Climate scientists go for ‘human tipping point’

Gabriel Levy with a piece on climate change. It featured in People and Nature on 11 May 2014.

A group of scientists headed by pioneer global warming researcher James Hansen is challenging the consensus view that humanity can avoid serious danger by holding the average temperature rise to two degrees above pre-industrial levels.

Warming should be limited to one degree centigrade to avoid “disastrous” consequences, Hansen and his colleagues write in an open-access paper published in December last year.[1]

Hansen et al also venture beyond the physical sciences to discuss the potential impact of global warming on human society and what should be done about it. They appeal to the public to act, rather than making the sort of “policy recommendations” to which society’s ruling elites usually try to confine scientists.

The danger to future generations is ultimately a “moral issue”, they argue. “As with the issue of slavery and civil rights, public recognition of the moral dimensions of human-made climate change may be needed to stir the public’s conscience to the point of action.”

Since the paper was published, Hansen has supported an attempt to sue the US government for failing to protect future generations against the effects of climate change. (His blog here  reports on progress.)

Tame as this all may sound to social and labour movement veterans, or to participants in radical environmental protests, I argue in this article that we should listen carefully to what Hansen and his colleagues are saying.

Fork in the road

We are at a “fork in the road to our energy and carbon future”, argue Hansen and his co-authors – who include not only climate scientists such as Pushker Kharecha and Makiko Sato but also the prominent sustainability researcher Johan Rockstrom and economists such as the shock-therapy-advocate-turned-development-wallah Jeffrey Sachs.

They ask: “Will we now feed our energy needs by pursuing difficult-to-extract fossil fuels, or will we pursue energy policies that phase out carbon emissions, moving on to the post-fossil fuel era as rapidly as practical?”

They estimate that carbon emissions need to fall by 6% per year from now onwards if the total amount of carbon in the atmosphere is to be kept at a safe level (350 parts per million (ppm).

Yes, it really is melting. Photo by Nick Russill, Flickr Creative Commons
Yes, it really is melting. Photo by Nick Russill, Flickr Creative Commons
They also decry the time wasted in tackling the issue, claiming that, had an effective tax on carbon emissions been imposed in 1995, the annual emissions cut needed would be just 2.5%.

Hansen et al say it is “still conceivable” that dangerous climate change can be averted, by means of energy conservation, low-carbon energy use and technology to sequester carbon in the soil and in forest regrowth on marginal lands. “The alternative pathway, which the world seems to be on now, is continued extraction of all fossil fuels, including development of unconventional fossil fuels such as tar sands, tar shale, hydrofracking to extract oil and gas, and exploitation of methane hydrates.”

If this goes on for another twenty years, followed by a 3% annual reduction in emissions between 2033 and 2150, the amount of carbon in the atmosphere would be 1022 gigatonnes (GtC),[2] more than twice as much as the level Hansen et al think is safe.

The paper also recites a litany of effects of global warming (and has a bibliography of the latest research on each): sea level rise, changing climate zones, the extermination of species, destruction of coral reef ecosystems, a rise in extreme weather, human health impacts, and aggravated impacts of fossil fuel mining.

One degree of separation

Hansen et al’s explanation of their target of one degree above pre-industrial temperatures – as opposed to the two degrees accepted by the intergovernmental summit on climate change at Copenhagen in 2009 and used as a marker in reports by the Intergovernmental Panel on Climate Change (IPCC) – makes interesting reading.[3]

The distinctions are “much greater and more fundamental than the numbers 1° and 2°C themselves might suggest”, they argue, for four reasons:

■ Climate simulations (computer-generated models of how the climate will change), including their own, usually do not include “slow feedbacks” (trends that, once in motion, accelerate the entire warming process) such as reduction of ice sheet size (which reduces the amount of warming sunlight that is reflected back into space) or the release of gases such as methane from thawing tundra. It’s reasonable to ignore those effects with a one degree change, but a two degree change makes them much more relevant.

