact out-dated and thus under-estimated: by way of example, consider the parlous state of high trophic-level fisheries, compared with the total marine PP.

    It's difficult to give a simple, blanket estimation of how much PP would be required to replace fossil-fueled farming technology, but if you're willing to make your own assumptions about standards of living and about proportion of energy used for farming, and replaced, then you can start doing some calculations of your own using the numbers here:

    http://www.evworld.com/library/energy_numbers.pdf


    [*Some references:

    mahb.stanford.edu

    www.globalchange.umich.edu

    www.eoearth.org

    www.civilizationsfuture.com
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    Moderator Response: [RH] hot linked urls that were breaking page format
  27. Here’s my calculation:

    Let’s take a FarmVille type of agricultural opperation 22 ha of arable land with 3 yokes of oxen

    Feed for 6 oxen: 40 kg/day x 365 days x 6= 87.6 t

    1 ha of Lolium multiflorum Lam. var. westerwoldicum or Lolium multiflorum Lam. var. italicum or Lolium perenne Lam will give give 45-55 tons of green fodder with 25% dry mater a year (60 to 80 t in a good year). It should feed 3 animals.

    Set aside 2 ha to feed the oxen.

    In Roman times an area 1 yoke of oxen could plow a day was 1 jugerum = 2530m2 = 0.25 ha
    3 yokes of oxen can do 0.75 ha/day
    20 ha / 0.75 ha/day = 26.66 days
    2 crop cycles a year require 53.33 day of work of 6 oxen and 4-5 people
    Add 2 rounds a year for other cultivation and harvest = 53.33 days

    Oxen would work about 4 months a year and rest 8 months.

    20 ha totals 107 days of 4-5 people = 1.3-1.6 manyears => 2 manyears (to be human and give them some time to relax)

    Compare to tractors and harvesters: 20 ha of corn = 440 hours = 2 months of work of one person

    2 ha to fuel the oxen is less than 9% of arable land of the farm. With better plows and higher productivity this number could be as low as 6%.

    The technology has been tested over extensive period and is readily available. I used Roman times plowing technology and productivity estimates, so I consider my calculation to be conservative. If there are no mistakes than this calculation proves that it is possible to cut fossil fuel emissions from agricultural tractors by 100% using working animals. Horses or other animals could be included in the mix if they are more suitable for work. Keeping 6 big animals on 22 ha doesn’t do any harm to the environment. Additional man power needed represents a huge opportunity to employ people in really green jobs.
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  28. I havent tried to do this calculation for rest of world, but for NZ (which is heavily agriculture based), it was pretty easy to supply farm fuel needs with biofuel, particularly if woody biofuels or algal fuel that use non-arable land. Could even do transport diesel. So, I dont think we would starve without fossil fuels. Doing biofuel for all the other things that we use fuel for (especially private vehicles) is another story altogether.
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  29. "widespread coral mortality is expected ~3°C above late 19th Century temperatures"

    A new study suggests widespread coral mortality at ~1.5ºC above late 19thC temps and close to universal degradation of all tropical corals by 2ºC.
    http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1674.html

    Discussed by one of the authors here:
    https://theconversation.edu.au/climate-change-guardrail-too-hot-for-coral-reefs-9610
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