Warming ends when emissions stop

Mann's article shows that temperatures will most likely quickly stop rising if we stop emitting CO2 and methane.

[See original chart here]

From Michael E Mann

A recent article in The Hill insisted that “scientists failed for decades to communicate” (1) the threat of climate change. The scientific paper on which the article was reporting did not really say that—it was instead providing a more nuanced discussion of sea level rise “tail risk”. But the irony here is that the opposite of what was asserted by the news article is arguably true. If anything, we scientists have failed to communicate the prospects for averting catastrophic warming. 

In the days when I was working on my PhD, in the early 1990s, we were taught that the warming of the planet would persist for decades even if we suddenly stopped burning fossil fuels and emitting carbon into the atmosphere. This is due to what is known as “thermal inertia”—the slow, sluggish response of the oceans. Climate models showed that surface warming would continue for 30 years or more, as the oceans slowly continue to warm, even after carbon pollution ceases. This so-called “committed warming” would seem to render our efforts to avert disaster somewhat futile. Even if we turned off the metaphorical carbon faucet, the water level of warming would continue to rise. Extending the metaphor, that water would soon spill from our kitchen sink onto the kitchen floor. With apologies to Greta Thunberg, rather than burning, our house would instead be flooding.

But that picture is fundamentally incomplete—there is a “drain” too in the form of the ocean carbon cycle. That drain causes the water level, i.e., the planetary temperature, to stabilize. Through a somewhat fortuitous coincidence of nature, there are offsetting tendencies in ocean physics and ocean chemistry. The positive “thermal inertia” (the physics) is almost perfectly offset by a negative “carbon cycle inertia” (the chemistry). To be more specific, the rate at which the ocean surface tends to continue to warm up due to the carbon already emitted is nearly identical to the rate at which the oceans absorb and bury atmospheric carbon dioxide (CO2), lowering the atmospheric greenhouse effect and cooling the lower atmosphere and surface. The two effects essentially cancel each other out. And so, instead, we get an essentially flat temperature curve—the stable metaphorical water level—when human carbon emissions approach zero.

In the old days, climate modelers would simply set the atmospheric CO2 constant to represent a scenario in which human carbon emissions cease. However, this amounted to an erroneous implicit assumption of zero carbon cycle inertia. In the newer, more realistic modeling framework, based on more comprehensive Earth system models, the oceans as well as the terrestrial biosphere are allowed to play an interactive role in the behavior of the system, which includes the key role of actively drawing down carbon from the atmosphere.

While this new more realistic framework emerged more than a decade ago (2), only far more recently has it truly penetrated public climate discourse. Arguably, both scientists and journalists are at fault (3) for the continued notion that we are due decades of additional warming even after we cease fossil fuel burning and other activities generating carbon pollution. We now know this is not true.

This is hardly a minor technical matter. It fundamentally changes our sense of agency in averting disaster. It means our efforts to reduce carbon emissions have a direct and immediate impact. It is the reason we can meaningfully define a “carbon budget”—there is a fixed amount of fossil fuel we can afford to burn and stay below critical planetary temperature levels such as 1.5°C or 2.0°C. We can estimate that budget and work toward policies that can keep us collectively within it, at least in principle.

Old habits die hard, and some scientists have remained skeptical of this revised understanding. Indeed, I myself took several years to accept the paradigm-shifting implications of this finding. But this finding appears quite robust, having been affirmed by a solid body of work over the past decade. The current state of the science is adroitly summarized in a comprehensive new review “The Zero Emissions Commitment and climate stabilization” by a team of nearly two dozen experts on this research topic in the current Frontiers in Science Lead Article by Palazzo Corner et al. (4).

Palazzo Corner et al. focus on the “Zero Emissions Commitment” or “ZEC”, which is defined as how much warming (if any) we can expect upon reaching zero carbon emissions. Technically, that is zero “net emissions”, as the possibility exists— at least theoretically—for artificial drawdown of atmospheric carbon, i.e., so-called “negative emissions”. Yet there is no evidence at present that such technology could be deployed at scale let alone in the rapid timeframe now necessary. To the extent that the ostensible promise of negative emissions technology may be little more than a techno-optimistic mirage, my preference is to omit the “net” prefix. What is truly required is a rapid phaseout of anthropogenic activities that produce carbon pollution.

Palazzo Corner et al. show that, on average, the various models used in the recent “ZECMIP” intercomparison study indicate a ZEC close to zero, at least on a 50-year timescale (greater uncertainties apply for longer timescales due to uncertainties in the longer-term behavior of, e.g., the global carbon cycle and for larger amounts of cumulative carbon emissions). For at least 1000 gigatons (trillion tons) of emitted carbon (“GtC”) (thus far, for comparison, we have burned about 680 GtC, so it is plausible we can remain below that limit), the average ZEC across models is not only close to zero but very slightly negative (just under −0.1°C).

