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Why it's urgent we act now on climate change

What the science says...

Select a level... Basic Intermediate Advanced

The ice sheet feedback doubles the climate sensitivity predicted by climate models. That means even the current CO2 level, if maintained long enough, will cause 2°C of further warming. To prevent tipping points, we must reduce CO2 from 390 to 350 ppm, which means leaving most remaining fossil fuels in the ground. One more decade of business as usual will make this impossible. It may not be obvious, but the urgency is very real.

Climate Myth...

It's not urgent

"There are many urgent priorities that need the attention of Congress, and it is not for me as an invited guest in your country to say what they are. Yet I can say this much: on any view, “global warming” is not one of them." (Christopher Monckton in testimony to the US Congress)

In 1992, 154 nations signed the United Nations Framework Convention on Climate Change, with the objective of achieving “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.” This raised the question: what exactly would constitute dangerous anthropogenic interference? In 2008, a team of climatologists led by James Hansen set out to answer that question, and came to the startling conclusion that we are already over the limit: the current level of atmospheric carbon dioxide is already in the danger zone.

The amount of CO2 in the atmosphere has increased from about 280 ppm preindustrially to 390 ppm today, and continues to rise by 2 ppm/year as we continue to burn fossil fuels. In their paper, “Target Atmospheric CO2”, Hansen et al argue we should aim to reduce it to 350 ppm in order to stabilize the Earth’s climate. And we must hurry, because that task will soon be an impossible one. Their reasoning is complicated, but worth taking some time to understand given that it concerns the future of the world.

The 350 ppm target is based not on climate modeling, but on how the climate has responded to past greenhouse gas changes in the real world. Estimating a CO2 target from paleoclimate is fraught with uncertainties, but the assumptions made by Hansen et al are not unreasonable ones. Likewise, their value judgements on what is “dangerous” are, in my opinion, no-brainers. Their paper covers a broad array of topics, but at its centre is the question: how sensitive is the Earth’s climate when you include “slow feedbacks”?

Climate sensitivity and slow feedbacks

Climate sensitivity is the amount of global warming you get from doubling CO2 (or an equivalent forcing, which is about 4 watts per square metre or W/m2), and determining its value is the key problem in modeling future climates. Usually we define climate sensitivity as including only “fast feedbacks” such as water vapor, sea ice, clouds, and dust (ice is a feedback because it affects the reflectivity or “albedo” of the surface). Because this definition comes from a landmark 1979 report by the National Academy of Sciences, whose lead author was Jule Charney, it is often called “Charney sensitivity”. For clarity I will call it “fast-feedback sensitivity”.

But in the long run (and as we shall see, the long run has current policy implications), what will be important is the climate sensitivity when you include not only fast feedbacks, but also “slow feedbacks” such as ice sheets. Greenhouse gases can also be a slow feedback, but Hansen et al do not count it as one because they want to know the long-term sensitivity to an unamplified greenhouse gas forcing.

Fast-feedback sensitivity is 3°C

There is a broad consensus that fast-feedback sensitivity is 3°C for a doubling of CO2. Model estimates come with large error bars that have proven difficult to reduce as climate models have become more realistic over the decades, because modeling all the positive and negative feedbacks is so complicated. However, studying past climate changes, which obviously include all existing feedbacks, allows us to circumvent that problem, and paleoclimate-based estimates converge on the same number, 3°C.

Hansen et al reconfirm this with ice core data, by comparing the Holocene (the relatively stable interglacial climate of the last 10,000 years) to the Last Glacial Maximum (LGM) 20,000 years ago. Most of the warming between those two intervals was caused by ice sheets and greenhouse gases, themselves slow feedbacks on tiny orbital forcings sustained over long periods. But for the purpose of finding fast-feedback sensitivity, those slow feedbacks are considered to be forcings (confusing, I know). It is then straightforward to compare the combined forcing (6.5 W/m2) to the global temperature change (5°C), and derive a fast-feedback sensitivity of 0.75°C per W/m2 or 3°C per CO2 doubling, as predicted.

But here we’re more concerned with slow-feedback sensitivity.

What about slow-feedback sensitivity?