■ Limiting temperature rise to one degree implies limiting future carbon emissions to only 130 gigatonnes (see below). And that implies using easy-to-access coal, oil and gas, and leaving alone fossil fuels that are more difficult to mine. But scenarios for world energy consumption that lead to two degrees of warming “necessarily imply expansion of fossil fuels into sources that are harder to get at, requiring greater energy using extraction techniques that are increasingly invasive, destructive and polluting”. Another turn of the screw.

■ The biosphere, particularly forests, and the soil, naturally suck carbon from the atmosphere, i.e. counteract carbon emissions from fossil fuel consumption and other human activity. Climate scientists measure the rate at which they do so as carefully as they monitor emissions. The rate can be assumed to stay the same with one degree of warming, but two degrees could let loose carbon cycle feedbacks that upset this process.

■ The warmer the atmosphere, the greater the level of emissions of non-carbon gases that contribute to further warming, the most important of these being methane (CH4), which has an especially powerful greenhouse effect.

Degrees, parts per million, gigatonnes

The scientific section of Hansen et al’s paper explains what they believe the one degree target means in terms of reducing carbon emissions.

Average global temperature is determined by the earth’s energy balance, and over the last 200 years that has been upset: less energy has been going out than coming in, because carbon and other atmospheric gases reduce the earth’s heat radiation to space. The main cause of this warming is human combustion of fossil fuels. Other factors affect the energy balance too, including the the use of aerosols (which slow down global warming), and natural factors such as the earth’s surface albedo (reflectivity) and solar radiation changes.

To prevent average temperature rising beyond 1°C above pre-industrial levels, the level of carbon in the atmosphere, currently above 400 parts per million (ppm) – up from about 320 ppm in 1960 – needs to return to 350ppm.[4] That number has been rising for the last 200 years, causing an average temperature increase of roughly 0.8°C. Fossil fuel combustion accounts for 80% of the change; most of the remainder results from deforestation and other changes in land use.

In terms of curtailing fossil fuel use, the number that matters most is the cumulative total of carbon released into the atmosphere – known in the trade as the “carbon budget”. (Politicians like to talk about annual rates of growth of emissions and other numbers that, in the big picture, don’t do much except to deceive people about the issues.)

Hansen et al calculate that, on top of the 370 gigatonnes of carbon released from fossil fuel combustion since the industrial revolution, humanity can comfortably release another 130 GtC, to make 500 GtC in total.

That’s the figure from which they derive their proposal to cut carbon emissions by 6% a year, and their observation that it could have been 2.5% if coordinated action had been taken in 1995.

The IPCC says that the world economy can work with a “carbon budget” of 840 GtC from carbon dioxide emissions, i.e. 370 GtC released so far and another 470 GtC to go. Hansen et al dispute this,[5] arguing that it could push the global climate “far outside the Holocene range”, which would be “dangerous and foolhardy”.

On top of their concerns about the two degrees target, they highlight problems in the key research papers used by the IPCC’s latest (fifth) report to determine the carbon budget that the two degrees target implies.[6] The papers use varying and uncertain assumptions (inevitably, since they are plotting the future); Hansen et al say the risk is too great.

Hansen et al also comment on calculations by environmentalist Bill McKibben, who accepted the two degrees target but concluded that the remaining “carbon budget” was not 470 GtC, but 128 GtC – almost exactly the same as Hansen et al’s 130 GtC using a one degree target.

The three main reasons for the discrepancy are (i) that Hansen et al make more optimistic assumptions about reforestation and land use changes ameliorating the effects of carbon emissions; (ii) that Hansen et al have ignored the additional effect of the greenhouse effect of gases other than carbon dioxide; and (iii) that the different research papers use different calculations of probability.
This is the point where climate science deniers shout: “they don’t even agree with each other!” To which I would reply: “well of course they don’t, you clowns. They are scientists. It’s their job to find out stuff, and to challenge, check and refine their own and each others’ findings.”

The difference between Hansen et al’s one degree target and the IPCC’s two degree target pales into insignificance when one considers the paralysed response of the world’s governments to global warming. Since the failure of the Copenhagen summit, governments have been committed to do little or nothing, and have allowed fossil fuel combustion to expand unimpeded. All the climate researchers appear to agree that this “policy” carries the danger of warming of between three and six degrees – all nightmare scenarios. What matters is how humanity is going to move from the path to which these governments are condemning it.