There is nonetheless a substantial range in estimated ZEC among the various individual models: anywhere from a cooling of −0.3°C to a warming of +0.3°C. Palazzo Corner et al. note, accordingly, that there is a roughly 66% likelihood that additional warming will be less than 0.3°C once zero emissions are reached. Conversely, that implies a 33% chance the warming could be more than this. Given we are currently at roughly 1.2°C warming relative to the pre-industrial era, that could mean reaching the oft-cited threshold for catastrophic warming of 1.5°C even if we were somehow to bring carbon emissions to zero today. While there is a good chance we would avert 1.5°C warming in that scenario, to paraphrase Clint Eastwood, we must ask ourselves one question: do we feel lucky?

Now, there are certainly some additional caveats to this story, and they are explored in some detail by Palazzo Corner et al. First of all, ZECMIP features only a subset of available climate system models, and the inferences drawn are quite limited beyond the 100- year time horizon, where the behavior of long-response components of the climate system—the ice sheets, the deep ocean, etc.—remains a bit vague. Unsurprisingly, there is a large degree of variation in model predictions beyond that time horizon, with some models indicating that additional warming could eventually kick in. Given the complexities of the ocean carbon cycle in particular and ocean mixing processes more generally (which are relevant for both carbon and heat burial), the seemingly coincidental balance between positive climate inertia and negative carbon cycle inertia is tenuous and subject to possible revision as scientific understanding continues to advance.

Another wild card is that other factors besides CO2 come into play when we examine future global temperature scenarios. Among these are sulfate aerosols (which exert a cooling effect) and black carbonaceous aerosols (which exert a warming effect) from coal burning and other short-lived greenhouse gases generated from human activity, such as methane, nitrous oxide, and lower atmospheric ozone pollution. In most scenarios, the effects of these competing short-term radiative constituents cancel each other out, constituting a near zero sum game as we phase out fossil fuel burning and the other underlying anthropogenic activities that generate them. But this depends on the details of policies impacting those activities, including, in the case of methane, agriculture, hydroelectric dam construction, and natural gas extraction. The cancellation is also dependent on us getting the radiative physics right. In the case of sulfate aerosols—particularly so-called “indirect effects” such as cloud nucleation—there is still substantial uncertainty. So, while long-term warming will largely be determined by what happens to CO2, these other contributors will matter too if the activities producing them continue.

Yet another caveat involves the precise magnitude of the carbon budgets that remain for avoiding critical warming thresholds. The amount of CO2 that can still be emitted for a 50% chance of staying below 1.5°C of warming is conventionally estimated to be roughly 100 GtC. At the current rate of emissions, we would run through that budget in less than a decade. Yet that estimate may be overly liberal as it is dependent on other assumptions. Among these is how we define the pre-industrial baseline relative to which net warming is measured. It has typically been taken to be the late 19th century (the mid-point of the first 50 years of available widespread surface temperature measurements). There is evidence, however, that human-caused warming began before that, perhaps as early as the mid-18th century. Taking into account the earlier human-caused warming potentially reduces the budget for averting 1.5°C warming by as much as 40% (5).

But the most significant caveat of all is that surface temperatures are not the only things that matter during the climate crisis. While some impacts, like extreme weather events, appear to be tied to surface warming, others, like rising sea levels and ice sheet destabilization, depend on the warming of the deep ocean. That would continue for decades and centuries to come (see Figure 1 from Palazzo Corner et al., 2023). Our earlier sink analogy, while useful for understanding the competing impacts on the warming level, is an imperfect one: even if surface temperature levels are constant, actual (rather than metaphorical) water levels will continue to rise for some time.

Moreover, as the ocean continues to absorb atmospheric carbon, ocean acidification—which impacts coral reefs and other calcareous ocean biota, such as mollusks and crustaceans—would continue to worsen, threatening food webs in the ocean. So, the penalty of procrastination remains, underscoring the importance of decarbonizing our societal machinery as rapidly as possible if we are to remain within our adaptive capacity as a civilization.

Nevertheless, this new study offers hope. At a time when climate advocates have become disillusioned by the lack of progress—and this is understandable given the “commitment gap” that still remains between what has been promised and what is required— this latest study reminds us that the obstacles to climate action are neither physical nor technological. At this point, they remain political. History teaches us that political obstacles can be overcome, so there remains both urgency and agency when it comes to the ongoing climate battle.

I often encounter people who maintain that it's pointless cutting emissions, because "it's too late", since the world will go on warming because of the oceans' thermal inertia.  Dr Mann's key point is that is wrong.   And that's very important — if we stop emissions now, there is a good chance that global temperatures will quickly stabilise.  It's the opposite of "too late".