We don’t currently have models that include slow feedbacks (which is why the IPCC hasn’t taken them into account), so paleoclimate is the only available tool to estimate them. Further complicating matters is the fact that slow-feedback sensitivity is not stable over geologic time. The ice sheet feedback will only work if there is ice to melt, thus climate sensitivity is higher when the planet has ice on it. On an ice-free Earth, the albedo feedback approaches zero, and slow-feedback sensitivity is about the same as fast-feedback sensitivity (remember, we’re not counting greenhouse gas feedbacks).

The planet is currently in an ice age, with a hundred-millennium cycle from brief “interglacial” periods like the Holocene, when ice sheets are confined to Antarctica and Greenland; to long “glacial” periods like 20,000 years ago, when global temperature plunged by 5°C, ice sheets covered much of Canada and Europe, and sea level fell by over 100 metres. The Northern Hemisphere has been in an ice age for the duration of the Quaternary period of glacial-interglacial cycles, which began 3 million years ago. Antarctica has been in an ice age for no less than 34 million years, or the second half of the 65-million-year Cenozoic era.

Hansen et al use the ice core record of the late Quaternary (the last few glacial-interglacial cycles) to estimate the recent slow-feedback sensitivity to a specified greenhouse gas forcing. As before, about half of the global temperature change in each cycle was from ice sheet feedbacks and half from greenhouse gas feedbacks (though they in turn were ultimately caused by tiny variations in the Earth’s orbit). Since here we’re defining greenhouse gases as a forcing and ice sheets as a feedback, the result is a slow-feedback sensitivity that is double the fast-feedback sensitivity, or 6°C.

However, all of this is ignoring greenhouse gas feedbacks, which we know exist in the real world. For the moment, the carbon cycle is acting as a negative feedback, as oceans and vegetation are removing some of our CO2 emissions (and we still stand a chance of getting back to a safe level). But as global warming continues, those carbon sinks are expected to fill up and start emitting CO2, as they have done during the glacial-interglacial cycles. If we warm the planet too much, we could trigger a release of methane (CH4) trapped on the ocean floor, with catastrophic effects. Eventually, excess CO2 is removed from the atmosphere by a negative weathering feedback, but this takes hundreds of millennia.

You’ll find some discussion of greenhouse gas feedbacks in a recent book review by Andy S, but for the moment it is worth noting that the most important thing Hansen et al 2008 ignores is likely to make things even worse.

So, during the late Cenozoic the total climate sensitivity to greenhouse gases has been 6°C. Half of that is from fast feedbacks, and the other half from slow feedbacks. In the early Cenozoic when there was no ice on the planet, or in a possible future in which we’ve melted all the ice, there is no ice-albedo feedback and the climate sensitivity is 3°C. If you counted greenhouse gas feedbacks as feedbacks and not forcings, you’d get an even higher slow-feedback sensitivity.

Are slow feedbacks still as strong?

But will there be an equally large ice-albedo feedback on global warming today, now only the ice sheets of Greenland and Antarctica remain? To answer that question, Hansen et al extend their paleoclimate survey back to before the advent of ice in Antarctica, zooming out to look at the entire 65 million years of the Cenozoic. On this timescale the orbital cycles that caused the glacial-interglacial flips are mere noise on top of a long-term cooling trend. And as it turns out, that long-term climate change can only be explained by CO2.

Hansen et al take sediment core data and make one simple adjustment to derive global deep ocean temperature. (Specifically, the oxygen isotope ratios which are used as a proxy for temperature are also affected by ice volume, so they assume only half of the change during the late Cenozoic ice age is due to temperature.) The resulting record tells us the deep ocean temperature difference between the peak warmth 50 million years ago and the recent glacial periods was a whopping 14°C.

That breaks down into 8°C cooling until 35 million years ago, a 3°C difference between then and today, and another 3°C between today and glacial periods. The latter is noticeably less than the 5°C observed in ice cores, and we know why: we would expect deep ocean temperature to have changed less than global temperature in the icy late Cenozoic as it approached the freezing point. Thus Hansen et al assume the 3°C difference between 35 million years ago and today also translates to about 5°C globally. The relationship is less clear for the ice-free early Cenozoic, so for the 8°C they allow a conservative range of ±50%.

Using the values of fast-feedback and slow-feedback climate sensitivity derived from the Quaternary glacial-interglacial cycles, Hansen et al calculate the total change in climate forcing required over the 50 million years of cooling. The ice-albedo feedback accounts for about half of the 10°C difference during the late Cenozoic, confirming their slow-feedback sensitivity estimate of 6°C, so only about 7 W/m2 of original forcing are required over that period. Assuming the 3°C fast-feedback sensitivity for the ice-free period, the forcing that caused the earlier 8°C cooling was 11 W/m2, give or take a few W/m2.