Scientists and society

When it comes to what should be done about climate change, Hansen et al call for “broad public support” for change, rather than keeping to the format of “policy recommendations” usually used in scientific papers. They highlight the “intergenerational injustice” implicit in global warming – “young people and future generations inheriting a situation in which grave consequences are assured, practically out of their control, but not of their doing”.

The paper’s specific policy proposals are in line with the “green new deal” (mainly, a carbon tax, see footnote below). That’s not a framework I accept, as I’ve written elsewhere on this site (e.g. here). But the important point to my mind is Hansen et al’s emphasis on taking these issues to a wider audience, outside of academia, outside of a privileged discussion between academics and politicians. Climate researchers in the UK also made such an effort recently, with the Radical Emissions Reduction conference organised by the Tyndall Centre. (See report here.)

There is scope here for building an alliance between scientists and social and labour movements, without which the sort of drastic social and political change required to steer humanity away from climate change will never happen.

Footnote: carbon taxes

The main policy proposal in Hansen et al’s paper is for a gradually-rising fee, or tax, to be paid on each tonne of carbon emitted into the atmosphere, so that these costs are “internalised within the economics of energy use”. A very readable book-length argument for the tax by the economist Shi-Ling Hsu, one of the paper’s co-authors, is cited.[7] In the book, Hsu reviews arguments for and against carbon taxes, and the experience of a carbon tax levied in the Canadian state of British Columbia. That one included a scheme for returning the revenue to the population and businesses via tax credits, with the aim of making fossil fuel consumption more expensive than other forms of economic behaviour.

Socialists, including me, have serious worries about this sort of policy proposal. In a capitalist economy, the most important choices about energy use are taken by large corporations. Both energy workers such as coal miners, and energy “consumers” (most of the rest of us, at least in developed countries) are trapped in a set of economic relationships over which we have little control. As long as those corporations call the tune, it’s difficult to see an effective tax that they would not sabotage.  And as a consumption tax, a carbon tax would always hit the poorest – notwithstanding the well-meaning schemes, of the sort discussed by Hsu, to compensate for that.

Perhaps socialists’ biggest problem with proposals for carbon taxes, though, is that they amount to a call for a type of Keynesian regulation of capitalism that history has swept past. In keeping with our larger view of the world, we see the transition away from the fossil-fuel-dominated economy in terms of a transition away from capitalism, together with all its other evils and inequalities.

A socialist critique of the carbon tax proposal is therefore pretty straightforward … and has been made at length by the economist Richard Smith, here and here. Fair play to Smith for taking up those arguments (a continuation of his critique of Herman Daly’s “steady state economics”). I worry, though, that he is missing the larger point: that scientists such as Hansen and his co-authors are appealing to society at large – instead of to “policymakers”, governments, etc – and this is an appeal we should welcome.

OK, so the climate scientists are mapping out strategies for social change within the liberal framework that they understand. They are not radical activists. They are probably unaware of, or indifferent to, some of the ideas about social change that people like Richard Smith and I spend our lives thinking about. But let’s underline the positive. Scientists are deciding not to hide away in their research labs or address themselves to political elites alone. They have shaken a leg and spoken their minds on political issues – arguing that “broad public support is needed”, that “as with the issue of slavery and civil rights” public recognition of the scale of the moral issue is needed, and that disaster awaits “unless a human ‘tipping point’ is reached soon”.

Surely we can take that away and run with it, offering our own interpretations of how such a “tipping point” can be achieved? GL, 15 May 2014.