Those who've sold their souls to oil and coal and gas want us to give up.  And we must not.

References

1. Elbein S. Catch-22: Scientific communication failures linked to faster-rising seas (2023). The Hill. Available at: https://thehill.com/policy/energy-environment/4057045- catch-22-scientific-communication-failures-linked-to-faster-rising-seas/ (Accessed July 10, 2023). 

2. Meinshausen M, Meinshausen N, Hare W, Raper SC, Frieler K, Knutti R, et al. Greenhouse-gas emission targets for limiting global warming to 2°C. Nature (2009) 458 (7242):1158–62. doi: 10.1038/nature08017 

3. Hertsgaard M, Huq S and Mann ME. How a little-discussed revision of climate science could help avert doom (2022). Washington Post. Available at: https://www. washingtonpost.com/outlook/2022/02/23/warming-timeline-carbon-budget-climatescience/ (Accessed July 10, 2023). 

4. Palazzo Corner S, Siegert M, Ceppi P, Fox-Kemper B, Frölicher T, Gallego-Sala A, et al. The Zero Emissions Commitment and climate stabilization. Front Sci (2023) 1:1170744. doi: 10.3389/fsci.2023.1170744 

5. Schurer A, Cowtan K, Hawkins E, Mann ME, Scott V, Tett SFB. Interpretations of the paris climate target. Nat Geosci (2018) 11:220–1. doi: 10.1038/s41561-018- 0086-8

Preventing a climate calamity is still possible.

 This is an informative video from Climate Adam.  He uses an analogy I've used before: a bathtub.  Virtually every year since 1850, the CO2 we push out into the atmosphere has risen.  Because the outflow from the atmosphere (natural carbon sinks) is less than what we're pumping into the air, the level of CO2 has risen.  Emissions have flatlined over the last 10 years, but they're still more than the removal of CO2 from the atmosphere via carbon sinks.  Using the analogy, the level of water (CO2) in the tub (atmosphere) is continuing to rise, just more slowly.  And thus temperatures continue to rise.  But if we could cut emissions so that they are the same as outflows, the level of water (CO2) would stop rising, and so would temperatures.

Adam makes the point that carbon sinks (where CO2 gets sucked out of the atmosphere) take up around 50% of emissions.  This is only a temporary help, because the carbon sinks (the sea, forests and marshes) are taking less and less out of the atmosphere.  They're filling up.  But it does mean that if we could cut emissions by 50%, the level of CO2 in the atmosphere, and therefore temperatures, would stop rising (or at least, rise more slowly), though we would still need to cut emissions over time to near zero.  It used to be thought that temperatures would go on rising for decades even after we achieved zero emissions, but this is no longer the scientific consensus.

Now, the good news is that together, emissions from electricity generation and land transport, on average across the world, are roughly 50% of total CO2 emissions.  If we could replace coal and gas in electricity generation, and convert the global car, lorry and bus fleets to electricity, we would have cut emissions by 50%.  In other words, stopping temperatures rising is achievable, and achievable over the next decade.  We would still have to achieve zero emissions, because with the oceans, the carbon sink reduction (the oceans offset and bury CO2) is offset by their thermal inertia — they will continue to release heat into the atmosphere as long as they are cooler than the atmosphere.   But switching to renewables and EVs would give us time to cut emissions from all the other more difficult sectors like cement, steel, air and sea transport and agriculture.

The other climate-warming gas Adam talks about is methane.  Methane comes from gas leaks, rubbish dumps, and cattle and sheep.  Methane has been rising fast, and shows no signs of peaking.  Over a ten-year time frame, methane is 80 times as potent a greenhouse gas as CO2.  But it quickly decays into CO2, so if we could cut methane emissions, the effects would be rapid.  One third of the rise in temperatures since pre-industrial times is from methane.  So, as we replace gas in electricity generation (and we will for now still need 5 - 10% gas generation to cover dunkelflaute events, because we don't have workable long-term storage), gas leaks will fall.  There are super emitters of methane from rubbish dumps.  And that's easy to stop: just cover your rubbish dumps with a thick layer of earth.  Finally, each of us can avoid beef, mutton and milk.  That's something we can directly do to cut emissions.  Turning vegetarian could be your single biggest step to cutting emissions!  (Buying an EV is another.)

The moral of all this is that we are far from helpless.  CO2 emissions have peaked.  Our task is to bend that curve down, until the level of CO2 in the atmosphere also peaks.  We have to turn the CO2 and methane taps off, and then we will actually be able to avoid a catastrophic climate future.

(One really scary factor driving increasing emissions is AI datacentres.  We need to stop their construction.  Now.)

The fossil fuel companies haven't given up ...

 .... they've embraced other tactics instead.