What was the forcing? The ice-albedo feedback contributed to the late Cenozoic cooling, but something caused it. The continents were close enough to their current positions 50 million years ago that their effect on albedo was negligible. The Sun’s brightness increased by 0.4%, a forcing of just 1 W/m2 and in the wrong direction. However, CO2 levels fell from over 1,000 ppm in the early Cenozoic to merely 170 ppm in Quaternary glacial periods, approximately a factor of eight, or 12 W/m2 — the only forcing which even comes close to explaining the observed cooling.

As an aside, the reason CO2 varied so greatly was that continental drift affected the geologic carbon cycle: the imbalance of emissions from volcanoes versus absorptions from weathering and fossil fuel formation. I say geologic carbon cycle because these processes are far slower than the cycle between atmosphere, ocean, and vegetation that is important on human timescales. CO2 increased from 65 to 50 million years ago as India’s relatively rapid motion reduced sedimentation in what is now the Indian Ocean, but subsequently decreased as the rise of the Himalayas exposed new rock to the air. This natural CO2 cycle is of mainly academic interest, because we are now emitting CO2 thousands of times faster than volcanoes can.

Proxy records of CO2 are uncertain (the error bars are small for the recent past when CO2 was low, but very large at its peak in the early Cenozoic), but nevertheless the broad sweep of CO2 must have been mainly responsible for Cenozoic climate change, with perhaps some contribution from other greenhouse gases. So Hansen et al calculate the CO2 history that best explains the temperature history. In their chosen scenario (which matches the glacial-interglacial cycles and predicts a peak of 1,000-2,000 ppm 50 million years ago, within the broad range of proxy-based estimates), CO2 was about 450 ppm just before Antarctica became glaciated. 35 million years ago 450 ppm was the freezing point, but if we pass it in the opposite direction it will be the melting point.

The greenhouse gas forcing and global temperature in the current interglacial is about halfway between the Quaternary glacial periods and the formation of the Antarctic ice sheet 35 million years ago. That means the slow albedo feedback is still very much in play. It means we can look forward to much more warming in the pipeline than previously thought. And it means 450 ppm, if sustained long enough for slow feedbacks to take effect, would eventually return the Earth to an ice-free state, raising the global sea level by 75 metres.

How much warming is in the pipeline?

The forcing associated with the dramatic human-caused CO2 spike since 1750 is about 1.8 W/m2 (and rising by 0.2-0.3 W/m2 per decade). However, as yet the climate has responded to only part of this forcing. We know this because the Earth is still gaining more heat than it is losing. This global energy imbalance tells us there is still warming in the pipeline on top of the 0.7°C we've seen so far.

The delay is caused by two sources of inertia in the climate system: the oceans and the ice sheets. Only the former is included in the climate models which IPCC projections are based on. The oceans warm quickly at first, reaching the first third of their response within a few years and the second third within a century, but take over a millennium to fully respond. The oceans are thus “hiding” about 0.6°C of future global warming. However, the long-term sensitivity of 6°C implies that the slow ice-albedo feedback will contribute another 1.4°C, making a total of 2°C (ie. 2.7°C above preindustrial temperature).

To put this in perspective, 2°C of further warming is enough to take us back to the Pliocene several million years ago, when sea level was 25 metres higher. Such a climate has not existed since before the evolution of humans.

How slow are slow feedbacks?

One of the scariest parts is that “slow feedbacks” may not be as slow as everyone used to think. Although in the past ice sheet collapses have taken millennia, perhaps that was only because orbital forcing changed very slowly. Perhaps ice sheets could melt faster if the climate changed faster. You only have to look at the glacial-interglacial cycles to see that ice sheets can melt faster than they build up. And though it takes a lot of energy to get ice sheets moving, once they are in motion they can collapse rapidly.

In the past, sea level changes of metres per century were not uncommon; instead it is the stability of the Holocene that is unusual. In a particularly dramatic example 14,000 years ago, the sea level rose 20 metres in just four centuries. Even during the last interglacial 125,000 years ago sea level was not as stable as once thought, apparently varying by several metres. In the present, we observe the ice sheets shrinking “100 years ahead of schedule” — the IPCC expected them to grow during this century! The fact that ice sheet models do not predict these events seen in the real world suggests they are missing important positive feedbacks.