See also “A Galileo for our time” (review of James Hansen’s book)
[1] Full title: “Assession ‘dangerous climate change’: required reduction of carbon emission to protect young people, future generations and nature” (Public Library of Science, 3 December 2013). There’s also an interview with James Hansen here.
[2] A gigatonne is one billion tonnes.
[3] In the sub-section of the report entitled “Implication for Carbon Emissions Target”, page 11
[4] See the Earth System Research Laboratory site, which updates the monthly average, here.
[5] See “Discussion” at the end of the paper
[6] The fifth assessment report is in the process of being published. See here
[7] Shi-Ling Hsu, The Case for a Carbon Tax: Getting Past Our Hang-Ups to Effective Climate Policy (Island Press, 2011)


  1. Since the paper was published, Hansen has supported an attempt to sue the US government for failing to protect future generations against the effects of climate change

    That would be laughed out of court. Climate change in a natural occuring event that has happened from day 1.. Thats why we've had ice-ages and little ice-ages. That's why we have a period called the dark ages. Some people think LIA's are caused by volcanic activity on this rock, others think the sun went through an abnormal cooling off period. What we know today is it's takes about 100,000 years for the photons at the sun's core to reach it's surface and about 8mins from the surface of the sun to reach earth. And every now and then we get blasted by gamma rays and raditiation burts and there is sweet fcuk all we can do except hope for the best and prepare for the worst. The last big blast was about 150 yrs ago, although as recent as 1989 Canada was blasted and it knocked out most of Qubec.

    On March 13, 1989 the entire province of Quebec, Canada suffered an electrical power blackout. Hundreds of blackouts occur in some part of North America every year. The Quebec Blackout was different, because this one was caused by a solar storm!

    We also know the sun is getting hotter and bigger and one day it will explode into a super nova. Now that'll happen in a few billion years but we don't have that long. We've only a few million years before the sun gets too hot to handle. And thats a very short window in the grand scheme of things.

    The paper also recites a litany of effects of global warming (and has a bibliography of the latest research on each): sea level rise, changing climate zones, the extermination of species

    Thats a great line.. Talk about double speak. Global warming and climate change AREN'T different cheeks of the same arse. It's like calling British agents IRA informers, it's double speak and meant to confuse people. Same as the data the throw up, reducing emmissions by X% per year or cubic meters. Meant to confuse. As for global warming I'm convinced that is man made. And the extreme weather patterns countries have been experiencing over the past few decades is all down to the buring of fossil fuels is a lie. My money is on HARRP creating funky weather patters and global warming. One day we will leave this rock and live on another and not all rocks have atmosphere's. I'm convinced the powers that be are using this place as a huge guinea pig to tweak things so when we jump into the US Enterprise we're ready to surive anywhere..

    The paper talks about 'extermination of species'.. Go an tell that to the dinosaurs who roamed the earth for 160million years..Some died of and some simply evolved into birds...
    Thats my two bits..

  2. Sorry.. blonde moment the HARRP link doesn't work..

    This will

  3. Frankie, 95% of peer reviewed studies by climatologists say there is climate change and also conclude it is human-made. Given that there cannot be any airtight certainty because of the nature of scientific study this figure is as solid as you can get.

    The scientists who conclude that climate change isn't caused by humans (the 5%) are more likely to be older scientists who use less modern methods of analysis.

    It wasn't that long ago that climate change was denied to be happening at all.

    Some say the Earth is too large to be affected by humankind's behaviour but look at the Ozone layer and the holes in it. Luckily we tackled CFCs.

    Even if and it is an unlikely if climate change isn't human-made acting to prevent greenhouse gases escaping will bring other benefits like less over-reliance on fossil fuels, cleaner planet, sustainable energy, etc.

    If it is true and we don't act to prevent it it will be catastrophic.

  4. Simon is it not possible that the 5 per cent are independent rather than old? what research I have done into climate change, which I'll give you is small, indicates that climate change, man made or not, is big business and people who disagree with official findings are ostracised and hurt financially.

  5. David- "Simon is it not possible that the 5 per cent are independent rather than old?"

    They tend to be older and use less modern means of analysis. They're not all "old" and they don't all use less modern means of analysis.

    There is no evidence to suggest that the 95% of climatologists mentioned are not independent.

  6. Simon, The official u.n report on climate change only had twelve authors all in establishment think tanks. I haven't the scientific knowledge to tell you if climate change (used to be global warming) is man made I do know that scientist who have spoken out against official finding have been ridiculed in the media without anybody proving they are wrong and in some cases they have lost affluent posts due to there stance.
    Here's a thought if climate change is so important why don't the global governments pushing these agendas actually take real measures against it instead of just taxing people six ways from Sundays. I smell a scam.