From a podcast by Michael E Mann on The Planet

Michael E Mann is one of the world's most influential climate scientists. The distinguished professor of atmospheric science at Penn State is known for the hockey stick graphs and as a defender of climate science while being targeted by climate change deniers. He's also the writer of the excellent book The New Climate War. He joined me this week in The Planet podcast. The excerpt of the interview is in this newsletter. 

The New Climate War. For decades, you have been fighting a well-funded disinformation campaign by the fossil fuel companies. Your book is about the New Climate War. Did you and other scientists win the first one?

The old Climate War was an effort of polluters, the fossil fuel companies, and conservative groups representing their interests to discredit the basic science and the scientific evidence of human-caused climate change. This war has essentially been won; we've reached the point where it just isn't credible anymore to deny that it's happening and deny that we can see the impacts because we're seeing them play out almost in real-time. 

But that doesn't mean that the fossil fuel industry has given up; they've turned to other tactics, which I detail in The New Climate War, in their effort to keep us addicted to fossil fuels. Because in the end, they don't care about the reason. They don't care about the path we take; they just care about the destination. So they want us disengaged, and they want us to remain reliant on fossil fuels. And so they lead us to deny that the problem exists or deflect our attention away from meaningful solutions, divide us, and get us fighting with each other; they want to make sure that we don't represent a United Front. 

They try to convince us that it's just about individual lifestyle choices so that we don't demand policy action and systemic changes. Or they can get us to believe that it's too late to do anything about the problem, which, ironically, potentially leads us to the same place of disengagement. 

So these are the tactics that we are now facing. And that's really what the book is about: helping people recognize these tactics and recognize how to push back on them because we can feel we are so close now to finally seeing the action that we worked for so hard and so long. But there are still these obstacles in our way. And we need to recognize those obstacles so we can finally act in a manner consistent with the challenge we face.

Do shorter showers help?  But are there behavioral changes we should take as individuals to reduce our carbon footprint? Like taking shorter showers or going on a biking holiday instead of flying to Tahiti? And I believe that you are, like me, a vegetarian?

I don't eat meat, but I guess I'm a pescetarian. So I'm not all the way to vegetarian yet. But indeed, I find that I'm happier, feel better, and feel healthier. So there are all of these things that we can do that decrease our environmental impact or our carbon footprint. They make us feel better, save us money, and set a good example for other people. 

So, of course, we should do all these things. But what we have to guard against is this argument that if we do these things, that solves the problem. And that that's all we need to do. Because that indeed does play into the agenda of polluters who would love to have us so focused on our individual carbon footprint that we fail to notice theirs. Seventy percent of our carbon emissions come from just one hundred polluters. And so, while we should do all these things that we can do to decrease our environmental impact, we also have to make sure that we hold polluters accountable. And we should also hold our policymakers or politicians accountable for acting on our behalf rather than acting in the interests of a small number of polluting interests.

In your book, you also mention the tactics used by the tobacco industry, or for instance, the gun lobby that promotes the line that "guns don't kill people, but people kill people." You also mentioned a "crying Indian" campaign?

If you grew up in the States in the 1970s, you remember this ad that profoundly impacted us. This tearful, Native American was canoeing down this river that's been polluted by all these strewn bottles and can liter, and it felt empowering. It felt like, yes, we need to clean up our environment. But it turns out it was a PR campaign that was hatched on Madison Avenue by Coca-Cola and the beverage industry. They wanted to convince us that we didn't need bottle bills. We didn't need systemic solutions. So they made it all about us to further their interests. Because the bottom line is that acting in a systemic way, a bottle bill, these regulations would solve this problem at its source, but it would cost them profits. And thanks to their very effective deflection campaign, we have one of our other great global environmental crises today: the plastic pollution crisis, thanks to the clever and effective use of a deflection campaign by the industry. We have to recognize they're doing that right now on carbon emissions and climate.

“The truth is bad enough”  On Twitter, I see examples of people who have given up all hope to stop climate change. They believe we have passed tipping points that make our future on this planet doomed anyway. They refer, for instance, to the methane escaping the thawing permafrost areas. I suppose that approach is not very motivating to take climate action?

I like to say that the truth is bad enough; we don't need to exaggerate. And you're absolutely right; you see a lot of this on social media, and some of this is authentic; a fair amount of these are good-hearted people, people who ironically would otherwise be on the front lines and demanding action. But they've been led astray by pretty clever manipulation. 

The people at the very top of this are not innocent. There are bad actors who want to convince us that it's too late because of simply the physical response of the climate system, as you alluded to this idea of runaway feedbacks. But that's not supported by science. There's no science that supports the idea that we are committed to some sort of runaway warming. The science pretty clearly now indicates that how much warming we get is a function of how much carbon we burn. And the flip side of that is if we bring our carbon emissions to zero, the warming, at least of the surface of our planet, stabilizes very quickly. 