If the ice sheets can begin to respond significantly on the timescale of a century or so, then the “slow” warming in the pipeline has near-term implications. Human civilization developed with the relatively stable sea level of the last seven millennia. More than a billion people currently live within 25 metres of sea level. Yet once an ice sheet begins to collapse there is no way to stop it from sliding into the ocean. We would be subjected to centuries of encroaching shorelines. But this tragedy we have set in motion can still be prevented, if we reduce CO2 before it is too late.

So where does the 350 target come from?

Humanity has become the driver of the Earth’s climate — human forcings are now far greater than natural ones — but that doesn’t mean we can control it. Unfortunately the climate system contains tipping points, beyond which the climate change we started would spiral out of our control.

The good news is that the inertia in the climate system means that even if CO2 has passed the “tipping level” (say, 350 ppm) for a given tipping point (say, an ice-free Arctic), we may not yet have passed the “point of no return”. The bad news is that nobody knows exactly where the point of no return is, and we probably won’t know until we’ve already passed it. Hypothetically at least, we might still be able to prevent a tipping point by bringing the global climate back into energy balance before it has time to fully respond.

As well as the paleoclimate-based estimate of warming in the pipeline, many of the changes currently unfolding confirm the conclusion that we have already exceeded the safe level of atmospheric CO2. Hansen et al estimate that restoring energy balance is necessary to save the Arctic sea ice (if it’s not already too late); to stop the expansion of the subtropics which will cause desertification in places like Australia; to prevent glacier loss which will cause water shortages; to relieve coral reefs from the twin stresses of global warming and ocean acidification; and of course to stabilize the ice sheets. All these problems are already beginning to occur, many faster than predicted.

How do we get the planet back in energy balance? The problem of setting a target is complicated by the existence of many other human effects on climate besides CO2, but CO2 is clearly the dominant one. It is the largest and fastest-growing forcing. The non-CO2 forcings roughly cancel out anyway: the warming effect of other greenhouse gases is offset by the temporary dimming effect of reflective particle pollutants (though the latter is not known with satisfactory precision). In the long run, CO2 is most important for the warming in the pipeline from slow feedbacks, because it has the longest lifetime in the atmosphere. Whichever way you look at it, CO2 is the main event.

So now we finally arrive at the central conclusion: a long-term target for atmospheric CO2. To restore the planet’s energy balance, we need to reduce CO2 to less than 350 ppm. The 350 number refers to CO2, not CO2-equivalent, for the reasons explained above. This is not to say other forcings should be ignored, but controlling them would not make much difference to the long-term CO2 target. The recommendation may be revised as we obtain better measurements of the total forcing and resulting energy imbalance, but 350 ppm provides a useful benchmark for the scale of action that is needed.

Can we get back to 350?

If Hansen is correct and ice sheets can respond faster than has been assumed, then his long-term CO2 target has near-term policy implications. We need to get CO2 back to 350 ppm as soon as possible. We still have a window of opportunity to get back to 350 ppm, but that window is rapidly slamming shut. Stabilizing the CO2 level will require rapidly reducing global emissions until carbon sinks can absorb carbon faster than we emit it. Hansen et al argue the only realistic way to reduce emissions fast enough is to phase out coal.

Why target coal? Because CO2 has such a long atmospheric lifetime, we must leave most of the remaining fossil fuels in the ground if we are to have any hope of achieving the 350 goal. Of the three conventional fossil fuels (coal, oil, and gas), coal has by far the largest reserves. The phaseout of coal needs to include any conversion of coal to oil or gas — using up coal reserves at a slower rate would make little difference, because the carbon would still build up in the atmosphere and much of it would stay there for a very long time. Remember, carbon sinks have limits. The fundamental problem is with the coal being burned at all.

Hansen et al calculate that if we phase out coal by 2030, CO2 could peak at around 425 ppm in 2050. Their scenario demands that we also not burn unconventional fossil fuels like tar sands and oil shale, whose reserves are virtually untapped but thought to contain even more carbon than coal. What about conventional oil and gas? There is dispute among energy experts over exactly how much oil and gas is left. Some think we’ve already burned about half of the available reserves and thus production must peak soon, while others argue there is more oil and gas if we want to go to the effort of extracting it. If the former is correct, or if the latter is correct but we leave the least accessible oil and gas in the ground, CO2 could peak at just 400 ppm as early as 2025.

Supposing that we succeed in halting the rise of CO2, we will still be left with the gargantuan task of removing it from the atmosphere. Natural carbon sinks would absorb about 25 ppm by the end of the century. Forestry and soil policies (for example, net reforestation by 2015) might be able to wipe off another 25 ppm.

It won’t be easy but it appears to be still possible to get back to 350 ppm by century’s end. On the other hand, if unlimited coal-burning continues for even one more decade, CO2 can be expected to remain in the danger zone for a very long time.

CO2 Emissions and Atmospheric Concentration with Coal Phaseout by 2030


Global warming is an increasingly urgent problem. The urgency isn't obvious because of the inertia of the climate system and the slowness of slow feedbacks. But we must act now before we push the climate beyond a tipping point where the situation spirals out of our control. As climate blogger Joe Romm likes to say, the time to act is yesterday.

Fast-feedback climate sensitivity is 3°C, but slow-feedback sensitivity is as high as 6°C when there are ice sheets on the planet, as there are today. Even worse, those slow feedbacks may not be nearly as slow as we used to think. This means there is a large amount of warming already “in the pipeline”, though it is not yet too late to prevent it. To do so we cannot avoid targeting the largest, fastest-growing, and longest-lived forcing; a greenhouse gas which has been a major cause of climate change over geologic time: CO2.

A CO2 level of 450 ppm (the lowest target being considered by governments) would eventually melt all the ice on the planet. Both observations of the climate change currently underway, and the paleoclimate-based estimate of slow-feedback sensitivity, suggest even the current level of 390 ppm is too high. If CO2 is at or above its current level for too long, it will eventually result in a planet unlike the one on which humans evolved: a planet 2°C warmer and with sea level 25 metres higher. Imagine waves crashing over an eight-storey building. It is hard to dispute that this would be “dangerous” climate change.

To stabilize the climate, we must return the Earth to energy balance. And in order to do that, we need to reduce CO2 to 350 ppm, as soon as possible. To meet this target we must leave most of the remaining fossil fuels in the ground. We need to 1) rapidly phase out coal (including coal-to-liquid-fuels), 2) not burn the tar sands and oil shale, 3) not burn the last drops of oil and gas, and 4) turn deforestation into reforestation. And we must hurry: one more decade of business as usual would make this goal practically impossible. If we fail, we face an uncertain future in which the only certainty is a continually shifting climate.

I’ll leave the final word to Hansen et al, whose concluding statements are pretty strongly worded coming from a dense, technical, peer-reviewed, scientific paper:

Present policies, with continued construction of coal-fired power plants without CO2 capture, suggest that decision-makers do not appreciate the gravity of the situation. We must begin to move now toward the era beyond fossil fuels. Continued growth of greenhouse gas emissions, for just another decade, practically eliminates the possibility of near-term return of atmospheric composition beneath the tipping level for catastrophic effects.

The most difficult task, phase-out over the next 20-25 years of coal use that does not capture CO2, is Herculean, yet feasible when compared with the efforts that went into World War II. The stakes, for all life on the planet, surpass those of any previous crisis. The greatest danger is continued ignorance and denial, which could make tragic consequences unavoidable.

Advanced rebuttal written by James Wight

Update August 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 5 August 2015 by MichaelK. View Archives

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Comments 1 to 25 out of 48:

  1. This is the only refutation I could find in the list by taxonomy that I thought might explain why "geo-engineering" doesn't solve the problem. After all, if geo-engineering would work, then that would reduce the urgency. So this is the perfect place (at least under the existing taxonomy) for addressing it. There is, after all, a a claim circulating the rumor mill now that sulfuric acid high altitude aerosols will solve the problem. I do not think we can explain the popularity of this belief solely in a one-sided reading of the Wikipedia article
  2. I'd like to see the Basic article expanded in various ways.  This article doesn't mention a time frame as to when we might see costly effects.  Sounds like we have at least hundreds of years if not thousands before Miami sinks beneath the waves.

    The article doesn't discuss any problems other than sea level rise.  Will climate change leave agriculture unphased and as productive or more productive than it currently is?  If production drops, how log before we might see climate based drops in production?