Now there might be some longer timescale responses. And we worry about this; the destabilization of ice sheets, for example. But we basically stop the warming of the planet if we stop polluting the atmosphere with carbon. It's so important to recognize that. What has happened here is that the forces of inaction, I call them the "inactivists" in the book, have actually tried to convince many climate advocates that it is too late, either because of this idea of runaway warming methane and feedback loops.

 But the science doesn't support the idea that we're close to any sort of runaway methane sort of bomb response to the climate system. So only if we warm the planet enough, if we do nothing, then yes, we start to enter into that realm. But we're not anywhere close to it now. So if we act now, that's not going to happen.

The other part of their approach is convincing us that our politics are so broken that there's no way that we can achieve meaningful action. And we see this in the wake of the COP 26 Glasgow Summit. You saw well-known climate change deniers like Marc Morano quoting out of context some climate advocates. That made it sound like the entire process had collapsed, that it's unsalvageable, and that there is no reason to even continue with these multilateral negotiations. And indeed, the fossil fuel industry would love nothing more than for us to give up on any possibility of climate action. And we see that some of that messaging was weaponized, in this case, by the forces of inaction. 

There are other examples that I talked about in the book. Online, there are bad state actors. Russia, for example, has promoted climate change denial; they want to monetize all of those fossil fuels that are buried beneath Russian soil. And they have worked for years, using Black Ops social media campaigns to influence American politics, European politics, and Canadian politics in a way that stymies meaningful climate action. And we know that they have armies of bots and trolls that pollute the social media space and are intended to take in well-meaning bystanders. These people would otherwise be on the frontlines, but they convinced them it's too late to do anything and that there's no possibility of meaningful policy action. They want these people on the sidelines rather than on the frontlines.

Nuclear energy.  An issue that came up several times in recent podcasts was nuclear energy. I remember once speaking with Jim Hanson about it, and he said that we don't have the luxury to pick and choose; we all want solar and wind, but we might have to go down that nuclear road as well. So is nuclear safe enough, and is it economically efficient enough, or should we go for renewables like wind and solar and become much more efficient? 

I respect Jim greatly, and I also respect the point of view of Jim and all other people who think that nuclear is an important option in addressing the climate crisis. But I am not convinced it is. And I go through that in some detail in the book in the New Climate War. Renewable energy is cheaper, and nuclear comes with risks like radiation, nuclear proliferation, and conflict. It is also really expensive, and it requires huge government subsidies to be viable. So if you're a free-market conservative, it doesn't make sense for you to be arguing for nuclear energy because it's not viable in the market against cheaper sources of energy. 

One of the arguments has been that we just can't scale up renewable energy fast enough. And then there are storage issues, the sun isn't always shining, and the wind isn't always blowing. A lot of that has been solved. We now have significant new technology for energy storage with smart grid technology. We have the tools now to solve this problem with renewable energy. I am convinced that that's the case. There are experts in this field who've made a compelling argument that that's the case, like Mark Jacobson of Stanford. And so there is a cheaper solution, and it comes with less risk. 

The only obstacle here isn't technological at this point; it's political. We just need policies that speed up this transition that's already underway from fossil fuels to renewable and clean energy. We can do it. I'm convinced that we can, and we don't have to follow this riskier path of nuclear or geoengineering or some of these other technologies that can supposedly save us.

Michael E  Mann.  Photo by Joshua Yospynd

Hope from Glasgow

 From an op-ed by Michael E Mann in the LA Times

For those looking for reasons to be cynical about the U.N. Climate Change Conference in Glasgow, Scotland — COP26 — there seemed to be more than ample cause early on. Yet for those looking for hope, grounds for this too emerged later.

COVID-related restrictions made it difficult for climate activists to participate in the proceedings, contributing to a feeling that the process favored the power brokers over the people. The fact that fossil fuel executives made up the largest delegation at the conference didn’t help matters.

Meanwhile, the leaders of the world’s largest carbon emitter, China, and petrostates Saudi Arabia and Russia were AWOL. Prime Minister Scott Morrison of Australia was shunned for his woefully inadequate climate commitments. Yes, there were pledges aplenty, but the “implementation gap” seemed ever more yawning. A leaked draft of the COP26 decision text lacked any mention of a fossil fuel phaseout.

There was understandable anxiety, despair and righteous anger on the part of young people given the insufficiency of the progress and the bad actors who are creating obstacles. This led some to insist that the talks were just more “blah, blah, blah,” that COP26 was dead on arrival, and even that the entire process should be abandoned.

But we believed walking away would be counterproductive. After all, the U.N. COP process provides the only multilateral framework for negotiating global climate policy. And while the speed of work had been inadequate, some real progress was being made in key areas: on deforestation, methane emissions and, most importantly, carbon dioxide emissions from fossil fuel burning.

By the end of the first week, the latest commitments from various countries for the first time appeared to offer a chance of keeping the warming of the planet below 2 degrees Celsius compared with preindustrial levels. That’s half of what we were heading toward prior to the 2015 Paris summit (COP21).

It’s not good enough, of course. We need to keep warming below 1.5 degrees Celsius to avert many of the worst impacts of climate change. But the latest commitments are meaningful and can be built upon.

The final COP26 decision statement, for the first time in a COP agreement, contains language directing all nations to increase efforts toward phasing down unabated coal and inefficient fossil fuel subsidies, though it gives no firm deadlines. Yes, the last-minute change from “phase out” to “phase down,” at the behest of India, was disappointing, and the reference to “unabated coal” leaves a dubious “carbon capture” loophole.

And while some worried that adding “inefficient” before subsidies introduced another loophole, we read it as an admission that such subsidies are by their very nature inefficient. Importantly, nations are also asked to return one year from now to strengthen their pledges, instead of waiting five years, as was set in the 2015 Paris agreement.

In another welcome development, a group of nations said they were creating plans to end fossil fuel extraction. The Beyond Oil and Gas Alliance, founded by Denmark and Costa Rica, includes France, Ireland, Sweden, Wales, Greenland and Quebec. While most of the largest oil and gas producers in the world, including the U.S. and Russia, are nowhere to be found in the alliance, some of the signatories are substantial producers or have substantial reserves. When Denmark made the decision in 2019 to begin its phaseout, it was the biggest oil producer in the European Union, and Greenland has huge reserves that it will forgo. Of course, this is only a first step.

But the biggest breakthrough was unexpected. On Wednesday, China and the U.S. — the world’s two largest climate polluters — said they would commit to “enhanced climate actions” to keep global warming to the limits set in the Paris agreement. Most critically, the statement included a commitment to phase down coal. And while we can’t yet quantify the impacts of this development, it presumably moves us closer to the 1.5 Celsius goal. This level of U.S.-China cooperation quickly shifted the entire COP26 narrative and outlook.

It is noteworthy that a similar bilateral agreement in 2014 brokered by the same two lead negotiators — China’s top climate envoy Xie Zhenhua and then-Secretary of State John F. Kerry — laid the groundwork for the Paris agreement a year later. This week’s agreement might prove even more important. Chinese President Xi Jinping and President Biden will meet virtually on Monday to discuss further actions.

The key aim of COP26 was to “keep 1.5C alive.” Despite pessimism among many heading into Glasgow, there is still reason to believe that’s possible. But only if the hard work begins now. We need to hold leaders accountable for their pledges and see to it that plans are carried out. Our future depends on it.

See also this report from the BBC.

The world is already ± 1.2 degrees warmer than pre-industrial times.

The iconic hockey stick extended

 From ArsTechnica

The climate “hockey stick” refers to a reconstruction of temperatures over the past 1,000 years. The data shows flattish temperatures over the last millennium, like the handle of a Hockey stick, ending in a "blade" of rapidly rising temperatures since the industrial revolution. The idea first appeared in a paper by Michael Mann and Raymond Bradley of the University of Massachusetts and Malcolm Hughes of the University of Arizona. The work became famous after appearing in a UN climate report, after which it was the focus of climate denial, hacking, defamation, and disinformation, all of which was dramatized in a recent BBC TV drama called “The Trick.”

Today, in a paper published by Nature, scientists show that the "handle" of the "hockey stick" extends back 9,500 years, while its "blade" is taller—the last decade was 1.5° C hotter than the average temperature over the last 11,700 years. "Human-caused global temperature change during the last century was likely faster than any changes during the last 24,000 years," said lead author Dr. Matt Osman of the University of Arizona.

To measure temperatures at times long before the invention of thermometers, scientists must use indirect proxies. For the new study, scientists carefully vetted over 500 proxy records from oceans around the world; the data shows the fossilized remains of plankton and microbes in sediments where the age is known from radiocarbon dating.

Researchers then used statistical methods to calculate sea surface temperatures from the chemical properties of those remains. “We spent seven years developing the models for the different kinds of marine temperature proxies, incorporating knowledge from biology and geochemistry and using the best statistical practice,” explained coauthor Dr. Jessica Tierney of the University of Arizona and leader of the lab in which this research was conducted.

The researchers combined the proxy temperatures with climate model simulations to account for the incomplete geographic distribution of data, and they cross-checked their results with independent records such as ice drilled from polar regions and stalagmites in caves.