    Over time frames like hundreds of years geo-engineering becomes more feasible.  And over longer time frames, smaller yearly investments can be made.

  3. Perhaps I'm on the wrong page, but...  The climate myth the way I've heard it is:  "Nothing is going to happen for a long time, so we don't need to do anything now."  This is mostly in the context of melting ice sheets in Greenland and the Antarctic.

    The arguments I would expect to see are:

    1)  There are short term problems.  For example ocean acidification and coral bleaching.  Heat waves.  Reductions in agricultural production.

    2)  Changes, especially cheap ones, take a long time to take effect.  For example, the U.S. car fleet turns over in 20 years.  If we stopped selling gasoline and diesel powered cars today and only allowed the sale of electric cars, it would take 20 years to get all the gasoline and diesel powered cars off the road.

    3)  There is huge inertia.  If we stopped emitting new CO2 today, and held existing concentrations constant, we would see the earth continue to warm up in quite some time.  

    With business as usual, we will see accelerating CO2 emissions causing deteriorating climate, and we will also see deteriorating climate as the Earth tries to reach equilibrium with the CO2 already emitted.  Both of these will mean that Miami will be flooded sooner (50 years) rather than later (100 years), plus we will have less time to react.


  4. Dr David Mills was on youtube years ago saying it is now impossible not to go over 440ppm...! He also said it was being debated whether it was possible to go over it and then come back down under it but seeing as that was years ago I'm sure someone has information on where that specific debate is now.

    (Dr David Mills was the candian guy who wanted to do Solar Thermal in Australia after having trained and invented processes in Australia but no dice so went to America and no dice, so, well... I suppose he gave in the end!)

  5. You said here that carbon concentrations will peak at 400 ppm in 2025 under the ideal situation, but it's only 2015 and we're already at 400 ppm, and I see no signs of global emission reductions happening soon. Is this evidence that we will pass the point of no return?

  6. anticorncob6...  The writer said concentrations "could" peak around 400ppm, but clearly we're screaming past that level right now. That was written four years ago, and I'd have to say was a very optimistic outlook.

  7. Oh, and regarding "point of no return..."  "Point of no return" would likely not be a term anyone would use since it leaves too many loose ends.

    We are currently at about 0.8C over preindustrial global temperature, and with thermal inertia we've banked about 1.2C of temperature rise no matter what we do. 

    That, in and of itself, means there are going to be aspects of climate change that we can't stop and will have to adapt to. After we pass 2C over preindustrial temps we risk passing tipping points where we don't know how much additional warming will result. Researchers are urging us not to pass that 2C limit. At around 0.2C/decade... meh, we have a little bit of time, but we desperately need to be enacting policies now that can keep us below that 2C limit.

  8. @6, There was a famous interview/commerical-I-suppose on Youtube a number of years ago(not sure how many) where Dr David Mills was saying there is now no way we can stay under the information being floated around does seem a little contradictory and the denial brigade can almost be forgiven for driving mack trucks through what seem like gaping holes of information. Yes, it all depends where you go for information of course.

    My point was that I'm guessing a lot more than 440ppm is locked in- I'm not sure how This David Mills character came up with his numbers so I am of course merely guessing/being potentially paranoid... the IPCC reports are known to be conservative by nature for instance and there was an article just recently on Sterling Engines being tested in South Africa over the last 4 years... combining this with the new phenomenons of formula-e racing and possibly Virgin competing with Tesla for the electric car market and Tesla itself saying it may just go into producing batteries the world does seem to be displaying something of a turn !

     (I could find that video but it may take some searching... the only relevant information was that he though 440ppm was locked in and they didn't know if it was possible to go over the limit and then come back down under at that time but that it would be impossible to not break it in the initial sense!)

  9. @7, another indicator worthy of attention in my mind is that Bjorn Lomborgs political message was that 3C was a more sensible target... what this indicates I don't like!

  10. Hi, I just read the book No One Is Too Small to Make a Difference by Greta Thunberg. Wow, what an emotional rollercoaster. I've played the Cranky Uncle game for hours, taken the edx101 course, surfed the skeptical science website, and argued with deniers.

    Book no one is too small Greta Thunberg

    Yet, only in 2022 have I heard about net zero emissions. Even then, I thought it was by the year 2050. Greta Thunberg makes the case that global climate change is an existential urgent crisis. That we need net zero by 2030. Is this really true?