But unlike earlier studies, the new work shows that, prior to our current warming, there was a slow, long-term warming of 0.5° C that started 9,500 years ago. It also shows that the "handle" of the climate "hockey stick" is straight, whereas in prior studies, the "handle" was warped, with early warming followed by cooling into preindustrial times.

The new results resolve a disagreement between climate models (which simulated warming) and proxy studies (which showed cooling). The problem was known as the “Holocene Temperature Conundrum.”

Dr. Samantha Bova of San Diego State University, who published a reconstruction of temperatures for the same time period earlier this year, agreed, saying, “Both reconstructions show no evidence for an early Holocene warm period.” She pointed out that her paper used a completely different method, so the fact that her research came to the same conclusion as the Tierney team “leaves little room for doubt that the Holocene was a period of long-term warming,” she said.

Note right scale is lower than left, for clarity

 

See also Forget the "hockey stick". Now we have the "scythe"

Forget the "hockey stick". Now we have the "scythe"

 From an article by Michael E Mann in Time Magazine.

“Widespread and severe”—that’s how climate scientists from around the world have described the impacts of climate change in a new United Nations report published today. The report’s findings further affirm warnings scientists like me have been sharing for decades. More than three decades ago, during a congressional hearing on a hot July 1988 afternoon in Washington, D.C., Dr. James E. Hansen told our elected officials that it was already possible to detect a warming of the planet due primarily to an increase in carbon dioxide concentrations from fossil fuel burning.

Hansen was prescient. It would take the United Nations’ Intergovernmental Panel on Climate Change (IPCC) another seven years after that to conclude that there was a “discernible human influence” on our climate. The IPCC, like many scientific institutions, is intrinsically conservative. So, when they state that the impacts of climate change are now “widespread and severe,”  it means that the impacts of climate change are now widespread and severe. Of course, you don’t need a scientific report to tell you that at this point. You need simply watch the unprecedented extreme weather disasters we’ve witnessed this summer play out in real time on our television screens and in our newspaper headlines.

With the release of the new Sixth Assessment report (“AR6”) on the science underlying the climate crisis, the news is not good. In addition to the finding that climate impacts are widespread and severe, the report shows that many severe impacts are locked in for the future.

Two decades ago, the so-called “hockey stick” curve, published by my co-authors and me in 1999, was featured in the all-important “summary for policy makers” (or “SPM”) of the 2001 Third IPCC Assessment report. The curve, which depicts temperature variations over the past 1,000 years based on “proxy” records such as tree rings, corals, and ice cores, showed the upward spiking of modern temperatures (the “blade”) as it dramatically ascends, during the industrial era, upward from the “handle” that describes the modest, slightly downward steady trend that preceded it.

Featured in the AR6 SPM now is an even longer hockey stick with an even sharper blade. [The "scythe"]

The new report also suggests that the recent warming is not only unprecedented over the past two millennia, but possibly, the past hundred millennia—let that sink in. As the IPCC report lays bare, we are engaged in a truly unprecedented and fundamentally dangerous experiment with the one planet we know that can support us and all other known life.

More than in its previous reports, the IPCC now truly connects the dots between fossil fuel burning, the warming of the planet, and the deadly extreme weather events we’re now enduring. And if we fail to act on the climate crisis, as the new report shows, we can expect more expansive wildfires, more intense hurricanes, hotter heat waves, and increasingly drenching flash floods. Given the horrific extreme weather we are already living through, you can trust me—we do not want this to get worse.

This is the cost we all are already paying for the delay that polluters have been sowing. It didn’t have to be this way. The fossil fuel industry knew a half century ago that their products—coal, oil, gas—would lead to the climate change future that we’re living in today. For them, the quick money was more important than being responsible corporate citizens to help build a sustainable future for mankind.

Instead, they spent millions of dollars on a massive disinformation campaign to convince the public and policymakers that climate change either wasn’t real, wasn’t a threat, or would be too expensive to do anything about (when in fact the opposite is very clearly true). They wrote a check that our children, grandchildren, and great-grandchildren will be forced to cash if we fail to act, and which will leave them with a climate that will become increasingly untenable for civilization as we know it. Thankfully, there’s still time to prevent that stark future from occurring.

The new IPCC report shows that we can prevent many of the worst impacts of climate change and keep warming below 1.5°C above preindustrial levels—the target of the global Paris Agreement. While some impacts—like more flooding in coastal areas, continued glacial melt and sea level rise—are now baked in, we can still take steps to ensure they don’t get much more severe. If we can reduce carbon emissions dramatically, and keep warming below 1.5°C, we could, for example, hold sea level rise to just a couple feet over the next century. If we fail, the report shows we could ultimately be facing 20 feet or more of global sea level rise, a scenario where we’d be forced to say farewell to the major coastal cities of the world.