    As a millennial I feel a lot of the same emotions that the older generations are out of touch when I say I cannot get a job or having trouble with the basics like a roof over my head, running water, heat in winter. I find I get scolded by the older generations and they offer out of touch simplistic solutions blaming the victim or even calling me a liar.

    Did I get distracted by the pandemic, George Floyd's murder, and possible nuclear war between Russia and Ukraine? With all my climate activist since 2016 did I really miss that we only have a 50% chance to avoid a climate catastrophe of runaway greenhouse effect if we go for a 2 degree Celsius increase by 2050 or whatever Thungberg said in her book?

    How urgent is climate change? Thank you in advance. :)

  11. "PollutionMonster at 14:13 PM on 8 March 2023"
    "How urgent is it?" is a value question. Another value question is "How much threat to diversity does humanity's anthropocentrism" cause to the long-term survival of species-populations in the wild (10,000 years)? And I agree, how do we quantify "How much threat"?

    In an anthropocentric (human-centered) context, judging from what I'm witnessing, we were out of time long ago.

    I need only point to the proliferation of nuclear warheads and greenhouse gases to bolster my case. I don't see much genuine effort by governments and corporations to do the real work, and make long-term decisions for the benefit of humanity and biodiversity's long-term existence; we continue to pass the buck to future generations.

  12. PollutionMonster @10,

    You ask about the timing for reaching net zero carbon. That single timing doesn't properly capture the task in hand.

    The science strongly suggests that increasing global temperatures by more than +1.5ºC risks potential dramatic climate change. To prevent such rise, there is just one scenario presented within the IPCC AR6 that fits the bill - SSP1-1.9.

    AR6 SPM Fig8.a

    This SSP1-1.9 scenario does include a timing of 2050 for net zero carbon but it also requires a halving of global net carbon emissions by 2030 and large net negative carbon emissions post-2050. These net negative emissions amount to roughly extracting atmospheric CO2 equal to all the emissions post-2007 and storing them away safely. (There are many saline aquifers around the world which this CO2 could be desolved into after its extraction from the atmosphere. These extractions from the atmosphere are additional to the natural draw-down of CO2 into the oceans.)

    But it seems it is only the 'net zero' message that is being heard by politicians. So calling for an earlier 'net zero' is probably a useful message.

  13. "These extractions from the atmosphere are additional to the natural draw-down of CO2 into the oceans.)"

    And we have no idea if, at all, the global ocean will continue to act as a viable carbon sink, not to mention methane. Then there's the political will and economic resources to make the abrupt ideological and technological changes needed, assuming that critical tipping points were not breached long ago. I'm assuming that we don't know everything to know about the neew climate change and our test-tube earth mentality.


  14. EddieEvans @13,
    The net carbon sink into the oceans is far more predictable than the carbon interchange in/out of the biosphere. There is still some uncertainty and re-assessment (eg Watson et al 2020) in the matter but generally the only big variable is the ocean surface temperatures. So as long as we prevent massive SST rises, I would think it is safe to say "the global ocean will continue to act as a viable carbon sink." The actual size of that sink over the coming millennium will thus depend on how well we do preventing AGW but otherwise it's size is fairly predictable. What is far less predictable under AGW is the biosphere as a source/sink.

    You also raise the threat of methane, this usually focusing on natural feedbacks and the melting permafrost. In the past I was rather worried by the poor coverage of this subject in the scientific literature but having dug into the subject I now feel more comfortable about it. Additionally the absence of significant methane fluxes resulting from the significant permafrost melt in recent decades is a reassuring sign.

  15. According to the following article, we are on the precipe of multiple climate tipping points. As they say, "Hold onto your hat, we're in for a wild ride."

    Risky feedback loops are accelerating climate change, scientists warn by Emma Newburger, Climate, CNBC, Mar 6, 2023  

  16. MA Rogers has correctly clarified that the total harmful warming impact is what matters. Limiting the impact to 1.5 C needs to continue to be the focus. And the reality that the peak impact will almost certainly exceed 1.5 C needs to be understood to mean that wealthy people today need to be paying for safe/harmless technological extraction of CO2 from the atmosphere. That extraction will be expensive and never be profitable. And the spending of tax money on it rather than other things will never be "most" popular.