It’s possible to turn the ship around, but it won’t be easy. The IPCC has determined that planetary warming of 1.5°C (and possibly even 2°C) will be exceeded in a matter of decades “unless deep reductions in carbon dioxide, methane, and other greenhouse gas emissions occur in the coming decades.” That means we must reduce our carbon pollution from transportation, electricity and other sectors here in the U.S., and around the world. Climate change will be costly and disruptive, but it’s not yet beyond our capacity to adapt.

To limit warming to 1.5 degrees,

• Developed countries need to slash emissions by 50% by 2030, which means emissions need to fall by a compound 7.5% per annum.  This is feasible if we replace fossil fuels in electricity generation and transition our vehicle fleet to EVs and PHEVs.
• Developing countries (especially China)  need to build no new coal power stations and must start step-by-step replacement of their aging coal-fired power stations, as well as shift their car/lorry fleets to EVs
• To accelerate this process, fossil fuel subsidies must be withdrawn, and a carbon tax must be introduced.

It's not that hard, whatever the fossil fuel apologists say.

If we halve emissions we halve warming

 I had a Twitter exchange with Michael E Mann, the climatologist, about whether if we (the world) cut emissions by half over the next decade, whether the global temperature increase, currently 0.2 degrees C per decade, would fall. 

Me: Hi. A quick question. If we cut emissions by 50% by 2030, will the rate of increase in global temps start to fall, so the decadal increase in the 2030s is 0.1 degrees C as opposed to the current 0.2? And if we halve emissions again, will the increase fall again?

Michael E Mann: Roughly yes. The transient warming response is roughly linear in the incremental emissions, so cut emissions in half, you cut the warming in half.

Me:Thank you. That is excellent news. It's better than I've been thinking (I thought temps would go on rising at 0.2 degrees until emissions cease). It implies that we should front-load emissions cuts, doesn't it?

Michael E Mann: Yes.

If we cut emissions by half, the transient rise (i.e., on a decade-by-decade basis, as opposed to the longer-term rise over centuries) will also halve. In other words, the temperature rise in the 2030s could fall to 0.1 degree if we halved emissions. And if we halve emissions again, the decade-by-decade temperature increases will halve again, getting close to zero.

This is incredibly good news. We are not helpless to avert disastrous climate change. Because together, globally, emissions from electricity generation and land transport make up ~50% of total emissions, and renewables are cheaper than coal in electricity generation, while battery pack costs will reach $100 by late 2022, allowing EVs to have the same 'sticker price' as petrol/diesel cars. Indeed, The Driven has a report that BYD, China's largest EV manufacturer, will start selling an EV in Australia with a drive-away price of A$35,000 as of next year.

And a national fleet of EVs will be very useful for stabilising the grid, because even small ones store about 2 days of an average household's electricity use, while the grander EVs store 4 days. Since 'near firm' electricity generation requires just four hours of storage, an electric fleet attached to the grid will provide more than enough backup to stabilise the grid in all but the most extreme circumstances. EVs can be used to stabilise the grid either passively or actively. Passive stabilisation is where EVs don't charge when demand on the grid is high, but do when demand is low. Active stabilisation is when EVs put some of their stored power back into the grid when demand is high/supply low. Of course, charging pricing regimes will have to be revised, to reward owners for allowing some of their stored electricity to be used by the grid.

There are still ill-informed (or venal) troglodytes out there who oppose these shifts. But they are inevitable, because of the technological advances and cost declines in renewables and batteries. Inevitable. And the spread of carbon prices as the EU insists its trading partners introduce their own or face carbon tariffs on their exports to the EU will only accelerate these inexorable and unavoidable trends.

Source: NOAA

Earth will cross the climate danger threshold by 2026

I won't repeat the article from Scientific American; the author (Michael E Mann) says it better than I can.  You can read it here.  A key discussion in the article is how much global temperatures will rise if atmospheric CO2 doubles from the 280 ppm (parts per million) before industrialisation began to 560 ppm.  His estimate: 3 degrees centigrade.

The first chart below from the article shows different estimates of how much the world will warm based on different lines of evidence.

The second chart shows how temperatures will rise depending on just how sensitive the world's climate is to rising CO2.  In the article, the author points out that reducing aerosols (emitted along with CO2 by burning coal ) will cause global temps to rise.  So ironically, even as China slashes its emissions of CO2 global temps will rise/

Update, September 2026.  

First published in 2014, 12 years ago, Michael E Mann has been proved right.  We are well into the climate danger threshold.  Unprecedented heatwaves and droughts and bushfires in Europe, floods in China and Japan, record heat everywhere.  The so-famous "pause" the denialists talked about (the small black circled inset on the lower chart) was just a blip, as the climate scientists said it would be, and the temperature increase has accelerated.