    That is the challenge. Leadership has to do something unpopular and unprofitable to benefit future generations. The diversity of developed socioeconomic-political systems is tragically lacking in the development of that type of leadership. And it is now undeniable that humanity only has a future if it develops governing of all significant human activity in ways that understandably limit and correct harm done.

    A related point is that it is harmful to cause increased CO2 to be absorbed in the oceans. The fact that CO2 will continue to be absorbed in the oceans is not a positive.

    Also, a lack of significant methane release from massive thawing of permafrost (a miss named item) is not a helpful positive.

    It is essential to remain focused on the need to end harmful activity regardless of its developed popularity or profitability abnd related popular 'perceived to be positive' misunderstandings (and that applies to authoritarian as well as democratic governing).

  17. I read all the responses, and I want to thank all of you. :) Climate justice is a major part of climate change. That rich nations including the United States, France, and United Kingdom need to reach zero emissions by 2030 so that poorer nations have time to develop and have some emissions until 2050.

    Thunberg in her book referenced some specific page of the IPCC page 100 or so stating that there is a 50% chance of runaway greenhouse effects beyond human control at 2C and only 34% chance at 1.5C. Is this true? That there really is that high a chance that climate change will be the end of everything? Did I misread? I haven't read the source material, navigating the IPCC report is difficult.

  18. PM @17... Would you have the precise quote from Thunberg's book related to "50% chance of runaway greenhouse effects beyond human control at 2°C"? 

    My suspicion is that's not an entirely correct assessment, though I'm confident Thunberg's book went through a thorough review by researchers prior to publication. My understanding is, past 2°C we move into a realm of much greater uncertainties. Also, even at 2°C significant feedbacks (say, from methane releases) remain long tail uncertainties. But I could be wrong.

  19. Most of the quote is here in this NPR article. Risk of setting off irreversible chain reactions NPR.

    I would have to reread the book to get the exact quotes, I read in local bookstore.

    ""The popular idea of cutting our emissions in half in 10 years only gives us a 50% chance of staying below 1.5 degrees [Celsius], and the risk of setting off irreversible chain reactions beyond human control." Thunberg


  20. Hm... Yeah, those are quotes from 2019 and I think she's probably conflating two issues. One being the likelihood of staying below 1.5°C or 2°C, and the other being the likelihood of setting off irreversible feedbacks. To my understanding, they're two different issues with very different confidence levels. 

  21. I"m with Rob. The writing of that specific sentence could be clearer. The "50% chance" part is definitely associated with the "staying below 1.5 degrees", but the comma that follows that separates the "50% chance" probability from the "risk of setting off irreversible chain reactions".

    Two possible re-writes that would make the writer's intentions clearer:

    1. "The popular idea of cutting our emissions in half in 10 years only gives us a 50% chance of staying below 1.5 degrees [Celsius]." It also brings a "risk of setting off irreversible chain reactions beyond human control."
    2. "The popular idea of cutting our emissions in half in 10 years only gives us a 50% chance of" avoiding two outcomes: "staying below 1.5 degrees [Celsius], and the risk of setting off irreversible chain reactions beyond human control."

    Expect "The Usual Suspects" to insist that the only possible interpretation is the one that fits their preconceived notions of Greta Thunberg.

  22. Bob Loblaw @21

    I am unsure who "The Usual Suspects" are. I am pretty good at debunking  obvert denial, but I still have a knowledge gap when it comes to the subtler aspects of climate change.

  23. PM (may I call you PM?):

    There is a classic line at the end of  the movie Casablanca, where the police captain (Renault) says to Rick (the main character played by Humphrey Bogart), "round up the usual suspects". The connotation is that the police have a list of people they know are usually associated with many crimes, and they'll take the blame.

    I'm basically pointing out that there are certain players in the climate change "debates" who will most certainly take the least charitable interpretation of that quote. We've seen them do similar, many times before.

  24. MARoger@

    "The net carbon sink into the oceans is far more predictable than the carbon interchange in/out of the biosphere."

    Using the global ocean as a carbon sink has consequences for biodiversity, increasing acidification. There's no free lunch, and no eternal waste disposal for the Anthropocene, I gather. I'm not up to date on the latest research; I left the ocean as a sink with Roger Revelle. I will update my understanding for sure.  There are no positives in any of these GHG matters.

  25. Eddie:

    SkS did a series on the ocean acidification issue a number of years back.

    Part 0 provides an index to the series.

    After it was complete, it was turned into a downloadable booklet.

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